JP2009259387A - Optical head device and optical information recording or reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head device and an optical information recording and reproducing apparatus which can record information and reproduce the recorded information at any of optical recording media, such as a next generation optical recording medium, in which the wavelength of the light source is made to be shorter, the numerical aperture of the objective lens is made to be higher, and the thickness of the recording medium is made to be thinner, and conventional recording media of DVD and CD standards. <P>SOLUTION: A light having a wavelength of 405 nm, emitted from optics 1a, is input to an objective lens 4a as a collimated light, and is focused on a disk 5a having a thickness of 0.1 mm. A light having a wavelength of 650 nm, emitted from optics 1b, is input to the objective lens 4a as a diverged light, and is focused on a disk 5b having a thickness of 0.6 mm. A light having a wavelength of 780 nm, emitted from optics 1c, is input to the objective lens 4a as a diverged light, and is focused on a disk 5c having a thickness of 1.2 mm. A spherical aberration, which remains for the light having a wavelength of 650 nm or 780 nm, is decreased by the change of the magnification of the objective lens 4a, further the decreased spherical aberration is decreased by using a wavelength selective filter 3a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an optical head device and an optical information recording / reproducing apparatus for performing recording and reproduction on a plurality of types of optical recording media having different substrate thicknesses.

The recording density in the optical information recording / reproducing apparatus is inversely proportional to the square of the diameter of the focused spot formed on the optical recording medium by the optical head apparatus. That is, the smaller the diameter of the focused spot, the higher the recording density. The diameter of the focused spot is proportional to the wavelength of the light source in the optical head device and inversely proportional to the numerical aperture of the objective lens. That is, as the wavelength of the light source is shorter and the numerical aperture of the objective lens is higher, the diameter of the focused spot becomes smaller.

On the other hand, when the optical recording medium is tilted with respect to the objective lens, the shape of the focused spot is disturbed by coma aberration, and the recording / reproducing characteristics are deteriorated. The coma aberration is inversely proportional to the wavelength of the light source, and proportional to the cube of the numerical aperture of the objective lens and the substrate thickness of the optical recording medium. Therefore, when the substrate thickness of the optical recording medium is the same, the margin of inclination of the optical recording medium with respect to the recording / reproducing characteristics becomes narrower as the wavelength of the light source is shorter and the numerical aperture of the objective lens is higher.

Therefore, in an optical information recording / reproducing apparatus in which the wavelength of the light source is shortened and the numerical aperture of the objective lens is increased in order to increase the recording density, the optical recording medium is used in order to ensure a margin of inclination of the optical recording medium with respect to the recording / reproducing characteristics. The substrate thickness is reduced.

In the CD (compact disc) standard having a capacity of 650 MB, the wavelength of the light source is 780 nm, the numerical aperture of the objective lens is 0.45, and the substrate thickness of the disc is 1.2 mm. In the DVD (Digital Versatile Disc) standard with a capacity of 4.7 GB, the wavelength of the light source is 650 nm, the numerical aperture of the objective lens is 0.6, and the substrate thickness of the disc is 0.6 mm.

A normal optical head device is designed to cancel spherical aberration for a disk with a substrate thickness with an objective lens. Remains and cannot be recorded or played back correctly. In view of this, an optical head device having a compatible function capable of performing recording and reproduction on both a DVD standard disk and a CD standard disk has been proposed.

As a first example of a conventional optical head device that can perform recording and reproduction on both a DVD standard disc and a CD standard disc, there is an optical head device described in Patent Document 1. FIG. 24 shows the configuration of this optical head device.

In FIG. 24, the optical system 1f and the optical system 1g include a semiconductor laser and a photodetector that receives reflected light from the disk. The wavelength of the semiconductor laser in the optical system 1f is 650 nm, and the wavelength of the semiconductor laser in the optical system 1g is 780 nm. The interference filter 2c functions to transmit light having a wavelength of 650 nm and reflect light having a wavelength of 780 nm.

The light emitted from the semiconductor laser in the optical system 1f passes through the interference filter 2c and the wavelength selection filter 3c, enters the objective lens 4b as parallel light, and is collected on the DVD standard disk 5b having a substrate thickness of 0.6 mm. To be lighted. The reflected light from the disk 5b passes through the objective lens 4b, the wavelength selection filter 3c, and the interference filter 2c in the opposite directions, and is received by the photodetector in the optical system 1f.

The light emitted from the semiconductor laser in the optical system 1g is reflected by the interference filter 2c, passes through the wavelength selection filter 3c, enters the objective lens 4b as parallel light, and meets the CD standard with a substrate thickness of 1.2 mm. It is condensed on the disk 5c. The reflected light from the disk 5c passes through the objective lens 4b and the wavelength selection filter 3c in the opposite direction, is reflected by the interference filter 2c, and is received by the photodetector in the optical system 1g. The objective lens 4b has spherical aberration that cancels spherical aberration that occurs when light having a wavelength of 650 nm incident as parallel light on the objective lens 4b passes through a substrate having a thickness of 0.6 mm.

FIG. 25A is a plan view of the wavelength selection filter 3c, and FIG. 25B is a cross-sectional view of the wavelength selection filter 3c. The wavelength selection filter 3c has a configuration in which a concentric phase filter pattern 6b and a dielectric multilayer film 7f are formed on a glass substrate 8c. When the effective diameter of the objective lens 4b indicated by a dotted line in the drawing is 2d, the phase filter pattern 6b is formed only in a circular region having a diameter 2e smaller than this.

The cross section of the phase filter pattern 6b has a four-level step shape as shown in the figure. The height of each stage of the phase filter pattern 6b is set so that the phase difference of light passing through the part with and without the pattern at each stage is 2π (equivalent to 0) with respect to the wavelength of 650 nm. At this time, this phase difference is 1.67π (equivalent to −0.33π) for a wavelength of 780 nm.

Therefore, the phase filter pattern 6b does not change the phase distribution for light with a wavelength of 650 nm, and changes the phase distribution for light with a wavelength of 780 nm. When the wavelength selection filter 3c is not used, spherical aberration remains when light having a wavelength of 780 nm incident as parallel light on the objective lens 4b passes through a substrate having a thickness of 1.2 mm. On the other hand, the phase filter pattern 6b is designed to reduce spherical aberration in which a change in phase distribution with respect to light having a wavelength of 780 nm remains.

On the other hand, the dielectric multilayer film 7f is formed only outside the circular region having the diameter 2e. The dielectric multilayer film 7f functions to transmit all light having a wavelength of 650 nm and reflect all light having a wavelength of 780 nm. Along with this, it functions to adjust the phase difference between the light passing through the circular region having a diameter of 2e and the light passing through the outside of the region with respect to the wavelength of 650 nm to an integral multiple of 2π. That is, in the wavelength selection filter 3c, all light having a wavelength of 650 nm is transmitted, all light having a wavelength of 780 nm is transmitted within a circular region having a diameter of 2e, and all light is reflected outside the circular region having a diameter of 2e. Therefore, if the focal length of the objective lens 4b is fb, the effective numerical apertures for light with wavelengths of 650 nm and 780 nm are given by d / fb and e / fb, respectively. For example, d / fb = 0.6 and e / fb = 0.45 are set.

As a second example of a conventional optical head device that can perform recording and reproduction on both a DVD standard disc and a CD standard disc, there is an optical head device described in Patent Document 2. FIG. 26 shows the configuration of this optical head device.

The modules 27a and 27b include a semiconductor laser and a photodetector that receives reflected light from the disk. The wavelength of the semiconductor laser in the module 27a is 650 nm, and the wavelength of the semiconductor laser in the module 27b is 780 nm. The interference filter 2c functions to transmit light having a wavelength of 650 nm and reflect light having a wavelength of 780 nm.

Light emitted from the semiconductor laser in the module 27a passes through the interference filter 2c, the collimator lens 10d, and the aperture control element 21c, enters the objective lens 4b as parallel light, and is a DVD standard disk 5b having a substrate thickness of 0.6 mm. Focused on top. The reflected light from the disk 5b passes through the objective lens 4b, the aperture control element 21c, the collimator lens 10d, and the interference filter 2c in the reverse direction and is received by the photodetector in the module 27a.

The light emitted from the semiconductor laser in the module 27b is reflected by the interference filter 2c, passes through the collimator lens 10d and the aperture control element 21c, enters the objective lens 4b as diverging light, and has a substrate thickness of 1.2 mm. The light is focused on the CD standard disk 5c. The reflected light from the disk 5c passes through the objective lens 4b, the aperture control element 21c, and the collimator lens 10d in the reverse direction, is reflected by the interference filter 2c, and is received by the photodetector in the module 27b.

The objective lens 4b has spherical aberration that cancels spherical aberration that occurs when light having a wavelength of 650 nm incident as parallel light on the objective lens 4b passes through a substrate having a thickness of 0.6 mm. Spherical aberration remains when light having a wavelength of 780 nm incident on the objective lens 4b as parallel light passes through a substrate having a thickness of 1.2 mm. However, when light having a wavelength of 780 nm is incident on the objective lens 4b as diverging light, A new spherical aberration is caused by a change in magnification of the objective lens 4b, and this acts in a direction to reduce the remaining spherical aberration.

FIG. 27A is a plan view of the opening control element 21c, and FIG. 27B is a cross-sectional view of the opening control element 21c. The aperture control element 21c has a configuration in which a dielectric multilayer film 7g and a phase compensation film 28 are formed on a glass substrate 8c. When the effective diameter of the objective lens 4b indicated by a dotted line in the drawing is 2d, the dielectric multilayer film 7g is formed only outside a circular region having a smaller diameter 2e. The dielectric multilayer film 7g functions to transmit all light having a wavelength of 650 nm and reflect all light having a wavelength of 780 nm.

That is, in the aperture control element 21c, all light having a wavelength of 650 nm is transmitted, and all light having a wavelength of 780 nm is transmitted within a circular area having a diameter of 2e, and is entirely reflected outside a circular area having a diameter of 2e. Therefore, assuming that the focal length of the objective lens 4b is fb, effective numerical apertures for light with wavelengths of 650 nm and 780 nm are given by d / fb and e / fb, respectively. For example, d / fb = 0.6 and e / fb = 0.45 are set.

On the other hand, the phase compensation film 28 is formed only in a circular region having a diameter of 2e. The phase compensation film 28 functions to adjust the phase difference between light passing through a circular area having a diameter of 2e and light passing outside the area to an integral multiple of 2π with respect to a wavelength of 650 nm.

JP 10-334504 A JP-A-9-274730

In recent years, in order to further increase the recording density, a next generation standard has been proposed in which the wavelength of the light source is further shortened, the numerical aperture of the objective lens is further increased, and the substrate thickness of the optical recording medium is further reduced. For example, in the document “International Symposium on Optical Memory 2000, Technical Digest, pages 24 to 25”, the wavelength of the light source is 405 nm, the numerical aperture of the objective lens is 0.7, and the substrate thickness of the disk is 0. A next-generation standard with a capacity of 17 GB and a thickness of 12 mm has been proposed. In this case, there is a demand for an optical head device having a compatible function capable of performing recording and reproduction on both a next-generation standard disk and a conventional DVD standard disk or CD standard disk.

As a first example, the wavelength selection filter in the conventional optical head device shown in FIG. 24 is a next-generation standard having a light source wavelength of 405 nm, an objective lens numerical aperture of 0.7, and a disk substrate thickness of 0.1 mm. Consider a case where the method is applied as a method compatible with the DVD standard. Recording is performed using a semiconductor laser having a wavelength of 405 nm for a next-generation standard disk having a substrate thickness of 0.1 mm, and using a semiconductor laser having a wavelength of 650 nm for a DVD standard disk having a substrate thickness of 0.6 mm. Perform playback. The objective lens has spherical aberration that cancels spherical aberration that occurs when light having a wavelength of 405 nm incident as parallel light on the objective lens passes through a substrate having a thickness of 0.1 mm.

The cross section of the phase filter pattern in the wavelength selective filter is a five-level step. The height of each stage of the phase filter pattern is set so that the phase difference of light passing through the part with and without the pattern at each stage is 2π (equivalent to 0) with respect to the wavelength of 405 nm. At this time, this phase difference is 1.25π (equivalent to −0.75π) for a wavelength of 650 nm.

Therefore, the phase filter pattern does not change the phase distribution for light having a wavelength of 405 nm, and changes the phase distribution for light having a wavelength of 650 nm. When the wavelength selection filter is not used, spherical aberration remains when light having a wavelength of 650 nm incident as parallel light on the objective lens passes through a substrate having a thickness of 0.6 mm. The phase filter pattern is designed to reduce spherical aberration in which a change in phase distribution with respect to light having a wavelength of 650 nm remains. FIG. 28 shows the design result of the phase filter pattern. The column on the left is the height of incident light on the objective lens normalized by the focal length of the objective lens. The right column indicates the number of stages of the corresponding phase filter pattern.

On the other hand, the dielectric multilayer film functions to transmit all light having a wavelength of 405 nm and reflect all light having a wavelength of 650 nm. At the same time, the wavelength difference of 405 nm functions to adjust the phase difference between the light passing through the circular area and the light passing outside the area to an integral multiple of 2π. That is, in the wavelength selection filter, all light having a wavelength of 405 nm is transmitted, all light having a wavelength of 650 nm is transmitted within a circular area, and is reflected entirely outside the circular area. The effective numerical apertures for light having wavelengths of 405 nm and 650 nm are set to 0.7 and 0.6, for example.

FIG. 29 shows a calculation result of the wavefront aberration at the position of the best image plane where the standard deviation of the wavefront aberration with respect to light having a wavelength of 650 nm is minimized. FIG. 29A shows a case where no wavelength selection filter is used. FIG. 29B shows a case where a wavelength selection filter is used. In the figure, the horizontal axis represents wavefront aberration, and the vertical axis represents the height of incident light on the objective lens normalized by the focal length of the objective lens. The standard deviation of the wavefront aberration is reduced to 0.054λ by using a wavelength selective filter. This value is lower than 0.07λ, which is an allowable value of the standard deviation of wavefront aberration, which is known as a Marechal standard.

However, as shown in FIG. 28, since the number of concentric regions constituting the phase filter pattern is as many as 19, the width of each region is narrowed. If the focal length of the objective lens is 2.57 mm, for example, the width of the outermost region is about 7.7 μm. Normally, a stepped element having a multi-level cross section is manufactured by a photolithography method using a plurality of photomasks, but there is an error of 2 to 3 μm in alignment of the photomasks. Therefore, it is extremely difficult to produce a wavelength selective filter having a phase filter pattern with a narrow width of each region as described above with a desired accuracy.

As a second example, the change in magnification of the objective lens in the conventional optical head device shown in FIG. 26 is the next generation standard with a light source wavelength of 405 nm, an objective lens numerical aperture of 0.7, and a disk substrate thickness of 0.1 mm. Consider a case where the method is applied as a method compatible with the conventional DVD standard. Recording and playback using a semiconductor laser with a wavelength of 405 nm for a next-generation standard disk with a substrate thickness of 0.1 mm, and a semiconductor laser with a wavelength of 650 nm for a DVD standard disk with a substrate thickness of 0.6 mm I do. The objective lens has spherical aberration that cancels spherical aberration that occurs when light having a wavelength of 405 nm incident as parallel light on the objective lens passes through a substrate having a thickness of 0.1 mm.

Since light with a wavelength of 405 nm enters the objective lens as parallel light, the magnification of the objective lens with respect to the light with a wavelength of 405 nm is zero. On the other hand, spherical light remains when light having a wavelength of 650 nm incident as parallel light on the objective lens is transmitted through a substrate having a thickness of 0.6 mm. When light having a wavelength of 650 nm is made incident on the objective lens as diverging light, new spherical aberration is caused by the change in magnification of the objective lens, and this works in a direction to reduce the remaining spherical aberration. The magnification of the objective lens with respect to light having a wavelength of 650 nm is set to 0.076.

The dielectric multilayer film in the aperture control element functions to transmit all light having a wavelength of 405 nm and reflect all light having a wavelength of 650 nm. That is, in the aperture control element, all light with a wavelength of 405 nm is transmitted, all light with a wavelength of 650 nm is transmitted within a circular region, and is reflected entirely outside the circular region. Effective numerical apertures for light having wavelengths of 405 nm and 650 nm are set to 0.7 and 0.6, for example. On the other hand, the phase compensation film functions to adjust the phase difference between the light passing through the circular region and the light passing outside the region to an integer multiple of 2π with respect to the wavelength of 405 nm.

FIG. 30 shows a calculation result of the wavefront aberration at the position of the best image plane where the standard deviation of the wavefront aberration with respect to light having a wavelength of 650 nm is minimized. In the figure, the horizontal axis represents wavefront aberration, and the vertical axis represents the height of incident light on the objective lens normalized by the focal length of the objective lens. The standard deviation of the wavefront aberration is reduced to 0.095λ by using the objective lens magnification change. However, this value exceeds 0.07λ, which is an allowable value of the standard deviation of wavefront aberration, which is known as a Marechal criterion.

A combination of the wavelength selection filter in the conventional optical head device shown in FIG. 24 and the magnification change of the objective lens in the conventional optical head device shown in FIG. 26 is used as a method for compatibility with the next generation standard and the conventional DVD standard. The case where it applies is also considered.

However, in the phase filter pattern in the wavelength selection filter, the change in phase distribution with respect to light having a wavelength of 650 nm is a spherical surface that remains when light having a wavelength of 650 nm incident as parallel light on the objective lens passes through a substrate having a thickness of 0.6 mm. Designed to reduce aberrations. Therefore, the spherical aberration that remains when light having a wavelength of 650 nm incident as diverging light on the objective lens passes through a substrate having a thickness of 0.6 mm is not reduced by using the wavelength selection filter, but becomes larger. .

As described above, when the wavelength of the light source is short and the numerical aperture of the objective lens is high, the wavelength selection filter in the conventional optical head device shown in FIG. 24 and the magnification change of the objective lens in the conventional optical head device shown in FIG. There is a problem that the method cannot be applied.

The present invention solves the above-described problems in a conventional optical head device for performing recording and reproduction on a plurality of types of optical recording media having different substrate thicknesses, and further increases the recording density. Next-generation standard optical recording medium in which the numerical aperture of the objective lens is further increased, the substrate thickness of the optical recording medium is further reduced, and the conventional DVD standard optical recording medium and CD standard optical recording medium It is an object of the present invention to provide an optical head device and an optical information recording or reproducing device having compatible functions capable of recording and reproducing any of the above.

In order to achieve such an object, the invention described in claim 1 includes a first light source that emits light of a first wavelength, a second light source that emits light of a second wavelength, and a third wavelength. A light source of the first wavelength emitted from the first light source in the forward path, and emitted from the second light source. The second wavelength light and the third wavelength light emitted from the third light source are transmitted through the objective lens through the first type optical recording medium and the second type optical recording, respectively. Selectively guided to the medium and the third type of optical recording medium, and reflected light of the first wavelength reflected by the first type of optical recording medium in the return path; Reflected light of the second wavelength light reflected by the optical recording medium, and the third type of optical recording In the optical head device including an optical system that selectively guides the reflected light of the third wavelength reflected by the medium to the photodetector through the objective lens, the first, second and second And a wavelength selection filter that provides a change in intensity distribution depending on the wavelength of incident light with respect to the light of the first, second, and third wavelengths in a common optical path of light of the three wavelengths. And

According to a second aspect of the present invention, in the first aspect of the invention, the first, second and third wavelengths are approximately 405 nm, approximately 650 nm and approximately 780 nm, respectively.

According to a third aspect of the present invention, in the first or second aspect of the invention, the distance from the incident surface to the reflective surface of the first, second, and third types of optical recording media is approximately 0.1 mm, respectively. It is approximately 0.6 mm and approximately 1.2 mm.

The invention according to claim 4 is the first region according to any one of claims 1 to 3, wherein the wavelength selective filter is outside a circle having a diameter smaller than an effective diameter of the objective lens. And a second region that is inside the circle, the first region is incident light for at least one of the first, second, and third wavelengths. Most of the incident light is not transmitted for at least one of the first, second and third wavelengths, and the second region is the first region. Transmitting the majority of incident light for the second and third wavelengths, and transmitting the first region for at least one of the first, second and third wavelengths; The phase difference from the light transmitted through the second region is set to an integer multiple of approximately 2π. And said that you are.

The invention according to claim 5 is the invention according to claim 4, wherein the first and second regions have first and second dielectric multilayer films, respectively, and each layer in the first dielectric multilayer film. And the thickness or the number of layers of the second dielectric multilayer film are different from each other.

According to a sixth aspect of the present invention, in the invention according to any one of the first to third aspects, the wavelength selective filter is outside a first circle having a first diameter smaller than an effective diameter of the objective lens. A first region that is, a second region that is inside the first circle and outside the second circle having a second diameter smaller than the first diameter, and the inside of the second circle And the first region transmits most of the incident light for the first wavelength, and for the second and third wavelengths. The second region does not transmit most of the incident light, the second region transmits most of the incident light for the first and second wavelengths, and does not transmit the incident light for the third wavelength. Most of the light is not transmitted and the third region transmits most of the incident light for the first, second and third wavelengths. The phase difference between the light transmitted through the first region, the light transmitted through the second region, and the light transmitted through the third region with respect to the first wavelength is an integer of approximately 2π. The phase difference between the light transmitted through the second region and the light transmitted through the third region is set to an integer multiple of approximately 2π with respect to the second wavelength. It is characterized by that.

According to a seventh aspect of the invention, in the sixth aspect of the invention, the first, second and third regions have first, second and third dielectric multilayer films, respectively. The thickness or number of layers of each layer in the dielectric multilayer film, the thickness or number of layers of each layer in the second dielectric multilayer film, and the thickness or number of layers of each layer in the third dielectric multilayer film , Different from each other.

The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the magnification of the objective lens with respect to the light of the first wavelength, and the magnification of the objective lens with respect to the light of the second wavelength. At least one of the magnification and the magnification of the objective lens with respect to the light of the third wavelength is different from the other two.

The invention according to claim 9 has at least one light source, an objective lens, and at least one photodetector, and emits light emitted from the light source in the forward path via the objective lens. An optical head device including an optical system that guides the reflected light from the optical recording medium in the return path to the photodetector through the objective lens in a return path, wherein the optical system receives the optical recording from the light source. Spherical aberration correction means provided in the optical path capable of correcting spherical aberration that occurs in the optical path to the medium, and an optical axis shift between the spherical aberration correction means and the objective lens in the optical path. And coma aberration correcting means capable of correcting coma aberration.

According to a tenth aspect of the present invention, in the ninth aspect of the invention, the at least one light source includes a light source that emits light having a wavelength of about 405 nm.

The invention according to claim 11 is the invention according to claim 9 or 10, wherein the at least one type of optical recording medium includes an optical recording medium having a distance from the incident surface to the reflecting surface of about 0.1 mm. It is characterized by.

The invention according to claim 12 is the invention according to any one of claims 9 to 11, wherein the coma aberration correcting means is the objective lens, and the objective lens is tilted in the direction of the optical axis deviation. The coma aberration is corrected.

The invention according to claim 13 is the invention according to any one of claims 9 to 11, wherein the coma aberration correcting means is an optical element provided in the optical path, and the optical element is offset from the optical axis. The coma aberration is corrected by tilting or moving in the direction of.

The invention according to claim 14 is the invention according to claim 13, wherein the optical element is a lens designed so as not to satisfy a sine condition.

According to a fifteenth aspect of the present invention, in the optical information recording or reproducing apparatus, the optical head device according to any one of the first to eighth aspects and the first type using the light of the first wavelength. Recording or reproduction on the optical recording medium, recording or reproduction on the second type optical recording medium using the second wavelength light, and the third type using the third wavelength light. And a recording or reproducing circuit that selectively performs recording or reproduction on an optical recording medium.

According to a sixteenth aspect of the present invention, there is provided an optical information recording or reproducing device, the optical head device according to any one of the ninth to fourteenth aspects, and a recording or reproducing circuit that performs recording or reproducing on the optical recording medium. It is characterized by having.

In the optical head device and the optical information recording or reproducing device of the present invention, the remaining spherical aberration is reduced by using the magnification change of the objective lens for the first wavelength light or the second wavelength light, By using the wavelength selective filter, the reduced spherical aberration in the magnification of the corresponding objective lens is further reduced. When reducing the remaining spherical aberration using only the wavelength selective filter, the spherical aberration to be reduced by the wavelength selective filter is large, so the number of concentric regions constituting the phase filter pattern in the wavelength selective filter is large. The width becomes narrow, and it is difficult to manufacture the wavelength selective filter with a desired accuracy.

However, when reducing the remaining spherical aberration using the magnification change of the objective lens and further reducing this reduced spherical aberration using the wavelength selective filter, the spherical aberration to be reduced by the wavelength selective filter is small. Since the number of concentric regions constituting the phase filter pattern in the selection filter is small and the width of each region is wide, it is easy to manufacture the wavelength selection filter with a desired accuracy. Further, when the remaining spherical aberration is reduced using only the change in magnification of the objective lens, the reduced spherical aberration exceeds the allowable value. However, when the remaining spherical aberration is reduced using the magnification change of the objective lens and the reduced spherical aberration is further reduced using the wavelength selection filter, the further reduced spherical aberration is less than the allowable value.

Therefore, according to the present invention, an optical recording medium of the next generation standard in which the wavelength of the light source is further shortened to further increase the numerical aperture of the objective lens and the substrate thickness of the optical recording medium is further reduced in order to further increase the recording density. It is possible to realize an optical head device and an optical information recording / reproducing apparatus having compatible functions capable of performing recording and reproduction on both conventional DVD standard optical recording media and CD standard optical recording media.

As is apparent from the above description, the optical head device of the present invention includes a first light source that emits light of a first wavelength, a second light source that emits light of a second wavelength, and a photodetector. And the wavelength selective filter, the objective lens, and the light emitted from the first light source are guided to the first optical recording medium having the first substrate thickness through the wavelength selective filter and the objective lens, and from the second light source. Is emitted to the second optical recording medium having the second substrate thickness through the wavelength selection filter and the objective lens, and the reflected light from the first and second optical recording media is guided to the objective lens and the wavelength selection filter. An optical system that leads to a photodetector through the first optical recording medium, performs recording and reproduction with respect to the first optical recording medium using light of the first wavelength, and uses second light with the second wavelength. An optical head device for recording and reproducing with respect to an optical recording medium, for light of a first wavelength The magnification of the objective lens is different from the magnification of the objective lens with respect to the light of the second wavelength, and the wavelength selection filter is a spherical surface remaining for the light of the first wavelength or the light of the second wavelength at the magnification of the corresponding objective lens. The phase distribution is changed so as to reduce the aberration.

The optical information recording / reproducing apparatus of the present invention includes the optical head apparatus of the present invention, a recording / reproducing circuit that generates an input signal to the light source and a reproducing signal from the optical recording medium, and transmission of the input signal. A switching circuit for switching the path and a control circuit for controlling the operation of the switching circuit according to the type of the optical recording medium.

Therefore, the effects of the optical head device and the optical information recording or reproducing device of the present invention are that the wavelength of the light source is further shortened to further increase the numerical aperture of the objective lens in order to further increase the recording density, and the substrate thickness of the optical recording medium is increased. Has a compatible function that can perform recording and reproduction on both the next-generation standard optical recording medium, which is thinner, and the conventional DVD standard optical recording medium and CD standard optical recording medium. is there.

The reason is that the remaining spherical aberration is reduced by using the magnification change of the objective lens with respect to the light of the first wavelength or the light of the second wavelength, and the magnification of the corresponding objective lens by using the wavelength selection filter. This is because the spherical aberration after this reduction is further reduced.

It is a figure which shows 1st embodiment of the optical head apparatus of this invention. It is a figure which shows the wavelength selection filter used for 1st embodiment of the optical head apparatus of this invention, (a) is the top view seen from one surface, (b) is the top view seen from the other surface, (C) is sectional drawing. (A) is a figure which shows the structure of the optical system of wavelength 405nm used for 1st embodiment of the optical head apparatus of this invention, (b) is the photodetector with which the optical system shown to (a) was equipped. FIG. (A) is a figure which shows the structure of the optical system of wavelength 650nm used for 1st embodiment of the optical head apparatus of this invention, (b) is the photodetector with which the optical system shown to (a) was equipped. FIG. It is a figure which shows the design result of the phase filter pattern in the wavelength selection filter used for 1st embodiment of the optical head apparatus of this invention. It is a figure which shows the calculation result of the wavefront aberration with respect to the light of wavelength 650nm in 1st embodiment of the optical head apparatus of this invention, (a) is when not using a wavelength selection filter using the magnification change of an objective lens, (B) is a figure at the time of using a wavelength selective filter further using the magnification change of an objective lens. FIG. 5A is a diagram showing a design result of wavelength dependency of transmittance with respect to the dielectric multilayer film in the wavelength selective filter used in the first embodiment of the optical head device of the present invention, and FIG. It is a figure which shows the design result of wavelength dependency of. It is a figure which shows 2nd embodiment of the optical head apparatus of this invention. It is a figure which shows the wavelength selection filter used for 2nd embodiment of the optical head apparatus of this invention, (a) is the top view seen from one surface, (b) is the top view seen from the other surface, (C) is sectional drawing. (A) is a figure which shows the structure of the optical system of wavelength 780nm used for 2nd embodiment of the optical head apparatus of this invention, (b) is the photodetector with which the optical system shown to (a) was equipped. FIG. It is a figure which shows the calculation result of the wavefront aberration with respect to the light of wavelength 780nm in 2nd embodiment of the optical head apparatus of this invention, (a) is when not using a wavelength selection filter using the magnification change of an objective lens, (B) is a figure at the time of using a wavelength selective filter further using the magnification change of an objective lens. It is a figure which shows 3rd embodiment of the optical head apparatus of this invention. It is a figure which shows the aperture control element used for 3rd embodiment of the optical head apparatus of this invention, (a) is a top view, (b) is sectional drawing. It is a figure which shows the structure of the optical system of wavelength 650nm used for 3rd embodiment of the optical head apparatus of this invention. It is a figure which shows 4th Embodiment of the optical head apparatus of this invention. It is a figure which shows the aperture control element used for 4th embodiment of the optical head apparatus of this invention, (a) is a top view, (b) is sectional drawing. It is a figure which shows the structure of the optical system of wavelength 780nm used for 4th embodiment of the optical head apparatus of this invention. It is a figure which shows 5th Embodiment of the optical head apparatus of this invention. It is a figure which shows 6th Embodiment of the optical head apparatus of this invention. It is a figure which shows 1st embodiment of the optical information recording or reproducing | regenerating apparatus of this invention. It is a figure which shows 2nd embodiment of the optical information recording or reproducing | regenerating apparatus of this invention. It is a figure which shows 3rd embodiment of the optical information recording or reproducing | regenerating apparatus of this invention. It is a figure which shows 4th Embodiment of the optical information recording or reproducing | regenerating apparatus of this invention. It is a figure which shows the structure of the 1st example of the conventional optical head apparatus. It is a figure which shows the wavelength selection filter used for the 1st example of the conventional optical head apparatus, (a) is a top view, (b) is sectional drawing. It is a figure which shows the structure of the 2nd example of the conventional optical head apparatus. It is a figure which shows the aperture control element used for the 2nd example of the conventional optical head apparatus, (a) is a top view, (b) is sectional drawing. It is a figure which shows the design result of the phase filter pattern in a wavelength selection filter in the case of applying the wavelength selection filter used for the 1st example of the conventional optical head apparatus as a compatible method of a next generation standard and the conventional DVD standard. It is a figure which shows the calculation result of the wavefront aberration with respect to the light of wavelength 650nm when applying the wavelength selection filter used for the 1st example of the conventional optical head device as a compatible method of the next generation standard and the conventional DVD standard, (A) is a figure when not using a wavelength selection filter, (b) is a figure at the time of using a wavelength selection filter. It is a figure which shows the calculation result of the wavefront aberration with respect to the light of wavelength 650nm when applying the magnification change of the objective lens used for the 2nd example of the conventional optical head apparatus as a compatible method of the next generation standard and the conventional DVD standard. is there.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(First Embodiment of Optical Head Device) FIG. 1 shows a first embodiment of an optical head device according to the present invention. The optical system 1a and the optical system 1b include a semiconductor laser and a photodetector that receives reflected light from the disk. The wavelength of the semiconductor laser in the optical system 1a is 405 nm, and the wavelength of the semiconductor laser in the optical system 1b is 650 nm.

The interference filter 2a functions to transmit light having a wavelength of 405 nm and reflect light having a wavelength of 650 nm. The light emitted from the semiconductor laser in the optical system 1a passes through the interference filter 2a and the wavelength selection filter 3a, enters the objective lens 4a as parallel light, and is on a next-generation standard disk 5a having a substrate thickness of 0.1 mm. It is condensed to. The reflected light from the disk 5a passes through the objective lens 4a, the wavelength selection filter 3a, and the interference filter 2a in opposite directions, and is received by the photodetector in the optical system 1a.

The light emitted from the semiconductor laser in the optical system 1b is reflected by the interference filter 2a, passes through the wavelength selection filter 3a, enters the objective lens 4a as diverging light, and meets the DVD standard with a substrate thickness of 0.6 mm. It is condensed on the disk 5b. The reflected light from the disk 5b passes through the objective lens 4a and the wavelength selection filter 3a in the opposite direction, is reflected by the interference filter 2a, and is received by the photodetector in the optical system 1b.

The objective lens 4a has spherical aberration that cancels spherical aberration that occurs when light having a wavelength of 405 nm incident as parallel light on the objective lens 4a passes through a substrate having a thickness of 0.1 mm. Since light with a wavelength of 405 nm enters the objective lens 4a as parallel light, the magnification of the objective lens 4a with respect to light with a wavelength of 405 nm is zero.

On the other hand, spherical aberration remains when light having a wavelength of 650 nm incident as parallel light on the objective lens 4a is transmitted through a substrate having a thickness of 0.6 mm. When light having a wavelength of 650 nm is made incident on the objective lens 4a as diverging light, new spherical aberration is caused by a change in magnification of the objective lens 4a, and this acts in a direction to reduce the remaining spherical aberration. The magnification of the objective lens 4a with respect to light having a wavelength of 650 nm is set to 0.076.

Here, the angle formed by the paraxial light beam traveling from the object point toward the predetermined height r of the objective lens 4a with the optical axis of the objective lens 4a is θo, and the paraxial light beam traveling from the predetermined height r of the objective lens 4a toward the image point. Is the angle formed by the optical axis of the objective lens 4a with θi, the magnification of the objective lens 4a is given by tan θo / tan θi.

If the distance from the object point to the object side principal point of the objective lens 4a is lo and the distance from the image side principal point to the image point of the objective lens 4a is li, tan θo = r / lo and tan θi = r / li are obtained. Since light having a wavelength of 405 nm enters the objective lens 4a as parallel light, θo = 0 and lo = ∞, and the magnification of the objective lens 4a is zero. Since light having a wavelength of 650 nm enters the objective lens 4a as diverging light, θo ≠ 0 and lo are finite. The value of lo at this time, that is, the position of the object point is determined so that the magnification of the objective lens 4a is 0.076.

FIG. 2A is a plan view seen from one surface of the wavelength selective filter 3a. FIG. 2B is a plan view seen from the other surface of the wavelength selective filter 3a. FIG. 2C is a cross-sectional view of the wavelength selection filter 3a. In the wavelength selection filter 3a, a concentric phase filter pattern 6a is formed on a glass substrate 8a. Further, dielectric multilayer films 7a and 7b are formed on the glass substrate 8b. The wavelength selection filter 3a has a configuration in which the surface of the glass substrate 8a where the phase filter pattern 6a is not formed and the surface of the glass substrate 8b where the dielectric multilayer films 7a and 7b are not formed are bonded together with an adhesive. .

When the effective diameter of the objective lens 4a indicated by a dotted line in the drawing is 2a, the phase filter pattern 6a is formed only in a circular region having a diameter 2b smaller than this. The cross section of the phase filter pattern 6a has a four-level step shape as shown in FIG. The height of each stage of the phase filter pattern 6a is set so that the phase difference of the light passing through the part with and without the pattern at each stage is 2π (equivalent to 0) with respect to the wavelength of 405 nm. At this time, this phase difference is 1.25π (equivalent to −0.75π) for a wavelength of 650 nm.

Therefore, the phase filter pattern 6a does not change the phase distribution for light with a wavelength of 405 nm, and changes the phase distribution for light with a wavelength of 650 nm. When the wavelength selection filter 3a is not used, when the magnification of the objective lens 4a is set to 0.076, light having a wavelength of 650 nm incident as parallel light on the objective lens 4a passes through a substrate having a thickness of 0.6 mm. Residual spherical aberration is reduced. The phase filter pattern 6a is designed such that a change in phase distribution with respect to light having a wavelength of 650 nm further reduces this reduced spherical aberration at the magnification 0.076 of the objective lens 4a.

On the other hand, the dielectric multilayer film 7a is formed only in a circular area having a diameter of 2b, and the dielectric multilayer film 7b is formed only outside a circular area having a diameter of 2b. The dielectric multilayer film 7a functions to transmit all light having a wavelength of 405 nm and light having a wavelength of 650 nm, and the dielectric multilayer film 7b functions to transmit all light having a wavelength of 405 nm and reflect all light having a wavelength of 650 nm. To do.

The phase difference between the light transmitted through the dielectric multilayer film 7a and the light transmitted through the dielectric multilayer film 7b is adjusted to an integral multiple of 2π with respect to the wavelength of 405 nm. That is, in the wavelength selection filter 3a, all light having a wavelength of 405 nm is transmitted, all light having a wavelength of 650 nm is transmitted within a circular region having a diameter of 2b, and all light is reflected outside the circular region having a diameter of 2b. Accordingly, if the focal length of the objective lens 4a is fa, the effective numerical apertures for light with wavelengths of 405 nm and 650 nm are given by a / fa and b / fa, respectively. For example, a / fa = 0.7 and b / fa = 0.6 are set.

FIG. 3A shows the configuration of the optical system 1a. Light emitted from the semiconductor laser 9a having a wavelength of 405 nm is collimated by the collimator lens 10a. The collimated outgoing light is incident on the polarization beam splitter 11 as P-polarized light and is almost 100% transmitted, passes through the quarter-wave plate 12, is converted from linearly polarized light to circularly polarized light, and travels toward the disk 5a. .

The reflected light from the disk 5a passes through the quarter-wave plate 12 and is converted from circularly polarized light into linearly polarized light whose outgoing path and polarization direction are orthogonal. The converted reflected light is incident on the polarization beam splitter 11 as S-polarized light and is reflected almost 100%, passes through the cylindrical lens 13a and the lens 14a, and is received by the photodetector 15a. The photodetector 15a is installed in the middle of the two focal lines of the cylindrical lens 13a and the lens 14a.

FIG. 3B shows the configuration of the photodetector 15a. The reflected light from the disk 5a forms a light spot 16a on the light receiving portions 17a to 17d divided into four. When the outputs from the light receiving portions 17a to 17d are respectively represented by V17a to V17d, the focus error signal is obtained from the calculation of (V17a + V17d) − (V17b + V17c) by a known astigmatism method. The track error signal is obtained from the calculation of (V17a + V17b) − (V17c + V17d) by a known push-pull method. The RF signal from the disk 5a is obtained from the calculation of V17a + V17b + V17c + V17d.

FIG. 4A shows the configuration of the optical system 1b. The light emitted from the semiconductor laser 9b having a wavelength of 650 nm is collimated by the collimator lens 10b, about 50% is transmitted through the half mirror 18a, is transmitted through the concave lens 19a, and is converted from parallel light to divergent light, and is converted to the disk 5b. Head.

Reflected light from the disk 5b is transmitted from the concave lens 19a to be converted from convergent light to parallel light, approximately 50% is reflected by the half mirror 18a, is transmitted by the cylindrical lens 13b and the lens 14b, and is received by the photodetector 15b. Is done. The photodetector 15b is installed in the middle of the two focal lines of the cylindrical lens 13b and the lens 14b.

FIG. 4B shows the configuration of the photodetector 15b. The reflected light from the disk 5b forms a light spot 16b on the light receiving portions 17e to 17h divided into four. When the outputs from the light receiving portions 17e to 17h are respectively expressed as V17e to V17h, the focus error signal is obtained from the calculation of (V17e + V17h) − (V17f + V17g) by a known astigmatism method. The track error signal is obtained from the phase difference of V17e + V17h and V17f + V17g by a known phase difference method. The RF signal from the disk 5b is obtained from the calculation of V17e + V17f + V17g + V17h.

FIG. 5 shows a design result of the phase filter pattern 6a in the wavelength selection filter 3a. The left column indicates the height of the incident light on the objective lens 4a normalized by the focal length of the objective lens 4a. The right column is the number of stages of the corresponding phase filter pattern 6a.

FIG. 6 shows a calculation result of the wavefront aberration at the position of the best image plane where the standard deviation of the wavefront aberration with respect to light having a wavelength of 650 nm is minimized. FIG. 6A shows a case where the wavelength selection filter 3a is not used by using the magnification change of the objective lens 4a. FIG. 6B shows a case where the wavelength selection filter 3a is further used by using the magnification change of the objective lens 4a. In the figure, the horizontal axis represents wavefront aberration, and the vertical axis represents the height of incident light on the objective lens 4a normalized by the focal length of the objective lens 4a.

The standard deviation of the wavefront aberration is reduced to 0.047λ by further using the wavelength selective filter 3a using the magnification change of the objective lens 4a. This value is lower than 0.07λ, which is an allowable value of the standard deviation of wavefront aberration, which is known as a Marechal standard. Further, as shown in FIG. 5, since the number of concentric regions constituting the phase filter pattern 6a is as small as 5, the width of each region is widened. If the focal length of the objective lens 4a is 2.57 mm, for example, the width of the outermost region is about 59.1 μm. Therefore, it is very easy to manufacture the wavelength selective filter 3a having the phase filter pattern 6a having a wide width in each region as described above with a desired accuracy.

Each of the dielectric multilayer films 7a and 7b in the wavelength selective filter 3a has a configuration in which, for example, a high refractive index layer made of titanium dioxide and a low refractive index layer made of silicon dioxide, for example, are alternately stacked. FIG. 7A shows the design result of the wavelength dependence of the transmittance for the dielectric multilayer films 7a and 7b, and FIG. 7B shows the design result of the wavelength dependence of the phase of the transmitted light for the dielectric multilayer films 7a and 7b. Show.

The dotted line and the alternate long and short dash line in the figure are design results for the dielectric multilayer films 7a and 7b, respectively. As shown in FIG. 7A, the dielectric multilayer film 7a transmits all light having a wavelength of 405 nm and light having a wavelength of 650 nm, and the dielectric multilayer film 7b transmits all light having a wavelength of 405 nm and transmits all light having a wavelength of 650 nm. You can see that it reflects.

Further, as shown in FIG. 7B, the phase of the transmitted light of the dielectric multilayer films 7a and 7b matches the wavelength of 405 nm, so that the phase difference of the transmitted light is adjusted to an integral multiple of 2π. I understand. When the thickness of each layer of the dielectric multilayer film is increased, the wavelength dependence curve of the transmittance shown in FIG. 7A and the wavelength dependence curve of the phase of the transmitted light shown in FIG. Shift to.

Further, when the thickness of each layer is reduced, the wavelength dependence curve of transmittance shown in FIG. 7A and the wavelength dependence curve of transmitted light phase shown in FIG. 7B are both shifted to the left. . Therefore, regarding the dielectric multilayer film 7a, the thickness of each layer is changed within a range in which the transmittance at wavelengths of 405 nm and 650 nm is approximately 100%. Regarding the dielectric multilayer film 7b, the thickness of each layer is changed within a range in which the transmittance at a wavelength of 405 nm is approximately 100% and the transmittance at a wavelength of 650 nm is approximately 0%. Adjustment is made so that the phases of the transmitted light of the dielectric multilayer films 7a and 7b at the wavelength of 405 nm coincide.

As a result, the above design can be realized. At the wavelength of 405 nm, the phase of the transmitted light of the remaining one dielectric multilayer film may be adjusted on the basis of the phase of the transmitted light of one dielectric multilayer film. This adjustment is possible if there is a degree of freedom.

(Second Embodiment of Optical Head Device) FIG. 8 shows a second embodiment of the optical head device of the present invention. The optical system 1a, the optical system 1b, and the optical system 1c include a semiconductor laser and a photodetector that receives reflected light from the disk. The wavelength of the semiconductor laser in the optical system 1a is 405 nm, the wavelength of the semiconductor laser in the optical system 1b is 650 nm, and the wavelength of the semiconductor laser in the optical system 1c is 780 nm.

The interference filter 2a functions to transmit light having a wavelength of 405 nm and reflect light having a wavelength of 650 nm. The interference filter 2b functions to transmit light having wavelengths of 405 nm and 650 nm and reflect light having a wavelength of 780 nm. The light emitted from the semiconductor laser in the optical system 1a passes through the interference filter 2a, the interference filter 2b, and the wavelength selection filter 3b, enters the objective lens 4a as parallel light, and has a substrate thickness of 0.1 mm. The light is condensed on the disk 5a.

The reflected light from the disk 5a passes through the objective lens 4a, the wavelength selection filter 3b, the interference filter 2b, and the interference filter 2a in the reverse direction and is received by the photodetector in the optical system 1a.

The light emitted from the semiconductor laser in the optical system 1b is reflected by the interference filter 2a, passes through the interference filter 2b and the wavelength selection filter 3b, enters the objective lens 4a as divergent light, and has a substrate thickness of 0.6 mm. Are condensed on the DVD standard disk 5b. The reflected light from the disk 5b passes through the objective lens 4a, the wavelength selection filter 3b, and the interference filter 2b in the opposite directions, is reflected by the interference filter 2a, and is received by the photodetector in the optical system 1b.

Furthermore, the light emitted from the semiconductor laser in the optical system 1c is reflected by the interference filter 2b, passes through the wavelength selection filter 3b, enters the objective lens 4a as diverging light, and meets the CD standard with a substrate thickness of 1.2 mm. It is condensed on the disk 5c. The reflected light from the disk 5c passes through the objective lens 4a and the wavelength selection filter 3b in the opposite directions, is reflected by the interference filter 2b, and is received by the photodetector in the optical system 1c.

The objective lens 4a has spherical aberration that cancels spherical aberration that occurs when light having a wavelength of 405 nm incident as parallel light on the objective lens 4a passes through a substrate having a thickness of 0.1 mm.

Since light with a wavelength of 405 nm enters the objective lens 4a as parallel light, the magnification of the objective lens 4a with respect to light with a wavelength of 405 nm is zero. On the other hand, spherical aberration remains when light having a wavelength of 650 nm incident as parallel light on the objective lens 4a is transmitted through a substrate having a thickness of 0.6 mm. When light having a wavelength of 650 nm is made incident on the objective lens 4a as diverging light, new spherical aberration is caused by a change in magnification of the objective lens 4a, and this acts in a direction to reduce the remaining spherical aberration. The magnification of the objective lens 4a with respect to light having a wavelength of 650 nm is set to 0.076.

Further, spherical light remains when light having a wavelength of 780 nm incident as parallel light on the objective lens 4a passes through a substrate having a thickness of 1.2 mm. When light having a wavelength of 780 nm is made incident on the objective lens 4a as diverging light, new spherical aberration is caused by a change in magnification of the objective lens 4a, and this acts in a direction to reduce the remaining spherical aberration. The magnification of the objective lens 4a with respect to light having a wavelength of 780 nm is set to 0.096.

Here, the angle formed by the paraxial light beam traveling from the object point toward the predetermined height r of the objective lens 4a with the optical axis of the objective lens 4a is θo, and the paraxial light beam traveling from the predetermined height r of the objective lens 4a toward the image point. Is the angle formed by the optical axis of the objective lens 4a with θi, the magnification of the objective lens 4a is given by tan θo / tan θi.

If the distance from the object point to the object side principal point of the objective lens 4a is lo and the distance from the image side principal point to the image point of the objective lens 4a is li, tan θo = r / lo and tan θi = r / li are obtained. Since light having a wavelength of 405 nm enters the objective lens 4a as parallel light, θo = 0 and lo = ∞, and the magnification of the objective lens 4a is zero.

Since light having a wavelength of 650 nm enters the objective lens 4a as diverging light, θo ≠ 0 and lo are finite. The value of lo at this time, that is, the position of the object point is determined so that the magnification of the objective lens 4a is 0.076. Since light having a wavelength of 780 nm is incident on the objective lens 4a as diverging light, θo ≠ 0 and lo are finite. The value of lo at this time, that is, the position of the object point is determined so that the magnification of the objective lens 4a is 0.096.

FIG. 9A is a plan view seen from one surface of the wavelength selective filter 3b. FIG. 9B is a plan view seen from the other surface of the wavelength selective filter 3b. FIG. 9C is a cross-sectional view of the wavelength selection filter 3b. In the wavelength selection filter 3b, a concentric phase filter pattern 6a is formed on a glass substrate 8a. Further, dielectric multilayer films 7c, 7d, and 7e are formed on the glass substrate 8b. The wavelength selection filter 3b has a configuration in which the surface of the glass substrate 8a where the phase filter pattern 6a is not formed and the surface of the glass substrate 8b where the dielectric multilayer films 7c, 7d and 7e are not formed are bonded together with an adhesive. It is.

When the effective diameter of the objective lens 4a indicated by a dotted line in the drawing is 2a, the phase filter pattern 6a is formed only in a circular region having a diameter 2b smaller than this. The cross section of the phase filter pattern 6a has a four-level step shape as shown in FIG. The height of each stage of the phase filter pattern 6a is set so that the phase difference of the light passing through the part with and without the pattern at each stage is 2π (equivalent to 0) with respect to the wavelength of 405 nm. At this time, this phase difference is 1.25π (equivalent to −0.75π) and 1.04π (equivalent to −0.96π) for wavelengths of 650 nm and 780 nm, respectively.

Therefore, the phase filter pattern 6a does not change the phase distribution for light with a wavelength of 405 nm, and changes the phase distribution for light with wavelengths of 650 nm and 780 nm. When the wavelength selection filter 3b is not used, when the magnification of the objective lens 4a is set to 0.076, light having a wavelength of 650 nm incident as parallel light on the objective lens 4a passes through a substrate having a thickness of 0.6 mm. Residual spherical aberration is reduced. The phase filter pattern 6a is designed such that a change in phase distribution with respect to light having a wavelength of 650 nm further reduces this reduced spherical aberration at the magnification 0.076 of the objective lens 4a.

On the other hand, the dielectric multilayer film 7c is formed only in a circular region having a diameter 2c smaller than the diameter 2b. The dielectric multilayer film 7d is formed only outside the circular region having the diameter 2c and inside the circular region having the diameter 2b. The dielectric multilayer film 7e is formed only outside the circular region having the diameter 2b. The dielectric multilayer film 7c functions to transmit all light having a wavelength of 405 nm, light having a wavelength of 650 nm, and light having a wavelength of 780 nm. The dielectric multilayer film 7d functions to transmit all light having a wavelength of 405 nm and light having a wavelength of 650 nm and reflect all light having a wavelength of 780 nm. The dielectric multilayer film 7e functions to transmit all light having a wavelength of 405 nm and reflect all light having a wavelength of 650 nm and light having a wavelength of 780 nm.

For the wavelength of 405 nm, the phase difference between the light transmitted through the dielectric multilayer film 7c, the light transmitted through the dielectric multilayer film 7d, and the light transmitted through the dielectric multilayer film 7e is adjusted to an integral multiple of 2π. For a wavelength of 650 nm, the phase difference between the light transmitted through the dielectric multilayer film 7c and the light transmitted through the dielectric multilayer film 7d is adjusted to an integral multiple of 2π. That is, in the wavelength selection filter 3b, all light having a wavelength of 405 nm is transmitted, all light having a wavelength of 650 nm is transmitted within a circular region having a diameter of 2b, and all light is reflected outside the circular region having a diameter of 2b. All light having a wavelength of 780 nm is transmitted within a circular region having a diameter of 2c, and all light is reflected outside the circular region having a diameter of 2c.

Therefore, when the focal length of the objective lens 4a is fa, the effective numerical apertures for light with wavelengths of 405 nm, 650 nm, and 780 nm are given by a / fa, b / fa, and c / fa, respectively. For example, a / fa = 0.7, b / fa = 0.6, and c / fa = 0.45 are set.

The configuration of the optical system 1a is as shown in FIG. The configuration of the photodetector 15a provided in the optical system 1a is as shown in FIG. The configuration of the optical system 1b is as shown in FIG. The configuration of the photodetector 15b provided in the optical system 1b is as shown in FIG.

FIG. 10A shows the configuration of the optical system 1c. The light emitted from the semiconductor laser 9c having a wavelength of 780 nm is divided into three light beams of 0th order light and ± 1st order diffracted light by the diffractive optical element 20. These lights are collimated by the collimator lens 10c, and about 50% are transmitted through the half mirror 18b, are transmitted through the concave lens 19b, are converted from parallel light into divergent light, and travel toward the disk 5c. The three reflected lights from the disk 5c are transmitted through the concave lens 19b and converted from convergent light into parallel light, about 50% are reflected by the half mirror 18b, and are transmitted through the cylindrical lens 13c and the lens 14c to be detected by the photodetector 15c. Is received. The photodetector 15c is installed in the middle of the two focal lines of the cylindrical lens 13c and the lens 14c.

FIG. 10B shows the configuration of the photodetector 15c. Of the three reflected lights from the disk 5c, the zero-order light from the diffractive optical element 20 forms a light spot 16c on the light receiving portions 17i to 17l divided into four. The + 1st order diffracted light from the diffractive optical element 20 forms a light spot 16d on the light receiving portion 17m. The −1st order diffracted light from the diffractive optical element 20 forms a light spot 16e on the light receiving portion 17n.

When the outputs from the light receiving portions 17i to 17n are respectively expressed as V17i to V17n, the focus error signal is obtained from the calculation of (V17i + V17l) − (V17j + V17k) by a known astigmatism method. The track error signal is obtained from the calculation of V17m-V17n by a known three beam method. The RF signal from the disk 5c is obtained from the calculation of V17i + V17j + V17k + V171.

The design result of the phase filter pattern 6a in the wavelength selective filter 3b is as shown in FIG. Further, the calculation result of the wavefront aberration at the position of the best image plane where the standard deviation of the wavefront aberration with respect to light having a wavelength of 650 nm is minimized is as shown in FIG.

FIG. 11 shows a calculation result of the wavefront aberration at the position of the best image plane where the standard deviation of the wavefront aberration with respect to light having a wavelength of 780 nm is minimized. FIG. 11A shows a case where the wavelength selection filter 3b is not used by using the magnification change of the objective lens 4a. FIG. 11B shows a case where the wavelength selection filter 3b is further used by using the magnification change of the objective lens 4a. In the figure, the horizontal axis represents wavefront aberration, and the vertical axis represents the height of incident light on the objective lens 4a normalized by the focal length of the objective lens 4a.

The standard deviation of the wavefront aberration is reduced to 0.021λ by using the change in magnification of the objective lens 4a and further using the wavelength selective filter 3b. This value is lower than 0.07λ, which is an allowable value of the standard deviation of wavefront aberration, which is known as a Marechal standard. Further, as shown in FIG. 5, since the number of concentric regions constituting the phase filter pattern 6a is as small as 5, the width of each region is widened. If the focal length of the objective lens 4a is 2.57 mm, for example, the width of the outermost region is about 59.1 μm. Therefore, it is very easy to manufacture the wavelength selective filter 3b having the phase filter pattern 6a having a wide width in each region as described above with a desired accuracy.

Each of the dielectric multilayer films 7c, 7d, and 7e in the wavelength selection filter 3b has a configuration in which high refractive index layers made of, for example, titanium dioxide and low refractive index layers made of, for example, silicon dioxide are alternately stacked. is there. FIG. 7A shows the wavelength dependence of the transmittance of the dielectric multilayer films 7c, 7d, and 7e. FIG. 7B shows the wavelength dependence of the phase of the transmitted light with respect to the dielectric multilayer films 7c, 7d, and 7e. The design results are shown. Solid lines, dotted lines, and alternate long and short dash lines in the figure are design results for the dielectric multilayer films 7c, 7d, and 7e, respectively.

From FIG. 7A, the dielectric multilayer film 7c transmits all light having a wavelength of 405 nm, light having a wavelength of 650 nm, and light having a wavelength of 780 nm. The dielectric multilayer film 7d transmits all light having a wavelength of 405 nm and light having a wavelength of 650 nm and reflects all light having a wavelength of 780 nm. It can be seen that the dielectric multilayer film 7e transmits all light having a wavelength of 405 nm and reflects all light having a wavelength of 650 nm and light having a wavelength of 780 nm.

Further, from FIG. 7B, the phase of the transmitted light of the dielectric multilayer films 7c, 7d, and 7e is matched to the wavelength of 405 nm, so that the phase difference of the transmitted light is adjusted to an integral multiple of 2π. I understand that. Moreover, since the phase of the transmitted light of the dielectric multilayer films 7c and 7d is in agreement with the wavelength of 650 nm, it can be seen that the phase difference of the transmitted light is adjusted to an integral multiple of 2π.

When the thickness of each layer of the dielectric multilayer film is increased, the wavelength dependence curve of the transmittance shown in FIG. 7A and the wavelength dependence curve of the phase of the transmitted light shown in FIG. Shift to. On the other hand, when the thickness of each layer is reduced, the wavelength dependence curve of the transmittance shown in FIG. 7A and the wavelength dependence curve of the phase of the transmitted light shown in FIG. Shift to.

Further, when the number of layers of the dielectric multilayer film is increased, the wavelength dependence curve of the transmittance shown in FIG. 7A and the wavelength dependence curve of the phase of the transmitted light shown in FIG. Becomes sudden. On the other hand, when the number of layers is reduced, both the wavelength dependence curve of the transmittance shown in FIG. 7A and the wavelength dependence curve of the phase of the transmitted light shown in FIG. Become.

Therefore, regarding the dielectric multilayer film 7c, the thickness and the number of layers are changed within a range in which the transmittance at wavelengths of 405 nm, 650 nm, and 780 nm is approximately 100%. Regarding the dielectric multilayer film 7d, the thickness and the number of layers are changed so that the transmittance at wavelengths of 405 nm and 650 nm is approximately 100% and the transmittance at a wavelength of 780 nm is approximately 0%. Regarding the dielectric multilayer film 7e, the thickness and the number of layers are changed so that the transmittance at a wavelength of 405 nm is approximately 100% and the transmittance at wavelengths of 650 nm and 780 nm is approximately 0%. Adjustment is made so that the phases of the transmitted light of the dielectric multilayer films 7c, 7d, and 7e at the wavelength of 405 nm match and the phases of the transmitted light of the dielectric multilayer films 7c and 7d at the wavelength of 650 nm match.

The above design can be realized by satisfying these conditions. At a wavelength of 405 nm, the phase of the transmitted light of the remaining two dielectric multilayer films may be adjusted based on the phase of the transmitted light of one dielectric multilayer film. Therefore, this adjustment is possible if there are two degrees of freedom, ie, the thickness of each layer and the number of layers of the dielectric multilayer film. Further, at the wavelength of 650 nm, the phase of the transmitted light of the remaining one dielectric multilayer film may be adjusted with reference to the phase of the transmitted light of one dielectric multilayer film. Therefore, this adjustment is possible if there is one degree of freedom of the thickness of each layer of the dielectric multilayer film.

In the embodiment shown in FIGS. 1 and 8, the wavelength selection filters 3a and 3b are driven in the focusing direction and the tracking direction by an actuator together with the objective lens 4a. When only the objective lens 4a is driven in the focusing direction and the tracking direction by the actuator, the center of the phase filter pattern 6a in the wavelength selection filters 3a and 3b and the center of the objective lens 4a are shifted in the focusing direction and the tracking direction. Therefore, aberration occurs in light that enters the objective lens 4a as divergent light and undergoes a phase distribution change by the phase filter pattern 6a. However, when the wavelength selection filters 3a and 3b are driven in the focusing direction and the tracking direction by the actuator together with the objective lens 4a, such aberration does not occur.

In the embodiment shown in FIGS. 1 and 8, the normal lines of the wavelength selection filters 3a and 3b are slightly inclined with respect to the optical axis of the objective lens 4a. When the normal lines of the wavelength selection filters 3a, 3b are parallel to the optical axis of the objective lens 4a, the stray light reflected by the wavelength selection filters 3a, 3b is a photodetector 15a provided in the optical systems 1a, 1b, 1c. , 15b, 15c, and offset occurs in the focus error signal and the track error signal. However, such an offset does not occur when the normal lines of the wavelength selection filters 3a and 3b are slightly inclined with respect to the optical axis of the objective lens 4a.

In the wavelength selection filter 3a shown in FIG. 2 and the wavelength selection filter 3b shown in FIG. 9, the phase filter pattern 6a is formed on the glass substrate 8a, and the dielectric multilayer films 7a, 7b, 7c, 7d, and 7e are formed on the glass substrate 8b. Is formed. On the other hand, a configuration in which the phase filter pattern is formed integrally with the substrate by molding glass or plastic is also possible. A configuration in which a phase filter pattern or a dielectric multilayer film is formed on the objective lens is also possible.

(Third Embodiment of Optical Head Device) FIG. 12 shows a third embodiment of the optical head device of the present invention. The optical system 1a and the optical system 1d include a semiconductor laser and a photodetector that receives reflected light from the disk. The wavelength of the semiconductor laser in the optical system 1a is 405 nm, and the wavelength of the semiconductor laser in the optical system 1d is 650 nm. The interference filter 2a functions to transmit light having a wavelength of 405 nm and reflect light having a wavelength of 650 nm.

The light emitted from the semiconductor laser in the optical system 1a passes through the interference filter 2a and the aperture control element 21a, enters the objective lens 4a as parallel light, and is incident on the next-generation standard disk 5a having a substrate thickness of 0.1 mm. Focused. The reflected light from the disk 5a passes through the objective lens 4a, the aperture control element 21a, and the interference filter 2a in the reverse direction and is received by the photodetector in the optical system 1a.

The light emitted from the semiconductor laser in the optical system 1d is reflected by the interference filter 2a, passes through the aperture control element 21a, enters the objective lens 4a as diverging light, and meets the DVD standard with a substrate thickness of 0.6 mm. It is condensed on the disk 5b. The reflected light from the disk 5b passes through the objective lens 4a and the aperture control element 21a in the opposite direction, is reflected by the interference filter 2a, and is received by the photodetector in the optical system 1d. The objective lens 4a has spherical aberration that cancels spherical aberration that occurs when light having a wavelength of 405 nm incident as parallel light on the objective lens 4a passes through a substrate having a thickness of 0.1 mm.

Since light with a wavelength of 405 nm enters the objective lens 4a as parallel light, the magnification of the objective lens 4a with respect to light with a wavelength of 405 nm is zero. On the other hand, spherical aberration remains when light having a wavelength of 650 nm incident as parallel light on the objective lens 4a is transmitted through a substrate having a thickness of 0.6 mm. When light having a wavelength of 650 nm is made incident on the objective lens 4a as diverging light, new spherical aberration is caused by a change in magnification of the objective lens 4a, and this acts in a direction to reduce the remaining spherical aberration.

The magnification of the objective lens 4a with respect to light having a wavelength of 650 nm is set to 0.076. Here, the angle formed by the paraxial light beam traveling from the object point toward the predetermined height r of the objective lens 4a with the optical axis of the objective lens 4a is θo, and the paraxial light beam traveling from the predetermined height r of the objective lens 4a toward the image point. Is the angle formed by the optical axis of the objective lens 4a with θi, the magnification of the objective lens 4a is given by tan θo / tan θi. If the distance from the object point to the object side principal point of the objective lens 4a is lo and the distance from the image side principal point to the image point of the objective lens 4a is li, tan θo = r / lo and tan θi = r / li are obtained.

Since light having a wavelength of 405 nm is incident on the objective lens 4a as parallel light, θo = 0 and lo = ∞, and the magnification of the objective lens 4a is zero. Since light having a wavelength of 650 nm is incident on the objective lens 4a as diverging light, θo ≠ 0 and lo are finite. At this time, the value of lo, that is, the position of the object point, has a magnification of 0.076 for the objective lens 4a. It is determined as follows.

FIG. 13A is a plan view of the opening control element 21a, and FIG. 13B is a cross-sectional view of the opening control element 21a. The opening control element 21a has a configuration in which dielectric multilayer films 7a and 7b are formed on a glass substrate 8b. When the effective diameter of the objective lens 4a indicated by a dotted line in the drawing is 2a, the dielectric multilayer film 7a is formed only in a circular region having a diameter 2b smaller than this. The dielectric multilayer film 7b is formed only outside the circular region having the diameter 2b.

The dielectric multilayer film 7a functions to transmit all light having a wavelength of 405 nm and light having a wavelength of 650 nm. The dielectric multilayer film 7b functions to transmit all light having a wavelength of 405 nm and reflect all light having a wavelength of 650 nm. The phase difference between the light transmitted through the dielectric multilayer film 7a and the light transmitted through the dielectric multilayer film 7b is adjusted to an integral multiple of 2π with respect to the wavelength of 405 nm. That is, in the aperture control element 21a, all light having a wavelength of 405 nm is transmitted, all light having a wavelength of 650 nm is transmitted within a circular region having a diameter of 2b, and all light is reflected outside the circular region having a diameter of 2b. Accordingly, if the focal length of the objective lens 4a is fa, the effective numerical apertures for light with wavelengths of 405 nm and 650 nm are given by a / fa and b / fa, respectively. For example, a / fa = 0.7 and b / fa = 0.6 are set.

The configuration of the optical system 1a is as shown in FIG. 3A, and the configuration of the photodetector 15a provided in the optical system 1a is as shown in FIG. 3B.

FIG. 14 shows the configuration of the optical system 1d. The light emitted from the semiconductor laser 9b having a wavelength of 650 nm is converted into parallel light by the collimator lens 10b, approximately 50% is transmitted through the half mirror 18a, and is transmitted through the spherical aberration correction element 22a and the concave lens 19a to be converted into divergent light from the parallel light. Converted to the disk 5b. Reflected light from the disk 5b is transmitted through the concave lens 19a and the spherical aberration correction element 22a to be converted from convergent light into parallel light, about 50% is reflected by the half mirror 18a, and transmitted through the cylindrical lens 13b and the lens 14b. Light is received by the photodetector 15b. The photodetector 15b is installed in the middle of the two focal lines of the cylindrical lens 13b and the lens 14b. The configuration of the photodetector 15b provided in the optical system 1d is as shown in FIG.

One surface of the spherical aberration correction element 22a is a flat surface, and the other surface is an aspheric surface. The spherical aberration correction element 22a changes the phase distribution with respect to light having a wavelength of 650 nm. When the spherical aberration correction element 22a is not used, when the magnification of the objective lens 4a is set to 0.076, light having a wavelength of 650 nm incident on the objective lens 4a as parallel light passes through a substrate having a thickness of 0.6 mm. Spherical aberration remaining in is reduced. The spherical aberration correction element 22a is designed so that a change in phase distribution with respect to light having a wavelength of 650 nm substantially completely corrects the reduced spherical aberration at the magnification 0.076 of the objective lens 4a. The spherical aberration correcting element 22a can be integrated with the concave lens 19a.

Each of the dielectric multilayer films 7a and 7b in the opening control element 21a has a configuration in which, for example, a high refractive index layer made of titanium dioxide and a low refractive index layer made of silicon dioxide, for example, are alternately stacked. The design result of the wavelength dependency of the transmittance for the dielectric multilayer films 7a and 7b is as shown in FIG. The design result of the wavelength dependence of the phase of the transmitted light with respect to the dielectric multilayer films 7a and 7b is as shown in FIG. 7B.

(Fourth Embodiment of Optical Head Device) FIG. 15 shows a fourth embodiment of the optical head device of the present invention. The optical system 1a, the optical system 1d, and the optical system 1e include a semiconductor laser and a photodetector that receives reflected light from the disk. The wavelength of the semiconductor laser in the optical system 1a is 405 nm, the wavelength of the semiconductor laser in the optical system 1d is 650 nm, and the wavelength of the semiconductor laser in the optical system 1e is 780 nm. The interference filter 2a functions to transmit light having a wavelength of 405 nm and reflect light having a wavelength of 650 nm. The interference filter 2b functions to transmit light having wavelengths of 405 nm and 650 nm and reflect light having a wavelength of 780 nm.

The light emitted from the semiconductor laser in the optical system 1a passes through the interference filter 2a, the interference filter 2b, and the aperture control element 21b, enters the objective lens 4a as parallel light, and meets the next-generation standard with a substrate thickness of 0.1 mm. It is condensed on the disk 5a. The reflected light from the disk 5a passes through the objective lens 4a, the aperture control element 21b, the interference filter 2b, and the interference filter 2a in the reverse direction, and is received by the photodetector in the optical system 1a.

The light emitted from the semiconductor laser in the optical system 1d is reflected by the interference filter 2a, passes through the interference filter 2b and the aperture control element 21b, enters the objective lens 4a as divergent light, and has a substrate thickness of 0.6 mm. Are condensed on the DVD standard disk 5b. The reflected light from the disk 5b passes through the objective lens 4a, the aperture control element 21b, and the interference filter 2b in the reverse direction, is reflected by the interference filter 2a, and is received by the photodetector in the optical system 1d.

Furthermore, the light emitted from the semiconductor laser in the optical system 1e is reflected by the interference filter 2b, passes through the aperture control element 21b, enters the objective lens 4a as divergent light, and meets the CD standard with a substrate thickness of 1.2 mm. It is condensed on the disk 5c. The reflected light from the disk 5c passes through the objective lens 4a and the aperture control element 21b in the opposite direction, is reflected by the interference filter 2b, and is received by the photodetector in the optical system 1e. The objective lens 4a has spherical aberration that cancels spherical aberration that occurs when light having a wavelength of 405 nm incident as parallel light on the objective lens 4a passes through a substrate having a thickness of 0.1 mm.

Since light with a wavelength of 405 nm enters the objective lens 4a as parallel light, the magnification of the objective lens 4a with respect to light with a wavelength of 405 nm is zero. On the other hand, spherical aberration remains when light having a wavelength of 650 nm incident as parallel light on the objective lens 4a is transmitted through a substrate having a thickness of 0.6 mm. When light having a wavelength of 650 nm is made incident on the objective lens 4a as diverging light, new spherical aberration is caused by a change in magnification of the objective lens 4a, and this acts in a direction to reduce the remaining spherical aberration. The magnification of the objective lens 4a with respect to light having a wavelength of 650 nm is set to 0.076.

Further, spherical light remains when light having a wavelength of 780 nm incident as parallel light on the objective lens 4a passes through a substrate having a thickness of 1.2 mm. When light having a wavelength of 780 nm is made incident on the objective lens 4a as diverging light, new spherical aberration is caused by a change in magnification of the objective lens 4a, and this acts in a direction to reduce the remaining spherical aberration. The magnification of the objective lens 4a with respect to light having a wavelength of 780 nm is set to 0.096.

Here, the angle formed by the paraxial light beam traveling from the object point toward the predetermined height r of the objective lens 4a with the optical axis of the objective lens 4a is θo, and the paraxial light beam traveling from the predetermined height r of the objective lens 4a toward the image point. Is the angle formed by the optical axis of the objective lens 4a with θi, the magnification of the objective lens 4a is given by tan θo / tan θi. If the distance from the object point to the object side principal point of the objective lens 4a is lo and the distance from the image side principal point to the image point of the objective lens 4a is li, tan θo = r / lo and tan θi = r / li are obtained. Since light having a wavelength of 405 nm enters the objective lens 4a as parallel light, θo = 0 and lo = ∞, and the magnification of the objective lens 4a is zero.

Since light having a wavelength of 650 nm is incident on the objective lens 4a as diverging light, θo ≠ 0 and lo are finite. At this time, the value of lo, that is, the position of the object point, has a magnification of 0.076 for the objective lens 4a. It is determined as follows. Since light having a wavelength of 780 nm is incident on the objective lens 4a as diverging light, θo ≠ 0 and lo are finite. At this time, the value of lo, that is, the position of the object point, has a magnification of 0.096 for the objective lens 4a. It is determined as follows.

FIG. 16A is a plan view of the aperture control element 21b. FIG. 16B is a cross-sectional view of the opening control element 21b. The opening control element 21b has a configuration in which dielectric multilayer films 7c, 7d, and 7e are formed on a glass substrate 8b. When the effective diameter of the objective lens 4a indicated by a dotted line in the drawing is 2a, the dielectric multilayer film 7c is formed only in a circular region having a diameter 2c smaller than the smaller diameter 2b. The dielectric multilayer film 7d is formed only outside the circular region having the diameter 2c and inside the circular region having the diameter 2b. The dielectric multilayer film 7e is formed only outside the circular region having the diameter 2b.

The dielectric multilayer film 7c functions to transmit all light having a wavelength of 405 nm, light having a wavelength of 650 nm, and light having a wavelength of 780 nm. The dielectric multilayer film 7d functions to transmit all light having a wavelength of 405 nm and light having a wavelength of 650 nm and reflect all light having a wavelength of 780 nm. The dielectric multilayer film 7e functions to transmit all light having a wavelength of 405 nm and reflect all light having a wavelength of 650 nm and light having a wavelength of 780 nm. Further, with respect to the wavelength of 405 nm, the phase difference between the light transmitted through the dielectric multilayer film 7c, the light transmitted through the dielectric multilayer film 7d, and the light transmitted through the dielectric multilayer film 7e is adjusted to an integral multiple of 2π. . For a wavelength of 650 nm, the phase difference between the light transmitted through the dielectric multilayer film 7c and the light transmitted through the dielectric multilayer film 7d is adjusted to an integral multiple of 2π.

That is, in the aperture control element 21b, all light having a wavelength of 405 nm is transmitted, all light having a wavelength of 650 nm is transmitted within a circular region having a diameter of 2b, and all light is reflected outside the circular region having a diameter of 2b. All of the light having a wavelength of 780 nm is transmitted within a circular region having a diameter of 2c, and is entirely reflected outside the circular region having a diameter of 2c. Therefore, when the focal length of the objective lens 4a is fa, the effective numerical apertures for light with wavelengths of 405 nm, 650 nm, and 780 nm are given by a / fa, b / fa, and c / fa, respectively. For example, a / fa = 0.7, b / fa = 0.6, and c / fa = 0.45 are set.

The configuration of the optical system 1a is as shown in FIG. 3A, and the configuration of the photodetector 15a provided in the optical system 1a is as shown in FIG. 3B. The configuration of the optical system 1d is as shown in FIG. 14, and the configuration of the photodetector 15b provided in the optical system 1d is as shown in FIG. 4B.

FIG. 17 shows the configuration of the optical system 1e. The light emitted from the semiconductor laser 9c having a wavelength of 780 nm is divided into three light beams of 0th order light and ± 1st order diffracted light by the diffractive optical element 20. These lights are collimated by the collimator lens 10c, and about 50% are transmitted through the half mirror 18b, and are transmitted through the spherical aberration correction element 22b and the concave lens 19b to be converted from parallel light into divergent light, and travel toward the disk 5c. . The three reflected lights from the disk 5c are transmitted through the concave lens 19b and the spherical aberration correction element 22b and converted from convergent light to parallel light, and about 50% are reflected by the half mirror 18b, and transmitted through the cylindrical lens 13c and the lens 14c. Then, the light is received by the photodetector 15c. The photodetector 15c is installed in the middle of the two focal lines of the cylindrical lens 13c and the lens 14c. The configuration of the photodetector 15c provided in the optical system 1e is as shown in FIG.

One surface of the spherical aberration correction element 22b is a flat surface, and the other surface is an aspheric surface. The spherical aberration correction element 22b changes the phase distribution with respect to light having a wavelength of 780 nm. When the spherical aberration correction element 22b is not used, when the magnification of the objective lens 4a is set to 0.096, light having a wavelength of 780 nm incident as parallel light on the objective lens 4a passes through a substrate having a thickness of 1.2 mm. Spherical aberration remaining in is reduced. The spherical aberration correction element 22b is designed so that a change in phase distribution for light having a wavelength of 780 nm corrects this reduced spherical aberration at the magnification 0.096 of the objective lens 4a almost completely. Note that the spherical aberration correction element 22b can be integrated with the concave lens 19b.

Each of the dielectric multilayer films 7c, 7d, and 7e in the aperture control element 21b has a configuration in which high refractive index layers made of, for example, titanium dioxide and low refractive index layers made of, for example, silicon dioxide are alternately stacked. . The design result of the wavelength dependence of the transmittance for the dielectric multilayer films 7c, 7d, and 7e is as shown in FIG. 7A, and the wavelength dependence of the phase of the transmitted light with respect to the dielectric multilayer films 7c, 7d, and 7e. The design result is as shown in FIG.

In the embodiment shown in FIGS. 12 and 15, when the objective lens 4a is driven in the tracking direction by the actuator, the centers of the spherical aberration correction elements 22a and 22b and the center of the objective lens 4a are shifted in the tracking direction. The aberration correction elements 22a and 22b receive a change in phase distribution, and coma aberration occurs in the light incident on the objective lens 4a as divergent light.

However, this coma aberration can be corrected by tilting the objective lens 4a in the radial direction of the disks 5a, 5b, and 5c by an actuator (not shown). When the objective lens 4a is tilted in the radial direction of the disks 5a, 5b, and 5c, coma aberration occurs. Therefore, the objective lens 4a generates a coma aberration that cancels the coma aberration caused by the center deviation between the objective lens 4a and the spherical aberration correction elements 22a and 22b by adjusting the inclination of the objective lens 4a in the radial direction. The coma aberration caused by the center deviation between 4a and the spherical aberration correction elements 22a and 22b is corrected.

(Fifth and Sixth Embodiments of Optical Head Device) FIG. 18 shows a fifth embodiment of the optical head device of the present invention. In the present embodiment, relay lenses 23a and 23b are provided between the interference filter 2a and the aperture control element 21a in the embodiment shown in FIG. FIG. 19 shows a sixth embodiment of the optical head apparatus of the present invention. In the present embodiment, relay lenses 23a and 23b are provided between the interference filter 2b and the aperture control element 21b in the embodiment shown in FIG.

In general, when the thickness of the substrate of the disc deviates from the design value, the shape of the focused spot is disturbed by spherical aberration caused by the substrate thickness deviation, and the recording / reproducing characteristics deteriorate. This spherical aberration is inversely proportional to the wavelength of the light source and proportional to the fourth power of the numerical aperture of the objective lens. Therefore, the shorter the wavelength of the light source and the higher the numerical aperture of the objective lens, the more the margin of disc substrate thickness deviation with respect to the recording / reproducing characteristics. Narrow. When the wavelength of the semiconductor laser 9a as the light source is 405 nm and the numerical aperture of the objective lens 4a is 0.7, this margin is not sufficient, so that it is necessary to correct the substrate thickness deviation of the disk 5a.

When either one of the relay lenses 23a and 23b is moved in the optical axis direction by an actuator (not shown), the magnification of the objective lens 4a changes and the spherical aberration changes. Therefore, by adjusting the position of one of the relay lenses 23a and 23b in the optical axis direction and generating spherical aberration in the objective lens 4a that cancels out the spherical aberration caused by the substrate thickness deviation of the disk 5a, the objective lens 4a generates the spherical aberration. The substrate thickness deviation is corrected, and the adverse effect on the recording / reproducing characteristics is eliminated.

In the embodiment shown in FIGS. 18 and 19, when the objective lens 4a is driven in the tracking direction by the actuator, the centers of the spherical aberration correction elements 22a and 22b and the center of the objective lens 4a are shifted in the tracking direction. The aberration correction elements 22a and 22b change the phase distribution, and coma aberration occurs in the light that enters the objective lens 4a as divergent light.

However, this coma aberration can be corrected by tilting or moving one of the relay lenses 23a, 23b in the radial direction of the disks 5a, 5b, 5c by an actuator (not shown). In this case, one of the relay lenses 23a and 23b is designed so as not to satisfy the sine condition. When both of the relay lenses 23a and 23b satisfy the sine condition, coma aberration does not occur even if they are tilted or moved in the radial direction of the disks 5a, 5b, and 5c. On the other hand, when either one of the relay lenses 23a and 23b does not satisfy the sine condition, coma aberration occurs when this is tilted or moved in the radial direction of the disks 5a, 5b, and 5c.

Accordingly, the coma aberration that cancels the coma aberration caused by the center deviation between the objective lens 4a and the spherical aberration correction elements 22a and 22b by adjusting the radial inclination or position of one of the relay lenses 23a and 23b is determined as the relay lens. By generating either one of 23a and 23b, the coma aberration caused by the center deviation between the objective lens 4a and the spherical aberration correcting elements 22a and 22b is corrected.

In the embodiments shown in FIGS. 12, 15, 18, and 19, the aperture control elements 21a and 21b are driven in the tracking direction by the actuator together with the objective lens 4a. When only the objective lens 4a is driven in the tracking direction by the actuator, the centers of the dielectric multilayer films 7a, 7b, 7c, 7d, and 7e in the aperture control elements 21a and 21b and the center of the objective lens 4a are shifted in the tracking direction. Accordingly, light having wavelengths of 650 nm and 780 nm transmitted through the aperture control elements 21a and 21b in the forward path is partially reflected by the aperture control elements 21a and 21b in the return path, and the effective numerical aperture for light having the wavelengths of 650 nm and 780 nm is reduced. .

However, when the aperture control elements 21a and 21b are driven in the tracking direction by the actuator together with the objective lens 4a, such a decrease in the numerical aperture does not occur.

In the embodiments shown in FIGS. 12, 15, 18, and 19, the normal lines of the aperture control elements 21a and 21b are slightly inclined with respect to the optical axis of the objective lens 4a. When the normal lines of the aperture control elements 21a and 21b are parallel to the optical axis of the objective lens 4a, the stray light reflected by the aperture control elements 21a and 21b is a photodetector 15a provided in the optical systems 1a, 1d, and 1e. , 15b, 15c, and offset occurs in the focus error signal and the track error signal. However, such an offset does not occur when the normal lines of the aperture control elements 21a and 21b are slightly inclined with respect to the optical axis of the objective lens 4a.

The opening control element 21a shown in FIG. 13 and the opening control element 21b shown in FIG. 16 have a configuration in which dielectric multilayer films 7a, 7b, 7c, 7d, and 7e are formed on a glass substrate 8b. On the other hand, a configuration in which a dielectric multilayer film is formed on the objective lens is also possible.

(First Embodiment of Optical Information Recording or Reproducing Device) FIG. 20 shows a first embodiment of the optical information recording or reproducing device of the present invention. In the present embodiment, recording / reproducing circuits 26a and 26b, a switching circuit 25a, and a control circuit 24a are added to the first embodiment of the optical head apparatus of the present invention shown in FIG. The recording / reproducing circuit 26a generates an input signal to the semiconductor laser 9a provided in the optical system 1a based on a recording signal to the disk 5a, and outputs an output signal from the photodetector 15a provided in the optical system 1a. Based on this, a reproduction signal from the disk 5a is generated.

The recording / reproducing circuit 26b generates an input signal to the semiconductor laser 9b provided in the optical system 1b based on a recording signal to the disk 5b, and outputs an output signal from the photodetector 15b provided in the optical system 1b. Based on this, a reproduction signal from the disk 5b is generated. The switching circuit 25a switches the transmission path of the input signal from the recording / reproducing circuit 26a to the semiconductor laser 9a and the transmission path of the input signal from the recording / reproducing circuit 26b to the semiconductor laser 9b. The control circuit 24a transmits an input signal from the recording / reproducing circuit 26a to the semiconductor laser 9a when the disk 5a is inserted, and transmits an input signal from the recording / reproducing circuit 26b to the semiconductor laser 9b when the disk 5b is inserted. Thus, the operation of the switching circuit 25a is controlled.

(Second Embodiment of Optical Information Recording or Reproducing Device) FIG. 21 shows a second embodiment of the optical information recording or reproducing device of the present invention. In the present embodiment, a recording / reproducing circuit 26c, a switching circuit 25b, and a control circuit 24b are added to the first embodiment of the optical head apparatus of the present invention shown in FIG. The recording / reproducing circuit 26c generates an input signal to the semiconductor laser 9a provided to the optical system 1a and the semiconductor laser 9b provided to the optical system 1b based on the recording signals to the disks 5a and 5b, respectively. Reproduction signals from the disks 5a and 5b are respectively generated based on output signals from the photodetector 15a provided in 1a and the photodetector 15b provided in the optical system 1b.

The switching circuit 25b switches the transmission path of the input signal from the recording / reproducing circuit 26c to the semiconductor lasers 9a and 9b. The control circuit 24b transmits an input signal from the recording / reproducing circuit 26c to the semiconductor laser 9a when the disk 5a is inserted, and transmits an input signal from the recording / reproducing circuit 26c to the semiconductor laser 9b when the disk 5b is inserted. Thus, the operation of the switching circuit 25b is controlled.

(Third Embodiment of Optical Information Recording or Reproducing Device) FIG. 22 shows a third embodiment of the optical information recording or reproducing device of the present invention. In the present embodiment, recording / reproducing circuits 26d, 26e, 26f, a switching circuit 25c, and a control circuit 24c are added to the second embodiment of the optical head apparatus of the present invention shown in FIG. The recording / reproducing circuit 26d generates an input signal to the semiconductor laser 9a provided in the optical system 1a based on a recording signal to the disk 5a, and outputs an output signal from the photodetector 15a provided in the optical system 1a. Based on this, a reproduction signal from the disk 5a is generated.

The recording / reproducing circuit 26e generates an input signal to the semiconductor laser 9b provided in the optical system 1b based on a recording signal to the disk 5b, and outputs an output signal from the photodetector 15b provided in the optical system 1b. Based on this, a reproduction signal from the disk 5b is generated. The recording / reproducing circuit 26f generates an input signal to the semiconductor laser 9c provided in the optical system 1c based on a recording signal to the disk 5c, and outputs an output signal from the photodetector 15c provided in the optical system 1c. Based on this, a reproduction signal from the disk 5c is generated.

The switching circuit 25c transmits an input signal from the recording / reproducing circuit 26d to the semiconductor laser 9a, an input signal from the recording / reproducing circuit 26e to the semiconductor laser 9b, and an input signal from the recording / reproducing circuit 26f to the semiconductor laser 9c. Switch the transmission path. The control circuit 24c transmits an input signal from the recording / reproducing circuit 26d to the semiconductor laser 9a when the disk 5a is inserted, and transmits an input signal from the recording / reproducing circuit 26e to the semiconductor laser 9b when the disk 5b is inserted. When the disc 5c is inserted, the operation of the switching circuit 25c is controlled so that the input signal is transmitted from the recording / reproducing circuit 26f to the semiconductor laser 9c.

(Fourth Embodiment of Optical Information Recording or Reproducing Device) FIG. 23 shows a fourth embodiment of the optical information recording or reproducing device of the present invention. In the present embodiment, a recording / reproducing circuit 26g, a switching circuit 25d, and a control circuit 24d are added to the second embodiment of the optical head apparatus of the present invention shown in FIG. The recording / reproducing circuit 26g includes a semiconductor laser 9a provided in the optical system 1a based on signals recorded on the disks 5a, 5b, and 5c, a semiconductor laser 9b provided in the optical system 1b, and a semiconductor laser provided in the optical system 1c. 9c respectively generate an input signal to the optical system 1a, an optical detector 15a provided in the optical system 1b, an optical detector 15b provided in the optical system 1b, and an output signal from the optical detector 15c provided in the optical system 1c. The reproduction signals from the disks 5a, 5b, and 5c are generated based on the above.

The switching circuit 25d switches the transmission path of the input signal from the recording / reproducing circuit 26g to the semiconductor lasers 9a, 9b, 9c. The control circuit 24d transmits an input signal from the recording / reproducing circuit 26g to the semiconductor laser 9a when the disk 5a is inserted, and transmits an input signal from the recording / reproducing circuit 26g to the semiconductor laser 9b when the disk 5b is inserted. When the disc 5c is inserted, the operation of the switching circuit 25d is controlled so that the input signal is transmitted from the recording / reproducing circuit 26g to the semiconductor laser 9c.

As an embodiment of the optical information recording / reproducing apparatus of the present invention, it is also conceivable that a recording / reproducing circuit, a switching circuit, and a control circuit are added to the third to sixth embodiments of the optical head apparatus of the present invention. .

The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention. is there.

1a, 1b, 1c, 1d, 1e, 1f, 1g Optical systems 2a, 2b, 2c Interference filters 3a, 3b, 3c Wavelength selection filters 4a, 4b Objective lenses 5a, 5b, 5c Disks 6a, 6b Phase filter patterns 7a, 7b 7c, 7d, 7e, 7f, 7g Dielectric multilayer films 8a, 8b, 8c Glass substrates 9a, 9b, 9c Semiconductor lasers 10a, 10b, 10c, 10d Collimator lens 11 Polarizing beam splitter 12 1/4 wavelength plates 13a, 13b , 13c Cylindrical lens 14a, 14b, 14c Lens 15a, 15b, 15c Photodetector 16a, 16b, 16c, 16d, 16e Light spot 17a, 17b, 17c, 17d, 17e, 17f, 17g, 17h, 17i, 17j, 17k , 17l, 17m, 17n Light-receiving portions 18a, 18b Half mirror 19 , 19b Concave lens 20 Diffractive optical elements 21a, 21b, 21c Aperture control elements 22a, 22b Spherical aberration correction elements 23a, 23b Relay lenses 24a, 24b, 24c, 24d Control circuits 25a, 25b, 25c, 25d Switching circuits 26a, 26b, 26c , 26d, 26e, 26f, 26g Recording / reproducing circuit 27a, 27b Module 28 Phase compensation film

Claims (16)

A first light source that emits light of a first wavelength, a second light source that emits light of a second wavelength, a third light source that emits light of a third wavelength, an objective lens, and at least Has one photodetector,
Light of the first wavelength emitted from the first light source, light of the second wavelength emitted from the second light source, and light of the third wavelength emitted from the third light source in the forward path Are selectively guided to the first type optical recording medium, the second type optical recording medium, and the third type optical recording medium through the objective lens, respectively, and in the return path, the first type Reflected light of the first wavelength reflected by the optical recording medium, reflected light of the second wavelength reflected by the second type optical recording medium, and third type In an optical head device including an optical system that selectively guides the reflected light of the third wavelength light reflected by the optical recording medium to the photodetector through the objective lens,
A wavelength that gives a change in intensity distribution depending on the wavelength of incident light to the light of the first, second, and third wavelengths in the common optical path of the light of the first, second, and third wavelengths. An optical head device further comprising a selection filter. 2. The optical head device according to claim 1, wherein the first, second and third wavelengths are approximately 405 nm, approximately 650 nm and approximately 780 nm, respectively. The distances from the incident surface to the reflecting surface of the first, second, and third types of optical recording media are approximately 0.1 mm, approximately 0.6 mm, and approximately 1.2 mm, respectively. 3. The optical head device according to 1 or 2. The wavelength selective filter is at least divided into a first region outside the circle having a diameter smaller than the effective diameter of the objective lens and a second region inside the circle, and The region transmits most of the incident light with respect to at least one of the first, second, and third wavelengths, and is at least one of the first, second, and third wavelengths. The first region does not transmit most of the incident light for one, and the second region transmits most of the incident light for the first, second and third wavelengths, and the first, For at least one of the second and third wavelengths, the phase difference between the light transmitted through the first region and the light transmitted through the second region is set to an integer multiple of approximately 2π. The optical head device according to claim 1, wherein the optical head device is an optical head device. The first and second regions have first and second dielectric multilayer films, respectively, the thickness or number of layers in the first dielectric multilayer film, and the second dielectric multilayer film. 5. The optical head device according to claim 4, wherein the thickness or the number of layers in each of the layers differs from each other. The wavelength selective filter includes a first region that is outside a first circle having a first diameter smaller than the effective diameter of the objective lens, and a first region that is inside the first circle and smaller than the first diameter. A second region that is outside the second circle having a second diameter and a third region that is inside the second circle, wherein the first region is the first region Most of the incident light is transmitted for the wavelength, most of the incident light is not transmitted for the second and third wavelengths, and the second region is the first and second Most of the incident light is transmitted for the wavelength, most of the incident light is not transmitted for the third wavelength, and the third region is the first, second and third Transmitting a large portion of incident light with respect to a wavelength, transmitting light through the first region with respect to the first wavelength, and the second region. The phase difference between the light transmitted through the third region and the light transmitted through the third region is set to an integer multiple of approximately 2π, and the light transmitted through the second region with respect to the second wavelength; 4. The optical head device according to claim 1, wherein a phase difference with light transmitted through the third region is set to an integer multiple of approximately 2π. 5. The first, second and third regions have first, second and third dielectric multilayer films, respectively, and the thickness or number of layers of the first dielectric multilayer film, and the first 7. The optical head device according to claim 6, wherein the thickness or the number of layers in the second dielectric multilayer film and the thickness or the number of layers in the third dielectric multilayer film are different from each other. . At least one of a magnification of the objective lens with respect to the light of the first wavelength, a magnification of the objective lens with respect to the light of the second wavelength, and a magnification of the objective lens with respect to the light of the third wavelength is The optical head device according to claim 1, wherein the optical head device is different from the other two. And at least one light source, an objective lens, and at least one photodetector. In the forward path, the emitted light from the light source is guided to the at least one type of optical recording medium via the objective lens, and in the return path. In the optical head device including an optical system for guiding the reflected light from the optical recording medium to the photodetector through the objective lens, the optical system is a spherical surface generated in an optical path from the light source to the optical recording medium. It is possible to correct spherical aberration correction means provided in the optical path capable of correcting aberrations, and coma aberration caused by optical axis misalignment between the spherical aberration correction means and the objective lens in the optical path. An optical head device comprising: coma aberration correction means. 10. The optical head device according to claim 9, wherein the at least one light source includes a light source that emits light having a wavelength of about 405 nm. 11. The optical head device according to claim 9, wherein the at least one type of optical recording medium includes an optical recording medium having a distance from an incident surface to a reflecting surface of approximately 0.1 mm. The coma aberration correcting unit is the objective lens, and the coma aberration is corrected by tilting the objective lens in the direction of the optical axis deviation. Optical head device. The coma aberration correcting means is an optical element provided in the optical path, and the coma aberration is corrected by tilting or moving the optical element in the direction of the optical axis deviation. The optical head device according to any one of 9 to 11. 14. The optical head device according to claim 13, wherein the optical element is a lens designed not to satisfy a sine condition. Recording or reproduction with respect to the first type of optical recording medium using the optical head device according to any one of claims 1 to 8, and light of the first wavelength, and light of the second wavelength A recording or reproducing circuit for selectively performing recording or reproduction on the second type optical recording medium used, and recording or reproduction on the third type optical recording medium using the light of the third wavelength; An optical information recording / reproducing apparatus comprising: 15. An optical information recording or reproducing apparatus comprising: the optical head apparatus according to claim 9; and a recording or reproducing circuit that performs recording or reproduction on the optical recording medium.

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