JP3635516B2 - Optical disk device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk apparatus that maintains compatibility with information recording media (hereinafter referred to as optical disks) having different substrate thicknesses, and that enables effective use of laser light and downsizing of the apparatus.
[0002]
[Prior art]
The conceptual configuration of a conventional optical disk apparatus is as shown in FIG. In the figure, linearly polarized laser light emitted from the semiconductor laser 101 is converted into substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 103, and passes through the λ / 4 plate 104 to become circularly polarized light. . Thereafter, the laser light is deflected by the deflecting prism 105 and enters the objective lens 106, and is condensed by the objective lens 106 to form and irradiate the optical disc 107 with a laser spot having a small diameter.
[0003]
On the other hand, the laser light reflected by the optical disk 107 becomes circularly polarized light opposite to the outward path, is converted into substantially parallel light again by the objective lens 106, is deflected by the deflecting prism 105, and passes through the λ / 4 plate 104. By passing through the λ / 4 plate 104, the laser light becomes linearly polarized light orthogonal to the forward path, enters the polarization beam splitter 103, is reflected by the polarization beam splitter 103, and is focused by the condenser lens 108. The laser light is received by the light receiving element 109, and an information signal and a servo signal are detected based on a signal from the light receiving element 109.
[0004]
For such an optical disc apparatus, there is a strong demand for an increase in recording capacity, and in order to meet such a demand, the wavelength of laser light is being shortened.
[0005]
In general, the spot diameter of the laser spot formed on the optical disc 107 is proportional to the wavelength λ of the laser beam, and the recording capacity increases in inverse proportion to the square of the wavelength λ. Therefore, the storage capacity can be increased by shortening the wavelength of the laser beam.
[0006]
However, some optical discs 107 have a strong wavelength dependence with respect to reflectance and recording power, and there is a problem that reproduction or recording cannot be performed if a short wavelength laser beam is used for the optical disc 107. That is, there is a problem that compatibility cannot be maintained.
[0007]
Therefore, a method using two laser beams having a wavelength (for example, 785 nm) and a shorter wavelength (for example, 650 nm) that have been conventionally used is conceivable. For this reason, two lasers that emit laser beams having different wavelengths are used. The simplest method is conceptually having two optical pickups by using a source and two objective lenses having optical characteristics corresponding to the respective wavelengths.
[0008]
However, such a configuration having two optical pickups causes an increase in size and cost of the apparatus, so that the optical disk apparatus can be configured by one optical pickup having two laser sources and one objective lens. It has been proposed to configure (for example, JP-A-6-259804).
[0009]
[Problems to be solved by the invention]
However, in the case of a configuration in which there are two laser sources and one objective lens, a part of the laser light in the optical path is separated, and the amount of the laser light emitted from the laser source using the separated laser light is reduced. When detecting with a light quantity detector or the like, it is difficult to separate the laser beams from both laser sources at an equal amount or a predetermined ratio. For this reason, gain adjustment is required when processing the signal from the light quantity detector, and there is a problem in that the cost is increased by the gain adjustment circuit.
[0010]
In addition, since it is difficult to properly control the amount of light to be separated, there is a problem that excessive amount of light is guided to the light amount detector and the laser light cannot be effectively used.
[0011]
Furthermore, when performing the optical path separation of the round trip path of the laser beam, the optical path is separated into substantially orthogonal paths, which makes it difficult to reduce the size of the apparatus.
[0012]
Accordingly, an object of the present invention is to provide an optical disc apparatus capable of suppressing the effective use of laser light, simplification of the apparatus, miniaturization, and cost increase while maintaining compatibility with conventional optical discs.
[0013]
[Means for Solving the Problems]
  In order to solve the above-mentioned problems, the invention according to claim 1 includes two information recording media having different substrate thicknesses, two laser sources that emit laser beams having different wavelengths corresponding to the substrate thickness, and the laser sources. In an optical disk apparatus having an objective lens for condensing laser light from a laser beam and forming a laser spot with a small diameter on an information recording medium, an incident laser disposed between the laser source and the objective lens Depending on the polarization state of the lightRoadA polarizing optical path separating means for separating the optical path from the return path, and a laser beam from the laser source incident on the polarizing optical path separating means. A first phase shifter for generating a phase difference, and a light receiving means for receiving the laser beam in the return path separated by the polarizing optical path separating means.The thickness of the first phase shifter is D1, the wavelengths of the two laser sources are λ1 and λ2, and the refractive indices of the first phase shifter with respect to the ordinary rays of the wavelengths λ1 and λ2 are no (λ1), no (λ2), The refractive index of the first phase shifter for the extraordinary rays of wavelengths λ1 and λ2 is ne (λ1) and ne (λ2), and the phase difference caused by the laser light of wavelengths λ1 and λ2 passing through the first phase shifter is δ (λ1 ), Δ (λ2),
  δ (λ1) = (2π / λ1) × (no (λ1) −ne (λ1)) × D1 ... (Formula A)
  δ (λ2) = (2π / λ2) × (no (λ2) −ne (λ2)) × D1 ... (Formula B)
  δ (λ1) = (2n + 1) × δ (λ2) = (2N + 1) π ... (Formula C)
      However, n = 0, 1, 2, 3... N = 1, 2, 3.
  The thickness D1 of the first phase shifter is set so as to satisfy the expressions A, B, and C.The laser light having a predetermined light amount out of the laser light incident on the polarizing optical path separating means can be made incident on, for example, a light amount detector provided in front.
[0014]
  The invention according to claim 2The setting of the first phaser is
  δ (λ1) = 2nπ and δ (λ2) = (N + 1) π (formula D)
  Or
  δ (λ2) = 2nπ and δ (λ1) = (N + 1) π (Equation E)
  The thickness D1 of the first phase shifter is set so as to satisfy the expressions A, B, D or A, B, E.It is characterized by doing so.
[0015]
  The invention according to claim 3 is:A second phase shifter that is provided between the polarizing optical path separating means and the objective lens and causes a phase difference of approximately ¼ wavelength in the laser light passing through the region; and a first phase shifterAt least one of them is provided integrally with the polarizing optical path separating means, and the apparatus can be miniaturized.
[0016]
In the invention according to claim 4, at least one of the first phase shifter or the second phase shifter is formed of a vapor deposition phase difference film so that the first phase shifter or the second phase shifter can be made sufficiently thin. It is characterized by that.
[0017]
The invention according to claim 5 is formed by a polarizing diffraction grating that diffracts and transmits the laser light in accordance with the polarization state of the laser light incident on the polarizing optical path separation means so that the forward path and the backward path do not intersect at right angles. It is characterized by that.
[0018]
According to a sixth aspect of the present invention, there is provided a light receiving means comprising two light receiving elements for receiving the return laser beam separated by the polarizing light path separating means, and each light receiving element of the light receiving means includes a polarizing light path separating means. Laser light distribution means for splitting the separated backward laser beam or changing the optical path according to the wavelength of the laser beam and receiving the laser beam is provided, and the laser beam reflected by the information recording medium having a different substrate thickness is used as the information. A light receiving element corresponding to the recording medium can receive light.
[0019]
The invention according to claim 7 is characterized in that a diffraction grating for diffracting incident laser light is used as the laser light distribution means, and the angle of the laser light distribution direction distributed by the laser light distribution means is reduced. And
[0020]
The invention according to claim 8 is disposed between the polarizing optical path separating means and the laser light distributing means, and for one laser light having a different wavelength, is approximately an integral multiple of the wavelength of the laser light. For the other laser beam, a third phase shifter that generates a phase difference of approximately ½ times the wavelength of the laser beam is provided to change the polarization state of the laser beam. According to the present invention, the laser beam is divided by the laser beam distribution means or the optical path is changed according to the wavelength of the laser beam.
[0021]
The invention according to claim 9 is characterized in that the third phase retarder can be made thin and necessary by forming the third phase retarder with a vapor deposition phase difference film.
[0022]
The invention according to claim 10 is characterized in that the third phase shifter is provided integrally with the laser beam distribution means.
[0023]
According to the eleventh aspect of the present invention, the laser beam distribution unit is formed of a polarizing diffraction grating that diffracts and transmits according to the polarization state of the incident laser beam, and the angle of distribution by the laser beam distribution unit is reduced. It is characterized by that.
[0024]
The invention according to claim 12 is a laser unit in which the two laser sources and the light receiving means are housed in one.
[0025]
The invention according to claim 13 is characterized in that the two laser sources are semiconductor lasers, and the active layers are arranged so that their directions are orthogonal to each other.
[0026]
According to the fourteenth aspect of the present invention, the first phase shifter causes a phase difference that is approximately an integral multiple of the wavelength of the laser beam from one laser source, and the laser beam from the other laser source. It is characterized in that the polarization state of each laser beam is made the same when a phase difference of approximately ½ wavelength is generated and incident on the polarizing optical path separating means.
[0027]
The invention according to claim 15 is characterized in that the laser unit is integrally provided with the first phase shifter, the polarizing optical path separating means and the second phase shifter.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical disc apparatus according to the present embodiment.
[0029]
Laser light having different wavelengths is emitted from the first and second semiconductor lasers 1 a and 1 b, and is collimated by the collimating lens 3. Thereafter, the laser light enters the phase shifter 4 that is the first phase shifter, and a predetermined phase difference is generated in the phase shifter 4 and enters the polarization beam splitter 5.
[0030]
As shown in FIG. 2, the polarization beam splitter 5 has a characteristic of transmitting approximately 100% of P-polarized laser light and reflecting approximately 100% of S-polarized laser light. By using a polarizing beam splitter with such transmission and reflection characteristics for a wide range of wavelengths, sufficient polarization characteristics can be obtained for different wavelengths, and a highly efficient optical system for both wavelengths can be obtained. There are benefits that can be realized.
[0031]
As a result, when the laser light emitted from the phase shifter 4 includes an S-polarized component, the S-polarized component is reflected by the polarization beam splitter 5, collected by the condenser lens 13, and received by the light amount detector 14. The
[0032]
On the other hand, the P-polarized component is transmitted without being reflected by the polarization beam splitter 5 and is incident on the λ / 4 plate 6 which is the second phase shifter. The phase is changed by λ / 4 by the λ / 4 plate 6 to become circularly polarized light, which is incident on the deflecting prism 7 and deflected. Thereafter, the light is condensed by the objective lens 8 and the first or second optical disk 9a, 9b is irradiated with a laser beam of a minute spot.
[0033]
The laser beams reflected by the first and second optical disks 9a and 9b follow substantially the same optical path as the forward path, are focused by the objective lens 8, are deflected by the deflecting prism 7, and are incident on the λ / 4 plate 6. Then, the λ / 4 plate 6 is made S-polarized light orthogonal to the outward path, enters the polarization beam splitter 5, and is reflected by the polarization beam splitter 5 approximately 100%.
[0034]
The reflected laser light is converged by the detection lens 11 and received by the light receiving element 12 as the light receiving means, and servos of the information signal, tracking signal, and focus signal are performed using a known method based on the signal from the light receiving element 12. A signal is detected.
[0035]
The wavelengths of the laser beams emitted from the first and second semiconductor lasers 1a and 1b are 785 nm for the first semiconductor laser 1a and 650 nm for the second semiconductor laser 1b, and the first optical disk 9a has a thick substrate. A (1.2 mm) low-capacity optical disk will be described, and the second optical disk 9b will be described as a thin-film (0.6 mm) large-capacity optical disk.
[0036]
The first semiconductor laser 1a is oscillated when recording / reproduction is performed on the first optical disk 9a, and the second semiconductor laser 1b is oscillated when recording / reproduction is performed on the second optical disk 9b.
[0037]
Of course, it goes without saying that the above-described wavelengths and substrate thicknesses are merely examples. In the following description, for convenience, the first semiconductor laser 1a is referred to as a long wavelength laser 1a, the second semiconductor laser 1b is referred to as a short wavelength laser 1b, and these are collectively referred to as a laser 1. Further, the optical disk 9a having a thick substrate is referred to as a low density disk 9a, the optical disk 9b having a thin substrate thickness is referred to as a high density disk 9b, and these are collectively referred to as an optical disk 9.
[0038]
As the detection lens 11, for example, a cylindrical lens having one spherical surface can be applied. For example, an astigmatism method can be applied to the focus signal, and a phase difference method or the like can be applied to the tracking signal. It is possible to apply.
[0039]
As the optical characteristics of the polarizing beam splitter 5 described above, as shown in FIG. 3, the P-polarized laser beam may be reflected by approximately 100% and the S-polarized laser beam may be transmitted by approximately 100%. In the case of having such characteristics, it is apparent from the following description that the phase difference generation conditions in the phase shifter 4 and the λ / 4 plate 6 may be set in accordance with the characteristics of the polarization beam splitter. In the following description, it is assumed that the polarization beam splitter 5 has the characteristics as shown in FIG.
[0040]
Furthermore, although the case where the phase shifter 4 and the λ / 4 plate 6 are single plates will be described, the present invention is not limited to this, and it is also possible to use a laminate in which the optical axes are orthogonal to each other. Is possible.
[0041]
The function of the phase shifter 4 will be described with reference to FIG. Generally, a semiconductor laser has a laser chip 1c as shown in the figure, and laser light polarized in a direction parallel to the active layer 1d is emitted from the active layer 1d of the laser chip 1c. Therefore, in FIG. 1, it is assumed that the direction of the active layer 1d of each laser chip 1c in the laser 1 is set in the vertical direction on the paper surface.
[0042]
Since the laser light incident on the polarization beam splitter 5 at this time is both P-polarized light, when the laser light is not guided to the light amount detector 14, that is, when the laser light incident on the polarization beam splitter 5 is passed as it is. Therefore, it is not necessary to cause a phase difference by the phase shifter 4.
[0043]
On the other hand, when a part of the laser light incident on the polarization beam splitter 5, for example, about 10 (%) of the laser light reaching the optical disk 9 is guided to the light amount detector 14, the phase shifter is set so as to satisfy the expressions 1 to 3 described later. A thickness D1 of 4 may be set.
[0044]
That is, when about 10 (%) of the laser beam reaching the optical disk 9 is incident on the light quantity detector 14, the optical axis of the phase shifter 4 is tilted by about 9 degrees with respect to the P-polarized surface, and the phase shift of the phase shifter 4 By generating λ / 2, an S-polarized component may be generated and incident on the polarization beam splitter 5.
[0045]
The wavelength of the laser beam from the laser 1 is λ1, λ2, the wavelength λ1, λ2, the refractive index of the phase shifter 4 for ordinary rays of λ1, λ2, respectively, If ne (λ1) and ne (λ2), the phase differences δ (λ1) and δ (λ2) generated when the laser beams having the wavelengths λ1 and λ2 pass through the phase shifter 4 are
δ (λ1) = (2π / λ1) (no (λ1) −ne (λ1)) D1 (1)
δ (λ2) = (2π / λ2) (no (λ2) −ne (λ2)) D1 (2)
It becomes.
[0046]
In order for the phase difference to be both λ / 2 with respect to the laser beams having the wavelengths λ1 and λ2, the phase difference δ (λ1) and the phase difference δ (λ2)
δ (λ1) = (2n + 1) δ (λ2) = (2N + 1) π (3)
However, n = 0, 1, 2, 3,..., N = 1, 2, 3,.
Satisfy this relationship.
[0047]
For the long wavelength laser 1a, the amount of emitted light is detected by a rear light detector (not shown) built in the long wavelength laser 1a. In the case where the amount of emitted light is detected using about 10% (%) of the reaching laser beam, the thickness D1 of the phase shifter 4 is set as follows.
[0048]
That is, the laser light from the long wavelength laser 1a only needs to pass through without being reflected by the polarization beam splitter 5, so there is no need to generate a phase difference with respect to the laser light by the phase shifter 4. Even if a phase difference occurs, the phase difference only needs to be an integral multiple of the wavelength λ.
δ (λ1) = 2nπ (4)
[0049]
On the other hand, for the short wavelength laser 1b, the optical axis of the phase shifter 4 is tilted by about 9 degrees with respect to the P polarization plane by the above-described method, and the phase difference generated in the phase shifter 4 is different from that of the short wavelength laser 1b. What is necessary is just to set it as (lambda) / 2 with respect to a laser beam.
δ (λ2) = (N + 1) π (5)
[0050]
Then, the thickness D1 of the phase shifter 4 may be set so that the phase differences δ (λ1) and δ (λ2) expressed by Equations 1 and 2 satisfy Equations 4 and 5.
[0051]
For the short wavelength laser 1b, the amount of emitted light is detected by a back light detector (not shown) built in the short wavelength laser 1b. Even when the amount of emitted light is detected using about 10% of the laser beam to reach, the thickness D1 of the phase shifter 4 may be set by the method described above.
[0052]
Next, when the laser light from the optical disk 9 is deflected by the deflecting prism 7 and enters the polarizing beam splitter 5, and substantially all of the laser light incident by the polarizing beam splitter 5 is reflected and guided to the light receiving element 12, that is, A case where the polarization beam splitter 5 performs optical path separation between the forward path and the return path will be described.
[0053]
In this case, as can be seen from the characteristics shown in FIG. 2, the laser beam on the return path only needs to be S-polarized light, and the laser light immediately after being emitted from the polarization beam splitter 5 on the forward path is P-polarized light. It is sufficient for the phase difference to be different by λ / 2 by passing through 6 twice. That is, a phase difference of λ / 4 may be generated by passing through the λ / 4 plate 6 as much as possible.
[0054]
The thickness D2 of the λ / 4 plate 6 satisfying this condition is such that the refractive index with respect to the ordinary rays with respect to the wavelengths λ1 and λ2 of the λ / 4 plate 6 is No (λ1), No (λ2), and the refractive index with respect to the extraordinary ray is Ne ( Assuming that λ1) and Ne (λ2), the phase differences δ (λ1) and δ (λ2) generated in the laser beams having the wavelengths λ1 and λ2 are
δ (λ1) = (2π / λ1) (No (λ1) −Ne (λ1)) D2 (6)
δ (λ2) = (2π / λ2) (No (λ2) −Ne (λ2)) D2 (7)
So these are
δ (λ1) = (2n + 1) δ (λ2) = (2N + 1) (π / 2) (8)
n = 0, 1, 2, 3,..., N = 1, 2, 3,.
The thickness D2 of the λ / 4 plate 6 may be determined so as to satisfy the above.
[0055]
As described above, by setting the thickness of the phase shifter 4 in accordance with the purpose, it is possible to generate a desired phase difference for each laser beam having a different wavelength. The laser beam can be separated and extracted.
[0056]
Therefore, even when the separately extracted laser light is received by the light amount detector 14, since the light amount of the received laser light is a predetermined light amount, gain adjustment becomes unnecessary, and the gain adjustment circuit becomes unnecessary. Further, since the extracted laser light has a necessary and sufficient light amount, the laser light can be effectively used, and the degree of freedom in designing the optical system can be increased.
[0057]
Furthermore, since a λ / 4 plate that generates a phase difference of λ / 4 with respect to light of different wavelengths is provided, the polarization state of the laser light of either wavelength is completely orthogonal between the forward path and the return path. Therefore, the polarization beam splitter 5 can perform the optical path separation of the forward path and the backward path with high efficiency, and can increase the utilization efficiency of the laser beam.
[0058]
Note that the phase shifter 4 and the λ / 4 plate 6 can be provided integrally with the polarization beam splitter 5. In this case, the number of components can be reduced, so that the apparatus can be reduced in size and cost.
[0059]
In particular, the phase retarder 4 and the λ / 4 plate 6 can be formed to have a necessary and sufficient thickness by using the phase retarder 4 and the λ / 4 plate 6 as vapor deposition phase difference films, and these materials can be used. There is no need to use expensive birefringent crystals, which can greatly contribute to downsizing and low cost of the apparatus.
[0060]
As a material for the vapor deposition phase difference film, Ta₂O_Five, SnO₂Etc. can be used.
[0061]
Here, the necessary and sufficient thickness means the following. Conventionally, for example, when the wavelength λ = 650 nm and the thickness of the phase shifter 4 is λ / 4, λ / 4 = 162.5 nm, which is a necessary and sufficient thickness. It is very difficult to form by cutting and so on and to incorporate it. Therefore, the thickness of the phase shifter is set to λ / 4 + kλ (k: integer), and only the thickness is increased while the same phase difference is generated. However, since the deposition retardation film does not require such processing and assembly, a phase retarder having a thickness of λ / 4 = 162.5 nm can be used as an actual dimension.
[0062]
Next, a second embodiment of the present invention will be described with reference to the drawings. In addition, about the same structure as 1st Embodiment, the same code | symbol is used and description is abbreviate | omitted suitably.
[0063]
FIG. 5 is a diagram showing a schematic configuration of the optical disc apparatus according to the present embodiment. The present embodiment is characterized in that a polarizing diffraction grating 15 is used instead of the polarizing beam splitter 5 in FIG. The polarizer 4 and the λ / 4 plate 6 are integrally provided on the polarizing diffraction grating 15. Of course, there is no necessity to provide these integrally, but there is an advantage that the above-described effects can be obtained by providing them integrally.
[0064]
The polarizing diffraction grating 15 has a grating groove 15a, and transmission and diffraction occur depending on the polarization state of the laser light incident on the grating groove 15a.
[0065]
As such a polarizing diffraction grating 15, for example, LiNbO_Three(Subscript) may be a polarization hologram having a grating groove, or a narrow pitch (about ½ of the wavelength λ) and a deep grating groove (Optical Vol. 20, No. 8, pp. 36). (August 1991) Hideo Maeda et al. High-density dual grating for magneto-optical head). In the present embodiment, LiNbO is used as the polarizing diffraction grating 15._ThreeA case where a lattice groove is formed on the substrate will be described.
[0066]
The laser beam from the laser 1 is a laser beam that travels in parallel to the groove direction of the grating groove 15a (right direction in FIG. 5; hereinafter the same), and is orthogonal to the grating groove 15a by the phase shifter 4 (vertical direction in FIG. When the same polarization component is generated, the polarization component is diffracted and enters the light amount detector 14.
[0067]
On the other hand, the polarization component parallel to the grating groove 15a (in the direction perpendicular to the paper surface in FIG. 5; the same applies hereinafter) passes through the polarizing diffraction grating 15, is converted into circularly polarized light by the λ / 4 plate 6, and is applied to the optical disk 9. The
[0068]
The laser light reflected by the low-density disk 9a becomes polarized light orthogonal to the grating grooves 15a by the λ / 4 plate 6, thereby being diffracted by the polarizing diffraction grating 15, and the diffracted light is focused by the collimating lens 3. The light receiving element 12 receives the light and detects an information signal and a servo signal.
[0069]
As the configuration of the polarizing diffraction grating 15 and the light receiving element 12, a region divided as shown in FIGS. 6 and 7 is possible. However, this is merely an example, and the present invention is not limited to this.
[0070]
The polarizing diffraction grating 15 shown in FIG. 6 includes three regions A, B, and C, and the laser light is diffracted in a direction corresponding to the grating groove 15a formed in each region A, B, and C. The light receiving element 12 is divided into four regions E, F, G, and H as shown in FIG.
[0071]
Then, the laser light diffracted in the region A in FIG. 6 is set so as to enter the central portion of the region E and the region F of the light receiving element 12, and the focus signal Fo is changed between the region E and the region F by the knife edge method. It is detected from the difference between the photoelectric signals.
[0072]
The laser beams diffracted in the regions B and C are incident on the regions G and H of the light receiving element 12, respectively, and the track signal Tr is detected from the difference between the photoelectric signals in the regions G and H.
[0073]
Further, the information signal is transmitted from regions E, F, G. It is detected from the sum of photoelectric signals from H or a part thereof.
[0074]
In this way, when the optical path separation of the round trip path is performed by the polarizing diffraction grating 15, the forward path and the return path are not perpendicular to each other.
[0075]
In addition, since the polarizing diffraction grating is divided into a plurality of areas to detect servo signals, servo signal generating optical elements such as a cylindrical lens and a knife edge prism, which have been necessary in the past, are no longer necessary. The number of parts can be reduced and the cost can be reduced.
[0076]
Next, a third embodiment of the present invention will be described with reference to the drawings. The same components as those in the first and second embodiments are denoted by the same reference numerals, and the description thereof is omitted as appropriate.
[0077]
In each of the above-described embodiments, the light receiving means is composed of one light receiving element 12, and the reflected light from the low density disk 9a and the high density disk 9b is received by the light receiving element 12.
[0078]
However, the present invention is not limited to this, and the two light receiving elements 17 and 18 are used, for example, to make the light receiving element 17 a dedicated element for detecting a servo signal or the like for the low density disk 9a. As a dedicated element for detecting a servo signal or the like for the high-density disk 9b, the light receiving elements 17 and 18 can be easily adjusted and various high-quality detection signals can be obtained.
[0079]
FIGS. 8 to 11 illustrate the configuration according to the first embodiment, but the same configuration can be applied to the second embodiment in principle.
[0080]
The laser light distribution means 16 and 19 shown in FIGS. 8 and 9 are irrespective of the wavelength, that is, regardless of whether the light is reflected from the low density disk 9a or the reflected light from the high density disk 9b. In this configuration, the incident laser light is divided and incident on the light receiving elements 17 and 18. Further, the laser beam distribution means 21 and 22 shown in FIGS. 10 and 11 change the optical path of the incident laser beam depending on the wavelength, that is, the reflected light from the low density disk 9a or the reflected light from the high density disk 9b. In other words, the light is incident on the corresponding light receiving elements 17 and 18.
[0081]
That is, in FIG. 8, a half mirror 16 which is a laser beam distribution unit is provided in the optical path between the detection lens 11 and the light receiving elements 17 and 18, and the laser beam from the detection lens 11 is divided into two by the half mirror 16. Each of them is received by light receiving elements 17 and 18.
[0082]
When recording / reproducing with respect to the low density disk 9a by the laser beam from the long wavelength laser 1a, the servo signal and the information signal are detected by the photoelectric signal from the light receiving element 17. When recording / reproducing with respect to the high-density disk 9b by the laser beam from the short wavelength laser 1b, the servo signal and the information signal are detected by the signal from the light receiving element 18.
[0083]
In FIG. 9, a diffraction grating 19 serving as a laser beam distribution unit is provided in the optical path between the detection lens 11 and the light receiving elements 17 and 18, and the laser light from the detection lens 11 is divided into two by the diffraction grating 19. The light receiving elements 17 and 18 receive the light respectively.
[0084]
When recording / reproducing with respect to the low density disk 9a by the laser beam from the long wavelength laser 1a, the servo signal and the information signal are detected by the signal from the light receiving element 17. Further, when recording is generated on the high-density disk 9b by the laser beam from the short wavelength laser 1b, the servo signal and the information signal are detected by the signal from the light receiving element 18.
[0085]
FIG. 10 shows a configuration in which a phase shifter 20 as a third phase shifter and a polarization optical element 21 such as a polarization beam splitter as laser beam distribution means are sequentially provided in the optical path between the detection lens 11 and the light receiving elements 17 and 18. It has become.
[0086]
The phase shifter 20 causes an integer multiple phase difference for the laser light from the long wavelength laser 1a, and a phase difference of approximately λ / 2 for the laser light from the short wavelength laser 1b. Let Thereafter, the light is incident on the polarizing optical element 21 to perform optical path separation.
[0087]
As a result, the laser light from the long wavelength laser 1a reflected by the low-density disk 9a is converted into S-polarized light by the phase shifter 20 and is incident on the polarizing optical element 21, and is reflected by the polarizing optical element 21 to receive approximately 100%. Incident on the element 17. Further, the laser light from the short wavelength laser 1 b becomes P-polarized light by the phase shifter 20 and enters the polarizing optical element 21, and substantially 100% of the polarizing optical element 21 passes through and enters the light receiving element 18. .
[0088]
Therefore, when recording / reproducing with respect to the low density disk 9a by the laser from the long wavelength laser 1a, the servo signal and the information signal are detected based on the output of the light receiving element 17, and the laser signal from the short wavelength laser 1b is used to increase When recording / reproducing is performed on the density disk 9b, servo signals and information signals are detected based on the output of the light receiving element 18.
[0089]
In FIG. 11, a phase shifter 20 as a third phase shifter and a polarizing diffraction grating 22 are sequentially provided in the optical path between the detection lens 11 and the light receiving elements 17 and 18. The phase shifter 20 causes an integer multiple phase difference for the laser light from the long wavelength laser 1a, and a phase difference of approximately λ / 2 for the laser light from the short wavelength laser 1b. Let Thereafter, the light is incident on the polarizing diffraction grating 22 and is incident on the light receiving elements 17 and 18. The polarizing diffraction grating 22 may have the same configuration as the polarizing diffraction grating 15.
[0090]
The laser light from the long wavelength laser 1a becomes polarized light orthogonal to the grating groove 22a of the polarizing diffraction grating 22 by the phase shifter 20 (left and right in FIG. 11), and is diffracted by the polarizing diffraction grating 22 to be received. Incident on the element 17.
[0091]
On the other hand, the laser light from the short wavelength laser 1b is rotated by 90 degrees in the polarization direction by the phase shifter 20 and becomes polarized parallel to the grating groove 22a of the polarizing diffraction grating 22 (direction perpendicular to the paper surface in FIG. 11). Thus, the light passes through the polarizing diffraction grating 22 and enters the light receiving element 18.
[0092]
Thus, when recording / reproducing with respect to the low density disk 9a by the laser light from the long wavelength laser 1a, the servo signal and the information signal are detected from the light receiving element 17 based on the signal. When recording / reproducing with respect to the high-density disk 9b by the laser beam from the short wavelength laser 1b, the servo signal and the information signal are detected based on the signal from the light receiving element 18.
[0093]
Note that the use of the diffraction grating 19 and the polarizing diffraction grating 22 as the laser beam distribution means can reduce the angle of the laser beam distribution direction, which is advantageous in that the apparatus can be downsized.
[0094]
Further, since the polarization directions of the two laser beams having different wavelengths incident on the polarizing optical element 21 and the polarizing diffraction grating 22 are made substantially orthogonal using the phase shifter 20, the two laser beams having different wavelengths are completely separated. Accordingly, light can be received by the corresponding light receiving elements 17 and 18, so that the use efficiency of the laser light is increased and the information signal and servo signal having a high S / N can be detected.
[0095]
Next, a fourth embodiment of the present invention will be described with reference to the drawings. In addition, about the same structure as 1st-3rd embodiment, description is abbreviate | omitted suitably using the same code | symbol.
[0096]
In the description so far, the case where the long wavelength laser 1a and the short wavelength laser 1b are formed separately has been described. However, the present invention is not limited to this, and a laser unit in which two lasers 1 are housed in one case as shown in FIGS. 12 and 13 may be used.
[0097]
FIGS. 12 and 13 show the case where the laser unit is used in the configuration according to the second embodiment. However, it should be noted that the laser unit may be used in the first embodiment. Nor.
[0098]
As shown in FIG. 12, the laser unit is provided with two laser chips and one light receiving element 12 as shown in FIG. The laser chip is indicated by 23a and 23b. Each laser chip 23a, 23b emits laser light having the same wavelength as emitted from the laser 1, that is, laser light having a wavelength of 635 nm from the laser chip 23a, and laser light having a wavelength of 785 nm is emitted from the laser chip 23b. Shall.
[0099]
The polarization direction of the laser beam with a wavelength of 635 nm is perpendicular to the active layer of the laser chip 23a (TM mode in FIG. 4), and the polarization direction of the laser beam with a wavelength of 785 nm is parallel to the active layer of the laser chip 23b. (TE mode in FIG. 4).
[0100]
At this time, since the polarization direction of the laser light when entering the polarizing diffraction grating 15 needs to be polarized parallel to the grating groove 15a (direction perpendicular to the paper surface in FIG. 12), for example, each laser chip The phases of the active layers 23a and 23b are orthogonal to each other, or a phase difference of an integral multiple is generated for one wavelength and a phase difference of approximately λ / 2 is generated for the other wavelength. The thickness of the child 4 is set.
[0101]
As shown in FIG. 13, the phase shifter 4, the polarizing diffraction grating 15 and the λ / 4 plate 6 may be provided integrally, and these are attached to the laser light emission window of the laser unit 23. Also good.
[0102]
By using the laser unit in this way, it is possible to reduce the number of parts and the size of the apparatus, and to reduce the man-hours for assembling the optical system and thereby reduce the cost.
[0103]
In addition, since each component is integrated, it is possible to obtain high reliability against changes in temperature, humidity, and changes with time.
[0104]
Even when the active layers of the two laser chips 23a and 23b are arranged so as to be orthogonal to each other and the polarization directions of the laser beams emitted from the laser chips 23a and 23b are orthogonal to each other, Since the polarization state of the laser light incident on the polarizing optical path separating means 15 can be made the same by the optical element 4, it is possible to increase the utilization efficiency of the forward and backward laser light.
[0105]
Further, when using different types of laser sources in which the polarization directions of the laser beams emitted from the laser chips 23a and 23b are orthogonal to the active layers of the laser chips 23a and 23b, the directions of the active layers are attached in parallel. Even in such a case, a phase difference of approximately an integral multiple of the wavelength is produced for one laser beam, and a phase difference of approximately ½ the wavelength is produced for the other laser beam. Since the phase shifter 4 is provided to the polarizing optical path separating means 15, the polarization state of each laser light when entering the polarizing optical path separating means 15 can be made the same, and the utilization efficiency of the laser light in the forward path and the backward path can be increased. Become.
[0106]
【The invention's effect】
According to the first aspect of the present invention, it is possible to cause a predetermined phase difference between the two laser beams having different wavelengths by the first phase shifter, and the polarizing optical path separating means according to the phase difference. It becomes possible to easily adjust the light quantity ratio of the reflected and transmitted laser light.
[0107]
  Therefore, the same phase difference is generated for the two lasers, and the same amount of laser light can be guided to the light quantity detector or the like.comeThe laser light can be used effectively, the circuit gain can be simplified by eliminating the gain adjustment of the signal from the light quantity detector, and the degree of freedom in designing the optical system can be increased.
[0108]
  According to the invention of claim 2,A phase difference can be generated only for one laser beam, and a part of the laser beam can be reflected by the polarizing optical path separating means and guided to a light quantity detector, etc., enabling effective use of the laser beam. In addition, the circuit can be simplified by eliminating the gain adjustment of the signal from the light quantity detector, and the degree of freedom in designing the optical system can be increased.
[0109]
According to the invention of claim 3, since at least one of the first phase shifter and the second phase shifter is provided integrally with the polarizing optical path separating means, the apparatus can be miniaturized.
[0110]
According to the fourth aspect of the present invention, since at least one of the first phase shifter and the second phase shifter is formed by the vapor deposition phase difference film, each phase shifter can be made sufficiently thin. At the same time, it is not necessary to use an expensive birefringent crystal as the material of each phase shifter, so that the apparatus can be reduced in size and cost.
[0111]
According to the invention of claim 5, since the polarizing diffraction grating is used as the polarizing optical path separating means, the forward path and the backward path can be configured not to be orthogonal to each other, and the apparatus can be miniaturized and the polarizing property can be reduced. Servo signals are detected by dividing the diffraction grating into multiple areas, eliminating the need for servo signal generating optical elements such as cylindrical lenses and knife edge prisms, which were required in the past, and reducing the number of parts In addition, the cost can be reduced.
[0112]
According to the sixth aspect of the present invention, the light receiving means for receiving the laser beam reflected by the information recording medium is provided with the light receiving element corresponding to the wavelength of the laser beam. The light receiving element can be adjusted, and a highly accurate servo signal can be detected.
[0113]
According to the seventh aspect of the invention, since the diffraction grating is used as the laser beam distribution means, the angle of the laser beam distribution direction can be reduced, and the apparatus can be miniaturized.
[0114]
According to the eighth aspect of the present invention, the third phaser provided between the polarizing optical path separating unit and the laser beam allocating unit causes the first laser beam to have a substantially integer wavelength of the laser beam. Since the phase difference is doubled and a phase difference of approximately ½ times the wavelength of the laser beam is generated for the other laser beam, the polarization directions of the two laser beams having different wavelengths are the same. Can be made orthogonal to each other, and two laser beams having different wavelengths can be completely separated by the laser beam distribution means. Therefore, light can be efficiently received by the light receiving means, and information signals and servo signals with high S / N can be detected.
[0115]
According to the invention of claim 9, since the retardation film formed by vapor deposition is used for the third phase shifter, the third phase shifter can be made thin and necessary and the third phase shifter can be made. Since it is not necessary to use an expensive birefringent crystal as a material for the child, the apparatus can be reduced in size and cost.
[0116]
According to the invention of claim 10, since the third phase shifter and the laser beam distribution means are integrated, the apparatus can be miniaturized.
[0117]
According to the invention of the eleventh aspect, since the polarizing diffraction grating is used as the laser beam distribution unit, the angle of distribution by the laser beam distribution unit can be reduced, and the apparatus can be miniaturized.
[0118]
In addition, by dividing the polarizing diffraction grating into a plurality of regions, laser light for servo signal detection can be generated. Optical elements for servo signal generation such as cylindrical lenses and knife edge prisms that have been required in the past This eliminates the need for parts and reduces the cost of the apparatus.
[0119]
According to the twelfth aspect of the present invention, since the laser unit in which the two laser sources and the light receiving means are housed in one case is used, the number of parts can be reduced and the apparatus can be downsized.
[0120]
According to the invention of claim 13, even if the active layers of the two laser chips are arranged so as to be orthogonal to each other, and the polarization directions of the laser beams emitted from the laser chips are orthogonal to each other, Since the polarization state of the laser light incident on the polarizing optical path separating means can be made the same, the utilization efficiency of the forward and backward laser light can be increased.
[0121]
According to the fourteenth aspect of the present invention, when using different types of laser sources in which the polarization direction of the laser light emitted from the laser chip is orthogonal to the active layer of the laser chip, the direction of the active layer is set. Even when mounted in parallel, a phase difference of approximately an integral multiple of the wavelength is produced for one laser beam, and a phase difference of approximately a half of the wavelength is produced for the other laser beam. Since the first phaser is provided so as to be generated, the polarization state of each laser beam when entering the polarizing optical path separating means can be made the same, and the utilization efficiency of the laser light in the forward path and the backward path can be increased. Is possible.
[0122]
According to the fifteenth aspect of the present invention, since the first phaser, the polarizing optical path separating means and the second phaser are integrally provided in the laser unit, the number of parts of the optical system can be greatly reduced, It is possible to reduce the man-hours for assembling the optical system, reduce the cost, and reduce the size of the device.
[0123]
In addition, since each component is integrated, it is possible to obtain high reliability against changes in temperature, humidity, and changes with time.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an optical disc apparatus applied to the description of a first embodiment.
FIG. 2 is a characteristic diagram of a polarizing beam splitter.
FIG. 3 is a characteristic diagram of a polarizing beam splitter having characteristics opposite to those in FIG.
FIG. 4 is a perspective view of a laser chip.
FIG. 5 is a schematic configuration diagram of an optical disc apparatus applied to the description of the second embodiment.
6 is a configuration diagram of a polarizing diffraction grating used in FIG. 5;
7 is a configuration diagram of a light receiving element used in FIG. 5;
FIG. 8 is a schematic configuration diagram of an optical disc device applied to the description of the third embodiment.
FIG. 9 is another schematic configuration diagram of an optical disk device applied to the description of the third embodiment.
FIG. 10 is another schematic configuration diagram of an optical disk device applied to the description of the third embodiment.
FIG. 11 is another schematic configuration diagram of an optical disk device applied to the description of the third embodiment.
FIG. 12 is a schematic configuration diagram of an optical disc device applied to the description of the fourth embodiment.
FIG. 13 is another schematic configuration diagram of an optical disk device applied to the description of the fourth embodiment.
FIG. 14 is a schematic configuration diagram of a general optical disc apparatus applied to the description of a conventional technique.
[Explanation of symbols]
1a First semiconductor laser element
1b Second semiconductor laser element
4,20 phaser
5 Polarizing beam splitter
6 λ / 4 plate
8 Objective lens
9a, 9b optical disc
12, 17, 18 Light receiving element
14 Light intensity detector
15,22 Polarizing diffraction grating
16 half mirror
19 Diffraction grating
21 Polarizing optical element
23 Laser unit
Ic laser chip
Id active layer

Claims (15)

Two information recording media having different substrate thicknesses, two laser sources emitting laser beams having different wavelengths corresponding to the substrate thickness, and condensing the laser beams from the laser sources to the information recording medium In an optical disk apparatus having an objective lens that forms a laser spot with a small diameter,
And is disposed, the polarizing optical path separating means for performing forward path and the backward path of the optical path separating the laser beam according to the polarization state of the incident laser beam between the laser source and the objective lens,
A first phase shifter disposed between the laser source and the polarizing optical path separating unit to cause a predetermined phase difference in the laser light from the laser source incident on the polarizing optical path separating unit;
Have a light receiving means for receiving the laser beam on the return path separated by the polarizing optical path separating means,
The thickness of the first phase shifter is D1, the wavelengths of the two laser sources are λ1 and λ2, and the refractive index of the first phase shifter with respect to the ordinary rays of wavelengths λ1 and λ2 are no (λ1), no (λ2), and wavelength The refractive index of the first phase shifter for the extraordinary rays of λ1 and λ2 is ne (λ1) and ne (λ2), and the phase difference caused by the laser light of wavelengths λ1 and λ2 passing through the first phase shifter is δ (λ1) , Δ (λ2),
δ (λ1) = (2π / λ1) × (no (λ1) −ne (λ1)) × D1 ... (Formula A)
δ (λ2) = (2π / λ2) × (no (λ2) −ne (λ2)) × D1 ... (Formula B)
δ (λ1) = (2n + 1) × δ (λ2) = (2N + 1) π ... (Formula C)
However, n = 0, 1, 2, 3... N = 1, 2, 3.
An optical disc apparatus characterized in that the thickness D1 of the first phase shifter is set so as to satisfy the expressions A, B, and C. The setting of the first phaser is
δ (λ1) = 2nπ and δ (λ2) = (N + 1) π (formula D)
Or
δ (λ2) = 2nπ and δ (λ1) = (N + 1) π (Equation E)
2. The optical disc apparatus according to claim 1, wherein the thickness D1 of the first phase shifter is set so as to satisfy the expressions A, B, D or A, B, E. A second phase shifter that is provided between the polarizing optical path separating means and the objective lens and that causes a phase difference of approximately ¼ wavelength in laser light passing through the region; and at least one of the first phase shifters 3. The optical disc apparatus according to claim 1, wherein one is provided integrally with the polarizing optical path separating means.   4. The optical disk device according to claim 1, wherein at least one of the first phase shifter and the second phase shifter is a vapor deposition phase difference film. 5.   5. The optical disk according to claim 1, wherein the polarizing optical path separating means is a polarizing diffraction grating that diffracts and transmits the laser light according to the polarization state of the incident laser light. apparatus.   The light receiving means is composed of two light receiving elements that receive the backward laser beam separated by the polarizing optical path separating means, and the laser light from the polarizing optical path separating means is divided into the respective light receiving elements. 6. An optical disc apparatus according to claim 1, further comprising laser beam distribution means for receiving light by changing an optical path in accordance with the wavelength of the laser beam.   7. The optical disk apparatus according to claim 6, wherein the laser beam distribution means is a diffraction grating that diffracts the incident laser beam.   For one of the laser beams having different wavelengths, disposed between the polarizing optical path separating unit and the laser beam distributing unit, a phase difference of approximately an integer multiple of the wavelength of the laser beam is generated. 7. The optical disk apparatus according to claim 6, further comprising a third phase shifter that causes a phase difference of about ½ times the wavelength of the laser beam to the other laser beam.   9. The optical disk apparatus according to claim 8, wherein the third phase shifter is a vapor deposition phase difference film.   The optical disk apparatus according to claim 8 or 9, wherein the third phase shifter is provided integrally with the laser beam distribution means.   11. The optical disc apparatus according to claim 8, wherein the laser beam distribution unit is a polarizing diffraction grating that diffracts and transmits light according to a polarization state of incident laser beam.   6. The optical disc apparatus according to claim 1, wherein a laser unit in which the two laser sources and the light receiving means are housed in one case is used.   13. The optical disk apparatus according to claim 12, wherein the two laser sources are semiconductor lasers, and the active layers are arranged so that the directions of the active layers are orthogonal to each other.   The first phase shifter causes a phase difference that is approximately an integral multiple of the wavelength of the laser light to the laser light from one of the laser sources, and the laser to the laser light from the other laser source. 13. The optical disk device according to claim 12, wherein a phase difference of approximately ½ times the wavelength of light is generated.  15. The optical disk apparatus according to claim 1, wherein the first phaser, the polarizing optical path separating unit, and the second phaser are integrally provided in the laser unit. .

Images