JP2009295244A - Optical element, optical pickup, and optical information processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain compatibility in two different optical recording media by forming good spots at both of optical recording media having at least two substrates different in thickness each other using a single objective lens. <P>SOLUTION: The phase difference of phase shifter surface is limited in a certain range in order not to degrade the signal level by maintaining a spot for a thickness t1 requiring no aberration correction in good condition by an aberration correction element (phase shifter surface), and a spot for condensing on a substrate with a thickness t2 in the range is aberration-corrected. As for the spot for the thickness t1, it is limited to a range of level difference height H of the phase shifter surface for obtaining the phase difference capable of securing signal level of about 50 percent or more. The level difference structure is designed in order to correct aberration in the spot of optical recording medium having thickness t2. Consequently, with a single objective lens, a good spot can be formed in both optical recording mediums having thickness t1 and t2, respectively, and high reproduced signal level can be obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a condensing optical system that condenses a light beam from a light source onto optical recording media having different substrate thicknesses, and relates to an optical element, an optical pickup, and an optical information processing apparatus included in the condensing optical system. .

  Optical recording media such as a CD having a recording capacity of 0.65 GB and a DVD having a recording capacity of 4.7 GB are widely used as means for storing video information, audio information, or data on a computer. In recent years, “Blu-ray Disc” (hereinafter referred to as “BD”) and “HD-DVD” (hereinafter referred to as “HD”), which have further increased capacities, are becoming popular. As a means for improving the recording density of the optical recording medium, in an optical pickup for writing or reading information on the optical recording medium, the numerical aperture (hereinafter referred to as NA) of the objective lens is increased, or the wavelength of the light source is increased. It is effective to reduce the beam spot focused on the optical recording medium by the objective lens by shortening the length.

  Therefore, for example, in the “CD optical recording medium”, the NA of the objective lens is 0.50 and the wavelength of the light source is 790 nm, whereas the recording density is higher than that of the “CD optical recording medium”. In the “DVD optical recording medium”, the NA of the objective lens is 0.65 and the wavelength of the light source is 660 nm. In the “BD optical recording medium” in which the recording density is further increased, a capacity of 25 GB is realized by using light with an objective lens NA of 0.85 and a light source wavelength of 405 nm. In another “HD optical recording medium”, the wavelength of the light source is the same as 405 nm, but a capacity of 15 GB was realized using an objective lens with NA of 0.65.

  The former increases the capacity by shortening the wavelength and increasing the NA, compared to the DVD system, and the latter allows the linear recording density to be improved by improving signal processing instead of increasing the NA. The capacity has been increased by adopting.

  BD and HD are common in that a blue-violet semiconductor laser light source having an oscillation wavelength of 405 nm is used, but the optical recording media have substrate thicknesses of 0.1 mm and 0.6 mm, respectively. Incidentally, the substrate thicknesses of CD and DVD optical recording media are 1.2 mm and 0.6 mm, respectively.

  In a recording / reproducing apparatus capable of reproducing and / or recording high-density information such as BD and HD, it is desirable to be able to reproduce and / or record CDs and DVDs that are currently widely used. In order to suppress an increase in cost, it is desirable that BD, HD, DVD, and CD can be reproduced and / or recorded by one optical system.

  For this purpose, a light source having an appropriate wavelength is selected according to the type of optical recording medium to be recorded and reproduced, and an appropriate optical process is applied to the selected light flux, and the substrate thickness of each optical recording medium is determined. It is necessary to correct spherical aberration caused by the difference.

As a method for recording or reproducing different optical recording media using one optical pickup, a means using one objective lens and a phase difference adjusting surface has been proposed (see Patent Document 1).
Japanese Patent No. 3613745

  However, in the description of Patent Document 1, a phase difference is given only to a region in a single ring shape, and an aberration caused by a different substrate thickness is corrected. This is because the recording density is designed to be compatible with DVDs and CDs lower than the BD and HD standards. In Patent Document 1, the shape of wavefront aberration when a DVD objective lens and a phase adjusting element are passed through a CD transparent substrate is such that the NA of the CD (numerical aperture) is compared with the phase of the wavefront near the optical axis as shown in FIG. The shape has a large aberration only around the radial position corresponding to (). Therefore, the region where the phase step is formed only needs to be near the periphery of the CD NA.

  However, when a high NA objective lens with a short wavelength of about 0.85 NA is used to correct aberrations caused by different substrate thicknesses, the wavefront aberration is very large as shown in FIG. There is a problem that correction is insufficient if only a phase difference is given to a single ring-shaped range that can be realized by the above method.

  The present invention is directed to solving the above-mentioned problems of the prior art. A single objective lens forms a good spot between at least two types of optical recording media having different substrate thicknesses, and two types of different types are used. An object of the present invention is to provide an optical element, an optical pickup, and an optical information processing apparatus that are compatible with an optical recording medium.

  In order to achieve the above object, the optical element according to claim 1 of the present invention is configured such that the light beam from the light source is collected by the condensing optical system and the information on the first optical recording medium is passed through the substrate having the thickness t1. Light of wavelength λ1 is condensed on the recording layer, and light of wavelength λ2 is condensed on the information recording layer of the second optical recording medium via a substrate having a thickness t2 different from the thickness t1. In an optical element used for an optical pickup that performs one or more of recording, reproduction, and erasing on an optical recording medium, a condensing optical system emits a light beam on a recording surface of the first optical recording medium through a substrate having a thickness t1. Due to the difference between the objective lens designed to collect light and the thickness t1 and thickness t2 of the substrate, the spherical aberration generated when the light is condensed on the information recording layer of the second optical recording medium is reduced. The light flux from the light source is divided into multiple regions by uneven steps in the optical axis direction And an aberration correction element having at least one phase shifter surface for imparting a phase difference to the surface, and the step height H of the uneven shape of the phase shifter surface is (Equation 1)

の範囲に設定されていることを特徴とする。

It is characterized by being set in the range of.

  Thereby, it is possible to correct the spherical aberration generated in the spot of the information recording layer through the substrate having the thickness t2 by giving a phase difference to the incident light of the objective lens on the phase shifter surface, and the thickness t1. The information recording layer via the substrate can suppress the adverse effect on the phase shifter surface, and the spot can be condensed well, on the recording surfaces of the optical recording media having different substrate thicknesses t1 and t2. A good spot can be formed.

  The optical element described in claim 2 is characterized in that, in the optical element of claim 1, the coefficients k1 and k2 of (Equation 1) satisfy the following condition “k1 = k2 + 1”.

  As a result, the difference in height of the concavo-convex shape in the optical axis direction on the phase shifter surface can be reduced, the manufacturing yield of the optical element can be increased, and the cost of the optical element can be reduced.

  Further, in the optical element according to claims 3 to 5, in the optical element according to claims 1 and 2, the wavelengths λ1 and λ2 of the light source satisfy the following conditions “375 nm ≦ λ1 ≦ 435 nm” and “375 nm ≦ λ2 ≦ 435 nm”. Or satisfying the following conditions “375 nm ≦ λ1 ≦ 435 nm” “630 nm ≦ λ2 ≦ 690 nm”, or satisfying the following conditions “375 nm ≦ λ1 ≦ 435 nm” “760 nm ≦ λ2 ≦ 820 nm” And

  As a result, as the first optical recording medium and the second optical recording medium, good spots can be formed on both the optical recording mediums in which BD and HD, or BD and DVD, or BD and CD are combined. it can.

  The optical pickup according to claim 6 is characterized in that the phase shifter surface of the optical element according to any one of claims 1 to 5 is formed integrally with the objective lens and at least one surface. And

  This eliminates the need to adjust the optical axes of the objective lens and the phase shifter surface, reduces the number of components, and records the optical recording medium with a substrate thickness different from the substrate thickness at the time of designing the objective lens. A good spot with less aberration can be formed on the surface, and an optical pickup can be obtained in which adverse effects are suppressed with respect to the spot on the recording surface of the optical recording medium having substantially the same substrate thickness as the design.

  An optical information processing apparatus according to a seventh aspect includes the optical pickup according to the sixth aspect.

  Thereby, it is possible to realize an optical information processing apparatus capable of recording, reproducing or erasing at least two types of optical recording media having different substrate thicknesses.

  According to the present invention, it is possible to form a good spot on an optical recording medium having at least two different substrate thicknesses with a single objective lens, and it is compatible with two different optical recording media. There is an effect that a low-cost optical pickup and an optical information processing apparatus can be obtained.

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

(Embodiment 1)
FIG. 1 is a schematic diagram showing the overall configuration of an optical pickup according to Embodiment 1 of the present invention. As shown in FIG. 1, a compatible optical pickup that records or reproduces two types of optical recording media 201 and 202 with different NAs (numerical apertures) by using a single objective lens 106 with the same light source wavelength. It is.

  The substrate thicknesses t1 and t2 of the first and second optical recording media 201 and 202 used in the configuration of the optical pickup shown in the first embodiment are 0.1 mm and 0.6 mm, respectively, corresponding to BD and HD. To do. The NAs of the optical recording media 201 and 202 are 0.85 and 0.65, and the wavelength λ1 (= λ2) of the light source is about 405 nm.

  For the optical recording medium 201 and the optical recording medium 202, the optical pickup includes a semiconductor laser 101, a polarizing beam splitter 102, a coupling lens 103, a mirror 104, a quarter wavelength plate 105, an objective lens 106, a detection lens 107, and a light receiving element. An element 108 and an aberration correction element 501 are included. The center wavelength of the semiconductor laser 101 as the light source is 405 nm, and the NA of the objective lens 106 is 0.85.

  The light emitted from the semiconductor laser 101 passes through the polarization beam splitter 102 and is converted into substantially parallel light by the coupling lens 103. The light that has passed through the coupling lens 103 is deflected by the mirror 104. Then, the light is condensed on the recording surface of the optical recording medium 201 or the optical recording medium 202 via the quarter-wave plate 105, the aberration correction element 501, and the objective lens 106, thereby recording, reproducing or erasing information. Is called.

  Reflected light from the optical recording media 201 and 202 passes through the objective lens 106, the aberration correction element 501, and the quarter wavelength plate 105, and then is reflected by the mirror 104, and is converged by the coupling lens 103, and is polarized beam splitter. The light is separated from the forward light by 102 and is deflected and guided onto the light receiving element 108 by the detection lens 107, and a reproduction signal, a focus error signal, and a track error signal are detected.

  The objective lens 106 according to the first embodiment is optimally designed for the optical recording medium 201 having a thickness t = 0.0875 mm. Assuming a two-layer Blu-ray Disc optical recording medium having two information recording surfaces, the information recording surface is located at positions of 0.075 mm and 0.1 mm from the incident side of the light beam, so that the thickness t of its intermediate value = 0.0875 mm is used as the design median value, but is not limited to this. It may be set to 0.1 mm or 0.075 mm. In addition, spherical aberration occurs when a light beam is focused on a design center, for example, a substrate thickness different from a substrate thickness of 0.0875 mm, an information recording surface of 0.075 mm or 0.1 mm. In this case, the spherical aberration is corrected by moving the coupling lens 103 in the optical axis direction by the coil 113 and changing the light beam to divergent light or convergent light.

  FIG. 2 is a cross-sectional view of the wavefront aberration W when the light is condensed on a substrate (optical recording medium 202) having a thickness t2 = 0.6 mm in the above-described optical pickup. The horizontal axis in FIG. 2 is the normalized pupil radius (corresponding to NA 0.65), and the vertical axis is the amount of wavefront aberration. Since the amount of wavefront aberration is rotationally symmetric about the optical axis, the wavefront aberration amount is shown from the optical axis (position of normalized pupil radius 0) to the outermost side of the pupil (position of normalized pupil radius 1).

  Since the substrate thickness t2 = 0.6 mm is greatly deviated from the design value of the objective lens 106, large spherical aberration occurs. In order to correct this spherical aberration, an aberration correction element (phase shifter surface) 501 gives, for example, the phase difference shown in FIG. FIG. 4 is a cross-sectional view of the wavefront aberration W after passing through the aberration correction element 501. The amount of wavefront aberration W is reduced, and a favorable spot can be formed even on a substrate having a thickness t2 = 0.6 mm.

  FIG. 5 shows the spot peak intensity and spot diameter obtained by simulation through the aberration correction element (phase shifter surface) 501 when focused on the optical recording medium 201 having a substrate thickness t1 = 0.1 mm. . The horizontal axis represents the phase difference that the aberration correction element (phase shifter surface) 501 gives to the light beam. Near the phase difference of 180 (deg), the spot diameter is minimized, but at the same time, the spot peak intensity is also minimized. This indicates that the aberration correction element (phase shifter surface) 501 affects a focused spot with a substrate thickness t1 = 0.1 mm that does not need to be corrected.

  FIG. 6 shows the phase difference of the aberration correction element (phase shifter surface) 501 and the signal amplitude of the repetitive pattern of the recording mark 3T signal recorded on the optical recording medium 201 with the substrate thickness t1 = 0.1 mm by simulation. It is. As shown in FIG. 6, it can be seen that the 3T signal amplitude is minimized in the vicinity of the phase difference 180 (deg). The signal degradation is not unique to the 3T signal, and tends to be similar for all length signals.

  The aberration correction element (phase shifter surface) 501 limits the phase difference of the aberration correction element (phase shifter surface) 501 to a certain range in order to maintain a good spot that does not require aberration correction and prevent the signal level from being lowered. In this range, it is necessary to correct the aberration of the focused spot on the substrate having a thickness t2 = 0.6 mm. The signal level when there is no aberration correction element (phase shifter surface) 501 is the position where the phase difference is 0 (deg) (the signal amplitude is 1 by standardization). The range of the phase difference in which a signal level of about 50% or more can be secured with respect to this signal level is a range of 0 to 100 (deg) and 250 to 360 (deg) as shown in FIG.

  When this phase difference amount is converted into a step height H to be processed into the aberration correction element (phase shifter surface) 501, if the wavelength of the light source is λ1 and the refractive index of the aberration correction element material is n, the height of the step is H. The difference in optical path length is (Equation 2)

であり、段差高さＨで生じる位相差は（数３）

And the phase difference produced at the step height H is (Equation 3).

となる。また、段差高さＨは、波長λ１の整数倍（３６０°の整数倍）で同一の効果を生じるので、係数ｋ１を整数とすれば、位相差０〜１００（ｄｅｇ）に対応する段差高さＨは（数４）

It becomes. Further, since the step height H has the same effect at an integral multiple of the wavelength λ1 (an integral multiple of 360 °), if the coefficient k1 is an integer, the step height corresponding to a phase difference of 0 to 100 (deg) is obtained. H is (Equation 4)

となる。

It becomes.

  Similarly, if the coefficient k2 is an integer, the step height H corresponding to 250 to 360 (deg) is (Equation 5).

となる。

It becomes.

  When arranged, the range of the step height H is (Equation 6)

となる。

It becomes.

  By designing the step structure to limit the step height H of the aberration correction element (phase shifter surface) 501 to the above range and correct the aberration in the spot of the optical recording medium having the substrate thickness t2 = 0.6 mm. With one objective lens 106, good spots can be formed on both the optical recording media 201 and 202 having a substrate thickness t1 = 0.1 mm and t2 = 0.6 mm, and a high reproduction signal level can be obtained.

  As a result, a good spot with less aberration can be formed on the recording surface for the substrate thickness t2 different from the substrate thickness t1 at the time of designing the objective lens 106, and the light having the substrate thickness t1 substantially the same as at the time of design. The adverse effect of the aberration correction element (phase shifter surface) 501 can be suppressed even on spots on the recording surface of the recording medium 201.

(Embodiment 2)
FIG. 7 shows a phase distribution that gives three levels of phase within the range of 0 to 100 (deg) and 250 to 360 (deg) to the transmitted light of the aberration correction element (phase shifter surface) 501 according to the second embodiment of the present invention. It is a figure which shows an example. FIG. 8 is a diagram showing the wavefront aberration W after the wavefront aberration W shown in FIG. 2 is transmitted through the aberration correction element (phase shifter surface) 501 shown in FIG.

  By increasing the phase level given from the first embodiment, a good spot can be formed on the optical recording medium having the substrate thickness t2 = 0.6 mm. However, if the phase difference amount shown in FIG. 7 is processed as it is into the aberration correction element (phase shifter surface) 501, the convex portion becomes thin and high at the outer periphery of the normalized pupil radius, which makes processing extremely difficult. .

  Therefore, a phase difference of 1λ (wavelength) is added to the smaller phase difference to give the phase distribution shown in FIG. Also in the phase distribution shown in FIG. 9, the wavefront aberration W after passing through the aberration correction element (phase shifter surface) 501 is the same as in FIG. That is, the step height H of the concavo-convex shape of the aberration correction element (phase shifter surface) 501 is expressed by (Expression 7).

とすることにより、加工のし易い収差補正素子（位相シフタ面）５０１を得ることができる。

Thus, it is possible to obtain an aberration correction element (phase shifter surface) 501 that is easy to process.

(Embodiment 3)
FIG. 10 is a schematic diagram showing the overall configuration of the optical pickup according to the third embodiment of the present invention. As shown in FIG. 10, a single objective lens 106 is a compatible optical pickup that records or reproduces two types of optical recording media 201 and 203 with different NA (numerical aperture) using different light source wavelengths. is there.

  The substrate thicknesses t1 and t2 of the first and second optical recording media 201 and 203 used in the configuration of the optical pickup shown in FIG. 10 are 0.1 mm and 0.6 mm, respectively, and are compatible with BD and DVD. To do. The optical recording media 201 and 203 have NA of 0.85 and NA of 0.65, the wavelength λ1 of the light source is 405 nm, and λ2 is 660 nm.

  The light emitted from the semiconductor laser 101 passes through the polarization beam splitter 102, passes through the dichroic prism 109, and is converted into substantially parallel light by the coupling lens 103. The light that has passed through the coupling lens 103 is deflected by the mirror 104. Information is recorded, reproduced, or erased by being condensed on the recording surface of the optical recording medium 201 via the quarter-wave plate 105, the aberration correction element 501, and the objective lens 106.

  The reflected light from the optical recording medium 201 passes through the objective lens 106, the aberration correction element 501, and the quarter wavelength plate 105, is reflected by the mirror 104, is converged by the coupling lens 103, and passes through the dichroic prism 109. Then, the light is separated and deflected by the polarization beam splitter 102 and guided to the light receiving element 108 by the detection lens 107, and a reproduction signal, a focus error signal, and a track error signal are detected. The objective lens 106 used here is optimally designed so that the optical recording medium 201 having a substrate thickness t1 = 0.1 mm can be recorded and reproduced with high accuracy.

  The light emitted from the hologram laser 110 passes through the hologram 111, is reflected by the dichroic prism 109, passes through the coupling lens 103, and is deflected by the mirror 104. Information is recorded, reproduced, or erased by being condensed on the recording surface of the optical recording medium 203 via the quarter-wave plate 105, the aberration correction element 501, and the objective lens 106.

  The reflected light from the optical recording medium 203 passes through the objective lens 106, the aberration correction element 501, and the quarter wavelength plate 105, is reflected by the mirror 104, is converged by the coupling lens 103, and is reflected by the dichroic prism 109. Then, the light is separated from the forward light by the hologram 111 and is deflected and guided to a light receiving element (not shown) inside the hologram laser 110 to detect a reproduction signal, a focus error signal, and a track error signal.

  Here, the aberration correction element (phase shifter surface) 501 is the same as the HD recording medium 202 described in the first and second embodiments so that a good spot is formed on the recording surface of the DVD optical recording medium 203. The wavefront aberration is corrected by a simple method. At this time, the range of the step height H of the aberration correction element (phase shifter surface) 501 is expressed by (Equation 8).

とすることで、ＢＤ用の対物レンズ１０６で、ＢＤ，ＤＶＤの光記録媒体２０１，２０３の両方に良好なスポットを形成でき、高い再生信号レベルを得ることができる。

As a result, the BD objective lens 106 can form good spots on both the BD and DVD optical recording media 201 and 203, and a high reproduction signal level can be obtained.

(Embodiment 4)
In the fourth embodiment of the present invention, an optical recording medium 204 (CD) is used instead of the second optical recording medium 203 (DVD) in FIG. 10 described in the third embodiment, and the substrate thickness t2 is 1.2 mm. The light source wavelength λ2 of the laser 110 is 790 nm, and the NA is 0.5.

  The aberration correction element (phase shifter surface) 501 uses the same method as that of the HD recording medium 202 described in Embodiments 1 and 2 so that a good spot is formed on the recording surface of the optical recording medium 204. Is corrected. As a result, the BD objective lens 106 can form good spots on both the BD and CD optical recording media 201 and 204, and a high reproduction signal level can be obtained.

(Embodiment 5)
FIG. 11 is a diagram illustrating an example in which the phase shifter surface 502 is integrally formed on one surface of the objective lens 106 according to the fifth embodiment of the present invention. In the fifth embodiment, the phase shifter surface 502 is provided on the optical recording medium 201 side of the objective lens 106. However, the present invention is not limited to this configuration, and the phase shifter surface 502 may be provided on the mirror 104 side of the objective lens 106. Moreover, the phase shifter surfaces 502 may be provided on both surfaces of the objective lens 106. In addition, when providing in both surfaces, what is necessary is just to set the height of the phase shifter of a surface so that a desired phase difference may be given to the light beam which passes the phase shifter surface of both surfaces.

  As a result, it is not necessary to adjust the optical axes of the objective lens 106 and the phase shifter surface 502, the number of components can be reduced, and the recording can be performed on an optical recording medium having a substrate thickness different from the substrate thickness at the time of designing the objective lens. A good spot with less aberration can be formed on the surface, and adverse effects on the spot on the recording surface of the optical recording medium having substantially the same substrate thickness as the design can be suppressed.

(Embodiment 6)
FIG. 12 is a diagram illustrating an example of an optical information processing apparatus 700 according to the sixth embodiment of the present invention. The optical information processing apparatus 700 includes an optical pickup 100, a spindle motor 200, a seek motor 300, and a signal processing control unit 600. The optical pickup 100 has the same configuration as that described in the first embodiment. The spindle motor 200 is a means for rotating the optical recording medium. The seek motor 300 is means for moving the optical pickup 100 in the radial direction of the optical recording medium.

  The signal processing control unit 600 includes a CPU / memory 601, a semiconductor laser driving circuit 602, a current / voltage conversion circuit 603, a signal calculation circuit 604, a servo circuit 605, an actuator driving circuit 606, a spherical aberration correction element driving circuit 607, and a seek motor driving circuit. The CPU / memory 601 is connected to the external interface 800.

  The signal processing control unit 600 controls light emission of the semiconductor laser 101, rotation control of the spindle motor 200, position control of the seek motor 300, detection of a reproduction signal based on a signal from the light receiving element 108, and focus direction of the objective lens actuator 121. , Track direction control, and position control of the coupling lens 103 for spherical aberration correction.

  With this configuration, an optical information processing apparatus capable of recording, reproducing, or erasing can be realized for at least two types of optical recording media having different substrate thicknesses.

  The optical element, the optical pickup, and the optical information processing apparatus according to the present invention can form a good spot between at least two types of optical recording media having different substrate thicknesses with a single objective lens. Compatibility can be obtained with an optical recording medium, and it is useful as a condensing optical system for condensing a light beam from a light source onto optical recording media having different substrate thicknesses.

Schematic which shows the whole structure of the optical pick-up in Embodiment 1 of this invention. The figure which shows the cross-sectional shape of the aberration wavefront which occurs with the difference of the substrate thickness The figure which shows the cross-sectional shape of the aberration correction element (phase shifter surface) whose phase difference amount to correct | amend is 2 levels The figure which shows the cross-sectional shape of the aberration wave front after correction | amendment with the aberration correction element (phase shifter surface) of phase difference amount 2 level The figure which shows the relationship between spot peak intensity and spot diameter when it condenses on a recording medium through an aberration correction element (phase shifter surface) The figure which shows the relationship between the phase difference of an aberration correction element (phase shifter surface), and the 3T signal amplitude recorded on the optical recording medium The figure which shows the cross-sectional shape of the aberration correction element (phase shifter surface) whose correction phase difference amount is 3 levels The figure which shows the cross-sectional shape of the aberration wave front after correction | amendment with the aberration correction element (phase shifter surface) of phase difference amount 3 levels The figure which shows the cross-sectional shape of the aberration correction element (phase shifter surface) whose correction phase difference amount is 3 levels in Embodiment 2 of this invention. Schematic which shows the whole structure of the optical pick-up in Embodiment 3 of this invention. The figure which shows the example which formed the phase shifter surface integrally in one surface of the objective lens in Embodiment 5 of this invention The figure which shows an example of the optical information processing apparatus in Embodiment 6 of this invention The figure which shows the shape of a wavefront aberration when using the objective lens for DVD and passing through the transparent substrate of CD The figure which shows the shape of the aberration which occurs with different substrate thickness using the high NA objective lens

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Optical pick-up 101 Semiconductor laser 102 Polarizing beam splitter 103 Coupling lens 104 Mirror 105 1/4 wavelength plate 106 Objective lens 107 Detection lens 108 Light receiving element 109 Dichroic prism 110 Hologram laser 111 Hologram 113 Coil 121 Objective lens actuator 200 Spindle motor 201, 202, 203, 204 Optical recording medium 300 Seek motor 501 Aberration correction element 502 Phase shifter surface 600 Signal processing control unit 601 CPU / memory 602 Semiconductor laser drive circuit 603 Current / voltage conversion circuit 604 Signal operation circuit 605 Servo circuit 606 Actuator drive circuit 607 Spherical Aberration Correction Element Drive Circuit 608 Seek Motor Drive Circuit 609 Spindle Motor Drive Circuit 700 Light Broadcasting processing apparatus 800 External interface

Claims (7)

The light beam from the light source is condensed by the condensing optical system onto the information recording layer of the first optical recording medium via the substrate having the thickness t1, and the light having the thickness t2 different from the thickness t1. In an optical element used for an optical pickup in which light of wavelength λ2 is focused on an information recording layer of a second optical recording medium through a substrate and at least one of recording, reproduction, and erasing is performed on at least two types of optical recording media ,
An objective lens designed so that the condensing optical system condenses the light beam on the recording surface of the first optical recording medium via the substrate having the thickness t1;
Due to the difference between the thickness t1 and the thickness t2 of the substrate, the uneven step in the optical axis direction is reduced so as to reduce the spherical aberration generated when the light is condensed on the information recording layer of the second optical recording medium. And an aberration correction element having at least one phase shifter surface that is divided into a plurality of regions and gives a phase difference to the light flux from the light source,
The height H of the uneven shape of the phase shifter surface is (Expression 1)

An optical element characterized by being set in a range of The coefficients k1 and k2 in the above (Equation 1) are determined by the following condition “k1 = k2 + 1”.
The optical element according to claim 1, wherein: The wavelengths λ1 and λ2 of the light source satisfy the following condition “375 nm ≦ λ1 ≦ 435 nm”
“375 nm ≦ λ2 ≦ 435 nm”
The optical element according to claim 1, wherein: The wavelengths λ1 and λ2 of the light source satisfy the following condition “375 nm ≦ λ1 ≦ 435 nm”
“630nm ≦ λ2 ≦ 690nm”
The optical element according to claim 1, wherein: The wavelengths λ1 and λ2 of the light source satisfy the following condition “375 nm ≦ λ1 ≦ 435 nm”
“760nm ≦ λ2 ≦ 820nm”
The optical element according to claim 1, wherein:   6. An optical pickup, wherein the phase shifter surface of the optical element according to claim 1 is integrated with an objective lens and formed on at least one surface.   An optical information processing apparatus comprising the optical pickup according to claim 6.

Images