JP4758138B2 - Optical pickup and optical information processing apparatus using the same - Google Patents

Description

  The present invention relates to an optical pickup that performs at least one of recording, reproducing, and erasing information on a plurality of types of optical recording media, and an optical information processing apparatus using the optical pickup.

  As means for storing video information, audio information, or data on a computer, optical recording media such as a CD with a recording capacity of 0.65 GB and a DVD with a recording capacity of 4.7 GB are becoming widespread. In recent years, there has been an increasing demand for further improvement in recording density and increase in capacity.

  As means for increasing the recording density of such an optical recording medium, in an optical pickup that writes or calls information on the optical recording medium, the numerical aperture of the objective lens (hereinafter referred to as NA) is increased, or the light source By shortening the wavelength, it is effective to reduce the diameter of the beam spot condensed by the objective lens and formed on the optical recording medium. 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 780 nm, whereas the recording density is higher than that of the “CD optical recording medium”. In the “DVD optical recording medium” made, the NA of the objective lens is 0.65 and the wavelength of the light source is 660 nm. As described above, the optical recording medium is desired to further improve the recording density and increase the capacity. For this purpose, the NA of the objective lens is set to be larger than 0.65 or the wavelength of the light source is increased. It is desired to make it shorter than 660 nm.

  Two standards have been proposed for such a large-capacity optical recording medium and optical information processing apparatus. One is a “Blu-ray Disc” standard that satisfies a capacity equivalent to 22 GB by using a blue wavelength region light source and an NA 0.85 objective lens as described in Non-Patent Document 1. . The other is the “HD DVD” standard, as described in Non-Patent Document 2, which has the same blue wavelength but satisfies a capacity of 20 GB using an objective lens with NA 0.65. is there.

  The former increases the capacity by shortening the wavelength and increasing the NA as compared to DVD optical recording media, and the latter allows the linear recording density to be improved by devising signal processing instead of increasing the NA. The capacity is increased by narrowing the track pitch by adopting groove recording.

  Further, coma generated by the tilt of the optical recording medium is proportional to the thickness d of the optical recording medium and proportional to the third power of the NA of the objective lens. Therefore, to increase the density, it is necessary to make the optical recording medium thinner by increasing the NA of the objective lens. This is why the thickness of the CD optical recording medium is reduced from 1.2 mm to 0.6 mm of the DVD optical recording medium. In the “Blu-ray Disc” standard, a substrate thickness of 0.1 mm is adopted. Yes. On the other hand, “HD DVD” is standardized at 0.6 mm, which is the same as the DVD optical recording medium. There is an advantage that the equipment for the current DVD can be diverted for mass production of disk media.

An example of a method for achieving compatibility of these optical recording media is described in Patent Document 1.
JP 2004-30725 A Manju Oku et al. “What Blu-ray Disc Aims”, Nikkei Electronics 2003.03.31, p.135-150 Naoshi Yamada et al., “Next generation specification born from DVD“ HD DVD ””, Nikkei Electronics 2003.10.13, p.125-134

  As described above, two standards using a light source in the blue wavelength band have been proposed. However, as a user, it is desirable that these two standards of optical recording media can be handled by the same optical information processing apparatus without distinction. The simplest method for realizing this is to mount a plurality of optical pickups. However, with this method, it is difficult to achieve downsizing and cost reduction. Therefore, it is desired that the optical pickup be capable of recording or reproducing with a common light source and a common objective lens for the two blue standards. However, the following two problems exist in such a configuration.

1. Spherical aberration due to substrate thickness difference Infinite system incidence (the incident light flux on the objective lens is incident on a first blue light recording medium having a wavelength (λ) of 405 nm, NA of 0.85, and a substrate thickness (t) of 0.1 mm. Second blue light recording with a wavelength (λ) of 660 nm, NA of 0.65, and a substrate thickness (t) of 0.6 mm, using a single objective lens that minimizes wavefront aberration in a state where the light is incident as parallel light. When spot formation is performed on the medium by infinite system incidence, spherical aberration due to the difference in the substrate thickness is generated, which needs to be corrected.

2. Necessity of aperture limitation due to difference in NA Since the above-mentioned blue 2 standards have different NAs from 0.85 and 0.65, it is necessary to selectively switch them.

  Furthermore, there are CDs and DVDs that are conventional optical recording media at the user's hand. It is desirable that both these optical recording media and the new standard optical recording media can be handled by the same optical information processing apparatus. Similarly to the above, it is necessary to correct spherical aberration due to the difference in substrate thickness and wavelength and to switch the aperture due to the difference in NA.

  The present invention is directed to solving the problems of the prior art, and without increasing the number of components, two blue light recording media having different NA and substrate thickness, such as “Blu-ray Disc” standard, An optical pickup capable of forming a good spot for the “HD DVD” standard, and capable of forming a good spot for a conventional DVD-type optical recording medium or a CD-type optical recording medium, and light using the same An object is to provide an information processing apparatus.

In order to achieve this object, the optical pickup according to claim 1 performs recording or reproduction on the first and second optical recording media having the same wavelength (λ1) and different numerical apertures and substrate thicknesses. Further, in the optical pickup for recording or reproducing on the third and fourth optical recording media having different wavelengths (λ2, λ3; λ1 <λ2 <λ3) ,
Selectively the polarization direction of the three types of light sources having different wavelengths, the objective lens for condensing on each optical recording medium, and the wavelength (λ1) light beam condensed on the first and second optical recording media An aperture using a polarization plane switching element for switching and a liquid crystal element that selectively blocks and transmits the outer peripheral portion in two or more stages as an aperture corresponding to the first to fourth optical recording media for the incident light beam to the objective lens. A limiting element and a polarization-selective aberration correcting element for the second optical recording medium, and the optical path of the third and fourth optical recording media is a spherical aberration generated by the objective lens and the aberration correcting element. To correct
The magnification is a finite system .

The optical pickup described in claim 2 has the same wavelength (λ1) to be used, performs recording or reproduction on the first and second optical recording media having different numerical apertures and substrate thicknesses, and further uses the wavelength (λ2). , Λ3; in an optical pickup for recording or reproducing on the third and fourth optical recording media having different λ1 <λ2 <λ3), three types of light sources having different wavelengths and an objective for focusing on each optical recording medium A lens, a polarization plane switching element that selectively switches the polarization direction of a light beam having a wavelength (λ1) collected on the first and second optical recording media, and first and second light beams incident on the objective lens An aperture limiting element using a liquid crystal element that selectively shields and transmits the outer peripheral portion in two or more stages as an aperture corresponding to the recording medium, a polarization selective aberration correcting element for the second optical recording medium, and For transmitted light at wavelengths (λ1, λ3) Is a dead zone, a wavelength-selective aberration correction element that adds a predetermined aberration only to the transmitted light of the used wavelength (λ2), and wavelength selectivity according to the used wavelength (λ1, λ2, λ3) in front of the objective lens And the optical path of the fourth optical recording medium is characterized by a finite magnification for correcting spherical aberration generated by the objective lens and the wavelength-selective aberration correcting element.

The optical pickup described in claim 3 has the same wavelength (λ1) to be used, performs recording or reproduction on the first and second optical recording media having different numerical apertures and substrate thicknesses, and further uses the wavelength (λ2). , Λ3; in an optical pickup that performs recording or reproduction on the third and fourth optical recording media having different λ1 <λ2 <λ3), at least any two of three types of light sources having different wavelengths and four types of optical recording media In contrast to the above, the polarization direction of the light beam having the wavelength (λ1) condensed on the first and second optical recording media and the objective lens formed with a bonded type or diffraction surface for focusing at 0.07λrms or less. A polarization plane switching element that selectively switches and a liquid crystal element that selectively shields and transmits the outer peripheral portion in two or more stages as openings corresponding to the first and second optical recording media of the incident light beam to the objective lens. An aperture limiting element; And a polarization-selective aberration correcting element for optical recording medium, and a wavelength-selective aperture limiting element corresponding to the wavelength used (λ1, λ2, λ3) in front of the objective lens. .

The optical pickup according to claim 4 has the same wavelength (λ1) to be used, performs recording or reproduction on the first and second optical recording media having different numerical apertures and substrate thicknesses, and further uses the wavelength (λ2). , Λ3; in an optical pickup for recording or reproducing on the third and fourth optical recording media having different λ1 <λ2 <λ3), three types of light sources having different wavelengths and an objective for focusing on each optical recording medium A lens, an aperture limiting element using a liquid crystal element that selectively shields and transmits the outer peripheral portion in two or more stages as an opening corresponding to the first to fourth optical recording media, and a wavelength used. An expander optical system that switches a divergence state of a light beam from a light source of (λ1) is provided, and a light beam having a wavelength (λ1) is converged with respect to the first optical recording medium and a wavelength (λ1 with respect to the second optical recording medium). ) Luminous flux and third light Light flux of the wavelength (.lambda.2) for medium infinite system, the light flux of the wavelength ([lambda] 3) for the fourth optical recording medium is characterized in that enters the objective lens as a divergent system.

An optical information processing apparatus according to claim 5 uses the optical pickup according to any one of claims 1 to 4 to at least record, reproduce, and erase information on an optical recording medium. And one or more.

  According to the above configuration, it is possible to form a good spot on a blue optical recording medium having a different numerical aperture and substrate thickness with one objective lens, and also to provide a good spot on a conventionally used DVD or CD optical recording medium. In addition, information can be recorded, reproduced, and erased on a plurality of types of optical recording media by an optical information processing apparatus using this optical pickup.

  As described above, according to the present invention, it is possible to provide two blue optical recording media having different numerical apertures (NA) and substrate thicknesses with one objective lens, provided with means for performing predetermined aberration correction and aperture limitation. Spots can be formed, and a good spot can be formed on a conventional DVD-based optical recording medium or CD-based optical recording medium.

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

FIG. 1 shows an optical pickup according to Reference Example 1 of the embodiment of the present invention. “A first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” and “used wavelength of 405 nm”. , NA 0.65, light irradiation side substrate thickness of second blue light recording medium 0.6 mm ”is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, and erasing together.

  1 includes a semiconductor laser 101 having a wavelength of 405 nm, a collimator lens 102, a polarization plane switching element 103, a half mirror 104 ′, a deflection prism 105, a polarization selective aperture limiting element 106, and polarization selective aberration correction. An element 107, an objective lens 109, a detection lens 111, a light beam splitting means 112, and a light receiving element 113 are included.

  Here, the objective lens 109 is designed to minimize wavefront aberration in an infinite system with respect to “the first blue light recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm”. ing. In general, the tolerance becomes severer as the NA becomes higher. Therefore, it is more difficult to obtain desirable characteristics at NA 0.85 when compared with NA 0.85 and NA 0.65. This is because it is desirable to use an aspheric lens.

  The first and second blue light recording media 110a and 110b are optical recording media having different substrate thicknesses and different operating wavelengths. The first blue light recording medium 110a is an optical recording medium having a substrate thickness of 0.1 mm. The second blue light recording medium 110b is an optical recording medium having a substrate thickness of 0.6 mm. At the time of recording or reproducing, only one of the optical recording media is set in a rotating mechanism (not shown) and rotated at a high speed.

  First, a case where “a first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102, and the polarization direction is rotated by 90 degrees in the plane perpendicular to the paper surface by the polarization plane switching element 103. Transmitted, the optical path is deflected 90 degrees by the deflecting prism 105, passes through the dead zone through the polarization selective aperture limiting element 106 and the polarization selective aberration correcting element 107, enters the objective lens 109, and enters the first blue light recording medium 110a. Is condensed as a minute spot. Information is reproduced, recorded or erased by this spot. The light beam reflected from the first blue light recording medium 110a is again made substantially parallel light, reflected by the half mirror 104 ', converged by the detection lens 111, and deflected and divided into a plurality of optical paths by the light beam splitting means 112. It reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

  Next, a case where “a second blue light recording medium having a used wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102, and is transmitted as it is without being rotated in the polarization direction by the polarization plane switching element 103, and transmitted through the half mirror 104 ′. The deflection prism 105 deflects the optical path by 90 degrees, the polarization selective aperture limiting element 106 limits the NA to 0.65, the polarization selective aberration correcting element 107 adds a predetermined spherical aberration, and enters the objective lens 109. The light is condensed as a minute spot on the second blue light recording medium 110b. Information is reproduced, recorded or erased by this spot. The light beam reflected from the second blue light recording medium 110b is converted into substantially parallel light again, reflected by the half mirror 104 ′, converged by the detection lens 111, and deflected and divided into a plurality of optical paths by the light beam splitting means 112. It reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

Hereinafter, the optical component employed in Reference Example 1 will be described for compatibility with the two blue systems.

First, as a condition regarding the NA and the beam diameter, in the first reference example , it is necessary to switch the NA according to the optical recording medium. That is, NA is 0.85 in the first blue light recording medium 110a, and NA 0.65 in the second blue light recording medium 110b. When the focal length of the objective lens 109 is f and the effective diameter of the light beam used for condensing is φ, NA is given by the following equation (Equation 1).

よって、光記録媒体の種類に応じて、通過光束径を切り換える手段を用いればよい。そこで、光記録媒体に応じて、光源からの出射光の偏光方向を切り換える偏光面切換素子１０３と、偏光方向に応じて、反射，回折，吸収のいずれかの光学特性を利用して光束径の切り換えを行う偏光選択性開口制限素子１０６を選択すればよい。

Therefore, a means for switching the passing beam diameter may be used according to the type of the optical recording medium. Therefore, the polarization plane switching element 103 that switches the polarization direction of the light emitted from the light source according to the optical recording medium, and the light beam diameter by utilizing any one of reflection, diffraction, and absorption optical characteristics according to the polarization direction. The polarization selective aperture limiting element 106 to be switched may be selected.

  As the polarization plane switching element 103, a TN (twisted nematic) type liquid crystal may be used. The TN liquid crystal is generally known to rotate the polarization direction when a voltage is applied, and to transmit insensitively when no voltage is applied.

  As the polarization selective aperture limiting element 106, for example, a means for switching the beam diameter by transmission and reflection according to the polarization direction as shown in FIG. 2 may be used. The polarization selective aperture limiting element 106 has a structure shown in FIG. That is, the polarizing film 126 is sandwiched between the transparent glasses 127 and transmits a light beam polarized in a specific direction. Further, instead of the transparent glass 127, a highly transparent resin may be used. The polarizing region of the polarizing film 126 is as shown in FIG. That is, the polarization-selective aperture limiting element 106 transmits only a light beam polarized in a specific direction by the polarizing film 126 in the polarizing film forming region 129 at the outer peripheral portion. The diameter of the region 128 in the inner periphery of the polarization selective aperture limiting element 106 is NA 0.85, and in the case of an objective lens having an effective light beam diameter of 3 mm, a circular shape of about 2.3 mm so that the effective NA is 0.65. And If the effective beam diameter is other than 3 mm, the aperture diameter is changed in proportion to the effective beam diameter so that the effective NA is 0.65.

  In the case of the first blue light recording medium 110a, as shown in FIG. 4, no voltage is applied to the polarization plane switching element 103 which is a TN type liquid crystal. As a result, the light beam polarized in the direction parallel to the paper surface exiting from the collimator lens 102 is changed in polarization direction by 90 degrees by the polarization surface switching element 103 of the TN type liquid crystal and is polarized in the direction perpendicular to the paper surface. The selective aperture limiting element 106 transmits the light without being shielded and enters the objective lens 109.

  Next, in the case of the second blue light recording medium, a voltage is applied to the polarization plane switching element 103 which is a TN type liquid crystal. As a result, the light beam polarized in the direction parallel to the paper surface exiting from the collimating lens 102 is transmitted without changing the polarization direction by the polarization plane switching element 103, and the polarization selective aperture limiting element 106 forms a polarizing film on the outer peripheral portion. The light is shielded in the region 129 and is transmitted only from the region 128 on the inner periphery, and enters the objective lens 109.

In the first reference example , the polarization plane switching element 103 is between the collimating lens 102 and the half mirror 104 ′, but may be between the half mirror 104 ′ and the polarization selective aperture limiting element 106. In FIG. 3B, the circular through hole region 128 is formed on the inner peripheral side. However, the region 128 is not necessarily circular, and may be oval.

Further, the polarization selective aperture limiting element 106 of the first reference example may be a means for switching the beam diameter by diffraction as shown in FIG. 5 in accordance with the polarization direction. Specifically, a diffraction grating having polarization selectivity may be formed.

Further, as the polarization selective aperture limiting element 106 of the first reference example , for example, a polarization selective diffractive optical element may be configured using a birefringent medium to diffract the peripheral light. Here, with reference to FIG. 6A, the transmission characteristics of the polarized light flux with respect to the birefringent medium will be examined. FIG. 6A is a diagram showing a traveling path of a transmitted light beam when the light beam is incident on a general birefringent medium. When a light beam enters the birefringent medium, the traveling path of the light beam changes depending on the polarization of the incident light beam. That is, as shown in FIG. 6A, the path of the light beam polarized in the direction parallel to the plane of the paper with respect to the birefringent medium does not change when passing through the birefringent medium. This light beam is called an ordinary ray. On the other hand, when the light beam polarized in the direction perpendicular to the paper surface with respect to the birefringent medium passes through the birefringent medium, the path of the light beam changes. This light beam is called an extraordinary ray.

A polarization selective diffractive optical element according to the first reference example using such a birefringent medium will be described. FIG. 6B is a diagram illustrating a surface on which the light beam of the diffractive optical element in Reference Example 1 is incident, and FIG. 6C is a cross-sectional view taken along the line AA ′ in FIG.

The diffractive optical element shown in FIG. 6C includes an isotropic medium 131, a birefringent medium 132, and a glass 130 disposed so as to sandwich them. The birefringent medium 132 has a large number formed shape concentrically in the circumferential those formed in a sawtooth shape from the center of circle section, as shown in FIG. 6 (c). The isotropic medium 131 has a complementary shape to the birefringent medium 132 and is in close contact with the surface of the birefringent medium 132 formed in a sawtooth shape. The cross-sectional shape is not limited to this, and may be a surface whose height changes in a stepped shape as shown in FIG.

  An aperture limiting method using a diffractive optical element will be described with reference to FIGS. 6 (c) and 6 (d). FIG. 5 is a diagram showing a transmission state depending on the polarization direction of the light beam incident on the aperture limiting element. As shown in FIG. 6C, the birefringent medium 132 has a refractive index of no_405 (normal refractive index at a wavelength of 405 nm) and ne_405 (extraordinary light refractive index at a wavelength of 405 nm) according to the polarization direction of the incident light beam. . Here, no represents a refractive index (normal refractive index) for ordinary light, and ne represents a refractive index (abnormal light refractive index) for extraordinary light. Here, a case where the aperture limiting element is manufactured by selecting the isotropic medium 131 and the birefringent medium 132 so that the refractive indexes n1_405 and ne_405 of the isotropic medium 131 are equal to each other will be considered.

  The first blue light recording medium is incident with the polarization direction of the light beam being equal to the polarization direction of the extraordinary ray. Then, since the refractive indexes of the isotropic medium 131 and the birefringent medium 132 are the same, the light beam is transmitted without any influence. On the other hand, the second blue light recording medium is a light beam polarized in a direction orthogonal to the first blue light recording medium (ordinary light polarization direction). When the light beam enters, the isotropic medium 131 and the birefringent medium 132 have different refractive indexes. Therefore, diffraction occurs due to the shape of the boundary surface between the isotropic medium 131 and the birefringent medium 132 of the aperture limiting element, and the traveling path changes. As shown in FIG. 5, the aperture limiting element is a dead zone with respect to the first blue light recording medium. However, in the case of the second blue light recording medium, the light beam incident on the aperture limiting element is diffracted at the outer periphery. The diffraction direction may be condensed or scattered in a direction different from the spot focused on the optical recording medium with NA 0.65.

Furthermore, the polarization selective aperture limiting element 106 in the first reference example may be a means for switching the beam diameter by absorption as shown in FIG. 7 in accordance with the polarization direction.

  Next, an objective lens of NA 0.85 designed to have good aberration characteristics with respect to the first blue light recording medium having a used wavelength of 405 nm and a substrate thickness of 0.1 mm is used. FIG. 8 shows wavefront aberrations that occur when the second blue light recording medium having a thickness of 0.6 mm is used at NA 0.65. In FIG. 8, the horizontal axis represents the entrance pupil radius, and the vertical axis represents the wavefront aberration. FIG. 8 shows a two-dimensional cross-sectional shape of the phase difference distribution, but in actuality, the phase difference distribution is a rotationally symmetric three-dimensional distribution with respect to the vertical axis (NA = 0). The configuration, operation, and effect of the polarization selective aberration correcting element for correcting such generated aberration will be specifically described below.

First, a polarization selective aberration correcting element using the diffraction effect of a birefringent medium as in the aperture restriction will be described. FIG. 9 is a diagram illustrating a surface on which the light beam of the aberration correction element in the first reference example is incident. FIGS. 10A and 10B are each a line AA ′ of FIG. It is sectional drawing.

The aberration correcting element of the present reference example 1 shown in FIG. 10 (b) Fig. 10 (a) and is composed of isotropic medium 133 and the birefringent medium 134 and these are arranged manner to sandwich glass 130.. As shown in FIG. 10A, the birefringent medium 134 is formed in a sawtooth shape so that a large number of concentric circles are formed from the center to the circumference. The isotropic medium 133 has a complementary shape to the birefringent medium 134 and is in close contact with the surface of the birefringent medium formed in a sawtooth shape. The cross-sectional shape is not limited to this, and may be a surface whose height changes in a stepped shape as shown in FIG.

  An aberration correction method using a diffractive optical element will be described with reference to FIGS. 10 (a) and 10 (b). FIG. 11 is a diagram showing the shape of the transmitted light beam according to the polarization direction of the light beam incident on the aberration correction element (diffractive optical element) in FIG. As shown in FIG. 10A, the birefringent medium 134 has a refractive index of no_405 and ne_405 according to the polarization direction of the incident light beam. Here, no represents a refractive index (normal refractive index) for ordinary light, and ne represents a refractive index (abnormal light refractive index) for extraordinary light. Consider the case where an aberration correction element is manufactured by selecting the isotropic medium 133 and the birefringent medium 134 so that the refractive indexes n1_405 and ne_405 of the isotropic medium are equal.

  The first blue light recording medium is incident with the polarization direction of the light beam being equal to the polarization direction of the extraordinary ray. Then, since the refractive indexes of the isotropic medium 133 and the birefringent medium 134 are the same, the light flux having a wavelength of 405 nm is transmitted without any influence.

  On the other hand, the second blue light recording medium is a light beam polarized in a direction orthogonal to the first blue light recording medium (ordinary polarization direction). When the light beam enters, the isotropic medium 133 and the birefringent medium 134 have different refractive indexes. Therefore, diffraction occurs due to the shape of the boundary surface between the isotropic medium 133 and the birefringent medium 134 of the aberration correction element, and the traveling path is changed, so that spherical aberration can be corrected. As shown in FIG. 11, the aberration correction element is a dead zone with respect to the first blue light recording medium. However, in the case of the second blue light recording medium, the wavefront of the light beam incident on the aberration correction element is a straight line, whereas the wavefront of the light beam transmitted through the aberration correction element is a curve. This is an effect due to diffraction generated at the boundary surface between the birefringent medium and the isotropic medium in the aberration correction element, and thereby spherical aberration can be corrected.

  At this time, if the depth of the diffraction grating is appropriately adjusted, the diffraction efficiency of the light beam at the time of recording / reproduction of the second blue light recording medium can be maximized. In other words, the problem of light loss can be solved.

The birefringent material may be formed of an optical crystal such as calcite, LiNbO ₃ , or LiTaO ₃ . Alternatively, it may be formed of a polymer liquid crystal obtained by polymerizing and curing a liquid crystal, or a polymer material such as polycarbonate that exhibits birefringence by uniaxial stretching.

The aberration correction element is not limited to the one using diffraction as described above, and may be a correction method using zero-order light. A phase shifter element according to the first reference example using a birefringent medium will be described. In FIG. 12, a birefringent medium 134 of a birefringent material layer having an ordinary light refractive index of no_405 and an extraordinary light refractive index of ne_405 is formed on a transparent substrate having an isotropic refractive index, such as glass 130. When a light beam is incident on the birefringent medium 134 from a light source such as a semiconductor laser, the thickness of the birefringent medium changes as the transmitted light moves away from the optical axis toward the periphery, and the thickness is rotationally symmetric with respect to the optical axis. Etching is performed so as to have the property. The birefringent medium 134 having this rotational symmetry is shaped to correct the wavefront aberration of the transmitted light. The concave portion of the birefringent medium 134 formed in this way is filled with a transparent filler (isotropic medium) having an isotropic refractive index n1_405, and is a translucent substrate 2 having an isotropic refractive index. It is possible to produce a polarization selective aberration correcting element by sandwiching the birefringent medium 134 with a sheet of glass 130. The material is selected so that the refractive index n1_405 of the filler is substantially equal to the extraordinary light refractive index ne_405 of the birefringent medium 134.

  The first blue light recording medium is incident with the polarization direction of the light beam being equal to the polarization direction of the extraordinary ray. Then, since the refractive index is the same between the filler and the birefringent medium 134, a light beam having a wavelength of 405 nm is transmitted without any influence.

  On the other hand, the second blue light recording medium is a light beam polarized in a direction orthogonal to the first blue light recording medium (ordinary polarization direction). When the light beam enters, the filler and the birefringent medium 134 have different refractive indexes. A phase difference distribution proportional to the refractive index difference (ne_405-n1_405) between the birefringent material layer and the filler and the spatial distribution of the thickness of the birefringent medium 134 is generated. Therefore, a change occurs in the wavefront aberration. At this time, the thickness distribution of the birefringent medium 134 so that the spatial phase difference distribution generated in the phase shifter element cancels the phase difference distribution shown in FIG. 8 generated when the second blue light recording medium is used. By forming the wavefront, the wavefront can be optimized.

FIG. 13 shows an optical pickup according to Reference Example 2 of the embodiment of the present invention. “A first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” and “used wavelength of 405 nm”. , NA 0.65, light irradiation side substrate thickness of second blue light recording medium 0.6 mm ”is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, and erasing together.

  13 includes a semiconductor laser 101 having a wavelength of 405 nm, a collimating lens 102, a polarizing beam splitter 104, a deflecting prism 105, a guest-host type liquid crystal aperture limiting element 106a, a liquid crystal aberration correcting element 107a, and a quarter wavelength. The plate 108, the objective lens 109, the detection lens 111, the light beam splitting means 112, and the light receiving element 113 are included.

  Here, the objective lens 109 is designed to minimize wavefront aberration in an infinite system with respect to “the first blue light recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm”. ing. In general, the tolerance becomes severer as the NA becomes higher. Therefore, it is more difficult to obtain desirable characteristics at NA 0.85 when compared with NA 0.85 and NA 0.65. This is because it is desirable to use an aspheric lens.

  The first and second blue light recording media 110a and 110b are optical recording media having different substrate thicknesses and different operating wavelengths. The first blue light recording medium 110a is an optical recording medium having a substrate thickness of 0.1 mm. The second blue light recording medium 110b is an optical recording medium having a substrate thickness of 0.6 mm. At the time of recording or reproducing, only one of the optical recording media is set in a rotating mechanism (not shown) and rotated at a high speed.

  First, a case where “a first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimating lens 102, passes through the polarization beam splitter 104, and is deflected by 90 degrees in the optical path by the deflecting prism 105, thereby opening the guest-host type liquid crystal aperture It passes through the dead zone through the limiting element 106a and the liquid crystal aberration correction element 107a, passes through the quarter-wave plate 108, becomes circularly polarized light, enters the objective lens 109, and is collected as a minute spot on the first blue light recording medium 110a. To be lighted. Information is reproduced, recorded or erased by this spot. The light beam reflected from the first blue light recording medium 110a becomes circularly polarized light in the opposite direction to the outward path, again becomes substantially parallel light, passes through the quarter wavelength plate 108, and becomes linearly polarized light orthogonal to the forward path, The light is reflected by the polarization beam splitter 104, is converged by the detection lens 111, is deflected and divided into a plurality of optical paths by the light beam splitter 112, and reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

  Next, a case where “a second blue light recording medium having a used wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimating lens 102, passes through the polarization beam splitter 104, and is deflected by 90 degrees in the optical path by the deflecting prism 105, thereby opening the guest-host type liquid crystal aperture NA is limited to 0.65 by the limiting element 106a, a predetermined spherical aberration is added by the liquid crystal aberration correcting element 107a, enters the objective lens 109, and is condensed as a minute spot on the second blue light recording medium 110b. Information is reproduced, recorded or erased by this spot. The light beam reflected from the second blue light recording medium 110b becomes circularly polarized light opposite to the outward path, becomes again substantially parallel light, passes through the quarter-wave plate 108, and becomes linearly polarized light orthogonal to the outward path, The light is reflected by the polarization beam splitter 104, is converged by the detection lens 111, is deflected and divided into a plurality of optical paths by the light beam splitter 112, and reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

In the following, the optical component employed in the present reference example 2 is described for compatibility with the blue 2 system.

In Reference Example 2, a guest-host type liquid crystal is used as the aperture limiting element and functions as a selective annular light shielding filter as shown in FIG. FIGS. 14B and 14C are explanatory views showing the operation principle.

  The NA is changed according to the first and second blue light recording media 110a and 110b. Specifically, as shown in FIGS. 14B and 14C, a liquid crystal shutter having an annular pattern is used. And is used to transmit or shield the outer periphery of the light beam incident on the objective lens 109. As shown in FIGS. 14B and 14C, the guest-host type liquid crystal 136 is provided on the outer periphery, and when no voltage is applied, that is, in the off state, as shown in FIG. When a voltage is applied, that is, in an on state, the element is partially transmissive as shown in FIG.

  Next, FIG. 15A is a cross-sectional view showing the liquid crystal aberration correcting element, and the configuration and operating principle of the liquid crystal aberration correcting element will be described with reference to FIGS. 15B and 15C showing the electrode patterns. .

The configuration of the liquid crystal aberration correcting element 107a used in this reference example 2 will be described with reference to FIG. Glass substrates 137a and 137b are bonded by a conductive spacer 138 to form a liquid crystal cell. The inner surface of the glass substrate 137a has an electrode 139a, an insulating film 140a, and an alignment film 141a in this order from the inner surface, and the inner surface of the glass substrate 137b has an electrode 139b, an insulating film 140b, and an alignment film 141b in this order from the inner surface. It is coated. The electrode 139a is pattern-wired so that it can be connected to the control circuit by a connection line at the electrode lead-out portion 142.

  The electrode 139b is electrically connected to the electrode 139a formed over the glass substrate 137a by a conductive spacer 138. Therefore, the electrode 139b can be connected to the phase correction element control circuit by the connection line at the electrode lead-out portion 142. Liquid crystal 143 is filled in the liquid crystal cell.

Next, an electrode formed on the substrate that constitutes the liquid crystal aberration correction element 107a in the present Reference Example 2 and sandwiches the liquid crystal layer is formed such that the electrode pattern is formed concentrically around the optical axis in the present Reference Example 2. FIG. 15B or FIG. 15C is a conceptual diagram of the electrode pattern.

  Here, an NA 0.85 objective lens designed to have good aberration characteristics with respect to the first blue light recording medium having a use wavelength of 405 nm and a substrate thickness of 0.1 mm is used. Wavefront aberrations that occur when the 0.6 mm second blue light recording medium is used at NA 0.65 are shown in the upper part of FIGS. 16 (a) and 16 (c). In FIG. 16, the horizontal axis represents the entrance pupil radius, and the vertical axis represents the wavefront aberration. FIG. 16 shows a two-dimensional cross-sectional shape of the phase difference distribution, but in reality, the phase difference distribution is a rotationally symmetric three-dimensional distribution with respect to the vertical axis (NA = 0). The configuration of the liquid crystal aberration correction element for correcting such generated aberration, its operation, and effect will be specifically described below.

  The liquid crystal aberration correction element 107a applies a predetermined voltage to the power feeding section or the divided electrode as shown in FIGS. 15B and 15C, and freely adjusts the refractive index n of the liquid crystal in a concentric manner from n1 to n2. It is possible to change. When the refractive index n is changed, the optical path difference Δn · d (Δn is the change in refractive index, d is the cell thickness of the liquid crystal), that is, the wavelength is λ, and the phase difference Δn · d (2π / Λ).

  Here, the spherical aberration that occurs when the light is condensed on the second blue light recording medium is the upper portion of FIGS. 16 (a) and 16 (c). When the electrode of FIG. 15B is used, a phase difference as shown in the lower part of FIG. 16A is given to the light beam incident on the objective lens 109 from the light source side with respect to such spherical aberration. As described above, by adjusting the voltage applied to the power supply unit in each concentric zone of the liquid crystal element, the “wavefront aberration” can be canceled by the wavefront delay in each part of the light beam passing through the liquid crystal element. When the electrode shown in FIG. 15C is used, the phase difference as shown in the lower part of FIG. 16C is applied to the light beam incident on the objective lens 109 from the light source side with respect to such spherical aberration. By adjusting the voltage applied to the power supply unit of each concentric band of the liquid crystal element so that the wavefront aberration can be canceled, the “wavefront aberration” can be canceled due to the delay of the wavefront at each part of the light beam passing through the liquid crystal element.

  FIG. 16B shows the sum of the solid line (wavefront aberration) and the broken line (wavefront delay due to the liquid crystal element) in FIG. 16A, that is, the corrected wavefront aberration. It is much smaller than the original wavefront aberration (upper part in FIG. 16A). FIG. 16D shows the sum of the solid line (wavefront aberration) and the broken line (wavefront delay due to the liquid crystal element) in FIG. 16C, that is, the corrected wavefront aberration. It is much smaller than the original wavefront aberration (upper part in FIG. 16C).

FIG. 17 shows an optical pickup according to Reference Example 3 of the embodiment of the present invention. “A first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” and “used wavelength of 405 nm”. , NA 0.65, light irradiation side substrate thickness of second blue light recording medium 0.6 mm ”is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, and erasing together.

  17 includes a semiconductor laser 101 having a wavelength of 405 nm, a collimating lens 102, a polarizing beam splitter 104, a deflecting prism 105, a guest-host type liquid crystal aperture limiting element 106a, an aberration correcting diffractive optical element 107b, 1 / A four-wave plate 108, an objective lens 109, a detection lens 111, a light beam splitting means 112, and a light receiving element 113 are included.

  Here, the objective lens 109 is designed to minimize wavefront aberration in an infinite system with respect to “the first blue light recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm”. ing. In general, the tolerance becomes severer as the NA becomes higher. Therefore, it is more difficult to obtain desirable characteristics at NA 0.85 when compared with NA 0.85 and NA 0.65. This is because it is desirable to use an aspheric lens.

  The first and second blue light recording media 110a and 110b are optical recording media having different substrate thicknesses and different operating wavelengths. The first blue light recording medium 110a is an optical recording medium having a substrate thickness of 0.1 mm. The second blue light recording medium 110b is an optical recording medium having a substrate thickness of 0.6 mm. At the time of recording or reproducing, only one of the optical recording media is set in a rotating mechanism (not shown) and rotated at a high speed.

  First, a case where “a first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimating lens 102, passes through the polarization beam splitter 104, and is deflected by 90 degrees in the optical path by the deflecting prism 105, thereby opening the guest-host type liquid crystal aperture It passes through the dead zone through the limiting element 106a and the aberration correcting diffractive optical element 107b, passes through the quarter-wave plate 108, becomes circularly polarized light, enters the objective lens 109, and forms a minute spot on the first blue light recording medium 110a. Focused. Information is reproduced, recorded or erased by this spot. The light beam reflected from the first blue light recording medium 110a becomes circularly polarized light in the opposite direction to the outward path, again becomes substantially parallel light, passes through the quarter wavelength plate 108, and becomes linearly polarized light orthogonal to the forward path, The light is reflected by the polarization beam splitter 104, is converged by the detection lens 111, is deflected and divided into a plurality of optical paths by the light beam splitter 112, and reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

  Next, a case where “a second blue light recording medium having a used wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimating lens 102, passes through the polarization beam splitter 104, and is deflected by 90 degrees in the optical path by the deflecting prism 105, thereby opening the guest-host type liquid crystal aperture NA is limited to 0.65 by the limiting element 106a, a predetermined spherical aberration is added to the aberration correcting diffractive optical element 107b, enters the objective lens 109, and is condensed as a minute spot on the second blue light recording medium 110b. The Information is reproduced, recorded or erased by this spot. The light beam reflected from the second blue light recording medium 110b becomes circularly polarized light opposite to the outward path, becomes again substantially parallel light, passes through the quarter-wave plate 108, and becomes linearly polarized light orthogonal to the outward path, The light is reflected by the polarization beam splitter 104, is converged by the detection lens 111, is deflected and divided into a plurality of optical paths by the light beam splitter 112, and reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

Hereinafter, the optical component employed in Reference Example 3 will be described for compatibility with the two blue systems.

The aberration-correcting diffractive optical element used in Reference Example 3 is a diffractive optical element having no polarization dependency, not the polarization selectivity used in Reference Example 1. Therefore, it is not a complicated configuration in which a birefringent medium and an isotropic medium are sandwiched between glasses as in Reference Example 1, but a configuration in which a diffractive surface is provided on a substrate surface such as glass or plastic is easy to manufacture. Yes. As shown in FIG. 18A, the diffractive optical element 107b is composed of a plurality of annular zones around the optical axis. The diffractive optical element 107b is formed so that its cross section has a sawtooth shape as shown in FIG. 18B or a step shape as shown in FIG. 18C. For example, a diffractive optical element with a sawtooth cross section is advantageous because of its higher diffraction efficiency. As a method for creating a cross-sectional shape of a diffractive optical element, there are a method of applying a photolithography technique and a method of precision cutting with a diamond tool or the like. It is also possible to replicate a plurality of diffractive optical elements from a transparent material by forming a template in a mold and using injection molding or the so-called 2P method.

  As shown in FIGS. 19A and 19B, the diffraction grating of the diffractive optical element 107b has its zero-order light on the first blue light recording medium 110a via the objective lens 109 and the first-order diffracted light is The light is condensed on the second blue light recording medium 110b via the objective lens 109. Further, since the 0th-order light and the 1st-order diffracted light are not focused on the optical recording media having other substrate thicknesses, these diffracted lights have little influence on reading or recording.

  Note that the reason why the 0th-order diffracted light is selected to be NA 0.85 as the diffraction order is that the objective lens 109 is “first blue light recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm”. On the other hand, this is because the infinite system is designed to minimize the wavefront aberration. In FIG. 19, for the sake of simplicity, the quarter-wave plate 108 between the aberration correcting diffractive optical element 107b and the objective lens 109 shown in FIG. 17 is omitted.

As a specific example, the diffraction grating having a blazed cross-sectional shape shown in FIG. 20 has a diffraction grating depth d changed to 0 to 2 μm, and the base material is, for example, glass MLaC130 (nd = 69.4, νd) manufactured by HOYA. = 53.2) When the diffractive optical element is manufactured, the change in the diffraction efficiency of the diffraction grating is calculated. The diffraction efficiency ηm of the diffraction grating in this reference example 3 is expressed by the following equation (Equation 2).

（数２）中、ｄは格子溝深さ、ｍは回折次数、ｎは材料屈折率を示している。図２０は、横軸に回折格子の深さｄ、縦軸に回折格子の回折効率の変化を算出した結果を示す図である。図２０中の「Ｂ０」，「Ｂ１」，「Ｂ２」，「Ｂ３」はそれぞれ０次回折光、１次回折光、２次回折光、３次回折光の回折効率を示す。

In (Expression 2), d is the grating groove depth, m is the diffraction order, and n is the material refractive index. FIG. 20 is a diagram illustrating a result of calculating the diffraction grating depth d on the horizontal axis and the change in diffraction efficiency of the diffraction grating on the vertical axis. “B0”, “B1”, “B2”, and “B3” in FIG. 20 indicate the diffraction efficiencies of the 0th-order diffracted light, 1st-order diffracted light, 2nd-order diffracted light, and 3rd-order diffracted light, respectively.

As shown in FIG. 20, since the diffraction efficiency can be adjusted by the phase depth of the diffraction grating, if the phase depth is selected according to the irradiation power characteristics of the first blue light recording medium and the second blue light recording medium. Good. In general, the smaller the diameter spot, the more power is collected. The beam spot diameter on the optical recording medium is proportional to the wavelength λ and decreases in inverse proportion to NA, and the power increases in inverse proportion to the spot area. That is, when comparing NA 0.85 and NA 0.65, the power collected on the optical recording medium is larger at NA 0.85 at a ratio of (0.85 / 0.65) ² . Therefore, when the first blue light recording medium and the second blue light recording medium are used with the same material and the same linear velocity, the condensing power required for each medium is equivalent, and therefore the 0th order The efficiency ratio between the light and the first-order diffracted light may be set to 1: 1.7. That is, the phase depth may be selected in the vicinity of 0.32 μm.

  Alternatively, if only one of the first blue light recording medium and the second blue light recording medium is a reproduction-only optical information processing apparatus, if the reproduction side efficiency is reduced, the other optical recording medium can be used. On the other hand, it is possible to irradiate with sufficient power, and it is easy to increase the speed.

  Next, specific numerical examples regarding the shapes of the objective lens and the diffractive optical element will be described. As shown in FIGS. 19A and 19B, the diffractive optical element 107b is disposed on the light source side of the aspherical objective lens 109, and a diffraction grating is formed on the surface on the objective lens side.

  Further, the aspherical shape of the lens surface includes the coordinate X in the optical axis direction, the coordinate Y in the direction orthogonal to the optical axis, the paraxial radius of curvature R, the conical constant K, and higher order coefficients A, B, C, D, E, F ,..., A well-known aspherical expression is expressed by the following expression (Equation 3).

また、回折光学素子の位相関数Φ（ｒ）は、回折次数ｍ、波長λ、光軸からの半径ｒ、係数Ｃ１〜Ｃ５を用いて、次の式（数４）で表される。

The phase function Φ (r) of the diffractive optical element is expressed by the following equation (Equation 4) using the diffraction order m, the wavelength λ, the radius r from the optical axis, and the coefficients C1 to C5.

本参考例３における対物レンズは、使用波長４０５ｎｍ、ＮＡ０.８５、ｆ＝１.７６５ｍｍ、ｎｄ＝１.６９４、νｄ＝５３.２であり、図２１に、具体的データを示す。図２１中の記号は、以下のとおりである。「ＯＢＪ」は物点（光源としての半導体レーザ）を意味するが、対物レンズ１０９は「無限系」であり、曲率半径：ＲＤＹおよび厚さ：ＴＨＩの「ＩＮＦＩＮＩＴＹ（無限大）」は光源が無限遠にあることを意味する。なお、特に断らない限り、長さの次元を持つ量の単位は「ｍｍ」である。

The objective lens in Reference Example 3 has a working wavelength of 405 nm, NA of 0.85, f = 1.765 mm, nd = 1.694, and νd = 53.2. FIG. 21 shows specific data. The symbols in FIG. 21 are as follows. “OBJ” means an object point (semiconductor laser as a light source), but the objective lens 109 is an “infinite system”, and “INFINITY (infinity)” with a radius of curvature: RDY and a thickness: THI has an infinite light source. It means being in the distance. Unless otherwise specified, the unit of the quantity having the dimension of length is “mm”.

“S1” means the light source side surface of the diffractive optical element, and “S2” means the side surface of the optical recording medium. “S3” means the light source side surface of the optical pickup objective lens, and “S4” means the optical recording medium side surface. The thickness of the objective lens in Reference Example 3 is 2.38463 mm, and the thickness of 0.425496 mm described on the right side of the radius of curvature in the column of S4 indicates “working distance: WD”. “S5” is a light source side surface of the light irradiation side substrate of the optical recording medium 110, and “S6” is a surface that matches the recording surface. The space between these surfaces S5 and S6, that is, the substrate thickness is the first blue light. The recording medium is 0.1 mm, the second blue light recording medium is 0.6 mm, nd = 1.516330, and νd = 64.1. “EPD: entrance pupil diameter”, which is 3.0 mm for the first blue light recording medium and 2.3 mm for the second blue light recording medium. “WL: Wavelength” represents a used wavelength (405 nm).

  On the axis of the system obtained by combining the objective lens and the diffractive optical element, the wavefront aberration is 0.0027 λrms for the 0th order light and 0.0007 λrms for the 1st order diffracted light, and is suppressed to the Marshall limit of 0.07λ or less. ing.

Further, as an optical pickup in Reference Example 4 of the embodiment of the present invention, diffraction using first-order diffracted light for the first blue light recording medium and first-order diffracted light for the second blue light recording medium. The optical element was integrated with the objective lens.

  As shown in FIGS. 22A and 22B, a diffraction grating surface is formed on the incident surface on the light source side of the aspheric objective lens 109, and both the diffraction grating and the exit surface of the objective lens have an aspheric shape. did. Therefore, the first surface and the second surface are the diffraction grating and the exit surface of the integral condenser lens. Data of each aspherical lens manufactured by automatic design is as shown in FIG.

  On the axis of the system obtained by combining the objective lens and the diffractive optical element, the wavefront aberration is 0.0011λrms for the first blue light recording medium, 0.0005λrms for the second blue light recording medium, and the Marshall limit is 0.00. It is suppressed to 07λ or less.

FIG. 24 shows an optical pickup according to Reference Example 5 of the embodiment of the present invention. “A first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” and “used wavelength of 405 nm”. , NA 0.65, second blue light recording medium with light irradiation side substrate thickness of 0.6 mm ”and“ DVD optical recording medium with use wavelength of 660 nm, NA 0.65, light irradiation side substrate thickness of 0.6 mm ”and“ use. 1 is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, and erasing together a “CD optical recording medium having a wavelength of 785 nm, NA of 0.50, and a light irradiation side substrate thickness of 1.2 mm”.

  The main parts of the optical pickup shown in FIG. 24 are a semiconductor laser 101 having a wavelength of 405 nm, a collimating lens 102, a polarizing beam splitter 104, a trichromatic prism 115, a deflecting prism 105, a guest host type liquid crystal aperture limiting element 106a, and a liquid crystal aberration correcting element 107a. , A quarter wavelength plate 108, an objective lens 109, a detection lens 111, a light beam splitting means 112, a light receiving element 113, a blue optical system through which a light beam having a wavelength of 405 nm passes, a hologram unit 201, a collimating lens 202, a dichroic prism. 204, a light beam having a wavelength of 660 nm passing through a trichromatic prism 115, a deflecting prism 105, a guest-host type liquid crystal aperture limiting element 106a, a liquid crystal aberration correcting element 107a, a quarter-wave plate 108, and an objective lens 109 passes. D optical system, hologram unit 211, collimating lens 212, dichroic prism 204, trichromatic prism 115, deflecting prism 105, guest host type liquid crystal aperture limiting element 106a, liquid crystal aberration correcting element 107a, quarter wavelength plate 108, objective The optical system of CD which the light beam with a wavelength of 785 nm comprised from the lens 109 passes is comprised.

  That is, the trichromatic prism 115, the dichroic prism 204, the deflecting prism 105, the guest host type liquid crystal aperture limiting element 106a, the liquid crystal aberration correcting element 107a, the quarter wavelength plate 108, and the objective lens 109 are common to three or two optical systems. It is a part.

  Here, the objective lens 109 is designed to minimize wavefront aberration in an infinite system with respect to “the first blue light recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm”. ing. In general, the tolerance becomes tighter as the objective lens becomes higher NA and shorter wavelength, so it is more difficult to achieve desirable characteristics with blue NA 0.85. In particular, use an aspherical lens whose aberration is corrected with NA 0.85. This is because it is desirable.

  The first and second blue light recording media 110a and 110b, the DVD-based and CD-based optical recording media 110c and 110d are optical recording media having different substrate thicknesses and different operating wavelengths, respectively. The optical recording medium having a substrate thickness of 0.1 mm, the second blue optical recording medium 110b is an optical recording medium having a substrate thickness of 0.6 mm, and the DVD optical recording medium 110c is an optical recording medium having a substrate thickness of 0.6 mm. The CD optical recording medium 110d is an optical recording medium having a substrate thickness of 1.2 mm. At the time of recording or reproducing, only one of the optical recording media is set in a rotating mechanism (not shown) and rotated at a high speed.

  First, a case where “a first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 104 and the trichroic prism 115, and is deflected by 90 degrees by the deflecting prism 105. The guest-host type liquid crystal aperture limiting element 106a and the liquid crystal aberration correcting element 107a pass through the dead zone, pass through the quarter-wave plate 108, become circularly polarized light, enter the objective lens 109, and enter the first blue light recording medium 110a. Is condensed as a minute spot. Information is reproduced, recorded or erased by this spot. The light beam reflected from the first blue light recording medium 110a becomes circularly polarized light in the opposite direction to the outward path, again becomes substantially parallel light, passes through the quarter wavelength plate 108, and becomes linearly polarized light orthogonal to the forward path, The light is reflected by the polarization beam splitter 104, is converged by the detection lens 111, is deflected and divided into a plurality of optical paths by the light beam splitter 112, and reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

  Next, a case where “a second blue light recording medium having a used wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 104 and the trichroic prism 115, and is deflected by 90 degrees by the deflecting prism 105. The guest-host type liquid crystal aperture limiting element 106a limits NA to 0.65, the liquid crystal aberration correction element 107a adds a predetermined spherical aberration, passes through the quarter-wave plate 108, becomes circularly polarized light, and enters the objective lens 109. The light is condensed as a minute spot on the second blue light recording medium 110b. Information is reproduced, recorded or erased by this spot. The light beam reflected from the second blue light recording medium 110b becomes circularly polarized light opposite to the outward path, becomes again substantially parallel light, passes through the quarter-wave plate 108, and becomes linearly polarized light orthogonal to the outward path, The light is reflected by the polarization beam splitter 104, is converged by the detection lens 111, is deflected and divided into a plurality of optical paths by the light beam splitter 112, and reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

  Next, a description will be given of a case where “DVD optical recording medium having a used wavelength of 660 nm, NA of 0.65, and light irradiation side substrate thickness of 0.6 mm” is recorded, reproduced or erased. In recent years, a hologram unit in which a light receiving and emitting element is installed in one can and a light beam is separated using a hologram has been generally used for a pickup of a DVD-based optical recording medium. In FIG. 24, reference numeral 201 denotes a hologram unit configured by integrating a semiconductor laser 201a, a hologram 201b, and a light receiving element 201c. A 660 nm light beam emitted from the semiconductor laser 201a of the hologram unit 201 is transmitted through the hologram 201b, converted into parallel light by the collimator lens 202, transmitted through the dichroic prism 204, transmitted through the blue wavelength band, red, and The light beam in the infrared wavelength band is reflected in the direction of the deflecting prism 105 by the reflecting trichromatic prism 115, the optical path is deflected by 90 degrees by the deflecting prism 105, and is restricted to NA 0.65 by the guest-host type liquid crystal aperture limiting element 106a. A predetermined phase is added in the liquid crystal aberration correction element 107a, passes through the quarter-wave plate 108, becomes circularly polarized light or elliptically polarized light, enters the objective lens 109, and is condensed as a minute spot on the DVD optical recording medium 110c. Is done. Information is reproduced, recorded or erased by this spot. The light beam reflected from the DVD optical recording medium 110c is reflected by the deflecting prism 105 and the trichromatic prism 115, passes through the dichroic prism 204, and is converged by the collimating lens 202, and is converged by the hologram 201b in the same can as the semiconductor laser 201a. The light is diffracted in the direction of a certain light receiving element 201c and received by the light receiving element 201c. An information signal and a servo signal are detected from the light receiving element 201c.

  Next, a case where “CD optical recording medium having a used wavelength of 785 nm, NA of 0.50, and a light irradiation side substrate thickness of 1.2 mm” is recorded, reproduced, or erased will be described. As with the DVD optical recording medium, a hologram unit has been generally used for the CD optical recording medium. In FIG. 24, 211 indicates a hologram unit configured by integrating a semiconductor laser 211a, a hologram 211b, and a light receiving element 211c. The 785 nm light beam emitted from the semiconductor laser 211a of the hologram unit 211 is transmitted through the hologram 211b, converted into parallel light by the collimator lens 212, the red wavelength band light is transmitted, and the infrared wavelength band light beam is reflected. Reflected by the dichroic prism 204, transmits the light in the blue wavelength band, and reflects the light beams in the red and infrared wavelength bands, is reflected in the direction of the deflecting prism 105 by the trichromatic prism 115, and deflects the optical path by 90 degrees by the deflecting prism 105. Then, the NA is limited to 0.50 by the guest-host type liquid crystal aperture limiting element 106a, a predetermined phase is added in the liquid crystal aberration correcting element 107a, and it passes through the quarter wavelength plate 108 to be circularly polarized or elliptically polarized, and the objective lens 109 and a small spot on the CD optical recording medium 110d. It is collected as a light. Information is reproduced, recorded or erased by this spot. The light beam reflected from the CD-based optical recording medium 110d is reflected by the deflecting prism 105, the trichromatic prism 115, and the dichroic prism 204, converged by the collimating lens 212, and received by the hologram 211b in the same can as the semiconductor laser 211a. The light is diffracted in the direction of the element 211c and received by the light receiving element 211c. An information signal and a servo signal are detected from the light receiving element 211c.

In the following, the optical components employed in Reference Example 5 for blue 2 system, DVD, and CD compatibility will be described.

In this reference example 5 , recording or reproduction is performed on four types of optical recording media, namely, the first and second blue light recording media 110a and 110b, the DVD system, and the CD system optical recording media 110c and 110d. It is necessary to switch the opening. In the first blue light recording medium 110a, φ1 which is NA 0.85, in the second blue light recording medium 110b, φ2 which is NA 0.65, in the DVD optical recording medium 110c, φ3 which is NA 0.65, CD optical recording In the medium 110d, when φ4 that satisfies NA 0.50 is selected, φ1>φ3>φ2> φ4. Here, the reason why the aperture diameters are different for the same NA for φ3 and φ2 is that the longer the wavelength, the longer the focal length, and the same NA is obtained as is apparent from the equation (1). For this purpose, φ3 needs to be larger than φ2.

  A guest-host type liquid crystal aperture limiting element 106a is used as such a four-stage aperture limiting element. As shown in FIG. 25, it functions as a selective annular light shielding filter. The NA is changed in accordance with each optical recording medium. Specifically, the NA is composed of a liquid crystal shutter having an annular pattern, and the outer peripheral portion of the light beam incident on the objective lens 109 is selectively shielded. As shown in FIG. 25, a voltage on / off state is selectively selected for each region formed concentrically from the outside. The first blue light recording medium is transmitted through the entire surface, the DVD light recording medium is φ3, the second blue light recording medium is φ2, and the CD light recording medium is φ4. What should I do.

  Next, a single objective lens 109 having a minimum wavefront aberration with respect to the first blue light recording medium 110a having a wavelength of 405 nm and an NA of 0.85 and a substrate thickness of 0.1 mm is applied to the single objective lens 109 having an NA of 0.65 and a substrate thickness of 0.6 mm. When spot formation is performed on the second blue light recording medium 110b. As shown in FIG. 26 (a), wavefront aberration due to the difference in substrate thickness occurs.

  Further, a single objective lens 109 having a minimum wavefront aberration with respect to the first blue light recording medium 110a having a wavelength of 405 nm and an NA of 0.85 and a substrate thickness of 0.1 mm is added to the single objective lens 109 having an NA of 0.65 and a substrate thickness of 0.6 mm. When a light beam having a wavelength of 660 nm is spot-formed on the DVD optical recording medium 110c by infinite system incidence, spherical aberration due to the difference in wavelength and substrate thickness occurs as shown in FIG.

  Further, a single objective lens 109 having a minimum wavefront aberration with respect to the first blue light recording medium 110a having a wavelength of 405 nm and an NA of 0.85 and a substrate thickness of 0.1 mm is added to the single objective lens 109 having an NA of 0.50 and a substrate thickness of 1.2 mm. When spot formation is performed on the CD optical recording medium 110d. As shown in FIG. 26 (c), spherical aberration due to the difference in substrate thickness occurs.

The present reference example 5 includes a liquid crystal aberration correction element 107a similar to that of the reference example 2 in order to generate a spherical aberration having a polarity opposite to that of these spherical aberrations.

As an electrode configuration for correcting the above-described three different spherical aberrations, for example, a configuration as shown in FIG. 27 may be used. That is, a pair of continuous transparent electrodes 145 and 146 are formed, and metal electrodes 145a to 145c and 146a to 146c are formed on the transparent electrodes 145 and 146, respectively. The metal electrodes are each connected to an external signal source by metal wiring, and an arbitrary voltage can be supplied from each signal source. In Reference Example 5 , the second blue light recording medium and the DVD optical recording medium are recorded as the transparent electrode 145, and approximately half of each pupil radius position where the spherical aberration that occurs when attempting to record and reproduce is maximized. The transparent electrode 146 is formed at the point of the pupil radius where the spherical aberration that occurs when recording and reproduction of the CD-type optical recording medium is maximized.

Specifically, in the case of FIG. 26, the incident light beam diameters of the objective lens in each optical path in the first and second blue light recording media, DVD system, and CD system optical recording media are φ3.0 mm, φ2.3 mm, and φ1. The diameter of the light beam passing through the liquid crystal aberration correction element 107a is 3.0 mm, which is substantially the same as the optical path of the first blue light recording medium (actually, it has a margin of 0.1 to 0.2 mm). ) At this time, the pupil radius of the transparent electrode 145 may be 1.7 mm, and the pupil radius of the transparent electrode 146 may be 1.3 mm. In Reference Example 5 , three types of spherical aberration, namely, NA 0.65 blue, DVD, and CD are corrected. As is apparent from FIGS. 26A and 26B, the spherical aberration is maximized. Since the positions are substantially the same, the electrode patterns of the metal electrodes 145b and 146b that provide two types of peak positions may be used.

  Then, for the liquid crystal element having such an electrode pattern, for example, when the optical recording discriminating means (not shown) recognizes that the DVD optical recording medium is inserted, the position where the additional phase amount is maximized. When an applied voltage recorded in advance is applied to each electrode (metal electrode 145b) and it is recognized that a CD optical recording medium is inserted, the additional phase amount is at a position where the maximum value is obtained. A pre-recorded applied voltage is applied to each electrode (metal electrode 146b).

FIG. 28 shows an optical pickup according to the first embodiment of the present invention. “A first blue optical recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” and “a used wavelength of 405 nm, NA of 0.8. 65, “second blue light recording medium with a light irradiation side substrate thickness of 0.6 mm” and “DVD optical recording medium with a use wavelength of 660 nm, NA 0.65, light irradiation side substrate thickness of 0.6 mm” and “use wavelength of 785 nm, FIG. 2 is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, and erasing together a CD-based optical recording medium having an NA of 0.50 and a light irradiation side substrate thickness of 1.2 mm.

  The main parts of the optical pickup shown in FIG. 28 are a semiconductor laser 101 having a wavelength of 405 nm, a collimator lens 102, a polarization plane switching element 103, a half mirror 104 ′, a trichromatic prism 115, a deflection prism 105, and a guest-host type liquid crystal aperture limiting element 106a. , A polarization selective aberration correcting element 107, an objective lens 109, a detection lens 111, a light beam splitting means 112, a blue optical system through which a light beam having a wavelength of 405 nm passes, a hologram unit 201, a collimating lens 202, and a dichroic. A DVD optical system that includes a prism 204, a trichroic prism 115, a deflecting prism 105, a guest-host type liquid crystal aperture limiting element 106a, a polarization selective aberration correcting element 107, and an objective lens 109; A luminous flux having a wavelength of 785 nm is composed of a program unit 211, a collimating lens 212, a dichroic prism 204, a trichromatic prism 115, a deflecting prism 105, a guest host type liquid crystal aperture limiting element 106 a, a polarization selective aberration correcting element 107, and an objective lens 109. It consists of a CD optical system that passes through.

  That is, the trichroic prism 115, the dichroic prism 204, the deflecting prism 105, the guest-host type liquid crystal aperture limiting element 106a, the polarization selective aberration correcting element 107, and the objective lens 109 are common parts for three or two optical systems.

  Here, the objective lens 109 is designed to minimize wavefront aberration in an infinite system with respect to “the first blue light recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm”. ing. In general, the tolerance becomes tighter as the objective lens becomes higher NA and shorter wavelength, so it is more difficult to achieve desirable characteristics with blue NA 0.85. In particular, use an aspherical lens whose aberration is corrected with NA 0.85. This is because it is desirable.

  The first and second blue light recording media 110a and 110b, the DVD-based and CD-based optical recording media 110c and 110d are optical recording media having different substrate thicknesses and different operating wavelengths, and the first blue light recording medium 110a is a substrate. An optical recording medium having a thickness of 0.1 mm, an optical recording medium having a substrate thickness of 0.6 mm, a second blue optical recording medium 110b, an optical recording medium having a substrate thickness of 0.6 mm, and a DVD optical recording medium 110c. The CD optical recording medium 110d is an optical recording medium having a substrate thickness of 1.2 mm. At the time of recording or reproducing, only one of the optical recording media is set in a rotating mechanism (not shown) and rotated at a high speed.

  First, a case where “a first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102, and the polarization direction is rotated by 90 degrees in the plane perpendicular to the paper surface by the polarization plane switching element 103. The light passes through the trichromatic prism 115, the optical path is deflected by 90 degrees by the deflecting prism 105, passes through the guest-host type liquid crystal aperture limiting element 106a and the polarization selective aberration correcting element 107, passes through the dead band, and enters the objective lens 109. Is condensed as a minute spot on the blue light recording medium 110a. Information is reproduced, recorded or erased by this spot. The light beam reflected from the first blue light recording medium 110a is again made substantially parallel light, reflected by the half mirror 104 ', converged by the detection lens 111, and deflected and divided into a plurality of optical paths by the light beam splitting means 112. It reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

  Next, a case where “a second blue light recording medium having a used wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102 and passes through the polarization plane switching element 103 without rotating. 115, the optical path is deflected by 90 degrees by the deflecting prism 105, restricted to NA 0.65 by the guest-host type liquid crystal aperture limiting element 106a, a predetermined spherical aberration is added by the polarization selective aberration correcting element 107, and the objective lens 109 and is condensed as a minute spot on the second blue light recording medium 110b. Information is reproduced, recorded or erased by this spot. The light beam reflected from the second blue light recording medium 110b is converted into substantially parallel light again, reflected by the half mirror 104 ′, converged by the detection lens 111, and deflected and divided into a plurality of optical paths by the light beam splitting means 112. It reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

Next, a description will be given of a case where “DVD optical recording medium having a used wavelength of 660 nm, NA of 0.65, and light irradiation side substrate thickness of 0.6 mm” is recorded, reproduced or erased. As described in Reference Example 5 above, the hologram unit 201 in which the light receiving and emitting elements are installed in one can is generally used for the pickup of the DVD-based optical recording medium, and the semiconductor laser 201a, the hologram 201b, and the light receiving The element 201c is integrated. The 660 nm light beam emitted from the semiconductor laser 201a of the hologram unit 201 is transmitted through the hologram 201b, is converted into a predetermined finite light beam by the collimator lens 202, is transmitted through the dichroic prism 204, and is transmitted through the blue wavelength band. The light beams in the red and infrared wavelength bands are reflected in the direction of the deflecting prism 105 by the reflecting trichroic prism 115, the optical path is deflected by 90 degrees by the deflecting prism 105, and NA 0.65 by the guest-host type liquid crystal aperture limiting element 106a. Therefore, a predetermined spherical aberration is added by the polarization selective aberration correcting element 107, enters the objective lens 109, and is condensed as a minute spot on the DVD optical recording medium 110c. Information is reproduced, recorded or erased by this spot. The light beam reflected from the DVD optical recording medium 110c is reflected by the deflecting prism 105 and the trichroic prism 115, is converged by the collimating lens 202, and is directed toward the light receiving element 201c within the same can as the semiconductor laser 201a by the hologram 201b. The light is diffracted and received by the light receiving element 201c. An information signal and a servo signal are detected from the light receiving element 201c.

  Next, a case where “CD optical recording medium having a used wavelength of 785 nm, NA of 0.50, and a light irradiation side substrate thickness of 1.2 mm” is recorded, reproduced, or erased will be described. As with the DVD optical recording medium, the hologram unit 211 is generally used for the CD optical recording medium. The 785 nm light beam emitted from the semiconductor laser 211a of the hologram unit 211 formed by integrating the semiconductor laser 211a, the hologram 211b, and the light receiving element 211c is transmitted through the hologram 211b and is converted into a predetermined finite system light beam by the collimator lens 212. A trichromatic prism that transmits light in the red wavelength band and reflects light in the infrared wavelength band by the dichroic prism 204 that reflects, transmits light in the blue wavelength band, and reflects light in the red and infrared wavelength bands. 115 is reflected in the direction of the deflecting prism 105, the optical path is deflected by 90 degrees by the deflecting prism 105, restricted to NA 0.50 by the guest-host type liquid crystal aperture limiting element 106 a, and a predetermined spherical aberration in the polarization selective aberration correcting element 107. Is added to the objective lens 109. And is condensed as a minute spot on the CD optical recording medium 110d. Information is reproduced, recorded or erased by this spot. The light beam reflected from the CD-based optical recording medium 110d is reflected by the deflecting prism 105, the trichromatic prism 115, and the dichroic prism 204, converged by the collimating lens 212, and received by the hologram 211b in the same can as the semiconductor laser 211a. The light is diffracted in the direction of the element 211c and received by the light receiving element 211c. An information signal and a servo signal are detected from the light receiving element 211c.

In the following, the optical component employed in the first embodiment for blue 2 system, DVD, and CD compatibility will be described.

In the first embodiment, the guest-host type liquid crystal aperture limiting element 106a is the same as that of the reference example 5 of the above-described embodiment , and thus detailed description thereof is omitted, and the polarization selective aberration correcting element is used. This will be described below.

  A single objective lens 109 having a minimum wavefront aberration with respect to the first blue light recording medium 110a having a wavelength of 405 nm and an NA of 0.85 and a substrate thickness of 0.1 mm is added to a second objective having a substrate thickness of 0.6 mm and an NA of 0.65. When spot formation is performed on the blue light recording medium 110b, spherical aberration due to the difference in substrate thickness occurs as shown in FIG.

In the first embodiment, a polarization selective aberration correcting element 107 and a polarization plane switching element 103 are provided in order to generate a spherical aberration having a polarity opposite to the spherical aberration. The polarization selective aberration correcting element 107 and the polarization plane switching element 103 are the same as the polarization selective aberration correcting element and the polarization plane switching element of Reference Example 1, respectively. For the second blue light recording medium, Correction is performed in the same manner as in Reference Example 1.

Next, a single objective lens 109 having a minimum wavefront aberration with respect to the first blue light recording medium 110a having a wavelength of 405 nm and an NA of 0.85 and a substrate thickness of 0.1 mm is applied to the single objective lens 109 having an NA of 0.65 and a substrate thickness of 0.6 mm. In the case where a spot is formed on the DVD optical recording medium 110c of FIG. As shown in FIG. 26B, spherical aberration due to the difference in wavelength and substrate thickness occurs. However, in the first embodiment, since the polarization selective aberration correcting element 107 is inserted, the generated spherical aberration shape is different from that in FIG. Since the polarization selective aberration correcting element makes n1_405 and ne_405 equal, n1_660 and no_660 are different. That is, for the light beam having a wavelength of 660 nm, the isotropic medium and the birefringent medium have different refractive indexes. Therefore, when the polarization selective aberration correcting element is a diffractive optical element, diffraction occurs due to the shape of the interface between the isotropic medium and the birefringent medium, and when the polarization selective aberration correcting element is a phase shifter element, A spherical wave to which a phase difference corresponding to the thickness distribution is added is generated.

  Further, a single objective lens 109 having a minimum wavefront aberration with respect to the first blue light recording medium 110a having a wavelength of 405 nm and an NA of 0.85 and a substrate thickness of 0.1 mm is added to the single objective lens 109 having an NA of 0.50 and a substrate thickness of 1.2 mm. When spot formation is performed on the CD optical recording medium 110d, spherical aberration due to the difference in substrate thickness occurs as shown in FIG. However, since the polarization selective aberration correcting element 107 is inserted in the same manner as the above-described DVD-type optical recording medium, the spherical aberration shape is different from that in FIG.

In the first embodiment, the DVD and CD optical systems are configured in a finite system in order to generate spherical aberrations having opposite polarities to these spherical aberrations. An arbitrary spherical wave can be obtained by selecting a predetermined magnification as the finite system magnification, and a magnification that cancels the spherical aberration of the spherical wave shape may be selected.

FIG. 29 shows an optical pickup according to the second embodiment of the present invention. “A first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” and “a used wavelength of 405 nm, NA of 0.8. 65, “second blue light recording medium with a light irradiation side substrate thickness of 0.6 mm” and “DVD optical recording medium with a use wavelength of 660 nm, NA 0.65, light irradiation side substrate thickness of 0.6 mm” and “use wavelength of 785 nm, FIG. 2 is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, and erasing together a CD-based optical recording medium having an NA of 0.50 and a light irradiation side substrate thickness of 1.2 mm.

The configuration of the optical pickup according to the second embodiment is not limited to the first embodiment described above, and an optical device in which a blue aberration correction element and an aperture limiting element are disposed on the blue optical system side of the trichromatic prism 115. A system may be used in which a wavelength-selective aperture limiting element and a spherical aberration correcting element are arranged in front of the objective lens.

  As the wavelength-selective aperture limiting element in FIG. 29, an aperture limiting element capable of switching the aperture in three stages of blue, DVD, and CD as described in Japanese Patent Application No. 2003-21862 of the prior application by the present inventor. Use it. In addition, as the wavelength selective aberration correcting element, an element that performs blue correction as described in Japanese Patent Application No. 2002-226023 of the prior application by the present inventor, CD is a dead zone, and performs aberration correction only for DVD, CD May have a predetermined finite configuration.

FIG. 30 shows an optical pickup according to the third embodiment of the present invention. “A first blue optical recording medium having a used wavelength of 405 nm, NA of 0.85 and a light irradiation side substrate thickness of 0.1 mm” and “a used wavelength of 405 nm, NA of 0.8. 65, “second blue light recording medium with a light irradiation side substrate thickness of 0.6 mm” and “DVD optical recording medium with a use wavelength of 660 nm, NA 0.65, light irradiation side substrate thickness of 0.6 mm” and “use wavelength of 785 nm, FIG. 2 is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, and erasing together a CD-based optical recording medium having an NA of 0.50 and a light irradiation side substrate thickness of 1.2 mm.

The configuration of the optical pickup according to the third embodiment is the same as that of the second embodiment using the optical system in which a blue aberration correction element and an aperture limiting element are arranged on the blue optical system side of the trichromatic prism 115. A three-wavelength compatible objective lens 109 ′ is used as a lens, and a wavelength-selective aperture limiting element 106c is disposed in front of the objective lens 109 ′.

In Figure 30, a wavelength-selective aperture limit element, blue as in the second embodiment, DVD, may be used to switch capable aperture limiting element of the opening in the three stages of the CD. As the three-wavelength compatible objective lens 109 ′, a diffractive lens or a bonded lens may be used, and the magnification of the optical system may be changed in accordance with the lens characteristics.

FIG. 31 shows an optical pickup according to Embodiment 4 of the present invention. “A first blue optical recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” and “a used wavelength of 405 nm, NA of 0.8. 65, “second blue light recording medium with a light irradiation side substrate thickness of 0.6 mm” and “DVD optical recording medium with a use wavelength of 660 nm, NA 0.65, light irradiation side substrate thickness of 0.6 mm” and “use wavelength of 785 nm, FIG. 2 is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, and erasing together a CD-based optical recording medium having an NA of 0.50 and a light irradiation side substrate thickness of 1.2 mm.

  31 includes a semiconductor laser 101 having a wavelength of 405 nm, a collimator lens 102, a polarizing beam splitter 104, an expander optical system 116, a trichromatic prism 115, a deflecting prism 105, a guest-host type liquid crystal aperture limiting element 106a, A blue optical system that includes a quarter-wave plate 108, an objective lens 109, a detection lens 111, a light beam splitter 112, and a light receiving element 113, through which a light beam having a wavelength of 405 nm passes, a hologram unit 201, a collimator lens 202, and a dichroic prism 204. A DVD optical system through which a light beam having a wavelength of 660 nm passes, which includes a trichromatic prism 115, a deflecting prism 105, a guest-host type liquid crystal aperture limiting element 106a, a quarter-wave plate 108, and an objective lens 109; A light beam having a wavelength of 785 nm passing through the unit 211, the collimating lens 212, the dichroic prism 204, the trichromatic prism 115, the deflecting prism 105, the guest-host type liquid crystal aperture limiting element 106a, the quarter wavelength plate 108, and the objective lens 109 passes. It consists of a CD optical system. That is, the trichroic prism 115, the dichroic prism 204, the deflecting prism 105, the guest host type liquid crystal aperture limiting element 106a, the quarter wavelength plate 108, and the objective lens 109 are common components for three or two optical systems.

  The first and second blue light recording media 110a and 110b and the DVD and CD optical recording media 110c and 110d are optical recording media having different substrate thicknesses and operating wavelengths, respectively. 110a is an optical recording medium having a substrate thickness of 0.1 mm, the second blue optical recording medium 110b is an optical recording medium having a substrate thickness of 0.6 mm, and a DVD optical recording medium 110c is an optical recording medium having a substrate thickness of 0.6 mm. The recording medium, CD optical recording medium 110d, is an optical recording medium having a substrate thickness of 1.2 mm. At the time of recording or reproducing, only one of the optical recording media is set in a rotating mechanism (not shown) and rotated at a high speed.

  First, a case where “a first blue light recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 104, is converted into predetermined convergent light by the expander optical system 116, and is trichroic. The light beam is transmitted through the prism 115, deflected by 90 degrees by the deflecting prism 105, transmitted through the guest-host type liquid crystal aperture limiting element 106a, passed through the dead band, passed through the quarter-wave plate 108 and converted into circularly polarized light, and incident on the objective lens 109. The light is condensed as a minute spot on the first blue light recording medium 110a. Information is reproduced, recorded or erased by this spot. The light beam reflected from the first blue light recording medium 110a becomes circularly polarized light in the opposite direction to the outward path, again becomes substantially parallel light, passes through the quarter wavelength plate 108, and becomes linearly polarized light orthogonal to the forward path, The light is reflected by the polarization beam splitter 104, is converged by the detection lens 111, is deflected and divided into a plurality of optical paths by the light beam splitter 112, and reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

  Next, a case where “a second blue light recording medium having a used wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded or reproduced will be described. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 104, passes through the expander optical system 116 with an infinite system light beam, and is trichroic prism 115. , The optical path is deflected by 90 degrees by the deflecting prism 105, is restricted to NA 0.65 by the guest-host type liquid crystal aperture limiting element 106 a, passes through the quarter-wave plate 108 and becomes circularly polarized light, and enters the objective lens 109. Then, the light is condensed as a minute spot on the second blue light recording medium 110b. Information is reproduced, recorded or erased by this spot. The light beam reflected from the second blue light recording medium 110b becomes circularly polarized light opposite to the outward path, becomes again substantially parallel light, passes through the quarter-wave plate 108, and becomes linearly polarized light orthogonal to the outward path, The light is reflected by the polarization beam splitter 104, is converged by the detection lens 111, is deflected and divided into a plurality of optical paths by the light beam splitter 112, and reaches the light receiving element 113. An information signal and a servo signal are detected from the light receiving element 113.

Next, a description will be given of a case where “DVD optical recording medium having a used wavelength of 660 nm, NA of 0.65, and light irradiation side substrate thickness of 0.6 mm” is recorded, reproduced or erased. Further, as described in Reference Example 5 above, the hologram unit 201 in which the light emitting and receiving elements are installed in one can is used for the pickup of the DVD optical recording medium. A 660 nm light beam emitted from the semiconductor laser 201a of the hologram unit 201 is transmitted through the hologram 201b, converted into parallel light by the collimator lens 202, transmitted through the dichroic prism 204, transmitted through the blue wavelength band, red, and The light beam in the infrared wavelength band is reflected in the direction of the deflecting prism 105 by the reflecting trichromatic prism 115, the optical path is deflected by 90 degrees by the deflecting prism 105, and is restricted to NA 0.65 by the guest-host type liquid crystal aperture limiting element 106a. The light passes through the quarter-wave plate 108 to be circularly or elliptically polarized light, enters the objective lens 109, and is condensed as a minute spot on the DVD optical recording medium 110c. Information is reproduced, recorded or erased by this spot. The light beam reflected from the DVD optical recording medium 110c is reflected by the deflecting prism 105 and the trichroic prism 115, is converged by the collimating lens 202, and is directed toward the light receiving element 201c within the same can as the semiconductor laser 201a by the hologram 201b. The light is diffracted and received by the light receiving element 201c. An information signal and a servo signal are detected from the light receiving element 201c.

  Next, a case where “CD optical recording medium having a used wavelength of 785 nm, NA of 0.50, and a light irradiation side substrate thickness of 1.2 mm” is recorded, reproduced, or erased will be described. As with the DVD optical recording medium, the hologram unit 211 is generally used for the CD optical recording medium. The 785 nm light beam emitted from the semiconductor laser 211a of the hologram unit 211 is transmitted through the hologram 211b and is made a predetermined divergent light by the collimator lens 212, the light in the red wavelength band is transmitted, and the light beam in the infrared wavelength band is transmitted. Reflected by the dichroic prism 204 to be reflected, light in the blue wavelength band is transmitted, and light beams in the red and infrared wavelength bands are reflected in the direction of the deflecting prism 105 by the reflecting trichromatic prism 115, and the optical path is 90 by the deflecting prism 105. And is restricted to NA 0.50 by the guest-host type liquid crystal aperture limiting element 106a, passes through the quarter-wave plate 108, becomes circularly polarized light or elliptically polarized light, enters the objective lens 109, and enters the CD optical recording medium 110d. It is condensed as a fine spot on the top. Information is reproduced, recorded or erased by this spot. The light beam reflected from the CD-based optical recording medium 110d is reflected by the deflecting prism 105, the trichromatic prism 115, and the dichroic prism 204, converged by the collimating lens 212, and received by the hologram 211b in the same can as the semiconductor laser 211a. The light is diffracted in the direction of the element 211c and received by the light receiving element 211c. An information signal and a servo signal are detected from the light receiving element 211c.

In the fourth embodiment, since recording or reproduction is performed on four types of optical recording media, that is, the first and second blue light recording media 110a and 110b, DVD system, and CD system optical recording media 110c and 110d, there are four stages. It is necessary to switch the opening. In the first blue light recording medium 110a, φ1 which is NA 0.85, in the second blue light recording medium 110b, φ2 which is NA 0.65, in the DVD optical recording medium 110c, φ3 which is NA 0.65, CD optical recording In the medium 110d, when φ4 that satisfies NA 0.50 is selected, φ1>φ3>φ2> φ4. Here, the reason why the aperture diameters are different for the same NA for φ3 and φ2 is that the focal length is relatively increased as the wavelength is longer, and in order to obtain the same NA as apparent from (Equation 1) described above. Needs to be larger than φ2.

A guest-host type liquid crystal aperture limiting element 106a is used as such a four-stage aperture limiting element. As described in the reference example 5 , it functions as a selective annular light shielding filter as shown in FIG. The NA is changed in accordance with each optical recording medium. Specifically, the NA is composed of a liquid crystal shutter having an annular pattern, and the outer peripheral portion of the light beam incident on the objective lens 109 is selectively shielded.

  FIG. 32 is a characteristic diagram showing the relationship between the substrate thickness and the divergence of a general objective lens. The horizontal axis represents the thickness of the substrate, and the vertical axis represents the magnification of the objective lens in use as a function of the divergence of the light beam incident on the objective lens. Since the light beam emitted from the objective lens toward the substrate is always convergent light, the sign when the convergent light is incident on the objective lens is “+”, and the sign when the divergent light is incident is “−”. When this magnification is “0”, parallel light enters the objective lens. The curves in FIG. 32 are obtained by connecting magnifications that minimize the wavefront aberration with respect to each substrate thickness. For example, when the parallel light incidence is the best at the substrate thickness “B”, “−” increases as the substrate thickness increases. In other words, it is generally known that the divergent light becomes thinner as “+”, that is, convergent light is incident, as the thickness becomes thinner.

  Therefore, as shown in FIGS. 33A to 33D, convergent light is incident in the case of the first blue light recording medium 110a, and parallel in the case of the second blue light recording medium 110b and the DVD optical recording medium 110c. An objective lens shape with the best aberration is obtained when light is incident or when divergent light is incident on a CD optical recording medium. For example, in the case of the first blue light recording medium 110a, the under spherical aberration caused by the thin substrate thickness is canceled by the over aberration due to the convergent light. The description method of the lens data shown in FIG. 34 is the same as that described in FIG.

  Further, the selection magnification is not limited to the above-described example. From FIG. 32, in the case of the first blue light recording medium 110a, infinite system incidence, the second blue light recording medium 110b, and the DVD system optical recording medium 110c. Alternatively, the lens may be a lens that has the best aberration when diverging light is incident on the CD optical recording medium 110d. Alternatively, in the case of the first blue light recording medium 110a, the convergent light is incident, and in the case of the second blue light recording medium 110b, the DVD-based optical recording medium 110c, and the CD-based optical recording medium 110d, the divergent light is incident to provide the best aberration. It may be a lens.

  Further, as shown in FIG. 31, an expander optical system 116 may be used as means for switching the divergent state of the incident light beam to the objective lens 109 for the first and second blue light recording media 110a and 110b. This expander optical system 116 has lenses 116a and 116b having positive and negative and different powers arranged on the optical axis. By changing the inter-lens distance, the divergence state of the light beam that has passed through the expander optical system 116 is changed. It is done.

FIG. 35 is a transparent perspective view showing a schematic configuration of the optical information processing apparatus according to Embodiment 5 of the present invention.

An information recording / reproducing apparatus 10 that is an optical information processing apparatus is an apparatus that performs one or more of recording, reproducing, and erasing information on an optical recording medium 20 using an optical pickup 11. In the fifth embodiment, the optical recording medium 20 has a disk shape and is stored in a cartridge 21 of a protective case. The optical recording medium 20 is inserted and set into the information recording / reproducing apparatus 10 from the insertion port 12 in the direction of the arrow “on” together with the cartridge 21, rotated by the spindle motor 13, and information is recorded, reproduced or erased by the optical pickup 11. Is called. The optical recording medium 20 does not need to be placed in a protective case and may be in a bare state.

As the optical pickup 11, the optical pickup described in the first to fourth embodiments can be used as appropriate.

  An optical pickup according to the present invention and an optical information processing apparatus using the same are provided with means for performing predetermined aberration correction and aperture limitation, and are excellent for two blue optical recording media having different NA and substrate thickness with one objective lens. Spot formation is possible, and also good spot formation is possible on conventional DVD-type or CD-type optical recording media, and light that performs at least one of information recording, reproduction, and erasing on a plurality of types of optical recording media This is useful for an optical pickup of an information processing apparatus.

It shows a schematic configuration of an optical pickup in Reference Example 1 in the form status of the practice of the present invention The figure explaining operation | movement of the polarization-selective aperture limiting element in the reference example 1 of this Embodiment (A) of the polarization selective aperture limiting element in Reference Example 1 of the present embodiment is a structure, (b) is a diagram showing the polarization region of the polarizing film The figure which shows the characteristic of the polarization plane switching element of the TN type liquid crystal in the reference example 1 of this Embodiment The figure explaining the polarization selective aperture limiting element which switches a light beam diameter by the diffraction in the reference example 1 of this Embodiment (A) of the polarization selective diffractive optical element in Reference Example 1 of the present embodiment is a light beam transmission characteristic of a birefringent medium, (b) is a diffraction grating region, and (c) is a line AA ′ of (b). (D) is a figure which shows the step shape of the cross section of the AA 'line of (b). The figure explaining the polarization selective aperture limiting element which switches a light beam diameter by absorption in the reference example 1 of this Embodiment The figure which shows the wavefront aberration which generate | occur | produces when the objective lens designed in the favorable aberration characteristic with the 1st blue light recording medium in the reference example 1 of this Embodiment is used for a 2nd blue light recording medium. The figure showing the surface of the polarization selective diffraction grating formation area in which the light beam of the aberration correction element in Reference Example 1 of the present embodiment is incident FIG. 9 is a cross-sectional view taken along line A-A ′ of FIG. 9 in Reference Example 1 of the present embodiment, in which (a) is a saw-tooth shape and (b) is a step-like configuration example. The figure showing the shape of the transmitted light beam of the aberration correction element (diffractive optical element) shown in FIG. 10A in Reference Example 1 of the present embodiment The figure showing the shape of the transmitted light beam of the phase shifter element (diffractive optical element) using the birefringent medium in Reference Example 1 of the present embodiment The figure which shows schematic structure of the optical pick-up in the reference example 2 of embodiment of this invention. In Reference Example 2 of the present embodiment, (a) is a shutter region using a guest-host type liquid crystal as an aperture limiting element, and (b) and (c) are diagrams showing the operation principle. (A) which shows the liquid-crystal aberration correction element in the reference example 2 of this Embodiment is sectional drawing, (b), (c) is a figure which shows the electric power feeding part or division | segmentation electrode which applies a predetermined voltage. In Reference Example 2 of the present embodiment, (a) is the wavefront aberration (solid line) and the wavefront delay due to the liquid crystal element (broken line), (b) is the corrected wavefront aberration, and (c) is separate from the wavefront aberration (solid line). (D) is a diagram showing wavefront aberration after correction as a two-dimensional curve. The figure which shows schematic structure of the optical pick-up in the reference example 3 of embodiment of this invention. (A) of the aberration-correcting diffractive optical element in Reference Example 3 of the present embodiment is a front view, (b) is a sawtooth shape in a section taken along line AA ′ of (a), and (c) is a stepped shape. Figure (A) of the diffractive optical element in Reference Example 3 of the present embodiment is the second order through the objective lens, and the second order diffracted light is passed through the objective lens. Showing a state of focusing on a blue light recording medium The figure which shows the result of having calculated the groove depth of the diffraction grating on the horizontal axis in the reference example 3 of this Embodiment, and the change of the diffraction efficiency of the diffraction grating on the vertical axis | shaft. The figure which shows the lens data of the objective lens in the reference example 3 of this Embodiment In the reference example 4 of the embodiment of the present invention, the objective lens is provided with a diffraction grating surface (a) shows the 0th-order light on the first blue light recording medium through the objective lens, and (b) shows the 1st-order diffracted light. The figure which shows the state which condenses on a 2nd blue light recording medium via an objective lens The figure which shows the lens data of the objective lens in the reference example 4 of this Embodiment The figure which shows schematic structure of the optical pick-up in the reference example 5 of embodiment of this invention. The front view which shows the guest host type | mold liquid crystal aperture limiting element which functions as a selective annular light-shielding filter of the 4-step aperture limiting element in the reference example 5 of this Embodiment (A) focused on the first blue light recording medium by the objective lens having the smallest wavefront aberration in Reference Example 5 of the present embodiment, and (b) represents the wavefront aberration generated in the second blue light recording medium. Wavefront aberration occurring on a DVD optical recording medium, (c) is a diagram showing wavefront aberration occurring on a CD optical recording medium. The figure which shows the electrode structure of the liquid-crystal aberration correction element which correct | amends three different wavefront aberrations in the reference example 5 of this Embodiment. The figure which shows schematic structure of the optical pick-up in Embodiment 1 of this invention. The figure which shows schematic structure of the optical pick-up in Embodiment 2 of this invention. The figure which shows schematic structure of the optical pick-up in Embodiment 3 of this invention. The figure which shows schematic structure of the optical pick-up in Embodiment 4 of this invention. Characteristic diagram showing the relationship between the substrate thickness and the divergence of the objective lens in the fourth embodiment In Embodiment 4 , (a) is a first blue light recording medium, (b) is a second blue light recording medium, (c) is a DVD optical recording medium, and (d) is a CD optical recording medium. The figure which shows the state which condenses with the objective lens The figure which shows the lens data of the objective lens in this Embodiment 4 . A transparent perspective view showing a schematic configuration of an optical information processing apparatus in Embodiment 5 of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Information recording / reproducing apparatus 11 Optical pick-up 12 Insert port 13 Spindle motor 14 Carriage 20 Optical recording medium 21 Cartridge 22 Shutter 101, 201a, 211a Semiconductor laser 102, 202, 212 Collimating lens 103 Polarization surface switching element 104 Polarization beam splitter 104 'Half Mirror 105 Polarizing prism 106 Polarization selective aperture limiting element 106a Guest host type liquid crystal aperture limiting element 106c Wavelength selective aperture limiting element 107 Polarization selective aberration correcting element 107a Liquid crystal aberration correcting element 107b Aberration correcting diffractive optical element 107c Wavelength selective aberration Correction element 108 1/4 wavelength plates 109, 109 ′ Objective lens 110a First blue light recording medium 110b Second blue light recording medium 110c DVD-based optical recording medium 110d CD-based optical recording medium 111 Lens 112 Beam splitting means 113, 201c, 211c Light receiving element 115 Trichromatic prism 116 Expander optical system 116a, 116b Lens 126 Polarizing film 127 Transparent glass 128 Area 129 Polarizing film forming area 130 Glass 131, 133 Isotropic medium 132, 134 Refractive medium 136 Guest host type liquid crystal 137a, 137b Glass substrate 138 Conductive spacer 139a, 139b Electrodes 140a, 140b Insulating films 141a, 141b Alignment film 142 Electrode extraction part 143 Liquid crystals 145, 146 Transparent electrodes 145a, 145b, 145c, 146a, 146b , 146c Metal electrodes 201, 211 Hologram units 201b, 211b Hologram 204 Dichroic prism

Claims (5)

Recording or reproduction is performed on the first and second optical recording media having the same wavelength (λ1) and different numerical apertures and substrate thicknesses, and the wavelengths (λ2, λ3; λ1 <λ2 <λ3) are different. 3, In an optical pickup for recording or reproducing on a fourth optical recording medium,
Selectively the polarization direction of the three types of light sources having different wavelengths, the objective lens for condensing on each optical recording medium, and the wavelength (λ1) light beam condensed on the first and second optical recording media An aperture using a polarization plane switching element for switching and a liquid crystal element that selectively blocks and transmits the outer peripheral portion in two or more stages as an aperture corresponding to the first to fourth optical recording media for the incident light beam to the objective lens. A limiting element and a polarization-selective aberration correcting element for the second optical recording medium, and the optical path of the third and fourth optical recording media is a spherical aberration generated by the objective lens and the aberration correcting element. To correct
An optical pickup characterized by a finite magnification . Recording or reproduction is performed on the first and second optical recording media having the same wavelength (λ1) and different numerical apertures and substrate thicknesses, and the wavelengths (λ2, λ3; λ1 <λ2 <λ3) are different. 3, In an optical pickup for recording or reproducing on a fourth optical recording medium,
Selectively the polarization direction of the three types of light sources having different wavelengths, the objective lens for condensing on each optical recording medium, and the wavelength (λ1) light beam condensed on the first and second optical recording media a polarization plane switching element for switching, wherein the first light beam incident on the objective lens, selectively shielding the peripheral portion at two or more stages as an opening corresponding to the second optical recording medium, an opening using a liquid crystal element that transmits The limiting element, the polarization-selective aberration correcting element for the second optical recording medium , and the transmitted light at the used wavelengths (λ1, λ3) are dead zones, and only the transmitted light at the used wavelength (λ2). A wavelength-selective aberration correcting element for adding a predetermined aberration; and a wavelength-selective aperture limiting element corresponding to the used wavelength (λ1, λ2, λ3) in front of the objective lens, and the fourth optical recording medium. optical path of the wavelength-selective and the objective lens An optical pickup which is a magnification of a finite system for correcting the spherical aberration generated by the difference correction element. Recording or reproduction is performed on the first and second optical recording media having the same wavelength (λ1) and different numerical apertures and substrate thicknesses, and the wavelengths (λ2, λ3; λ1 <λ2 <λ3) are different. 3, In an optical pickup for recording or reproducing on a fourth optical recording medium,
Three types of light sources having different wavelengths, an objective lens on which at least any two of four types of optical recording media have a bonded or diffractive surface that collects light at 0.07 λ rms or less, and the first lens , A polarization plane switching element for selectively switching the polarization direction of a light beam having a wavelength (λ1) condensed on the second optical recording medium, and the first and second optical recording media for a light beam incident on the objective lens. depending selectively shield the outer peripheral portion at two or more stages as an aperture, the aperture limiting element using a liquid crystal element which transmits, said second polarization selective of the aberration correcting element for the optical recording medium, in addition, the use in front of the objective lens wavelengths (λ1, λ2, λ3) optical pickup for comprising the wavelength selectivity of the aperture limit element corresponding to. Recording or reproduction is performed on the first and second optical recording media having the same wavelength (λ1) and different numerical apertures and substrate thicknesses, and the wavelengths (λ2, λ3; λ1 <λ2 <λ3) are different. 3, In an optical pickup for recording or reproducing on a fourth optical recording medium,
And three different types of light sources wavelengths selectively periphery and an objective lens for focusing each optical recording medium, as an opening corresponding to the incident light beam to the first to fourth optical recording medium to said objective lens The first optical recording medium includes an aperture limiting element using a liquid crystal element that shields and transmits a portion in two or more stages, and an expander optical system that switches a divergence state of a light beam from the light source having the used wavelength (λ1). On the other hand, a light beam having a wavelength (λ1) is a convergent system, a light beam having a wavelength (λ1) with respect to the second optical recording medium, and a light beam having a wavelength (λ2) with respect to the third optical recording medium is an infinite system. An optical pickup characterized in that a light beam having a wavelength (λ3) is incident on the objective lens as a diverging system with respect to a fourth optical recording medium . An optical information processing apparatus for performing at least one of recording, reproduction and erasing of information on an optical recording medium using the optical pickup according to any one of claims 1 to 4. .

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