WO2002031824A1

WO2002031824A1 - Information recorder/reproducer

Info

Publication number: WO2002031824A1
Application number: PCT/JP2001/008869
Authority: WO
Inventors: Tetsuo Saimi; Keiichi Matsuzaki; Hidenori Wada; Seiji Nishino; Daisuke Ogata
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2000-10-10
Filing date: 2001-10-09
Publication date: 2002-04-18
Also published as: JP2004234697A

Abstract

An information recorder/reproducer (100) comprising a radiation light source (101) emitting light, means (115) for substantially collimating the light emitted from the radiation light source (101), and means (105) for converging the substantially collimated light to form a light spot on a recording layer (114) through a transparent substrate (113), wherein the collimate means (115) is subjected to chromatic aberration correction such that the substantially collimated light is substantially a plane wave regardless of shift in the wavelength of light emitted from the radiation light source (101), and the light converging means (105) is subjected to chromatic aberration correction such that a light spot is formed on the recording layer (114) regardless of shift in the wavelength of light emitted from the radiation light source (101).

Description

Technical field

The present invention relates to an information recording / reproducing apparatus for recording information on an information recording medium such as an optical disk and reproducing the information recorded on the information recording medium. Background art

Optical discs such as CDs (CompactDisk) and DVDs (DigitAlversatiElDisk) are known as large-capacity information recording media. In recent years, with an increase in the amount of information to be recorded on an information recording medium, an information recording medium having a larger capacity is required. In order to increase the capacity of an information recording medium, an optical spot formed by light irradiated to the information recording medium when recording information on the information recording medium and when reproducing the information recorded on the information recording medium. It is necessary to increase the information recording density by reducing the size of the data. In order to reduce the light spot, attempts have been made to make the laser light of the radiation source shorter.

The wavelength of light emitted from a radiation light source (for example, a semiconductor laser) used in an information recording / reproducing apparatus for recording information on an information recording medium or reproducing the information recorded on the information medium depends on individual differences (due to manufacturing differences). Deviations from the design values due to changes in Z or temperature. The aberration caused by such a wavelength shift is called chromatic difference. The wavelength dependence of the refractive index of an optical material (chromatic dispersion of the optical material) increases as the wavelength decreases. Therefore, when the wavelength of the radiation light source is shortened, chromatic aberration becomes a problem. For example, it is known that when the wavelength is blue-violet (407 nm), the chromatic dispersion is about three times that when the wavelength is infrared (780 nm) and red (650 nm). The aberration caused by this chromatic dispersion causes the optical disc The focus of the light spot generated on the laser is shifted. This is called chromatic aberration.

As one conventional technique for solving such a problem, a technique disclosed in JP-A-2000-193388 is known. In this technique, the chromatic aberration of the entire optical system is corrected by arranging an optical element for correcting chromatic aberration composed of two lenses per group in the optical path of the optical system.

However, in the information recording / reproducing apparatus having the above configuration, it is necessary to consider the characteristics of the entire optical system in order to perform chromatic aberration correction, and thus it is difficult to design.

Accordingly, the present invention has been made in view of such problems, and provides an easily designed information recording / reproducing apparatus for recording or reproducing information on a high-density information recording medium. The purpose is to do. Disclosure of the invention

An information recording / reproducing apparatus according to the present invention is an information recording / reproducing apparatus that records information on an information recording medium having a transparent substrate and a recording layer and reproduces the information recorded on the information recording medium, and emits light. A radiation light source; collimating means for substantially collimating the light emitted by the radiation light source; and the collimating means so that the converged light passes through the transparent substrate to form a light spot on the recording layer. Light converging means for converging light, wherein the collimating means is configured such that the substantially collimated light is substantially a plane wave regardless of a wavelength shift of the light emitted by the radiation light source. Chromatic aberration is corrected, and the light converging means is corrected for chromatic aberration so that a light spot is formed on the recording layer regardless of a wavelength shift of the light emitted from the radiation light source. To achieve the target.

The collimating unit may be included in a fixed optical system, and the light converging unit and the information recording medium may be included in a movable optical system.

The radiation light source may emit light having an anisotropic distribution, and the collimating means may include a light distribution converting means for converting the light of the anisotropic distribution into light having a substantially isotropic distribution. The light distribution conversion means may include a plurality of prisms.

The light distribution conversion means may include a plurality of cylindrical lenses.

The light converging unit may include a spherical aberration correcting unit that corrects a spherical aberration caused by a change in a thickness of the transparent substrate of the information recording medium. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing a configuration of an information recording / reproducing device 100 according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing a configuration of an information recording / reproducing device 200 according to Embodiment 2 of the present invention.

FIG. 3 is a diagram showing a configuration of an information recording / reproducing device 300 according to Embodiment 3 of the present invention.

FIG. 4 is a diagram showing a configuration of an information recording / reproducing device 400 according to Embodiment 4 of the present invention.

FIG. 5 is a diagram showing a configuration of an information recording / reproducing device 500 according to Embodiment 5 of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1)

FIG. 1 shows a configuration of an information recording / reproducing apparatus 100 according to Embodiment 1 of the present invention. The information recording / reproducing apparatus 100 records information on the information recording medium 106 or reproduces information recorded on the information recording medium 106.

The information recording / reproducing device 100 is composed of a radiation light source 101, a beam splitter 103, a collimating lens 102, an objective lens 105, a hologram 107, and a photodetector 1. 0 and 8.

The information recording medium 106 includes a transparent substrate 113 and a recording layer 114. Transparent substrate 1 As the substrate 13, a poly-one-ponate substrate (refractive index n = l. 58) was used.

The radiation light source 101 is, for example, a semiconductor laser that emits blue-violet laser light. The center wavelength of the laser light is 407 × 20 nm. The collimating lens 102 is designed so that defocus does not occur due to a wavelength shift within this wavelength band.

The collimating lens 102 is composed of two laminated lenses. The collimating lens 102 is formed by joining a biconvex lens formed of a material having a high refractive index and a concave lens formed of a material having a low refractive index. High refractive index materials are typically highly dispersed. Low refractive index materials typically have low dispersion. The collimating lens 102 corrects for chromatic aberration by utilizing the difference in dispersion between the high refractive index material and the low refractive index material. Examples of the material having a high refractive index include, but are not limited to, SK5, VC78, VC79, and BK7. Examples of the material having a low refractive index include, but are not limited to, FD15.

The objective lens 105 has a two-group, three-lens configuration. Specifically, a two-piece lens 110 including a concave lens formed of a low refractive index material and a convex lens formed of a high refractive index material, and a plano-convex front lens formed of a high refractive index material It consists of 11 and 11. The objective lens 105 is corrected for chromatic aberration by utilizing the difference in dispersion between these high-refractive-index materials and low-refractive-index materials. Examples of the material having a high refractive index include, but are not limited to, SK5, VC78, VC79, and BK7. The material having a low refractive index includes, for example, FD15, but is not limited thereto.

The objective lens 105 has a three-dimensional structure such that the distance between the objective lens 105 and the information recording medium 106 is constant during recording or reproducing information on the information recording medium 106. It is controlled to follow the movement. The plano-convex front lens 1 11 has a flat surface on the side facing the information recording medium 106 and the opposite side (ie, (On the side of the lens 110) is arranged to be aspherical. The advantages of this arrangement are as follows.

The first advantage is that, since one surface is flat, the aspherical optical axis of the other surface is not restricted by the manufacturing conditions when the plano-convex front lens 111 is manufactured. Therefore, when the aspherical shape of the plano-convex front lens 111 is manufactured by using a method such as injection or compression, high precision is not required for positioning the mold. Making both surfaces of the front lens aspherical will improve the performance of the designed lens. However, such front-end lenses are not easy to manufacture, and manufacturing errors have a large effect on lens performance. A front lens with one flat surface has less restrictions on manufacturing conditions than a case of manufacturing a front lens with two aspheric surfaces, and the effect of manufacturing errors on lens performance is small. For this reason, the performance of an actually manufactured lens can be made higher than that of a front lens having both aspheric surfaces.

The second advantage is that control of the objective lens 105 is facilitated. The air layer thickness between the objective lens 105 and the information recording medium 106 becomes constant, and the flow of air during rotation of the information recording medium 106 becomes substantially uniform. Therefore, since no Yang force or the like acts on the objective lens 105, it is not necessary to apply an excessive force to the objective lens 105 in order to keep the distance between the objective lens 105 and the information recording medium 106 constant.

The numerical aperture N A of the objective lens 105 was set between 0.80 and 0.92. An objective lens having such a high NA cannot be composed of one aspherical lens. In order to correct chromatic aberration, it is necessary to use glass materials having different dispersion as the material of the objective lens. Therefore, the objective lens 105 is composed of three lenses in two groups, a two-piece lens 110 and a front lens 111.

The photodetector 108 performs focus servo detection using a detection method called a spot size detection method (SSD: Spot Size Detection). In this method, when the wavelength of the laser light emitted from the radiation light source 101 is shifted, The light spot formed on the photodetector 108 by the ± first-order light beams diffracted by the hologram 107 moves symmetrically with respect to the focus point. Accordingly, even if the diffraction angle of the ± first-order light beam in the hologram 107 changes due to the wavelength shift, no error occurs in the detection support signal. The detection of the tracking error signal by the photodetector 108 also employs a method that does not cause an error due to the wavelength shift. The operation of the information recording / reproducing device 100 will be described.

When information is recorded on the information recording medium 106, the radiation light source 101 emits light modulated according to the information. The light passes through the beam splitter 103 and becomes parallel light by the collimating lens 102. The parallel light passes through the objective lens 105 and then the transparent substrate 113 to form a light spot on the recording layer 114. The state of the recording layer 114 where the light spot is formed changes according to the information (for example, the crystal state changes). As a result, information is recorded on the recording layer 114 as a change in the state of the recording layer 114.

When reproducing information recorded on the information recording medium 106, the radiation light source 101 emits unmodulated light. The light emitted by the radiation light source 101 passes through the beam splitter 103 and becomes parallel light by the collimating lens 102. The parallel light passes through the objective lens 105 and then through the transparent substrate 113 to form a light spot on the recording layer 114. In the recording layer 114, light forming a light spot is reflected at a reflectance according to the state of the recording layer 114. The light reflected by the recording layer 114 passes through the transparent substrate 113, the objective lens 105, and the collimator lens 102 again. Thereafter, the light is reflected 90 ° by the beam splitter 103 and enters the hologram 107. The hologram 107 diffracts the incident light into ± first-order light beams, and the diffracted light enters the photodetector 108. The photodetector 108 extracts an information signal indicating information recorded on the information recording medium 106 and a servo signal for tracking.

Beam splitter 103 and collimating lens 102 It functions as collimating means 1 15 which makes the light approximately parallel. The collimating means 115 is configured such that chromatic aberration caused by the chromatic dispersion of the beam splitter 103 and chromatic aberration caused by the chromatic dispersion of the collimating lens 102 are canceled as a whole.

As described above, in the collimating means 115, the chromatic aberration of the beam splitter 103 and the collimating lens 102 is corrected as a whole. Thereby, the light substantially collimated by the collimating means 115 becomes a substantially plane wave regardless of the wavelength shift of the radiation light source 101. The term `` planar wave '' means that the wavefront is not a perfect plane, but the deterioration of the characteristics of the optical system caused by the wavefront does not cause a problem in the design of an ordinary optical system. . The collimating means 1 15 is included in the fixed optical system (fixed portion) 116.

The objective lens 105 converges the light substantially collimated by the collimating means 115 so that the converged light passes through the transparent substrate 113 to form a light spot on the recording layer 114. Functions as light converging means. As described above, the objective lens 105 has a constant distance between the objective lens 105 and the information recording medium 106 during the recording or reproduction of information on the information recording medium 106. As described above, the information recording medium 106 is controlled so as to follow the three-dimensional movement. That is, the objective lens 105 and the information recording medium 106 are included in the movable optical system (movable part) 117. Therefore, the objective lens 105 has the chromatic aberration due to the power and chromatic dispersion of the objective lens 105, the chromatic aberration due to the chromatic dispersion of the transparent substrate 113, and the chromatic dispersion of the recording layer 114. The resulting chromatic aberration is configured to be canceled as a whole.

As described above, in the objective lens (light focusing means) 105, the chromatic aberration of the objective lens 105 and the information recording medium 106 is corrected as a whole. Thus, as long as the light substantially collimated by the collimating means 115 is substantially a plane wave, the objective lens (light focusing means) can be used regardless of the wavelength shift of the light emitted from the radiation light source 101. An optical spot is formed on the recording layer 114 by the light converged at 105. In the information recording / reproducing apparatus 100 according to the first embodiment of the present invention, since the collimating means 115 and the objective lens (light converging means) 105 are independently corrected for chromatic aberration, they are designed independently. be able to. For example, since the distance between the collimating means 115 and the objective lens (light converging means) 105 can be set arbitrarily, the degree of freedom in designing the entire optical system increases. Further, the accuracy of chromatic aberration correction of each optical system can be improved, and the overall optical performance of the information recording / reproducing device 100 is improved (chromatic aberration is reduced).

(Embodiment 2)

FIG. 2 shows a configuration of an information recording / reproducing apparatus 200 according to Embodiment 2 of the present invention. The same components as those of the information recording / reproducing apparatus 100 according to Embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The information recording / reproducing device 200 according to the second embodiment differs from the information recording / reproducing device 100 (FIG. 1) according to the first embodiment in that the beam splitter 103 and the hologram 107 are replaced. In addition, a beam splitter 210 composed of a polarization hologram 208 and a four-wavelength plate 209 is provided, and instead of the photodetector 108, a photodetector 211 and a photodetector 212 are provided. 2 1 3 is provided.

In the information recording / reproducing apparatus 200, the light emitted from the radiation light source 101 is transmitted through the beam splitter 210 without diffracting, and is collimated by the collimating lens 102. The light passes through the objective lens 105 and the transparent substrate 113 and converges on the recording layer 114. The light reflected by the recording layer 114 passes through the transparent substrate 113, the objective lens 105 and the collimating lens 102 again, and enters the beam splitter means 207. The light that has entered the beam splitting means 207 is rotated by 90 ° by the human / 4 wavelength plate 209, and is diffracted by the polarization hologram 208 into ± first-order light beams. Each of the ± primary light beams forms a light spot on photodetectors 2 12 and 2 13. The beam splitting means 207 corresponds to the embodiment 1 shown in FIG. It has a function combining the function of the beam splitter 103 and the function of the hologram 107.

The polarization hologram 208, the human four-wave plate 209, and the collimating lens 102 function as collimating means 214 for collimating the light emitted by the radiation light source 101. The collimator means 214 has a chromatic difference caused by the chromatic dispersion of the polarization hologram 208, a chromatic aberration caused by the chromatic dispersion of the λ / 4 wavelength plate 209, and a chromatic dispersion of the collimator lens 102. Chromatic aberration is canceled as a whole.

As described above, in the collimating means 2 14, the beam splitter means 2 07 and the collimating lens 102 are corrected for chromatic aberration as a whole. Thus, the light substantially collimated by the collimating means 214 becomes a substantially plane wave regardless of the wavelength shift of the radiation light source 101. The collimating means 2 14 is included in the fixed optical system (fixed portion) 210.

The objective lens 105 transmits the light substantially collimated by the collimating means 2 14 so that the converged light passes through the transparent substrate 113 to form a light spot on the recording layer 114. It functions as light converging means for converging. The objective lens 105 may have the same configuration as in the first embodiment. That is, the objective lens 105 is configured so that the chromatic aberration of the objective lens 105 and the information recording medium 106 is corrected as a whole.

As described above, in the objective lens (light focusing means) 105, the chromatic aberration of the objective lens 105 and the information recording medium 106 is corrected as a whole. Thus, as long as the light substantially collimated by the collimating means 2 14 is substantially a plane wave, the objective lens (light) can be emitted regardless of the wavelength shift of the light emitted from the radiation light source 101. Converging means) A light spot is formed on the recording layer 114 by the light converged at 105. The objective lens 105 and the information recording medium 106 are included in a movable optical system (movable part) 211. In the second embodiment of the present invention, since the collimating means 214 and the objective lens (light converging means) 105 are independently corrected for chromatic aberration, they are designed independently. can do. For example, since the distance between the collimating means 214 and the objective lens (light converging means) 105 can be set arbitrarily, the degree of freedom in designing the entire optical system increases. Further, the accuracy of chromatic aberration correction of each optical system can be improved, and the overall optical performance of the information recording / reproducing apparatus 200 can be improved.

(Embodiment 3)

FIG. 3 shows a configuration of an information recording / reproducing device 300 according to the third embodiment of the present invention. The same components as those of the information recording / reproducing apparatus 100 according to Embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The information recording / reproducing device 300 is composed of a radiation light source 101, a beam splitter 303, a collimating lens 302, a light distribution conversion means 304, an objective lens 105, and a hologram 100. 7 and a photodetector 108.

The information recording / reproducing apparatus 300 records information on the information recording medium 106 or reproduces information recorded on the information recording medium 106. The information recording medium 106 includes a transparent substrate 113 and a recording layer 114.

The light distribution conversion means 304 is used to correct the anisotropic distribution of light when a light source emitting light having an anisotropic distribution such as a semiconductor laser is used as the radiation light source 101. . The distribution of light emitted by a semiconductor laser differs between a direction parallel to the active layer of the semiconductor laser and a direction perpendicular to the active layer. Usually, there is a 2-3 times difference in the light divergence angle between the direction parallel to the active layer of the semiconductor laser and the direction perpendicular to the active layer. That is, light emitted from a radiation light source using a semiconductor laser or the like has an anisotropic distribution. If such anisotropic distribution of light is not corrected, the shape of the light spot formed on the information recording medium will be elliptical, which will adversely affect high-density recording and reproduction, and also impair the light use efficiency. Would.

The light distribution conversion means 304 is composed of two prisms, and functions as an anamorphic optical system for correcting the distribution of the light beam in a one-dimensional direction. Light distribution conversion The means 304 may be composed of three or more prisms. The light distribution conversion means 304 is configured to correct chromatic aberration caused by the chromatic dispersion of the prism. Light having an anisotropic distribution emitted from the radiation light source 101 passes through the beam splitter 303, the collimating lens 302, and the light distribution conversion means 304, and is substantially isotropically distributed. Is converted into a parallel light having The light converted by the light distribution conversion means 304 enters the objective lens 105. The term “having an isotropic distribution” means that the distribution of light is not completely isotropic, but the deterioration of the characteristics of the optical system caused by the distribution is not a problem in the design of an ordinary optical system. It means that. The collimating lens 302 and the beam splitter 103 can have the same configuration as the collimating lens 102 and the beam splitter 103 of the first embodiment, for example. The beam splitter 303, the collimating lens 302, and the light distribution correcting means 304 function as collimating means 305 for substantially collimating the light emitted from the radiation light source. The collimator means 304 is caused by the chromatic aberration caused by the chromatic dispersion of the beam splitter 303, the chromatic aberration caused by the chromatic dispersion of the collimator lens 302, and the chromatic dispersion of the light distribution conversion means 304 The chromatic aberration is configured to be canceled as a whole.

As described above, the beam splitter 303, the collimating lens 302, and the light distribution conversion unit 304 of the collimating unit 305 are chromatic aberration corrected as a whole. Thus, the light substantially collimated by the collimating means 305 becomes substantially a plane wave regardless of the wavelength shift of the radiation light source 101. The collimator 310 is included in the fixed optical system (fixed part) 310.

The collimated light substantially collimated by the collimating means 105 enters the objective lens 105 and then to the transparent substrate 113 to form a light spot on the recording layer 114. The objective lens 105 functions as a light converging unit that converges the substantially collimated light so that the converged light passes through the transparent substrate 113 and forms a light spot on the recording layer 114. . The objective lens 105 may have, for example, the same configuration as in the first embodiment. In the objective lens (light focusing means) 105, the chromatic aberration of the objective lens 105 and the information recording medium 106 is corrected as a whole. As a result, as long as the light substantially collimated by the collimating means 105 is substantially a plane wave, regardless of the wavelength shift of the light emitted from the radiation light source 101, the objective lens ( Light converging means) The light converged at 105 forms a light spot on the recording layer 114 '. The objective lens 105 and the information recording medium 106 are included in a movable optical system (movable part) 311.

In the information recording / reproducing apparatus 300 according to the third embodiment of the present invention, the collimating means 300 and the objective lens (light converging means) 105 are independently corrected for chromatic aberration. Can be designed. For example, since the distance between the collimating means 304 and the objective lens (light focusing means) 105 can be set arbitrarily, the degree of freedom in designing the entire optical system increases. Further, it is possible to improve the accuracy of the chromatic aberration correction of each optical system, and the overall optical performance of the information recording / reproducing apparatus 300 is improved. (Embodiment 4)

In the third embodiment, the light distribution conversion means 304 that converts light having anisotropic distribution into light having isotropic distribution has been described. Embodiment 4 shows another example of the light distribution conversion means.

FIG. 4 shows a configuration of an information recording / reproducing device 400 according to Embodiment 4 of the present invention. The same components as those of the information recording / reproducing apparatus 100 according to Embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The information recording / reproducing device 400 includes a radiation light source 101, a beam splitter 410, a collimating lens 402, a light distribution converting means 404, an objective lens 105, and a hologram. 107 and a photodetector 108. As the radiation light source 101, for example, a blue-violet semiconductor laser emitting light with anisotropic distribution is used.

The information recording / reproducing device 400 records information on the information recording medium 106, The information recorded on the recording medium 106 is reproduced. The information recording medium 106 includes a transparent substrate 113 and a recording layer 114.

The light distribution conversion means 404 is composed of two groups and three cylindrical lenses, and functions as an anamorphic optical system for correcting the distribution of a light beam in a one-dimensional direction. The light distribution conversion means 404 includes a concave cylindrical lens 405 and a convex cylindrical lens 406. The concave cylindrical lens 405 is formed by joining a concave cylindrical lens formed of a material having a low refractive index and a convex cylindrical lens formed of a material having a high refractive index. As the convex cylindrical lens 406, a convex cylindrical lens formed of a material having a high refractive index is used. The light distribution conversion means 404 may be composed of a plurality of cylindrical lenses. Such a light distribution conversion means 404 is configured to correct chromatic aberration caused by chromatic dispersion of the cylindrical lens, and converts light having an anisotropic distribution to a substantially isotropic distribution. Can be. The light distribution conversion means 404 performs chromatic aberration correction by utilizing the difference in dispersion between the high refractive index material and the low refractive index material. High refractive index materials include, but are not limited to, SK5, VC78, VC79, BK7, and the like. Examples of the material having a low refractive index include FD15, but are not limited thereto.

Light having an anisotropic distribution emitted from the radiation light source 101 passes through the beam splitter 403, the collimating lens 402 and the light distribution conversion means 404, and substantially distributes an isotropic distribution. Is converted into a parallel light. The light converted by the light distribution conversion means 404 enters the objective lens 105. The collimating lens 402 and the beam splitter 403 can have, for example, the same configurations as the collimating lens 102 and the beam splitter 103 of the first embodiment, respectively.

The beam splitter 403, the collimating lens 402, and the light distribution correcting means 404 function as a collimating means 407 for substantially collimating the light emitted from the radiation light source. The collimating means 407 is caused by the chromatic dispersion of the beam splitter 403 Chromatic aberration, chromatic aberration due to chromatic dispersion of the collimating lens 402, and chromatic aberration due to chromatic dispersion of the light distribution conversion unit 404 are configured to be canceled as a whole.

As described above, in the collimating means 407, the beam splitter 403, the collimating lens 402, and the light distribution converting means 404 are chromatic aberration corrected as a whole. Thus, the light collimated by the collimator 407 becomes substantially a plane wave regardless of the wavelength shift of the radiation light source 101. The collimating means 407 is included in the fixed optical system (fixed part) 410.

The collimated light substantially collimated by the collimating means 407 enters the objective lens 105 and then to the transparent substrate 113, and forms a light spot on the recording layer 114. The objective lens 105 functions as a light converging unit that converges the substantially collimated light so that the converged light passes through the transparent substrate 113 and forms a light spot on the recording layer 114. . The objective lens 105 may have, for example, the same configuration as in the first embodiment.

In the objective lens (light focusing means) 105, the chromatic aberration of the objective lens 105 and the information recording medium 106 is corrected as a whole. Accordingly, as long as the light substantially collimated by the collimating means 407 is substantially a plane wave, regardless of the wavelength shift of the light emitted from the radiation light source 101, the objective lens (light focusing Means) A light spot is formed on the recording layer 114 by the light converged at 105. The objective lens 105 and the information recording medium 106 are included in a movable optical system (movable part) 411.

In the information recording / reproducing apparatus 400 according to the fourth embodiment of the present invention, since the collimating means 407 and the objective lens (light converging means) 105 are independently corrected for chromatic aberration, they are independently controlled. Can be designed. For example, the distance between the collimating means 407 and the objective lens (light converging means) 105 can be set arbitrarily, which increases the degree of freedom in designing the entire optical system. Further, the accuracy of chromatic aberration correction of each optical system can be improved, and the overall optical performance of the information recording / reproducing device 400 can be improved. (Embodiment 5)

FIG. 5 shows a configuration of an information recording / reproducing device 500 according to the fifth embodiment of the present invention. The same components as those of the information recording / reproducing apparatus 100 according to Embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The information recording / reproducing device 500 includes a radiation light source 101, a beam splitter 503, a collimating lens 502, a spherical aberration correcting means 504, an objective lens 505, It includes a hologram 107 and a photodetector 509.

The information recording / reproducing device 500 records information on the information recording medium 106 or reproduces information recorded on the information recording medium 106. The information recording medium 106 includes a transparent substrate 113 and a recording layer 114.

The beam splitter 503 and the collimating lens 502 function as collimating means 514 for substantially collimating the light emitted from the radiation light source. The collimating lens 502 and the beam splitter 503 may have the same configuration as the collimating lens 102 and the beam splitter 103 of the first embodiment, for example. In the collimating means 5 14, the chromatic aberration of the beam splitter 503 and the collimating lens 502 is corrected as a whole. Thus, the light substantially collimated by the collimating means 5 14 substantially becomes a plane wave regardless of the wavelength shift of the radiation light source 101. The collimating means 5 14 is included in the fixed optical system (fixed portion) 5 12.

The transparent substrate 113 of the information recording medium 106 is manufactured by, for example, an injection molding method. The thickness of the transparent substrate 113 changes depending on the molding conditions and the like. When a semiconductor laser that emits light with a wavelength of 407 nm is used as the radiation source and an objective lens with a high NA of NA = 0.85 is used as the objective lens, the spherical surface changes when the thickness of the transparent substrate changes by about 1. Aberration occurs about 1 Ο ηι λ. In recording or reproducing information, the maximum allowable wavefront aberration is 4 O mA, while the maximum allowable spherical aberration is It is known to be about 2 Ο πιλ. In order to keep spherical aberration within an acceptable range, it is necessary to keep the change in the thickness of the transparent substrate within about 2 m, but it is difficult to secure such high accuracy in the actual manufacturing process. is there. Therefore, the spherical aberration correcting means 504 has a function of correcting spherical aberration caused by a change in the thickness of the transparent substrate caused by molding conditions and the like.

Next, a method of correcting spherical aberration will be described. The correction of the spherical aberration is performed by changing the distance between the biconvex lens 507 and the convex lens 508. More specifically, the light emitted from the radiation light source 101 passes through the beam splitter 503 and then the collimating lens 502 to become parallel light. The parallel light passes through the spherical aberration correcting means 504, the objective lens 505, and the transparent substrate 113 to form an optical spot on the recording layer 114. The light reflected by the recording layer 114 passes again through the transparent substrate 113, the objective lens 505, the spherical aberration correcting means 504 and the collimating lens 502, and the beam splitter 1503. Is reflected at 90 ° and enters the hologram 107. The hologram 107 diffracts the incident light into ± first-order light beams, and the diffracted light enters the photodetector 509. In the photodetector 509, in addition to the information signal indicating the information recorded on the information recording medium 106 and the support signal for tracking, the distance between the biconvex lens 507 and the convex lens 508 is increased. And a spherical aberration correction signal for determining the distance are extracted. Based on the spherical aberration correction signal, control means (not shown) changes the distance between the biconvex lens 507 and the convex lens 508 to correct the spherical aberration.

It is possible to detect the occurrence of spherical aberration, generate a spherical aberration correction signal for adjusting the distance between the biconvex lens 507 and the convex lens 508, and control the spherical aberration correction means 504. It should be understood that any possible configuration can be used for the information recording / reproducing device 500.

In the fifth embodiment, spherical aberration correcting means 504 is used to correct spherical aberration due to a change in the thickness of the transparent substrate 113. The spherical aberration correction means 504 is a biconvex lens 507 and a convex lens 508 in which a convex lens and a biconvex lens are joined. The configuration of the spherical aberration correcting means 504 is not limited to the above configuration.

The spherical aberration correcting means 504 and the objective lens 505 are substantially collimated so that the converged light passes through the transparent substrate 113 to form a light spot on the recording layer 114. Function as light converging means 5 15 for converging light. As described above, the objective lens 505 is connected to the information recording medium 106 so that the distance from the information recording medium 106 becomes constant while information is recorded or reproduced on the information recording medium 106. Follows the three-dimensional movement of. The distance between the biconvex lens 507 and the convex lens 508 of the spherical aberration correction means 504 is adjusted according to the thickness of the transparent substrate 113 of the information recording medium 106. The light converging means 5 15 is caused by the chromatic aberration caused by the chromatic dispersion of the biconvex lens 507 and the convex lens 508 in the spherical aberration correcting means 504, and by the power and chromatic dispersion of the objective lens 505. The chromatic aberration, the chromatic aberration caused by the chromatic dispersion of the transparent substrate 113, and the chromatic aberration caused by the chromatic dispersion of the recording layer 114 are cancelled as a whole.

In the light converging means 5 15, the chromatic aberration of the spherical aberration correcting means 504, the objective lens 505, and the information recording medium 106 is corrected as a whole. Thus, as long as the light substantially collimated by the collimating means 5 14 is substantially a plane wave, the light converging means 5 15 converges regardless of the wavelength shift of the light emitted from the radiation light source 101. A light spot is formed on the recording layer 114 by the emitted light. The spherical aberration correction means 504, the objective lens 505, and the information recording medium 106 are included in a movable optical system (movable part) 5 13.

Unlike the first to fourth embodiments, the objective lens 505 includes a plano-convex lens 510 and a front lens 511. When such an objective lens 505 is used, when the wavelength of the light emitted from the radiation light source 101 is shifted by about 1 nm, about 1Οπιλ is generated in spherical aberration. The spherical aberration correcting means 504 is configured to also correct such spherical aberration generated in the objective lens 505. In the information recording / reproducing apparatus 500 of the fifth embodiment of the present invention, the collimating means 514 and the light converging means 515 are each independently corrected for chromatic aberration, so that each of them must be designed independently. Can be. For example, since the distance between the collimating means 5 14 and the light converging means 5 15 can be set arbitrarily, the degree of freedom in designing the entire optical system increases. Further, it becomes possible to improve the accuracy of the chromatic aberration correction of each optical system, and the overall optical performance of the information recording / reproducing apparatus 500 is improved. Industrial applicability

An information recording / reproducing apparatus according to the present invention includes: a radiation light source that emits light; collimating means that substantially collimates the light emitted by the radiation light source; And light converging means for converging the light that has been substantially collimated so as to form light. Since each of the collimating means and the light converging means is independently corrected for chromatic aberration irrespective of the wavelength shift of the light emitted from the radiation light source, the optical system of the information recording / reproducing apparatus can be independently designed. Further, it becomes possible to improve the accuracy of the chromatic aberration correction of each optical system, thereby improving the optical performance of the entire information recording / reproducing apparatus.

Claims

The scope of the claims

1. An information recording / reproducing apparatus which records information on an information recording medium having a transparent substrate and a recording layer, and reproduces the information recorded on the information recording medium,

A radiation source that emits light,

Collimating means for substantially collimating the light emitted by the radiation light source,

Light converging means for converging the substantially collimated light so that the converged light passes through the transparent substrate to form a light spot on the recording layer;

An information recording / reproducing device, comprising:

The collimating means has been corrected for chromatic aberration so that the substantially collimated light is substantially a plane wave, irrespective of a shift in the wavelength of the light emitted from the radiation light source. Chromatic aberration correction is performed so that a light spot is formed on the recording layer regardless of a wavelength shift of the light emitted from the radiation light source.

2. The information recording / reproducing apparatus according to claim 1, wherein the collimating unit is included in a fixed optical system, and the light converging unit and the information recording medium are included in a movable optical system.

3. The radiation light source emits anisotropically distributed light, and the collimating unit includes a light distribution converting unit that converts the anisotropically distributed light into a substantially isotropically distributed light. The information recording / reproducing device according to item 1.

4. The information recording / reproducing apparatus according to claim 3, wherein the light distribution conversion unit includes a plurality of prisms.

5. The third aspect, wherein the light distribution conversion unit includes a plurality of cylindrical lenses. An information recording / reproducing apparatus according to the item.

6. The method according to claim 1, wherein the light converging unit includes a spherical aberration correcting unit configured to correct a spherical aberration caused by a change in a thickness of the transparent substrate of the information recording medium.