JP2004327012A - Optical head and optical recording / reproducing apparatus having the same - Google Patents

Abstract

A signal output from a light-source-light-quantity-controlling photodetector is limited to a light intensity emitted from a light source even in a state where spherical aberration generated when a substrate thickness of an optical recording medium is different from a reference value is corrected. Provide a dependent optical head.
An optical head that records and / or reproduces signals on an optical recording medium (10), wherein an opening for an objective lens (16H) for determining an opening of an objective lens (9) and a base material thickness of the optical recording medium are used as references. Spherical aberration correction means 5 and 6 for correcting spherical aberration generated when the value deviates from the value, light source light amount control opening 17H for limiting the light separated by light separating means 7, and A photodetector 15 for receiving light, and a photodetector 13 for receiving light reflected by the optical recording medium, wherein the optical path lengths to the spherical aberration correction means of both apertures are substantially equal, and The opening sizes of the two openings are set substantially equal.
[Selection diagram] Fig. 1

Description

  The present invention relates to an optical head used in fields such as optical information processing and optical communication, and an optical recording / reproducing apparatus including the optical head.

  In recent years, digital versatile discs (DVDs) have attracted attention as large-capacity optical recording media because digital versatile discs (DVDs) can record digital information at approximately six times the recording density of compact discs (CDs). However, as the capacity of information is further increased, an optical recording medium with higher density is demanded. Here, in order to achieve higher density than DVD (wavelength 660 nm, numerical aperture (NA) 0.6), it is necessary to shorten the wavelength of the light source and increase the NA of the objective lens. For example, when a blue laser of 405 nm is used and an objective lens of NA of 0.85 is used, a recording density five times that of DVD is achieved.

However, in the high-density optical recording medium device using the above-described blue laser, the reproduction and / or recording margin is very strict, that is, the tolerance for the characteristic change when performing reproduction or recording is very narrow, The occurrence of aberration due to a change in the base material thickness of the optical recording medium (change in the base material thickness) poses a problem. In this specification, “reproduction and / or recording” means “at least one of reproduction and recording”, which is described in a simplified manner.
In connection with the above problem, Patent Document 1 proposes an optical head intended to perform reproduction and recording by correcting an aberration due to a change in substrate thickness of an optical recording medium. Here, an example of this conventional optical head will be described with reference to the drawings.

  FIG. 9 is a schematic diagram schematically showing a configuration of a conventional optical head. Here, reference numeral 91 denotes a light source, 92 denotes a diffraction grating, 93 denotes a collimator lens, 94 denotes a polarizing beam splitter, 95 denotes a 波長 wavelength plate, 96 denotes an aberration correction lens group, 97 denotes an objective lens, 98 denotes an optical recording medium, Reference numeral 99 denotes a focusing lens, 100 denotes a multi-lens, and 101 denotes a photodetector.

  The light source 91 is a semiconductor laser that outputs coherent light for recording and reproduction to the recording layer of the optical recording medium 98. The diffraction grating 92 is an optical element in which an uneven pattern is formed on the surface of a glass substrate, divides an incident beam into three beams, and enables detection of a tracking error signal by a so-called three-beam method. The collimator lens 93 is a lens that converts divergent light emitted from the light source 91 into parallel light. The polarization beam splitter 94 is an optical element for separating light, and has different transmittance and reflectance depending on incident polarization. The 波長 wavelength plate 95 is an optical element that converts linearly polarized light into circularly polarized light, and is formed of a birefringent material.

As will be described later in detail, the aberration correcting lens group 96 is for correcting spherical aberration that occurs when the base material thickness of the optical recording medium 98 is different from a preset reference value. It is composed of a convex lens group 96b and a uniaxial actuator (not shown). Note that the reference value is more preferably set based on an optimum design base material thickness as the base material thickness of the optical recording medium 98.
The spherical aberration can be corrected by changing the distance between the concave lens group 96a and the convex lens group 96b. The objective lens 97 is a lens that condenses light on the recording layer of the optical recording medium 98. The focusing lens 99 is a lens that condenses the light reflected by the recording layer of the optical recording medium on the photodetector 101. The multi-lens 100 has a cylindrical incident surface, and a rotationally symmetric surface with respect to the optical axis of the lens, and is capable of detecting a focus error signal by a so-called astigmatism method for incident light. This gives astigmatism. Further, the photodetector 101 receives light reflected on the recording layer of the optical recording medium 98 and converts the light into an electric signal.

  The operation of the optical head thus configured will be described. The linearly polarized light emitted from the light source 91 is split into three beams by the diffraction grating 92, and the light split into the three beams is converted into parallel light by the collimator lens 93. The collimated light passes through the polarization beam splitter 94 and is incident on the quarter-wave plate 95, where linearly polarized light is converted into circularly polarized light. Next, the circularly polarized light transmitted through the quarter wavelength plate 95 is incident on the aberration correction lens group 96. Here, in order to correct the spherical aberration generated when the base material thickness of the optical recording medium 98 deviates from the reference value, the incident parallel light is converted into a concave lens group 96a and a convex lens group 96b constituting the aberration correction lens group 96. Is changed to divergent light or convergent light, and the converted light is incident on the objective lens 97 and generates spherical aberration in accordance with the degree of divergence or convergence of the incident light. The light is focused on the medium 98.

  Here, since the light having the wavefront aberration for correcting the wavefront aberration generated when the base material thickness of the optical recording medium 98 deviates from the reference value is collected by the objective lens 97, there is no aberration on the optical recording medium 98. That is, a light spot narrowed to the diffraction limit is formed. Next, the circularly polarized light reflected from the optical recording medium 98 passes through the aberration correcting lens group 96, is then input to the 波長 wavelength plate 95, and has a direction orthogonal to the linearly polarized light emitted from the light source 91. Converted to linearly polarized light. The linearly polarized light converted by the 波長 wavelength plate 95 is reflected by the polarization beam splitter 94 and converged by the focusing lens 99 without returning to the light source 91, and astigmatism is generated by the light entered by the multi-lens 100. And is condensed on the photodetector 101. The photodetector 101 outputs a focus error signal indicating a focus state of light on the optical recording medium 98, and outputs a tracking error signal indicating a light irradiation position.

  Here, the focus error signal and the tracking error signal are detected by a known technique, for example, by an astigmatism method and a three-beam method. Focus control means (not shown) controls the position of the objective lens 97 in the optical axis direction based on the focus error signal so that light is always focused on the optical recording medium 98 in a focused state. A tracking control unit (not shown) controls the position of the objective lens 97 based on the tracking error signal so that the light is focused on a desired track on the optical recording medium 98. Further, information recorded on the optical recording medium 98 is also obtained from the photodetector 101.

  Here, the fact that spherical aberration can be corrected using the aberration correcting lens group 96 will be described in detail. When the distance between the concave lens group 96a and the convex lens group 96b constituting the aberration correction lens group 96 is reduced, parallel light is converted into divergent light, and when the distance is increased, convergent light is converted into convergent light. That is, by changing the interval between the concave lens group 96a and the convex lens group 96b, light having power components having different signs can be generated. Here, when light having a power component is incident on the objective lens 97, the light converged by the objective lens 97 generates spherical aberration, and the sign thereof depends on the sign of the incident power component. Therefore, by using this spherical aberration, it is possible to correct the spherical aberration that occurs when the substrate thickness of the optical recording medium 98 deviates from the reference value.

  With the above configuration, the spherical aberration caused by the thickness of the base material of the optical recording medium 98 can be corrected by using the aberration correcting lens group 96, so that more stable reproduction and recording can be performed.

JP 2000-131603 A

  However, in the above-mentioned conventional optical head, the light amount detecting means necessary for controlling the light amount of the light emitted from the light source 91 is not disclosed, and a problem occurs depending on the position of the light amount detecting means. This will be described in detail with reference to FIG. Here, the optical head shown in FIG. 10 is different from the optical head shown in FIG. 9 in that the optical head in FIG. 10 further has a mirror and a light amount detecting means, and the quarter-wave plate is a mirror and an objective. It is the same as the optical head shown in FIG. 9 except that it is arranged between the lenses. Therefore, in FIG. 10, components that are not particularly described are the same as those in the case of the optical head shown in FIG. 9, and components denoted by the same reference numerals are the same as those in the case of the optical head in FIG. It is assumed that it has a similar function.

  In FIG. 10, 201 is a mirror, 202 is a condenser lens, and 203 is a light source light amount control photodetector. Here, the light amount detecting means includes a condenser lens 202 and a light source light amount controlling light detector 203.

  The mirror 201 is an optical element that reflects incident light and directs the light toward the optical recording medium 98. The mirror 201 transmits 5% of certain linearly polarized light and reflects 95% of the light, while being orthogonal to the linearly polarized light. It has the property of reflecting 100% of linearly polarized light.

  The operation of the optical head thus configured will be described. The linearly polarized light emitted from the light source 91 is split into three beams by the diffraction grating 92, and the light split into the three beams is converted into parallel light by the collimator lens 93. The collimated light passes through the polarization beam splitter 94 and enters the aberration correction lens group 96. Here, in order to correct the spherical aberration that occurs when the base material thickness deviates from the reference value, the incident parallel light changes the distance between the concave lens group 96a and the convex lens group 96b that form the aberration correction lens group 96. As a result, the light is converted into divergent light or convergent light. The converted light is incident on the mirror 201, a part (5%) of the light is transmitted, and almost (95%) is reflected, and the traveling direction is changed to the direction of the optical recording medium 98. The reflected light is incident on the quarter-wave plate 95, and the linearly polarized light is converted into circularly polarized light. The circularly polarized light is incident on the objective lens 97, and is changed according to the degree of divergence or convergence of the incident light. As a result, spherical aberration is generated, and the light is focused on the optical recording medium 98. Here, the light having the wavefront aberration that corrects the wavefront aberration that occurs when the optical recording medium 98 deviates from the reference value is condensed by the objective lens 97, so that there is no aberration on the optical recording medium 98, that is, the diffraction limit. A light spot narrowed down is formed.

  Next, the circularly polarized light reflected from the optical recording medium 98 is input to the 波長 wavelength plate 95 and is converted into linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light source 91. The linearly polarized light converted by the 波長 wavelength plate 95 is all reflected by the mirror 201, passes through the aberration correcting lens group 96, is reflected by the polarization beam splitter 94, and does not return to the light source 91, but focuses on the focusing lens 99. Are converged, and the light incident by the multi-lens 100 is given astigmatism and collected on the photodetector 101.

  The photodetector 101 outputs a focus error signal indicating a focus state of light on the optical recording medium 98, and outputs a tracking error signal indicating a light irradiation position. Here, the focus error signal and the tracking error signal are detected by a known technique, for example, by an astigmatism method and a three-beam method. Focus control means (not shown) controls the position of the objective lens 97 in the optical axis direction based on the focus error signal so that light is always focused on the optical recording medium 98 in a focused state. A tracking control unit (not shown) controls the position of the objective lens 97 based on the tracking error signal so that the light is focused on a desired track on the optical recording medium 98.

  Further, information recorded on the optical recording medium 98 is also obtained from the photodetector 101. The light transmitted through the mirror 201 is condensed by the condenser lens 202 on the light amount control light detector 203, and the light amount control light detector 203 responds to the light amount of the light emitted from the light source 1. Outputs electrical signals.

  The necessity of the above-mentioned light amount detecting means will be described. Since the light source 91 is formed of a semiconductor laser, the temperature rises when the light source 91 continuously emits light, and thus the amount of light emitted from the light source 91 even when the current for controlling the light source 91 is constant. Changes. Therefore, by detecting a part of the light emitted from the light source 91, it becomes possible to control the amount of light emitted from the light source 91.

  However, if the signal detected by the light amount detecting means fluctuates irrespective of the light amount of the light source 91, a serious problem occurs. For example, even if the light amount of the light source 91 is constant, if the signal output from the light amount detection unit decreases, the light source 91 is controlled so that the light amount of the emitted light increases, and the light amount during reproduction of the optical recording medium 98 is increased. Are emitted, and the information recorded on the optical recording medium 98 is erroneously erased. On the other hand, even if the light amount of the light source 91 is constant, when the signal output from the light amount detection unit increases, the light source 91 is controlled so that the light amount of the emitted light decreases, and the information is stored in the optical recording medium 98. During recording, the light amount required for recording is not reached, and recording is insufficient. That is, if the signal detected from the light amount detecting means does not change in accordance with the light amount emitted from the light source 91, a serious problem will occur.

  Here, FIG. 11 is a diagram schematically illustrating light incident on the objective lens 97 when the aberration correction lens group 96 is driven to correct the spherical aberration. In FIG. 11, when the base material thickness of the optical recording medium 98 is larger than the reference value, the interval between the concave lens group 96a and the convex lens group 96b becomes wide, and the light enters the objective lens 97 as convergent light. This state is shown by a solid line. When the base material thickness of the optical recording medium 98 is smaller than the reference value, the interval between the concave lens group 96a and the convex lens group 96b becomes narrow, and the light enters the objective lens 97 as divergent light. This state is indicated by a two-dot chain line. Here, it is assumed that the light used for the light amount detecting means is at the position A shown in FIG.

In FIG. 10, an opening (not shown) for limiting the amount of light passing therethrough is provided between the mirror 201 and the condenser lens 202, and this is schematically shown in FIG. 110H. The opening 110H is provided by forming a hole (opening) in the opening forming member 110. In this case, a member holding the convex lens group 96b can also serve as the opening forming member 110.
At this time, as can be seen from FIG. 11, when the concave lens group 96a is moving to correct the spherical aberration, the amount of light incident on the objective lens 97 is constant regardless of the position of the concave lens group 96a. The aberration correction lens group is designed, but the amount of light incident on the light source light amount control photodetector 203 depends on the position of the concave lens group 96a. As a result, the light amount detected by the light source light amount control light detector 203 changes.

  That is, as described above, although the light amount of the light source 91 has not changed, the amount of light incident on the light source light amount control light detector 203 has changed, and it is as if the light amount of the light source has changed. Such a signal is output, and there arises a problem that information recorded at the time of reproduction is erased or a required light amount cannot be output at the time of recording, and recording becomes insufficient.

  The present invention has been made in view of such a conventional problem, and even when spherical aberration is corrected, the signal output from the light source light amount control photodetector is limited only to the light amount emitted from the light source. It is a first object to provide a dependent optical head.

  Further, even when the thickness of the base material of the optical recording medium deviates from the reference value, and the spherical aberration caused by the deviation is corrected, the amount of light emitted from the light source can be accurately detected, and more stable reproduction can be performed. It is a second object of the present invention to provide an optical recording / reproducing apparatus capable of performing recording and recording.

In order to achieve the above object, an optical head according to the present invention is an optical head that records and / or reproduces a signal on an optical recording medium, wherein a light source and light emitted from the light source are recorded on the optical recording medium. An objective lens for converging light on the medium, an objective lens aperture for determining the aperture of the objective lens, and spherical aberration correction means for correcting spherical aberration generated when the substrate thickness of the optical recording medium deviates from a reference value A light separating unit disposed in an optical path from the spherical aberration correcting unit to the optical recording medium; a light source light amount controlling opening for restricting an aperture of the light separated by the light separating unit; A first photodetector for receiving the light whose aperture is limited by the aperture, and a second photodetector for receiving the light reflected by the optical recording medium, wherein Optical path length to the aperture for Wherein the correcting means optical light path length to the amount of source light controlling opening and is substantially equal, and an opening size of the light source light quantity controlling opening is equal to or substantially equal to the aperture size of the objective lens aperture.
In this case, even when the spherical aberration correction unit is driven, a signal output from the first photodetector that receives the light whose aperture is limited by the light source light amount control aperture is output from the light emitted from the light source. Since the signal corresponds to only the amount of light, the light source can be controlled using this signal, and more stable reproduction and recording can be performed.

In order to achieve the above object, an optical head according to another invention of the present application is an optical head that records and / or reproduces a signal on an optical recording medium, and includes a light source and light emitted from the light source. An objective lens for condensing light on the optical recording medium, a spherical aberration correcting unit for correcting a spherical aberration generated when a substrate thickness of the optical recording medium deviates from a reference value, and A light separating unit disposed in an optical path to an optical recording medium, a lens for converging the light separated by the light separating unit, a light source light amount control opening for restricting an aperture of the light converged by the lens, and It is characterized by having a first photodetector that receives light whose aperture is limited by the light source light quantity control aperture, and a second photodetector that receives light reflected by the optical recording medium.
In this case, even when the spherical aberration correction unit is driven, a signal output from the first photodetector (a photodetector that receives light whose aperture is limited by the light source light quantity control aperture) is output from the light source. Since the signal corresponds to only the amount of emitted light, the light source can be controlled using this signal, and more stable reproduction and recording can be performed. Further, the distance from the spherical aberration control means to the first photodetector can be shortened, which is advantageous for downsizing the optical head.

Further, in order to achieve the above object, an optical head according to still another invention of the present application is an optical head that records and / or reproduces a signal on an optical recording medium, and includes a light source and light emitted from the light source. An objective lens for condensing the reflected light on the optical recording medium, a spherical aberration correcting unit for correcting a spherical aberration generated when a substrate thickness of the optical recording medium deviates from a reference value, and the spherical aberration from the light source. A light separating means arranged in an optical path leading to the correcting means, a first light detector for receiving the light separated by the light separating means, and a second light receiving means for receiving the light reflected by the optical recording medium A photodetector.
In this case, even when the spherical aberration correction unit is driven, a signal output from the first photodetector (a photodetector that receives the light separated by the light separation unit) is output from the light source. Since the signal corresponds to only the amount of light, the light source can be controlled using this signal, and more stable reproduction and recording can be performed.

  In the optical head, it is preferable that the spherical aberration correction unit corrects the spherical aberration by generating at least one of convergent light and divergent light. Specifically, the spherical aberration correction unit includes a positive lens. It is preferable that the zoom lens includes a group and a negative lens group. This makes it possible to correct the spherical aberration that occurs when the base material thickness of the optical recording medium deviates from the reference value in both the forward path and the backward path of the optical head, and obtain a more stable control signal and reproduction signal. become able to.

  Further, in the optical head, it is preferable that the spherical aberration correction means is an optical element including a phase change layer disposed between a pair of substrates having a transparent conductive thin film. As a result, the spherical aberration correcting means is reduced, which is advantageous for downsizing the optical head.

  In particular, in the optical head, it is preferable that the light incident by the phase change layer is converted into divergent light or convergent light. Thus, the spherical aberration correction performance does not deteriorate even when the lens is shifted.

  In the above-mentioned optical head, it is preferable that the optical head further includes a base material thickness detecting means for detecting a base material thickness of the optical recording medium. Accordingly, deviations from the optimum base material thickness can be detected at all positions of the optical recording medium, so that more accurate spherical aberration correction can be performed, and stable control signals and reproduction signals can be obtained.

  Further, in the optical head, the base material thickness detecting means includes a light source, a lens for condensing light emitted from the light source on the optical recording medium, and a light for detecting light reflected by the optical recording medium. And a detector. Thus, since the aberration caused by the thickness of the base material of the optical recording medium is detected by another optical system, the aberration caused by the thickness of the base material of the optical recording medium can be simultaneously detected at the time of reproduction or recording.

  Still further, in the above-mentioned optical head, the base material thickness detecting means is configured to detect the first light near the optical axis of the light and the second light outside the first light based on two focal points. Preferably, the information on the thickness of the base material is detected. Thereby, the size of the optical head can be further reduced.

  Further, in the above optical head, it is preferable that the NA of the objective lens is 0.6 or more. This makes it possible to increase the tolerance for deviation of the substrate thickness of the optical recording medium from the reference value with respect to high density with a small aberration margin for recording and reproduction. Therefore, it is possible to contribute to a higher recording density.

  Still further, in the above-mentioned optical head, it is preferable that the wavelength of the light source is 450 nm or less. As a result, it is possible to increase the tolerance for deviation of the substrate thickness of the optical recording medium from the optimum substrate thickness for high density with a small aberration margin for recording and reproduction. Therefore, it is possible to contribute to a higher recording density.

  Still further, in order to achieve the above object, an optical recording / reproducing apparatus according to the present invention includes the above-mentioned optical head as an optical head for recording and / or reproducing a signal on an optical recording medium. . This makes it possible to detect a signal corresponding to the amount of light emitted from the light source even when the spherical aberration correction unit is driven, so that the light source can be controlled using this signal, and more stable reproduction and You will be able to record.

  According to the present invention, when the light quantity detecting means is arranged between the spherical aberration correcting means and the light source, or when the light quantity detecting means is arranged between the spherical aberration correcting means and the optical recording medium, the light source light quantity constituting the light quantity detecting means Positioning the control aperture at a position corresponding to the optical path length from the spherical aberration correction means to the objective lens aperture, or at a desired position in the converged light of the light quantity detection means, Even when the correction unit is driven, the signal output from the light amount detection unit becomes a signal corresponding only to the light amount of the light emitted from the light source, and the light output from the objective lens is controlled by controlling the light source using this signal. Can always be set to a desired value, so that more stable reproduction and recording can be performed.

  Further, by using this optical head, a stable control signal and a reproduced signal can be obtained even when the spherical aberration correcting means is driven, and an optical recording / reproducing apparatus capable of performing more stable recording can be realized. It becomes possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
(Embodiment 1)
In the first embodiment, an example of the optical head of the present invention will be described.

FIG. 1 is a configuration diagram of the optical head according to the first embodiment. In FIG. 1, reference numeral 1 denotes a light source, 2 denotes a diffraction grating, 3 denotes a collimator lens, 4 denotes a polarizing beam splitter, 5 denotes a concave lens, 6 denotes a convex lens, 7 denotes a mirror, 8 denotes a 、 wavelength plate, 9 denotes an objective lens, 10 is an optical recording medium, 11 is a condenser lens, 12 is a cylindrical lens, 13 is a photodetector (second photodetector), 14 is a lens, and 15 is a light source light quantity control photodetector (first photodetector). , 16 denotes an opening forming member formed with an objective lens opening 16H, and 17 denotes an opening forming member formed with a light source light amount control opening 17H.
The concave lens 5, the convex lens 6, and a one-axis actuator (not shown) constitute spherical aberration correction means. The lens 14, the light source light quantity control light detector 15, and the light source light quantity control opening 17H constitute light quantity detection means. The concave lens 5 constitutes a negative lens group, the convex lens 6 constitutes a positive lens group, and the mirror 7 constitutes a light separating means. That is, in this case, the negative lens group includes one concave lens 5, and the positive lens group includes one convex lens.

  Here, the light source 1 is a light source that outputs coherent light for recording / reproduction to the recording layer of the optical recording medium 10, and is constituted by, for example, a GaN-based semiconductor laser element (wavelength: 405 nm). The diffraction grating 2 is an optical element that divides an incident beam into three beams and enables detection of a tracking error signal by a so-called three-beam method, and has an uneven pattern formed on the surface of a glass substrate. The collimator lens 3 is a lens that converts divergent light emitted from the light source 1 into parallel light. The polarization beam splitter 4 is an optical element for separating light, and has different transmittance and reflectance depending on the polarization direction of incident light. As described in detail in connection with the prior art, the spherical aberration correction means corrects spherical aberration that occurs when the base material thickness of the optical recording medium 10 is different from the reference value. And a convex lens 6 and a uniaxial actuator (lens position changing means) (not shown). The spherical aberration can be corrected by changing the distance between the concave lens 5 and the convex lens 6.

  The mirror 7 is an optical element that reflects incident light and directs the light toward the optical recording medium 10. The mirror 7 transmits 5% of certain linearly polarized light and reflects 95% of the light, while being orthogonal to the linearly polarized light. It has the property of reflecting 100% of linearly polarized light. The 波長 wavelength plate 8 is an optical element that converts linearly polarized light into circularly polarized light, and is formed of a birefringent material. The objective lens 9 is a lens that focuses light on the recording layer of the optical recording medium 10, and has a numerical aperture (NA) of 0.85. The condensing lens 11 is a lens that condenses the light reflected on the recording layer of the optical recording medium 10 on the photodetector 13 (second photodetector). Further, the cylindrical lens 12 has a cylindrical incident surface and a rotationally symmetric surface with respect to the optical axis of the lens, so that a focus error signal can be detected for incident light by a so-called astigmatism method. To provide astigmatism. The photodetector 13 receives light reflected on the recording layer of the optical recording medium 10 and converts the light into an electric signal.

The lens 14 focuses the light transmitted through the mirror 7 on the light source light amount control photodetector 15 (first photodetector). The objective lens opening 16H limits the size of light incident on the objective lens, and determines the NA of the objective lens. In this case, the member holding the objective lens 9 also functions as the opening forming member 16. On the other hand, the light source light amount control opening 17H is used to limit the light amount of the light used for controlling the light amount of the light source. In this case, the member holding the lens 14 also serves as the opening forming member 17. I have.
In the present embodiment, the position of the light source light quantity control opening 17H is set such that the optical path length from the spherical aberration corrector is substantially equal to the optical path length from the spherical aberration corrector to the objective lens opening 16H. The size of the opening (opening size) is set to substantially the same size as the objective lens opening 16H.

The operation of the optical head thus configured will be described.
The linearly polarized light emitted from the light source 1 is split into three beams by the diffraction grating 2, and the light split into the three beams is converted into parallel light by the collimator lens 3. The parallel light passes through the polarization beam splitter 4 and is incident on the spherical aberration correcting means. Here, in order to correct the spherical aberration generated when the thickness of the base material deviates from the reference value, the incident parallel light is divergent light by changing the interval between the concave lens 5 and the convex lens 6 constituting the spherical aberration correcting means. The converted light is incident on the mirror 7, a part of which is transmitted, most of the light is reflected, and the traveling direction is changed so as to be directed to the optical recording medium 10.

The reflected light is incident on the quarter-wave plate 8 and linearly polarized light is converted into circularly polarized light. The circularly polarized light is incident on the objective lens 9 after its aperture is restricted by the objective lens opening 16H. Then, spherical aberration is generated according to the degree of divergence or convergence of the incident light, and the light is converged on the optical recording medium 10. Here, the light having the wavefront aberration that corrects the wavefront aberration that occurs when the base material thickness of the optical recording medium 10 deviates from the reference value is condensed by the objective lens 9, so that there is no aberration on the optical recording medium 10. That is, a light spot narrowed to the diffraction limit is formed.
Next, the circularly polarized light reflected from the optical recording medium 10 is input to the １ ／ wavelength plate 8 and converted into linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light source 1. The linearly polarized light converted by the 波長 wavelength plate 8 is entirely reflected by the mirror 7, passes through the spherical aberration correcting means, is reflected by the polarization beam splitter 4, and does not return to the light source 1, but does not return to the light source 1 Are converged, and astigmatism is given by the cylindrical lens 12, and condensed on the photodetector 13. The photodetector 13 outputs a focus error signal indicating a focused state of light on the optical recording medium 10, and outputs a tracking error signal indicating a light irradiation position.

  Here, the focus error signal and the tracking error signal are detected by a known technique, for example, by an astigmatism method and a three-beam method. Focus control means (not shown) controls the position of the objective lens 9 in the optical axis direction based on the focus error signal so that light is always focused on the optical recording medium 10 in a focused state. A tracking control unit (not shown) controls the position of the objective lens 9 based on the tracking error signal so that the light is focused on a desired track on the optical recording medium 10. Further, information recorded on the optical recording medium 10 is also obtained from the photodetector 13. The light transmitted through the mirror 7 is condensed by a lens 14 on a light source light quantity control photodetector 15, and the light source light quantity control photodetector 15 generates an electric signal corresponding to the light quantity of the light emitted from the light source 1. Is output.

Here, the light amount detecting means will be described in detail.
As described above, since the amount of light emitted from the light source 1 varies depending on the temperature and the like even when the current for driving the light source 1 is constant, the amount of light emitted from the light source 1 is detected. It is necessary to control the light source 1 based on this detection signal. However, if the detected signal fluctuates due to a factor other than the amount of light emitted from the light source 1, as described above, even though the amount of light emitted from the light source 1 has not changed, As a result, the amount of the applied light fluctuates, and a serious problem occurs. As described in the section of “Problems to be Solved by the Invention”, such a phenomenon can occur in an optical head using a spherical aberration correction unit that corrects spherical aberration by forming divergent light or convergent light. is there.

  This is because the distance from the spherical aberration corrector to the aperture 16 for the objective lens is different from the distance from the spherical aberration corrector to the aperture 17 for the light source light quantity control. Are different in the size of the openings.

  Therefore, in the present embodiment, the light source light amount control opening 17H is arranged at a position that is substantially the same distance as the distance from the spherical aberration correcting means to the objective lens opening 16H. Is set substantially equal to the size of the objective lens opening 16H. With this, even if the spherical aberration correction unit is driven, the signal detected by the light amount detection unit corresponds only to the change in the light amount emitted from the light source 1, so that the signal that can more appropriately control the light source 1 is output. It becomes possible to detect.

  Further, in the present embodiment, due to the configuration of the spherical aberration corrector, even if the light amount emitted from the light source 1 is constant, the distance between the lenses constituting the spherical aberration corrector changes, so Even when the light amount of the emitted light changes, the signal emitted from the light amount detection means changes exactly the same. Therefore, if the signal emitted from the light amount detection means is controlled to be constant, the objective This is very advantageous because the amount of light emitted from the lens 9 is constant.

  As described above, the light separating means is disposed between the spherical aberration correcting means and the lens 14, and the light source light amount controlling opening 17H for limiting the aperture of the light separated by the light separating means is provided with the light from the spherical aberration correcting means. The position is set so that the distance is substantially the same as the distance from the spherical aberration correcting means to the objective lens opening 16H, and further, the opening size is set substantially equal to the opening size of the objective lens opening 16H. In addition, the amount of light emitted from the objective lens can be set to a desired value without depending on environmental changes such as temperature, and even when the spherical aberration correction unit is being driven. Therefore, the information recorded on the optical recording medium by mistake during reproduction is not erased, and conversely, the signal emitted from the objective lens becomes too small, so that the reproduction signal and the control signal become small and the reproduction becomes impossible. The control does not become unstable. Further, there is no problem that the amount of light required at the time of recording becomes small and recording cannot be performed.

  In the present embodiment, the light amount detecting means includes the lens 14, the light source light amount controlling photodetector 15, and the light source light amount controlling opening 17H. However, there is no particular problem even if the lens 14 is not necessarily provided. .

(Embodiment 2)
Next, a second embodiment of the present invention will be described with reference to the drawings. The second embodiment is different from the above-described first embodiment only in that the position and the size of the light source light amount control opening 17H are different, and the other configurations are the same as the first embodiment. Therefore, in the present embodiment, components that are not particularly described are assumed to be the same as those in the first embodiment, and the components denoted by the same reference numerals as those in the first embodiment have the same functions as those in the first embodiment unless otherwise described. Shall have.

  FIG. 2 is a configuration diagram of an optical head according to Embodiment 2 of the present invention. Here, the lens 14 is disposed at a position where the distance from the spherical aberration corrector is shorter than the distance from the spherical aberration corrector to the objective lens opening 16H. The light source light quantity control opening 17H is disposed between the lens 14 and the light source light quantity control light detector 15. The operation of the optical head is the same as that described in the first embodiment, and will not be described here.

  Here, it will be described with reference to FIG. 3 that the amount of light becomes constant when an aperture is used in the converged light. FIG. 3 is a diagram showing what kind of light path the light incident on the spherical aberration correcting means is incident on the light source amount control photodetector 15. In this figure, the solid line shows the optical path when the spherical aberration that occurs when the substrate thickness of the optical recording medium is thicker (than the reference value) is corrected by the spherical aberration corrector. Further, the two-dot chain line indicates the optical path when the spherical aberration generated when the substrate thickness of the optical recording medium is thin (less than the reference value) is corrected by the spherical aberration correcting means. As can be seen from FIG. 3, when the light source light amount control opening 17H is disposed between the lens 14 and the spherical aberration correcting means, the light amount of light incident on the light source light amount control photodetector 15 becomes smaller than that of the concave lens 5 and the convex lens 6. It changes according to the distance. However, if the light source light control aperture 17H is arranged at the position (B) where the solid line and the two-dot chain line in the convergent light between the lens 14 and the light source light control photodetector 15 intersect, any spherical aberration will be corrected. However, the same amount of light is incident on the light source light amount control photodetector 15. That is, by arranging the light source light amount control opening 17H in the convergent light, the light source light amount control opening 17H is disposed at a distance equivalent to the distance from the spherical aberration correcting means to the objective lens opening 16H.

  Thus, as described in the first embodiment, even if the spherical aberration correction unit is driven, the signal detected by the light amount detection unit corresponds only to the fluctuation of the light amount emitted from the light source 1. Can be detected more appropriately. Further, in the present embodiment, the configuration of the spherical aberration corrector allows the light amount of the light emitted from the objective lens to be constant even if the light amount emitted from the light source 1 is constant. The signal emitted from the light amount detection means also undergoes exactly the same change even when it fluctuates due to the change. Therefore, it is very advantageous to control the signal emitted from the light amount detecting means so that the amount of light emitted from the objective lens becomes constant. Further, in this embodiment, since the light source light amount control opening 17H is arranged in the convergent light, the distance from the spherical aberration correction means to the light source light amount control opening 17H can be shortened. This is advantageous for miniaturization.

  As described above, by arranging the light source light quantity control opening 17H in the convergent light of the light quantity detection means, the light quantity of the light emitted from the objective lens can be changed regardless of the environmental change such as temperature and the spherical aberration. A desired value can be obtained even when the correction means is being driven. Therefore, a signal recorded by mistake during reproduction is not erased, and conversely, a signal emitted from the objective lens becomes too small, so that a reproduction signal and a control signal become small, and reproduction becomes impossible or control becomes unstable. Never be. Further, there is no problem that the amount of light required at the time of recording becomes small and recording cannot be performed. Further, the distance from the spherical aberration correcting means to the light source light amount control opening 17H can be shortened, which is advantageous for miniaturization of the optical head.

  In the first and second embodiments, the opening forming member 17 in which the light source light amount controlling opening 17H is formed is also used as a member for holding the lens 14, but there is no problem even if another member is provided.

(Embodiment 3)
Next, a third embodiment of the present invention will be described with reference to the drawings.
The present embodiment is different from the above-described first and second embodiments in that a light separating unit that separates light incident on a light amount detecting unit composed of a lens 14 and a light source light amount controlling photodetector 15 includes a light source and a spherical aberration. The third embodiment is the same as the first embodiment except that the second embodiment is arranged between the correction unit and the correction unit, and is different only in that the characteristics of the polarization beam splitter and the mirror are different. Therefore, in the present embodiment, components that are not particularly described are the same as those in the first embodiment, and components having the same reference numerals as those in the first embodiment have the same functions as those in the first embodiment unless otherwise described. Shall be.

  FIG. 4 is a configuration diagram of an optical head according to Embodiment 3 of the present invention. Here, reference numeral 41 denotes a polarization beam splitter, and reference numeral 42 denotes a mirror. The polarizing beam splitter 41 has a characteristic of transmitting 95% of linearly polarized light in a certain polarization direction and reflecting 5%, while reflecting 100% of polarized light in a direction perpendicular to the polarization direction. . Further, the mirror 42 has a characteristic of reflecting 100% regardless of the polarization direction. Further, the light amount detecting means composed of the lens 14 and the light source light amount controlling light detector 15 is configured to use the reflected light of the outward light of the polarization beam splitter 41. In this case, the light separating means is constituted by the polarization beam splitter 41.

The operation of the optical head thus configured will be described.
The linearly polarized light emitted from the light source 1 is split into three beams by the diffraction grating 2, and the light split into the three beams is converted into parallel light by the collimator lens 3. The parallelized light is partially reflected by the polarizing beam splitter 41, but is mostly transmitted. The transmitted light is incident on the spherical aberration correcting means. Here, in order to correct the spherical aberration that occurs when the thickness of the base material deviates from the reference value, the incident parallel light diverges by changing the distance between the concave lens 5 and the convex lens 6 that constitute the spherical aberration correction unit. The converted light is converted into light or convergent light, and the converted light is incident on the mirror 42, is all reflected by the mirror 42, and changes its traveling direction to the direction of the optical recording medium 10.

  The reflected light is incident on the quarter-wave plate 8 and linearly polarized light is converted into circularly polarized light. The circularly polarized light is subjected to the aperture limitation by the objective lens opening 16H, and then transmitted to the objective lens 9. The light is incident, generates spherical aberration according to the degree of divergence or convergence of the incident light, and is condensed on the optical recording medium 10. Here, since the light having the wavefront aberration for correcting the wavefront aberration generated when the substrate thickness of the optical recording medium 10 deviates from the reference value is condensed by the objective lens 9, there is no aberration on the optical recording medium 10. That is, a light spot narrowed down to the diffraction limit is formed.

  Next, the circularly polarized light reflected from the optical recording medium 10 is input to the １ ／ wavelength plate 8 and converted into linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light source 1. The linearly polarized light converted by the 波長 wavelength plate 8 is all reflected by the mirror 42, passes through the spherical aberration correcting means, is reflected by the polarization beam splitter 41, and does not return to the light source 1, but does not return to the light source 1. The light is converged by 11, is given astigmatism by a cylindrical lens 12, and is condensed on a photodetector 13. The photodetector 13 outputs a focus error signal indicating a focused state of light on the optical recording medium 10, and outputs a tracking error signal indicating a light irradiation position.

  Here, the focus error signal and the tracking error signal are detected by a known technique, for example, by an astigmatism method and a three-beam method. Focus control means (not shown) controls the position of the objective lens 9 in the optical axis direction based on the focus error signal so that light is always focused on the optical recording medium 10 in a focused state. A tracking control unit (not shown) controls the position of the objective lens 9 based on the tracking error signal so that the light is focused on a desired track on the optical recording medium 10. Further, information recorded on the optical recording medium 10 is also obtained from the photodetector 13. The light reflected by the polarization beam splitter 41 out of the light on the outward path is condensed by the lens 14 on the light source light quantity control photodetector 15, and the light source light quantity control photodetector 15 emits the light emitted from the light source 1. And outputs an electric signal corresponding to the amount of light.

  As in the present embodiment, the light separating means incident on the light quantity detecting means (comprising the lens 14 and the light source light quantity controlling light detector 15) is provided between the spherical aberration correcting means (comprising the concave lens 5 and the convex lens 6) and the light source. , The light used for the light amount detecting means does not fluctuate even when the spherical aberration correcting means is driven. Therefore, a signal corresponding to the amount of light emitted from the light source 1 can be reliably detected. If the signal is used to control the light source 1, the amount of light emitted from the objective lens can be kept constant. Is possible.

  As described above, by arranging the light quantity detecting means between the spherical aberration correcting means and the light source, the light quantity of the light emitted from the objective lens can be corrected without depending on environmental changes such as temperature. The desired value can be obtained even when the means is being driven. Therefore, a signal recorded erroneously at the time of reproduction is not erased, and conversely, a signal emitted from the objective lens becomes too small, so that a reproduction signal and a control signal become small, and reproduction becomes impossible or control becomes unstable. Never be. Further, there is no problem that the amount of light required at the time of recording becomes small and recording cannot be performed.

  In the present embodiment, the light amount detecting means is composed of the lens 14 and the light source light amount controlling light detector 15, but there is no particular problem even if the lens 14 is not provided.

  Further, in the first and second embodiments, a method using a concave lens and a convex lens is used as the spherical aberration correction means. Instead, a method using a positive lens group and a negative lens group may be used. FIG. 5 shows a configuration diagram of a spherical aberration correction unit (one-axis actuator is not shown) composed of a negative lens group 51 having a negative power and a positive lens group 52 having a positive power. Since each lens group is made of a glass material having a different Abbe number, it is possible to constitute a spherical aberration correcting means capable of correcting the chromatic aberration generated in the lens constituting the optical head, especially the objective lens. Further, in the method using a lens, it is possible to correct the spherical aberration in both the forward path and the backward path, so that a stable reproduction signal and control signal can be obtained.

Further, as the spherical aberration correcting means, a method using no lens may be used. For example, a method using a phase change layer disclosed in Japanese Patent Application Laid-Open No. 2002-109776 (Japanese Patent Application No. 2001-221927) may be used.
Hereinafter, an optical element used in the method using the phase change layer will be briefly described. FIG. 6 is a cross-sectional view of an optical element 60 using liquid crystal as the phase change layer, and FIG. 7 is a pattern diagram used for the optical element 60. In FIG. 6, reference numeral 61 denotes a first substrate, 62 denotes a second substrate disposed substantially parallel to the first substrate 61, and 63 denotes a voltage application disposed between the first substrate 61 and the liquid crystal 67. The electrode, 64 is a counter electrode disposed so as to be substantially parallel to and opposed to the voltage application electrode 63, 65 is a translucent resin film formed so as to cover the voltage application electrode 63, and 66 is so as to cover the counter electrode 64. The formed translucent resin film, 67 is a liquid crystal disposed between the translucent resin films 65 and 66 (between the voltage applying electrode 63 and the counter electrode 64), and 68 is a translucent film surrounding the liquid crystal 67. The sealing resin disposed between the conductive resin films 65 and 66 is shown, respectively.

  Here, the first substrate 61 and the second substrate 62 are made of, for example, glass and are translucent. The voltage application electrode 63 is an electrode for applying a desired voltage to the liquid crystal 67. This voltage application electrode 63 is formed on the main surface inside the first substrate 61 (the liquid crystal 67 side). The counter electrode 64 is an electrode for applying a desired voltage to the liquid crystal 67 together with the voltage application electrode 63. The counter electrode 64 is formed on the main surface inside the second substrate 62 (on the liquid crystal 67 side). The counter electrode 64 is translucent, and is made of, for example, ITO. The counter electrode 64 is formed substantially uniformly on at least a portion of the inner main surface of the second substrate 62 which faces the segment electrode.

  The translucent resin films 65 and 66 are alignment films for orienting the liquid crystal 67 in a predetermined direction, and are made of, for example, a polyvinyl alcohol film. The rubbing treatment of the translucent resin film 65 or 66 allows the liquid crystal 67 to be oriented in a predetermined direction. In addition, the liquid crystal 67 functions as a phase change layer that changes the phase of the incident light. The liquid crystal 67 is made of, for example, a nematic liquid crystal. By changing the voltage difference between the voltage application electrode 63 and the counter electrode 64, the refractive index of the liquid crystal 67 can be changed, thereby changing the phase of the incident light. The sealing resin 68 is for sealing the liquid crystal 67, and is made of, for example, an epoxy resin. In addition, as shown in FIG. 7, the voltage application electrode 63 is configured by concentric segment electrodes. This segment electrode is translucent and is made of, for example, ITO.

The operation of the optical element 60 configured as described above will be described.
A control voltage is externally applied to each of the segment electrodes of the voltage application electrode 63 of the optical element 60 so as to impart a phase of a power component to light incident on the optical element 60 of the present invention. Thus, the incident plane wave can be converted into a spherical wave, and the spherical wave is incident on the objective lens, thereby causing spherical aberration. This spherical aberration corrects the spherical aberration that occurs when the thickness of the optical recording medium 10 deviates from the design base material thickness (reference value). Here, as the phase change layer, liquid crystal whose refractive index changes according to the voltage is used, but PLZT (perovskite containing lead oxide, lanthanum, zirconium oxide, titanium oxide) whose thickness (volume) changes according to the voltage is used. (A transparent crystal having a structure) may be used.

  Since the PLZT is a solid, it does not require a substrate or a sealing resin as in the case of liquid crystal, so that the optical element can be made thin. In the method described in the first and second embodiments, since the optical system is constituted by a lens, it is possible to correct the aberration caused by the substrate thickness of the optical recording medium even in the forward path as well as in the backward path, and to provide a stable control signal. Can be obtained. Also, in the method described here, the optical element using the phase change layer corrects the aberration caused by the thickness of the base material of the optical recording medium, so that it is suitable for downsizing the optical head. In both the lens system and the system using the phase change layer, spherical aberration is corrected using convergent light and divergent light, so that spherical aberration correction performance does not deteriorate even if the objective lens shifts. .

  In the above-described embodiment, the spherical aberration correcting means is constituted by the concave lens, the convex lens, and the lens position changing means (not shown) for changing the distance between both lenses. However, such a concave lens and a convex lens are not provided. Also, the spherical aberration correction means can be configured only by changing the position of the collimator lens.

  Further, in the above embodiment, a single lens is used as the objective lens, but there is no problem even with a group lens having a high NA.

  In the above embodiment, an infinite optical head is described, but a finite optical head that does not use a collimator lens may be used.

  Further, in the above embodiment, the optical head of the polarization optical system is described, but the optical head of the non-polarization optical system may be used.

  Further, in the above embodiment, a method for detecting a deviation of the base material thickness of the optical recording medium 10 from the reference value is not described, but it is necessary to detect the deviation by a learning method before recording or reproducing the optical recording medium 10. Can be. Another method is described in JP-A-2000-171346. This method uses a spherical surface based on two focal positions of a first light beam closer to the optical axis of light reflected from an optical recording medium and a second light beam outside the first light beam. This is a method for detecting aberration. Another method is described in Japanese Patent Application Laid-Open No. 10-334575. Specifically, this method includes a light source, a first optical system that irradiates light emitted from the light source onto an optical recording medium (measurement target), and a first optical system that guides reflected light from the optical recording medium to a light receiving element. 2 optical systems. Here, the light source is composed of a laser, an LED or a lamp, and the first and second optical systems are composed of a convex lens or a combination of a convex lens and a concave lens. According to this configuration, the signal output from the light receiving element differs according to the substrate thickness, and a signal relating to the substrate thickness is obtained.

The present invention is more effective when the NA of the objective lens 9 is 0.6 or more.
As is well known, the accuracy tolerance when actually manufacturing a lens becomes difficult depending on the NA. The decenter between the first surface and the second surface of the lens is about 5 μm when molding is performed. FIG. 12 is a graph showing the relationship between the NA of the objective lens 9 and the amount of coma when the decenter between the first and second surfaces is 5 μm. As can be clearly understood from FIG. 12, when NA is larger than 0.6, coma due to decentering occurs. Further, considering other tolerances, the objective lens 9 having an NA larger than 0.6 causes considerable aberration due to the tolerance at the time of lens production.
Accordingly, the amount of aberration generated with respect to the deviation of the base material thickness of the optical recording medium from the reference value is extremely large when the NA of the objective lens 9 is 0.6 or more. Therefore, when the NA of the objective lens 9 is 0.6 or more, the aberration margin for recording becomes strict, so that a spherical aberration correcting means is required, and the present invention is particularly effective.
Similarly, when the wavelength is a very short wavelength of 450 nm or less, the amount of aberration generated due to the substrate thickness deviation increases, and the aberration margin for recording becomes severe. Therefore, spherical aberration correction means is required, and the present invention is particularly effective.

(Embodiment 4)
In the fourth embodiment, an example of the optical recording / reproducing apparatus of the present invention will be described. This optical recording / reproducing apparatus is an apparatus for recording and reproducing signals on and from an optical recording medium.

  FIG. 8 schematically shows a configuration of an optical recording / reproducing device 80 according to the fourth embodiment. The optical recording / reproducing device 80 includes an optical head 81, a motor 82, and a processing circuit 83. The optical head 81 is, for example, the same as that described in the first embodiment.

  The optical head 81 is the same as that described in the first embodiment, and a duplicate description will be omitted.

  Next, the operation of the optical recording / reproducing device 80 will be described. First, when the optical recording medium 10 is set in the optical recording / reproducing device 80, the processing circuit 83 outputs a signal for rotating the motor 82, and rotates the motor 82. Next, the processing circuit 83 drives the light source 1 to emit light. Light emitted from the light source 1 is reflected by the optical recording medium 10 and enters the photodetector 13. The photodetector 13 outputs to the processing circuit 83 a focus error signal indicating a focus state of light on the optical recording medium 10 and a tracking error signal indicating a light irradiation position. Based on these signals, the processing circuit 83 outputs a signal for controlling the objective lens 9, thereby condensing the light emitted from the light source 1 on a desired track on the optical recording medium 10. Further, the processing circuit 83 reproduces information recorded on the optical recording medium 10 based on a signal output from the photodetector 13. Further, a signal output from the light source light amount control photodetector 15 is input to a processing circuit 83, which controls the light source 1 so that the signal has a desired value, and is output from the objective lens 9. To a desired value.

  As described above, since the optical head of the first embodiment is used as the optical head, a desired amount of light is output from the objective lens even when the spherical aberration correction unit is driven, so that a stable control signal and reproduction signal can be obtained. Can be obtained, and more stable recording can be performed.

  As described above, the embodiment of the present invention has been described by way of example. However, the present invention is not limited to the above embodiment, and can be effectively applied to other embodiments based on the technical idea of the present invention. Can be.

  In the above embodiment, the optical recording medium for recording information only by light has been described. However, it is needless to say that the same effect can be obtained for an optical recording medium for recording information by light and magnetism.

  Further, in the above embodiment, the case where the optical recording medium is an optical disk has been described. However, the present invention can be applied to an optical information recording / reproducing apparatus that realizes similar functions, such as a card-shaped optical recording medium.

  The present invention is applied to an optical head used in the fields of optical information processing and optical communication, and an optical recording / reproducing apparatus equipped with such an optical head, when the base material thickness of the optical recording medium is different from a reference value. Even when the spherical aberration that occurs in the optical recording medium is corrected, an optical head in which the signal output from the light source light amount control photodetector depends only on the light amount emitted from the light source is provided. Provided is an optical recording / reproducing apparatus that can accurately detect the amount of light emitted from a light source and perform more stable reproduction and recording even when there is a deviation from a reference value and spherical aberration caused by the deviation is corrected. be able to.

  It is needless to say that the present invention is not limited to the embodiments described above, and various changes and improvements can be made without departing from the gist of the present invention.

FIG. 1 is a schematic diagram illustrating an example of an optical head according to a first embodiment of the present invention. FIG. 7 is a schematic diagram illustrating an example of an optical head according to a second embodiment of the present invention. FIG. 4 is an explanatory diagram illustrating an optical path of light when a spherical aberration correction unit is driven. FIG. 9 is a schematic diagram illustrating an example of an optical head according to Embodiment 3 of the present invention. It is a schematic diagram which shows another example of a spherical aberration correction means. FIG. 3 is an explanatory cross-sectional view illustrating an example of a spherical aberration correction unit having a phase change layer. FIG. 4 is an explanatory diagram illustrating an example of an electrode pattern of a spherical aberration correction unit having a phase change layer. FIG. 14 is a schematic diagram illustrating an example of an optical recording / reproducing device according to Embodiment 4 of the present invention. FIG. 9 is a schematic diagram illustrating an example of an optical head according to a conventional example. FIG. 11 is a schematic diagram illustrating an example of an optical head according to another conventional example. FIG. 4 is an explanatory diagram illustrating an optical path of light to an objective lens when a spherical aberration correction unit is driven in the optical head. 6 is a graph showing the relationship between the NA of the objective lens and the amount of aberration generated.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Light source 4,41 Polarization beam splitter 5 Concave lens 6 Convex lens 9 Objective lens 10 Optical recording medium 13 Photodetector 14 Lens 15 Light source light amount control light detector 16H Objective lens opening 17H Light source light amount control opening 51 Negative lens group 52 Positive Lens group 60 optical element 61 first substrate 62 second substrate 65, 66 translucent resin film 67 liquid crystal 80 optical recording / reproducing device 81 optical head

Claims (13)

An optical head that performs signal recording and / or reproduction on an optical recording medium,
A light source,
An objective lens for condensing light emitted from the light source on the optical recording medium,
An objective lens aperture for determining the aperture of the objective lens,
Spherical aberration correction means for correcting spherical aberration generated when the substrate thickness of the optical recording medium deviates from a reference value,
Light separating means arranged in an optical path from the spherical aberration correcting means to the optical recording medium,
A light source light amount control opening for limiting the opening of the light separated by the light separating means,
A first photodetector that receives light whose aperture is limited by the light source light quantity control aperture;
A second photodetector that receives light reflected by the optical recording medium;
Having an optical path length from the spherical aberration corrector to the objective lens aperture and an optical path length from the spherical aberration corrector to the light source light quantity control aperture are substantially equal, and The aperture size of the light source light quantity control aperture is set substantially equal to the aperture size of the objective lens aperture,
An optical head, characterized in that: An optical head that performs signal recording and / or reproduction on an optical recording medium,
A light source,
An objective lens for condensing light emitted from the light source on the optical recording medium,
Spherical aberration correction means for correcting spherical aberration generated when the substrate thickness of the optical recording medium deviates from a reference value,
Light separating means arranged in an optical path from the spherical aberration correcting means to the optical recording medium,
A lens that converges the light separated by the light separating means,
An aperture for controlling the amount of light emitted from the light source to limit the aperture of the light converged by the lens,
A first photodetector that receives light whose aperture is limited by the light source light quantity control aperture;
A second photodetector that receives light reflected by the optical recording medium;
An optical head comprising: An optical head that performs signal recording and / or reproduction on an optical recording medium,
A light source,
An objective lens for condensing light emitted from the light source on the optical recording medium,
Spherical aberration correction means for correcting spherical aberration generated when the substrate thickness of the optical recording medium deviates from a reference value,
Light separating means arranged in an optical path from the light source to the spherical aberration correcting means,
A first photodetector that receives the light separated by the light separating unit;
A second photodetector that receives light reflected by the optical recording medium;
An optical head comprising:   4. The optical head according to claim 1, wherein the spherical aberration correction unit corrects the spherical aberration by generating at least one of convergent light and divergent light. 5.   5. The optical head according to claim 4, wherein said spherical aberration correcting means includes a positive lens group and a negative lens group.   4. The optical head according to claim 1, wherein the spherical aberration correction unit is an optical element including a phase change layer disposed between a pair of substrates having a transparent conductive thin film. .   7. The optical head according to claim 6, wherein the light incident by the phase change layer is converted into divergent light or convergent light.   The optical head according to any one of claims 1 to 3, wherein the optical head further includes a substrate thickness detecting unit that detects a substrate thickness of the optical recording medium. The substrate thickness detection means,
A light source,
A lens for condensing light emitted from the light source on the optical recording medium,
A light detector for detecting light reflected by the optical recording medium,
9. The optical head according to claim 8, comprising:   The base material thickness detecting means may obtain information on the base material thickness based on two focal points of a first light near the optical axis of the light and a second light outside the first light. 9. The optical head according to claim 8, wherein the optical head detects.   The optical head according to any one of claims 1 to 3, wherein the NA of the objective lens is 0.6 or more.   4. The optical head according to claim 1, wherein a wavelength of the light source is 450 nm or less. 13. An optical recording / reproducing apparatus comprising the optical head according to claim 1 as an optical head for recording and / or reproducing signals on / from an optical recording medium.

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