JP4323632B2 - Aberration detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
Main departure Akira relates to an aberration detection apparatus for an optical system used in an optical information recording / reproducing apparatus for recording information on an optical information recording medium such as an optical disk (hereinafter sometimes referred to as an information carrier) or reproducing the recorded information. .
[0003]
[Prior art]
Obedience As an aberration correction means for an optical disk, one described in Japanese Patent Laid-Open No. 8-212611 has been known.
[0004]
FIG. 20 shows a schematic configuration of a conventional wavefront aberration correction method. In FIG. 20, 801 is a magneto-optical disk, 811 is a semiconductor laser, 812 is a collimator lens that converts a divergent light beam from the semiconductor laser 811 into a parallel light beam, 813 is an anamorphic prism that corrects the light beam into a circular cross section, 814 is a reflection mirror, Reference numeral 816 denotes a reflection mirror, 817 denotes an objective lens, and 818 denotes a liquid crystal element. 820 is a composite prism, 822 is an APC sensor for detecting and controlling the power of laser light, 825 is a half-wave plate, 826 is a polarization beam splitter, 829, 830 and 833 are light receiving elements, and 850 is a liquid crystal control. A circuit 854 is a microcomputer.
[0005]
In the apparatus of FIG. 20, the liquid crystal control circuit 850 is driven based on information from the memory, and the liquid crystal element 818 is controlled to correct the aberration. Specifically, when aberration occurs, the phase of the liquid crystal aberration correction element 818 is controlled in an open loop so that the wavefront aberration is minimized. When wavefront aberration changes due to temperature or the like, temperature detection is performed, and wavefront aberration is corrected based on the detected temperature and control information stored in advance in association with the temperature.
[0006]
In the example of FIG. 20, signals from the light receiving elements 829 and 830 for signal detection and the light receiving element 833 for error signal detection are input to the microcomputer 854 so that the detection signal of the light receiving element becomes good. The applied voltage applied to each element of the liquid crystal element 818 is determined.
[0007]
Further, the same publication discloses a method for measuring wavefront aberration using an interference system as a method for detecting aberration. Further, it is possible to correct the wavefront aberration based on a table calibrated in advance by obtaining the type of the disk and the control information of the liquid crystal necessary for correcting the wavefront aberration generated when the disk is used. It is disclosed. For this purpose, an interference system is built outside to form a measuring device and the wavefront aberration is measured, but a specific configuration of the interference system is not disclosed.
[0020]
[Problems to be solved by the invention]
in front In the conventional aberration correction method described above, a correction method is shown in which the wavefront aberration is changed by trial and error so that the S / N of the signal is the best, and as a result, a closed loop is formed so that the wavefront aberration is reduced. Yes.
[0021]
However, in this method, since the best point is obtained in a hill-climbing manner (by trial and error) while judging whether the signal is improved or worsened, it is difficult to perform control by a closed loop that takes a long time to detect and has a quick response.
[0022]
Main departure An object of the present invention is to provide an aberration detection apparatus that solves the conventional problems and can detect aberrations in real time or in a time according to real time and control them in a high-speed closed loop.
[0035]
[Means for Solving the Problems]
Up In order to achieve the above-mentioned object, the present invention detects the distribution by focusing on the fact that a characteristic distribution is generated by the aberration in the light distribution of the reflected light from the disk as a method capable of detecting the aberration in real time. Thus, the aberration is detected. Even if it is difficult to quantitatively grasp the amount of aberration, it is relatively easy to detect the type of aberration and whether or not the aberration is above a certain value.
[0036]
This aberration detection is performed, and the aberration correction element is driven within the time corresponding to real time or real time to correct the aberration, thereby improving the characteristics of the focused beam, resulting in good optical recording characteristics and reproduction signals. Can do.
[0037]
Main departure Akira has the following configuration.
[0038]
Main departure The aberration detection apparatus according to the first bright configuration includes a radiation source that emits a light beam, an objective lens that focuses the light beam on an information carrier, and is reflected on the information carrier and passes through the objective lens. A light beam branching means for separating the return light beam from the forward light beam; Depending on the type of aberration to be detected, the region where the phase advances / delays from the reference wavefront is defined as the specific region, The return light beam separated by the branching means Above A light deflector that divides and deflects a light beam that passes through the specific region and a light beam that passes through the other region; and a plurality of light detectors that receive the light beam that passes through the deflected specific region. And detecting aberrations by comparing signals from the plurality of light detection means.
[0039]
Also, Main departure The aberration detection apparatus according to the bright second configuration includes a radiation source that emits a light beam, an objective lens that focuses the light beam on an information carrier, and Depending on the type of aberration to be detected, the region where the phase advances / delays from the reference wavefront is defined as the specific region, A return light beam reflected on the information carrier and passed through the objective lens. Above A light deflector for splitting the light beam passing through the specific region and the light beam passing through the other region, and deflecting the light beam passing through the specific region in a direction different from the radiation light source; and the deflected light beam A plurality of light detecting means for receiving a light beam passing through the specific region, and detecting aberrations by comparing signals from the plurality of light detecting means.
[0040]
According to the first and second configurations, the aberration of the optical system can be detected in real time or time close to real time. Therefore, if the aberration correction element is driven based on the detection result, the aberration of the optical system can be reduced. Therefore, it is possible to reproduce information carriers (discs) having large surface wobbling and information carriers (discs) having different substrate thicknesses, which have been difficult in the past. In addition, since the tolerance of the information carrier can be relaxed, the information carrier can be easily manufactured.
[0041]
In the first and second configurations, it is preferable that the light deflecting unit is a hologram that divides and diffracts the light beam into a plurality of parts. By using such a hologram element, the light beam can be efficiently divided by one element, and the optical system can be made compact.
[0042]
In the first and second configurations, the plurality of light detection means includes a light detector divided into at least two parts, When the wavefront aberration is substantially zero, It is preferable that the light beam passing through the specific region is installed so as to irradiate the dividing line of the two-divided photodetector. According to such a configuration, when aberration occurs, the distribution of the light beam spot changes and a difference occurs in the output between the two photodetectors. By detecting this difference, the aberration can be stabilized with a simple configuration. Can be detected.
[0043]
In the first and second configurations, a substantially central portion of one of the two regions obtained by dividing the specific region into a region through which the light beam of the return path passes by a plane including the optical axis of the light beam. The area can be According to this configuration, coma aberration can be detected.
[0044]
Further, in the first and second configurations, the specific region is divided into two regions that are sandwiched between two concentric circles having different diameters around the optical axis of the light beam in the return path, on a plane including the optical axis. It can be made to substantially coincide with one area obtained in this way. According to this configuration, spherical aberration can be detected.
[0045]
In the first and second configurations, the light deflection unit is preferably a blazed hologram. According to such a configuration, since it is possible to use a highly efficient deflection unit as compared with a normal hologram, it is possible to detect aberration with high sensitivity.
[0046]
In the second configuration, it is preferable that the plurality of light detection units are arranged in the vicinity of the radiation light source and symmetrically with respect to the radiation light source. According to such a configuration, when a hologram is used as the light deflecting means, the + 1st order diffracted light and the −1st order diffracted light appearing at symmetrical positions with respect to the radiation light source can be efficiently received with the same diffraction efficiency. A good optical system can be formed.
[0047]
In the second configuration, the light deflecting means includes a hologram that diffracts only predetermined polarized light and a quarter-wave plate, and in the hologram, the forward light beam from the radiation source toward the information carrier is diffracted. The light beam in the return path is preferably divided into a plurality of parts and diffracted in different directions. According to this configuration, the light utilization efficiency of the optical system can be increased.
[0057]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0058]
(Embodiment 1)
FIG. 1 is a schematic configuration diagram of the aberration detection apparatus according to the first embodiment.
[0059]
A light beam emitted from a light source 101 such as a semiconductor laser passes through a half mirror 102, is converted into substantially parallel light by a collimator lens 103, passes through a wavefront conversion element 104, and is recorded and reproduced through the substrate of an optical disk 106 by an objective lens 105. Incident on the information surface.
[0060]
The light beam reflected on the recording / reproducing information surface is transmitted again through the substrate, transmitted through the objective lens 105, the wavefront conversion element 104, and the collimating lens 103, reflected by the half mirror 102, transmitted through the hologram 109, and diffracted. Then, it enters the photodetector 107 for signal detection. The photodetector 107 includes an information signal, a control signal such as a focus signal and a tracking signal, and a photodetector element such as a pin diode that detects aberration of the light beam. These detection elements may be configured independently for each signal detection, or may be combined with a plurality of functions. The detected aberration is processed by the signal processing circuit 108 to drive the wavefront conversion element 104.
[0061]
As the wavefront conversion element 104, for example, the following method can be used, and a liquid crystal sealed in a portion sandwiched between two glass substrates can be used. If the portion through which the light beam passes is divided into a plurality of regions and a voltage is applied to each region independently, the refractive index of the corresponding portion can be changed. The phase of the wavefront can be changed using this change in refractive index. If there is aberration in the light beam, the phase of the light beam partially changes. Therefore, the aberration can be corrected by driving the wavefront conversion element 104 so as to complement the changed phase. When the voltage is applied according to the degree of aberration, the aberration correction can be corrected more accurately.
[0062]
In a situation where there is no aberration in the optical system, no aberration is detected by the photodetector 107, and therefore the wavefront conversion element 104 is not changed, and it becomes an element equivalent to a simple glass parallel plate. However, when aberration occurs, the detection signal differs depending on the type of aberration.
[0063]
Three typical examples of aberration will be described below.
[0064]
As a first example, when the optical disk 106 is tilted, for example, coma aberration occurs when the light beam passes through the substrate of the optical disk. This coma aberration can be detected by the photodetector 107, and the wavefront conversion element 104 can be driven so as to cancel the coma aberration to correct the aberration. As a wavefront conversion method for correcting coma aberration, a method using a wavefront conversion element composed of multi-divided liquid crystals can be used.
[0065]
A method for detecting coma aberration will be described below.
[0066]
FIG. 2 shows the wavefront aberration when coma occurs. With respect to the reference wavefront 11 in the aperture, there is a wavefront advance 11a and a delay 11b with the optical axis 10 as a boundary. When the reference wavefront 11 is condensed, the positions where the advanced wavefront 11a and the delayed wavefront 11b converge with respect to the condensing point are defocused. Accordingly, it is possible to know the coma aberration occurrence state by taking out only the advanced wavefront or the delayed wavefront and detecting the focus state.
[0067]
FIG. 3 shows an example of an optical system for detecting coma aberration. Assume that the optical axis 10 passes through the origin of the XY coordinate system, and coma occurs in the Y-axis direction. In the return light beam 12 reflected from the optical disk and condensed, only the light beam that passes through the substantially central portion 13 of the region of Y> 0 is separated from the light beam that passes through the region other than the region 13 and divided into two The light detectors 17 a and 17 b are condensed to form a light spot 14. Here, when no aberration occurs, the light spot 14 is formed so as to be focused on the dividing lines of the photodetectors 17a and 17b. When coma occurs in the Y-axis direction, the phase of the light beam passing through the region 13 is advanced or delayed with respect to the light beam passing through other regions. In other words, the region 13 is set so that a light beam whose phase is advanced or delayed can be extracted. In the example of FIG. 3, the region 13 is exemplified as a semicircle, but is not limited thereto, and may be a circle, an ellipse, a rectangle, an arc shape, or the like.
[0068]
FIG. 4 shows the shape and formation position of the light beam 14 on the two-divided photodetector.
[0069]
FIG. 4A shows a case where the phase of the light beam passing through the region 13 is delayed, and the light beam is a light beam that is condensed behind the detection surface of the photodetector. At this time, since the light beam passes through the photodetector 17a, the output of the photodetector 17a becomes larger than the output of the photodetector 17b.
[0070]
FIG. 4B shows a case where there is no phase advance or delay of the light beam passing through the region 13 (that is, when there is no aberration), and the light beam is on the detection surfaces of the photodetectors 17a and 17b. The light beam is condensed on the dividing line between the two. At this time, the output of the photodetector 17a and the output of the photodetector 17b have the same magnitude.
[0071]
FIG. 4C shows a case where the phase of the light beam passing through the region 13 is advanced, and the light beam becomes a light beam that is condensed forward from the detection surface of the photodetector. At this time, since the light beam passes through the photodetector 17b, the output of the photodetector 17a becomes smaller than the output of the photodetector 17b.
[0072]
As described above, by detecting the difference signal between the output signals of the two-divided photodetectors 17a and 17b, the amount and sign of the coma aberration can be known for a minute coma aberration. If an aberration larger than a certain level is generated, the difference signal is saturated, so that it is impossible to know the amount of coma even if the sign of coma is known. In such a case, the amount of coma aberration can be measured by dividing the photodetector into multiple parts and calculating the signal.
[0073]
As a second example, in FIG. 1, for example, if the optical disk 106 has a different thickness, spherical aberration occurs when the light beam passes through the substrate. This spherical aberration can be detected by the detector 107, and the wavefront conversion element 104 can be driven so as to cancel the spherical aberration to correct the aberration. As a wavefront conversion method for correcting spherical aberration, a method using a wavefront conversion element formed of multi-divided liquid crystals can be used.
[0074]
A method for detecting spherical aberration will be described below.
[0075]
FIG. 5 shows wavefront aberration in which spherical aberration occurs. There are wavefront delays 21a and 21b symmetrically to the optical axis 10 with respect to the reference wavefront 21 in the aperture. When the reference wavefront 21 is condensed, the positions where the delayed wavefronts 21a and 21b converge with respect to the condensing point are defocused. Therefore, it is possible to know the state of occurrence of wavefront aberration by taking out only the delayed wavefront and detecting the focus state. Contrary to the above, wavefront aberration also occurs when the wavefront advances symmetrically to the optical axis 10.
[0076]
FIG. 6 shows an example of an optical system for detecting spherical aberration. The optical axis 10 passes through the origin of the XY coordinate system. The return light beam 22 reflected from the optical disk and collected passes through a region Y> 0 (half-ring region) 23 between two concentric circles having different diameters around the optical axis 10. Only the light beam to be separated is separated from the light beam passing through the region other than the region 23 and is condensed on the two photodetectors 17 a and 17 b to form the light spot 24. Here, when no aberration occurs, the light spot 24 is formed so as to be focused on the dividing line of the photodetectors 17a and 17b. When spherical aberration occurs, the phase of the light beam passing through the region 23 is advanced or delayed with respect to the light beam passing through other regions. In other words, the region 23 is set so that a light beam whose phase is advanced or delayed can be extracted. The radius of the ring and the width in the radial direction of the semi-ring-shaped region 23 can be set according to the state of wavefront aberration of the light beam.
[0077]
FIG. 7 shows the shape and formation position of the light beam 24 on the two-divided photodetector.
[0078]
FIG. 7A shows a case where the phase of the light beam passing through the region 23 is delayed, and the light beam is a light beam that is condensed behind the detection surface of the photodetector. At this time, since the light beam passes through the photodetector 17a, the output of the photodetector 17a becomes larger than the output of the photodetector 17b.
[0079]
FIG. 7B shows a case where there is no phase advance or delay of the light beam passing through the region 23 (that is, when there is no aberration), and the light beam is on the detection surfaces of the photodetectors 17a and 17b. The light beam is condensed on the dividing line between the two. At this time, the output of the photodetector 17a and the output of the photodetector 17b have the same magnitude.
[0080]
FIG. 7C shows a case where the phase of the light beam passing through the region 23 is advanced, and the light beam becomes a light beam that is condensed forward from the detection surface of the photodetector. At this time, since the light beam passes through the photodetector 17b, the output of the photodetector 17a becomes smaller than the output of the photodetector 17b.
[0081]
As described above, by detecting the difference signal between the output signals of the two-divided photodetectors 17a and 17b, the amount and sign of the spherical aberration can be known for a minute spherical aberration. If a large aberration occurs to some extent, the difference signal is saturated, so that the amount of spherical aberration cannot be known even if the sign of spherical aberration is known. In such a case, the amount of spherical aberration can be measured by dividing the photodetector into multiple parts and calculating the signal.
[0082]
As a third example, astigmatism occurs in FIG. 1 when the light beam passes through the substrate due to, for example, birefringence of the optical disk 106. This astigmatism is detected by the detector 107, and the wavefront conversion element 104 can be driven so as to cancel the astigmatism to correct the aberration. As a wavefront conversion method for correcting astigmatism, a method using a wavefront conversion element formed of multi-divided liquid crystals can be used.
[0083]
The astigmatism detection method can be performed based on the same concept as the above-described coma aberration and spherical aberration detection methods.
[0084]
In FIG. 1, the hologram 109 as the light deflecting means may be a blazed hologram. Thereby, it can be set as a highly efficient deflection means compared with a normal hologram.
[0085]
The light detector 107 is a light detection element divided into a plurality of regions such as an information signal, a control signal such as a focus signal and a tracking signal, and a pin diode for detecting light beam aberration. Also, the light detection element is divided into at least two parts, and the light beam deflected by the hologram 109 is set to fall on the dividing line of the two light detection elements.
[0086]
(Embodiment 2)
FIG. 8 is a schematic configuration diagram of the aberration detection apparatus according to the second embodiment.
[0087]
A light beam emitted from a light source 101 such as a semiconductor laser passes through a hologram 109, is converted into substantially parallel light by a collimator lens 103, passes through a wavefront conversion element 104, and is recorded and reproduced by an objective lens 105 over the substrate of the optical disk 106. Incident on the surface.
[0088]
The light beam reflected on the recording / reproducing information surface passes through the substrate again, passes through the objective lens 105, the wavefront conversion element 104, and the collimating lens 103, is diffracted by the hologram 109, and enters the photodetectors 107 and 111 for signal detection. To do. The photodetectors 107 and 111 include information signals, control signals such as a focus signal and tracking signal, and an element that detects aberration of the light beam. These detection elements may be configured independently for each signal detection, or may be combined with a plurality of functions. The detected aberration is processed by the signal processing circuit 108 to drive the wavefront conversion element 104.
[0089]
In a situation where there is no aberration in the optical system, no aberration is detected by the photodetectors 107 and 111, and therefore the wavefront conversion element 104 is not changed, and is an element equivalent to a simple glass parallel plate. When aberration occurs, it is detected by the same detection method as described in the first embodiment.
[0090]
According to the present embodiment, a more compact aberration detection apparatus can be obtained as compared with the first embodiment.
[0091]
(Embodiment 3)
FIG. 9 shows a specific method for detecting coma aberration.
[0092]
The hologram 109 is divided into a plurality of regions 109a to 109d, and photodetectors 107a to 107h are provided corresponding to the respective regions. That is, the region 109a corresponds to the photodetectors 107g and 107h, the region 109b corresponds to the photodetectors 107a and 107b, the region 109c corresponds to the photodetectors 107e and 107f, and the region 109d corresponds to the photodetectors 107c and 107d. Corresponding to The area division of the hologram 109 is performed according to the concept described with reference to FIG. In this manner, in order to divide and deflect the light beam into a plurality of parts depending on the region through which the light beam passes, it is possible to appropriately set the spatial frequency (pitch) and the diffraction direction of the hologram 109 for each region. .
[0093]
When it is assumed that coma has occurred in the Y-axis direction, the phase error is the largest between the region 109a and the region 109b on the detection hologram 109, and the phase error is relatively small in the region 109c and the region 109d. . Therefore, coma aberration can be detected by detecting these four regions. Since the coma aberration is symmetrical with respect to the X axis, it can be detected from the combination of the region 109a and the region 109c. Similarly, it is possible to detect from a combination of the region 109b and the region 109d.
[0094]
The photodetector 107 is in the vicinity of the light beam condensing point, and a so-called knife edge method is used.
[0095]
The far-field tracking error signal can be detected by detecting a light amount difference between the light beam passing through the Y> 0 portion and the light beam passing through the Y <0 portion of the hologram. That is, the far field tracking signal TE is
TE = [(107a) + (107b) + (107c) + (107d)]-[(107e) + (107f) + (107g) + (107h)]
It can be detected by looking at the signal.
[0096]
FIG. 10 shows a state of a light spot (hatched portion) by a light beam on the detector 107 when focus detection is performed by the knife edge method. In this case, assuming that there is no coma, all the light beams are collected on the dividing line of the two-divided photodetector as shown in FIG. When the focus is shifted and, for example, the optical disk 106 and the objective lens 105 are in a direction approaching each other, the outputs of the elements 107a, 107c, 107f, and 107h increase as shown in FIG. When the optical disk 106 and the objective lens 105 are away from each other, the outputs of the elements 107b, 107d, 107e, and 107g are increased as shown in FIG. Therefore, a focus signal can be obtained by processing these signals. That is, the focus signal FE is
FE = [(107c) + (107f)]-[(107d) + (107e)]
It can be detected by looking at the signal.
[0097]
FIG. 11 shows a state of a light spot (hatched portion) by a light beam on the light detector 107 when the focus is set (when focused).
[0098]
When no coma occurs, the outputs of all the photodetectors do not change substantially equally as shown in FIG.
[0099]
When coma of a certain polarity occurs, the outputs of the photodetectors 107a and 107g increase and the outputs of 107b and 107h decrease as shown in FIG. 11A, but the outputs of the photodetectors 107c, 107d, 107e, and 107f. The output does not change.
[0100]
When coma of opposite polarity occurs, the outputs of the photodetectors 107b and 107h increase and the outputs of 107a and 107g decrease as shown in FIG. 11C, but the outputs of the photodetectors 107c, 107d, 107e, and 107f. The output does not change.
[0101]
Therefore, a coma aberration detection signal can be obtained by processing these signals. That is, coma CM is
CM = [(107a) + (107g)]-[(107b) + (107h)]
It can be detected by looking at the signal.
[0102]
(Embodiment 4)
FIG. 12 shows a specific method for detecting spherical aberration.
[0103]
The hologram 109 is divided into a plurality of regions 109e to 109h, and photodetectors 107a to 107h are provided corresponding to the respective regions. That is, the region 109e corresponds to the photodetectors 107g and 107h, the region 109f corresponds to the photodetectors 107a and 107b, the region 109g corresponds to the photodetectors 107c and 107d, and the region 109h corresponds to the photodetectors 107e and 107f. Corresponding to The area division of the hologram 109 is performed according to the concept described with reference to FIG. In this manner, in order to divide and deflect the light beam into a plurality of parts depending on the region through which the light beam passes, it is possible to appropriately set the spatial frequency (pitch) and the diffraction direction of the hologram 109 for each region. .
[0104]
When it is assumed that spherical aberration has occurred, the phase error is greatest between the regions 109e and 109f and the regions 109g and 107h on the detection hologram 109. Therefore, spherical aberration can be detected by detecting these two regions. Since the spherical aberration is symmetric with respect to the X axis and the Y axis, it can be detected from a combination of the region 109e and the regions 109g and 109h. Similarly, it is possible to detect from the combination of the region 109f and the regions 109g and 109h.
[0105]
FIG. 13 shows a state of a light spot (hatched portion) by the light beam on the photodetector 107 when the focus is on.
[0106]
When spherical aberration does not occur, the outputs of all the photodetectors do not change substantially equally as shown in FIG.
[0107]
When spherical aberration with a certain polarity occurs, the focal point of the light beam passing through the holograms 109g and 109h in FIG. 12 is condensed behind the photodetector 107 as shown in FIG. As a result, the outputs of the photodetectors 107a and 107h increase and the outputs of the photodetectors 107b and 107g decrease, but the outputs of the photodetectors 107c, 107d, 107e, and 107f do not change.
[0108]
When spherical aberration of opposite polarity occurs, the focal point of the light beam passing through the holograms 109g and 109h in FIG. 12 is condensed in front of the photodetector 107 as shown in FIG. As a result, the outputs of the photodetectors 107b and 107g increase and the outputs of the photodetectors 107a and 107h decrease, but the outputs of the photodetectors 107c, 107d, 107e, and 107f do not change.
[0109]
Therefore, by processing these signals, a spherical aberration detection signal can be obtained. That is, the spherical aberration SA is
SA = [(107a) + (107h)]-[(107b) + (107g)]
It can be detected by looking at the signal.
[0110]
The far-field tracking error signal can be detected by detecting a light amount difference between the light beam passing through the Y> 0 portion and the light beam passing through the Y <0 portion of the hologram. That is, the far field tracking signal TE is
TE = [(107a) + (107b) + (107e) + (107f)]-[(107c) + (107d) + (107g) + (107h)]
It can be detected by looking at the signal.
[0111]
(Embodiment 5)
Astigmatism can be detected by applying the principle of the present invention. FIG. 14 shows a specific method for detecting astigmatism.
[0112]
The hologram 109 is divided into a plurality of areas 109i to 109m (109l is a missing number), and photodetectors 110a to 110m (110l is a missing number) are provided corresponding to each area. That is, the region 109i corresponds to the photodetectors 110i, 110j, 110k, and 110m, the region 109j corresponds to the photodetectors 110a, 110b, 110c, and 110d, the region 109k corresponds to the photodetectors 110e and 110f, and the region 109m corresponds to the photodetectors 110g and 110h. The area division of the hologram 109 is performed as follows. First, it is divided into a region (ring-shaped region) sandwiched between two concentric circles with different diameters around the optical axis and other regions. The former ring-shaped region is further divided into four by the X-axis and the Y-axis, and the opposing regions are taken as one set, and two sets of detection regions 109i and 109j are obtained. The latter area is divided into a Y> 0 area and a Y <0 area, which are 109k and 109m, respectively. In this manner, in order to divide and deflect the light beam into a plurality of parts depending on the region through which the light beam passes, it is possible to appropriately set the spatial frequency (pitch) and the diffraction direction of the hologram 109 for each region. .
[0113]
When it is assumed that astigmatism has occurred, the phase error between the region 109i and the region 109j is the largest on the detection hologram 109, and the phase error between the region 109k and the region 109m Intermediate value. Therefore, astigmatism can be detected by detecting these three regions.
[0114]
FIG. 15 shows a state of a light spot (hatched portion) by a light beam on the photodetector 110 when the focus is on.
[0115]
When astigmatism does not occur, the outputs of all the photodetectors 110 do not change substantially equally as shown in FIG.
[0116]
When astigmatism of a certain polarity occurs, the focal point of the light beam passing through the hologram 109i in FIG. 14 is condensed behind the photodetector 110 as shown in FIG. 15A, and the light beam passing through the hologram 109j is collected. The focal point is collected in front of the photodetector 110. As a result, the outputs of the photodetectors 110a, 110d, 110j, and 110k increase, and the outputs of the photodetectors 110b, 110c, 110i, and 110m decrease. The outputs of the photodetectors 110e, 110f, 110g, and 110h do not change.
[0117]
When astigmatism of opposite polarity occurs, the focus of the light beam that passes through the hologram 109j in FIG. 14 is condensed behind the photodetector 110 as shown in FIG. 15C, and the light beam that passes through the hologram 109i is focused. The focal point is collected in front of the photodetector 110. As a result, the outputs of the photodetectors 110a, 110d, 110j, and 110k are decreased, and the outputs of the photodetectors 110b, 110c, 110i, and 110m are increased. The outputs of the photodetectors 110e, 110f, 110g, and 110h do not change.
[0118]
Therefore, by processing these signals, an astigmatism detection signal can be obtained. That is, astigmatism AS is
AS = [(110a) + (110d) + (110j) + (110k)]-[(110b) + (110c) + (110i) + (110m)]
It can be detected by looking at the signal.
[0119]
Each embodiment using the hologram described above describes an example using light of + 1st order diffracted light or −1st order diffracted light for simplification of the photodetector. A blazed hologram can also be used. In this case, the aberration detection device can be formed as it is in this form. By using the blazed hologram, the amount of light received by the photodetector increases, so that highly sensitive aberration detection can be performed. Of course, the above method can also be used for holograms that are not blazed. At this time, it is necessary to design the photodetector so that the + 1st order and −1st order diffracted lights do not interfere with each other.
[0120]
In Embodiment 2 (FIG. 8), when a hologram that is not blazed is used as the hologram 109, the + 1st order diffracted light and the −1st order diffracted light can be received at substantially symmetrical positions near both sides of the light source 101. The photodetectors 107 and 111 may be installed, and the above-described aberration detection may be performed by both the photodetectors 107 and 111. With this configuration, the amount of received light is doubled compared to the case where aberration detection is performed using only one photodetector, and an aberration detection signal having a high S / N ratio can be obtained.
[0121]
Alternatively, in the second embodiment (FIG. 8), a polarization hologram that diffracts only polarized light may be used as the hologram 109, and this and a quarter wavelength plate may constitute the light deflection means. That is, as shown in FIG. 16, a radiation light source that emits polarized light is used as the light source 101, and a polarization hologram 109 is installed in a direction in which the emitted polarized light is transmitted. A quarter-wave plate 115 is installed between the wavefront conversion element 104 and the objective lens 105. The light beam emitted from the polarized radiation light source 101 passes through the polarization hologram 109 and becomes circularly polarized light by the quarter-wave plate 115. The circularly polarized beam reflected by the disk 106 passes through the quarter-wave plate 115 again to become a light beam polarized in a direction perpendicular to the polarization direction of the forward light beam. When this light beam is incident on the polarization hologram 109, most of the light beam is diffracted and incident on the photodetectors 107 and 111. Here, the photodetectors 107 and 111 are installed at substantially symmetrical positions near both sides of the light source 101. Aberration detection is performed using signals from both the photodetectors 107 and 111. Thus, by using the polarization hologram and the quarter-wave plate, the utilization efficiency of the light beam incident on the photodetector can be improved, and an aberration detection signal having a high S / N ratio can be obtained. it can.
[0122]
In each of the above embodiments, the method of detecting aberrations at high speed using the two-divided photodetector has been described. However, if the response speed of the photodetector can be increased, the light detection is divided into a plurality of parts in the same direction as the two-segment division. Aberration detection with higher accuracy can be performed using the instrument. As is apparent from FIGS. 10, 11, 13, and 15, when aberration occurs, the light distribution on the photodetector is greatly expanded. The magnitude of this spread is proportional to the magnitude of the aberration. Therefore, as the output is output to the photodetector away from the center of the optical axis of the light beam, the larger aberration is generated. It is also possible to process the signals output from a plurality of photodetectors, and to control and drive the aberration correction device (wavefront conversion element 104) stepwise with an analog value to perform more accurate aberration correction. . Since the liquid crystal used in the aberration correction device can change the refractive index substantially in proportion to the applied voltage, it is suitable as a device that controls in steps with analog values.
[0123]
In the above embodiment, only the case where the far field tracking method is used as the tracking method has been described. However, it is also possible to combine the commonly used phase difference detection tracking method, three beam tracking method, etc. with a design that is not so difficult. It is.
[0124]
Next, an embodiment in which the aberration detection apparatus is applied to an optical information recording / reproducing apparatus will be described.
[0125]
(Embodiment 6)
FIG. 17 shows an outline of the configuration of the optical information recording apparatus according to the sixth embodiment.
[0126]
In FIG. 17, a light beam 202 emitted from a semiconductor laser 201 is converted into substantially parallel light by a collimator lens 220, passes through an objective lens 205 including two aspheric lenses 203 and 204, and is recorded in the first recordable state. The light is incident on an information carrier 209 including an information layer 206, a second recordable recording information layer 208, and an optical separation layer 207 between the both recording information layers. Between the two aspheric lenses 203 and 204, there is a distance adjustment mechanism 210 that can change the distance between the two aspheric lenses. In this embodiment, a piezo element is used. When a high voltage is applied, the distance between the two aspheric lenses 203 and 204 is increased, and when the voltage is decreased, the two aspheric lenses 203 and 204 are The distance between 204 is shortened. When the light beam converged by the objective lens 205 is condensed on the first recordable recording information layer 206, the voltage applied to the piezo element is lowered so that the distance between the two aspheric lenses 203 and 204 is reduced. Shorten and correct spherical aberration. When the light beam converged by the objective lens 205 is condensed on the second recordable recording information layer 208, the voltage applied to the piezo element is increased so that the distance between the two aspheric lenses 203 and 204 is increased. Increase the length to correct spherical aberration. By reducing the spherical aberration with respect to the recording information layer by such a method, good recording / reproducing characteristics can be obtained.
[0127]
In the sixth embodiment, an electromagnetically driven actuator or motor can be used instead of the piezoelectric element. An actuator driven by ultrasonic waves can be used instead of the piezo element.
[0128]
Instead of using the two aspheric lenses 203 and 204, two convex lens groups, or one aspheric lens and one spherical lens can be used.
[0129]
(Embodiment 7)
FIG. 18 shows an outline of the configuration of the optical information recording apparatus according to the seventh embodiment.
[0130]
In FIG. 18, a light beam 202 emitted from a semiconductor laser 201 is converted into substantially parallel light by a collimator lens 220, passes through an objective lens 205 including two aspheric lenses 203 and 204, and is recorded in the first recordable state. The light is incident on an information carrier 209 including an information layer 206, a second recordable recording information layer 208, and an optical separation layer 207 between the both recording information layers. Between the objective lens 205 and the semiconductor laser 201 is a spherical aberration correction element 230 that can change an optical phase that is equal to the circumferential direction of a circle centered on the optical axis of the objective lens 205 and that is different in the radial direction. The lens 205 is disposed integrally.
[0131]
Since a phase error centered on the optical axis occurs due to the thickness error of the base material, recording is performed by adding the same amount of optical phase with the opposite polarity to the different optical phase in the radial direction caused by spherical aberration. The spherical aberration of the light beam condensed on the information layer can be canceled out.
[0132]
In the present embodiment, the spherical aberration correction element 230 is a liquid crystal element that is divided into a plurality of 3 to 7 regions in the radial direction by concentric circles centered on the optical axis. The voltage applied to the region is controlled to optimize the phase difference.
[0133]
In this embodiment, instead of using the two aspheric lenses 203 and 204, two convex lens groups, or one aspheric lens and one spherical lens can be used.
[0134]
(Embodiment 8)
In the sixth and seventh embodiments, a spherical aberration detection method using a hologram can be used for detecting spherical aberration. A method for detecting the spherical aberration of the optical disk will be described with reference to FIG.
[0135]
In FIG. 19, a light beam 202 emitted from the semiconductor laser 201 is converted into substantially parallel light by a collimator lens 220, passes through an objective lens 205 including two aspheric lenses 203 and 204, and is a first recordable recording information layer. The light is incident on an information carrier 209 including 206, a second recordable recording information layer 208, and an optical separation layer 207 between both recording information layers. Between the two aspheric lenses 203 and 204, there is a distance adjusting mechanism 210 that makes the distance between the two aspheric lenses constant. In this embodiment, a piezo element is used as the distance adjustment mechanism 210.
[0136]
The light beam reflected from the disk is reflected by the half mirror 302, passes through the aberration detection hologram 309, and enters the photodetector 307. The detected signal is processed by the signal amplification processing circuit 308 to drive the piezo element 210. By applying a high voltage in accordance with the detection signal, the distance between the two aspheric lenses 203 and 204 is increased, and by decreasing the voltage, the distance between the two aspheric lenses 203 and 204 is decreased. Become.
[0137]
When the light beam converged by the objective lens 205 is condensed on the first recordable recording information layer 206, the spherical aberration detection signal is detected, and the voltage applied to the piezo element 210 is lowered to reduce the two non-recording layers. Shorten the distance between spherical lenses to correct spherical aberration.
[0138]
When the light beam converged by the objective lens 205 is condensed on the second recordable recording information layer 208, the spherical aberration detection signal is detected with the opposite polarity to the above, and the voltage applied to the piezo element 210 is increased. Then, the spherical aberration is corrected by increasing the distance between the two aspheric lenses.
[0139]
As a specific method of detecting spherical aberration, the method described in FIGS. 5 to 7 or the fourth embodiment can be used.
[0140]
In this embodiment, instead of using the two aspheric lenses 203 and 204, two convex lens groups, or one aspheric lens and one spherical lens can be used.
[0141]
In this embodiment, the example in which the optical information recording apparatus in the sixth embodiment is combined with the spherical aberration detection apparatus has been described. However, the optical information recording apparatus in the seventh embodiment can be combined with the spherical aberration detection apparatus.
[0142]
Further, in the present embodiment, the case of combining the spherical aberration detection device having the configuration of FIG. 1 has been described, but the spherical aberration detection device having the configuration of FIG. 2 can also be combined.
[0143]
The present invention described above is not limited to the configuration specifically represented by the drawings, and various variations can be assumed.
[0144]
【The invention's effect】
Main departure According to Meiji, aberrations of the optical system can be detected in real time or in near real time. Therefore, if the aberration correction element is driven based on the detection result, the aberration of the optical system can be reduced. Therefore, it is possible to reproduce information carriers (discs) having large surface wobbling and information carriers (discs) having different substrate thicknesses, which have been difficult in the past. In addition, the information carrier can be easily manufactured.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an aberration detection apparatus according to a first embodiment of the present invention.
FIG. 2 is a conceptual diagram showing wavefront aberration when coma occurs.
FIG. 3 is a schematic configuration diagram showing an example of an optical system for detecting coma aberration.
4 is an explanatory diagram showing the shape and position of a light beam spot formed on the two-split photodetector in FIG. 3;
FIG. 5 is a conceptual diagram showing wavefront aberration when spherical aberration occurs.
FIG. 6 is a schematic configuration diagram showing an example of an optical system for detecting spherical aberration.
7 is an explanatory diagram showing the shape and position of a light beam spot formed on the two-split photodetector in FIG. 6;
FIG. 8 is a schematic configuration diagram of an aberration detection apparatus according to Embodiment 2 of the present invention.
FIG. 9 is a configuration diagram illustrating the detection principle of coma aberration according to the third embodiment of the present invention.
10 is an explanatory diagram showing a formation state of a light beam spot on the photodetector in FIG. 9 when focus detection is performed by the knife edge method.
11 is an explanatory diagram showing the formation state of a light beam spot on the photodetector in FIG. 9 when coma aberration occurs.
FIG. 12 is a configuration diagram showing the detection principle of spherical aberration according to the fourth embodiment of the present invention.
13 is an explanatory diagram showing a formation state of a light beam spot on the photodetector in FIG. 12 when spherical aberration occurs.
FIG. 14 is a configuration diagram showing the detection principle of astigmatism according to the fifth embodiment of the present invention.
15 is an explanatory diagram showing a formation state of a light beam spot on the photodetector in FIG. 14 when astigmatism occurs.
FIG. 16 is a schematic configuration diagram showing another configuration example of the aberration detection apparatus of the present invention.
FIG. 17 is a schematic configuration diagram of an optical information recording device according to a sixth embodiment of the present invention.
FIG. 18 is a schematic configuration diagram of an optical information recording device according to a seventh embodiment of the present invention.
FIG. 19 is a schematic configuration diagram of an optical information recording device according to an eighth embodiment of the present invention.
FIG. 20 is a schematic configuration diagram showing a conventional wavefront aberration correction method;
FIG. 21 is a cross-sectional view showing an example of the configuration of a single-sided readout two-layer type optical disc
[Explanation of symbols]
101 Light source
102 half mirror
103 collimating lens
104 Wavefront conversion element
105 Objective lens
106 Optical disc
107 photodetector
108 Aberration signal processing circuit
109 hologram
111 photodetector
115 quarter wave plate
201 Semiconductor laser
202 Light beam
203 first lens
204 Second lens
205 Objective lens
206 First recording information layer
207 Optical separation layer
208 Second recording information layer
209 Information carrier
210 Distance adjustment mechanism (piezo element)
220 collimating lens
230 Liquid Crystal Spherical Aberration Correction Element
302 half mirror
307 photodetector
308 Signal amplification processing circuit
309 hologram

Claims (9)

A radiation source emitting a light beam;
An objective lens for condensing the light beam on an information carrier;
A light beam branching means for separating a return light beam reflected on the information carrier and passed through the objective lens from a forward light beam;
Depending on the type of aberrations to be detected, a reference wavefront the phase is advanced / or delayed region specific region, wherein the return path separated by branching means light beam other than light beams and its passing through the specific region Light deflecting means for splitting and deflecting light beams that pass through the region;
A plurality of light detection means for receiving a light beam passing through the deflected specific region,
An aberration detection apparatus that detects aberration by comparing signals from the plurality of light detection means. A radiation source emitting a light beam;
An objective lens for condensing the light beam on an information carrier;
Depending on the type of aberrations to be detected, a reference wavefront the phase is advanced / or delayed region specific regions, is reflected on the information carrier through said returning path has passed through the objective lens optical beam the specific region A light deflector that divides a light beam into a light beam that passes through the other region and deflects the light beam that passes through the specific region in a direction different from the radiation light source;
A plurality of light detection means for receiving a light beam passing through the deflected specific region,
An aberration detection apparatus that detects aberration by comparing signals from the plurality of light detection means.   The aberration detection apparatus according to claim 1, wherein the light deflection unit is a hologram that divides and diffracts a light beam into a plurality of parts. The plurality of light detection means comprises a light detector divided into at least two parts,
3. The aberration detection according to claim 1 , wherein when the wavefront aberration is substantially zero, the light beam passing through the specific region is disposed so as to irradiate a dividing line of the two-divided photodetector. apparatus.   3. The specific region is a region at a substantially central portion of one of two regions obtained by dividing a region through which the light beam of the return path passes into a plane including the optical axis of the light beam. The aberration detection apparatus described.   The specific region substantially coincides with one region obtained by dividing a region sandwiched by two concentric circles having different diameters around the optical axis of the light beam in the return path into two by a plane including the optical axis. Item 3. The aberration detection device according to Item 1 or 2.   The aberration detection apparatus according to claim 1, wherein the light deflection unit is a blazed hologram.   The aberration detection device according to claim 2, wherein the plurality of light detection units are arranged in the vicinity of the radiation light source and symmetrically with respect to the radiation light source.   The light deflecting means comprises a hologram that diffracts only predetermined polarized light and a quarter-wave plate, and in the hologram, the forward light beam from the radiation source to the information carrier is not diffracted, and the light of the return path The aberration detection apparatus according to claim 2, wherein the beam is divided into a plurality of parts and diffracts in different directions.

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