JP4171969B2 - Optical regenerator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical reproducing apparatus for an optical recording medium, and more particularly to an optical reproducing apparatus for a super-resolution optical disc.
[0002]
[Prior art]
In recent years, as one of the optical discs that realize high-density optical information recording, super-resolution reproduction is performed by focusing laser light on an optical recording medium that undergoes physical or structural changes due to light irradiation. Optical discs (super-resolution optical discs) have been proposed.
[0003]
The reproduction limit of a mark or pit recorded on a conventional optical disc depends on the wavelength λ of the reproduction light in vacuum and the numerical aperture NA of the objective lens, and consists of a pair of marks (or pits) and a space. The reproduction limit of the pitch can be expressed as λ / (2 × NA). For example, if the length of the mark (or pit) and the length of the space are the same, the length of the reproduction limit of the mark (or pit) is λ / (4 × NA).
[0004]
On the other hand, a super-resolution optical disc can reproduce minute marks or pits exceeding the reproduction limit. For example, in JP-A-6-183152, a phase change material layer such as a BiTe alloy is formed on a disk on which pits are formed, and a liquid crystal region smaller than a focused light spot is formed to perform super-resolution reproduction. Is disclosed.
[0005]
Japanese Laid-Open Patent Publication No. 5-205314 discloses that a lanthanoid material layer is formed on a disk on which pits are formed, and a change in reflectance is caused by a temperature gradient to perform super-resolution reproduction.
[0006]
Further, in JP-A-11-250493, a super-resolution mask layer made of Sb is provided for a phase change recording layer made of GeSbTe, and an SiN intermediate layer of 30 nm is formed between the mask layer and the recording layer. Due to the structure formed in the thickness, in an optical system having a wavelength λ of 488 nm and a numerical aperture NA of 0.6 (reproduction limit mark length 200 nm), a reproduction signal from a recording mark having a mark length of 100 nm or less can be detected. Is disclosed.
[0007]
Furthermore, Kikukawa et al. In JJAP, 40, 3B, and 1624, in a ROM type optical disc in which minute pits are formed, have a structure in which Ge, Si, W, etc. are used as a reflective film, wavelength: 635 nm, NA: 0. 6 shows that a signal having a pit length of 200 nm can be super-resolved and reproduced using the optical system 6 (reproduction limit pit length 270 nm). In these super-resolution optical disks, it is possible to improve the recording density without greatly changing the optical system.
[0008]
[Problems to be solved by the invention]
In super-resolution reproduction, a sequence of marks (or pits) and spaces shorter than the reproduction limit is reproduced, but the spatial frequency of the reproduction signal at this time exceeds the diffraction limit of the optical system. Therefore, it is difficult to efficiently guide the reproduced light from these marks and pits to the light detection device. Therefore, by increasing the power of the laser beam, an opening smaller than the light spot diameter is generated on the recording medium, thereby increasing the modulation degree of the reproduction signal from the mark or pit. However, since the increase in the power of the laser beam leads to an increase in the amount of light incident on the photodetector, white noise in the reproduced signal increases. This increase in white noise decreases the signal to noise ratio (CNR). That is, the super-resolution reproduction described above has a problem that the signal-to-noise ratio tends to decrease for marks or pits shorter than the reproduction limit.
[0009]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to reproduce information with a high signal-to-noise ratio from an optical recording medium including a pit or mark having a length less than the reproduction limit. The object is to provide an optical regenerator.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, an optical reproducing apparatus of the present invention reproduces information on pits or marks of an optical recording medium by detecting reflected light or transmitted light of light irradiated on the optical recording medium. In the apparatus, an end detection means for detecting a signal at an end in the track direction in the reflected or transmitted light beam, and a center detection for detecting a signal in at least a central portion in the track direction in the reflected or transmitted light beam And a reproduction means for generating a subtraction signal between the signal detected by the end detection means and the signal detected by the center detection means, and reproducing the information from the subtraction signal. It is characterized by.
[0011]
According to said structure, an edge part detection means detects the edge part of the track direction in the light beam of reflected light or transmitted light. The end portion of the light beam contains many signals having a spatial frequency corresponding to a length that does not satisfy the reproduction limit of the recording medium. The center detecting means detects a signal at the center portion of the light flux in the track direction. The central portion of the light beam contains many signals having a spatial frequency corresponding to a length exceeding the reproduction limit. Then, the reproducing means generates a subtraction signal by subtracting the signal at the center portion from the signal at the detected end or vice versa. As a result, a space corresponding to a length longer than the reproduction limit can be obtained from a signal including both a spatial frequency signal corresponding to a length longer than the reproduction limit and a spatial frequency signal corresponding to a length less than the reproduction limit. The frequency signal can be reduced. Therefore, in the information recorded on the optical recording medium, it is possible to emphasize and reproduce a signal having a spatial frequency corresponding to a length that does not satisfy the reproduction limit. Moreover, since the common-mode noise included in the two signals is reduced by subtraction, the signal-to-noise ratio in the detected signal can be improved.
[0012]
As a result, it is possible to provide an optical reproducing apparatus capable of reproducing information with a high signal-to-noise ratio from an optical recording medium including a pit or mark having a length less than the reproduction limit.
[0013]
In order to solve the above-described problems, the optical reproducing apparatus of the present invention is characterized in that the end detection means and the center detection means are each constituted by individual photodetectors.
[0014]
According to said structure, the common mode noise in the signal converted into the electrical signal in each photodetector can be reduced easily.
[0015]
In order to solve the above problems, an optical reproducing apparatus of the present invention reproduces information on pits or marks of an optical recording medium by detecting reflected light or transmitted light of light irradiated on the optical recording medium. In the apparatus, a first detection unit that detects a signal having a spatial frequency higher than the reproduction limit of the entire reflected or transmitted light beam, and a second detection unit that detects a signal having a spatial frequency lower than the reproduction limit. And a reproducing means for generating a subtraction signal between the signal detected by the first detection unit and the signal detected by the second detection unit, and reproducing the information from the subtraction signal. Features.
[0016]
According to said structure, a 1st detection part detects the signal of the spatial frequency higher than the reproduction limit in the whole light beam, ie, the signal of the spatial frequency corresponding to the length which is less than a reproduction limit, and a 2nd detection part is A signal having a spatial frequency lower than the reproduction limit, that is, a signal having a spatial frequency corresponding to a length longer than the reproduction limit is detected. Then, the reproducing means generates a subtraction signal by subtracting the other from one of these two signals or vice versa. Accordingly, a signal having a spatial frequency longer than the reproduction limit is subtracted and reproduced. As a result, signals from pits or marks that are less than the reproduction limit are emphasized and reproduced. Moreover, since the common-mode noise included in the two signals is reduced by subtraction, the signal-to-noise ratio in the detected signal can be improved.
[0017]
As a result, it is possible to provide an optical reproducing apparatus capable of reproducing information with a high signal-to-noise ratio from an optical recording medium including a pit or mark having a length less than the reproduction limit.
[0018]
In order to solve the above problems, the optical reproducing apparatus of the present invention is characterized in that the first detection unit includes an end detection unit that detects an end signal in the reflected or transmitted light beam. And
[0019]
According to the above configuration, since the first detection unit detects the signal at the end of the reflected or transmitted light beam by the end detection means, the signal from the pit or mark having a length less than the reproduction limit is further detected. It can be detected in an enhanced manner.
[0020]
In order to solve the above problems, the optical reproducing apparatus of the present invention is characterized in that each of the first detection unit and the second detection unit is composed of an individual photodetector.
[0021]
According to said structure, the common mode noise in the signal converted into the electrical signal in each photodetector can be reduced easily.
[0022]
In order to solve the above problems, the optical reproducing apparatus of the present invention includes the pit or mark having a length equal to or shorter than (the wavelength of the light) / (4 × numerical aperture).
[0023]
According to the above configuration, a signal from a pit or mark having a length less than the reproduction limit can be reliably reproduced, and the recording density can be improved as compared with the conventional case.
[0024]
In order to solve the above-described problems, the optical reproducing apparatus of the present invention includes a super-resolution optical recording including, as the optical recording medium, pits or marks having a length that is less than or equal to the reproduction limit of the entire reflected light or transmitted light. It is characterized by using a medium.
[0025]
According to the above configuration, the signal of the pit or mark having a length less than the reproduction limit included in the reflected light or transmitted light from the super-resolution optical recording medium is further emphasized and reproduced, and the signal-to-noise ratio is increased. Can do.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
One embodiment of the present invention will be described with reference to FIGS. 1 to 3 as follows.
[0027]
As shown in FIG. 2, the optical reproducing apparatus 10 according to the present embodiment includes an optical recording medium driving unit 1, a light irradiation unit 2, a light detecting unit 3, and a signal processing unit (reproducing means) 4. .
[0028]
The optical reproducing apparatus 10 reproduces information recorded on a super-resolution optical disc (optical recording medium, super-resolution optical recording medium) 12 held in the optical recording medium driving unit 1. When reproducing information from the super-resolution optical disk 12, the light irradiation unit 2 irradiates the super-resolution optical disk 12 held by the optical recording medium driving unit 1 with light. Then, the light detection unit 3 detects the reflected light of the light irradiated on the super-resolution optical disc 12 as a signal. Then, the signal processing unit 4 processes (subtracts) the signal detected by the light detection unit 3 to reproduce information recorded on the super-resolution optical disk 12. The configuration is not limited to the reflected light from the super-resolution optical disc 12, but may be configured to detect transmitted light as a signal.
[0029]
Here, each part will be described in more detail.
[0030]
For example, as shown in FIG. 2, the optical recording medium driving unit 1 includes a spindle motor 11 that is a rotation driving unit for the super-resolution optical disk 12. A super-resolution optical disk 12 is held by the spindle motor 11. The spindle motor 11 drives the super-resolution optical disk 12 so as to rotate in a constant direction at a constant linear velocity or a constant rotation speed. In this embodiment, the super-resolution optical disk 12 is rotated so as to have a constant speed of 6 m / s.
[0031]
Examples of the super-resolution optical disk 12 include a disk in which a Ge reflective layer is formed (formed) on a polycarbonate substrate to a thickness of 15 nm. Information corresponding to the lengths of the pits and spaces is recorded on the polycarbonate substrate. These pits and spaces are continuously formed in a certain direction on the super-resolution optical disc 12. This direction is the track direction and is the same as the rotation direction of the super-resolution optical disk 12. That is, this track direction is a reproduction scan direction when reproducing information on the super-resolution optical disk 12. For example, in this embodiment, when the length of the shortest pit is 200 nm and the length of the shortest space is 200 nm, the shortest pitch composed of the pair of pits and spaces is 400 nm. In addition, (1,7) RLL is used as a modulation method, and the longest pit and space are both 800 nm.
[0032]
The light irradiation unit 2 includes a laser diode 21, a collimator lens 22, a polarization beam splitter 23, a quarter wavelength plate 24, and an objective lens 25. This laser diode 21 is a means for irradiating light to the super-resolution optical disk and irradiates laser light having a wavelength λ. The objective lens 25 includes a drive unit 26. The drive unit 26 drives the objective lens 25 in a two-dimensional direction in order to perform focus servo and tracking servo of light irradiated on the super-resolution optical disc 12. The objective lens 25 has a predetermined numerical aperture NA. In the present embodiment, the wavelength (λ) of the laser light emitted from the laser diode 21 is 630 nm, and the numerical aperture (NA) of the objective lens 25 is 0.6. Therefore, the length of the reproduction limit pit or space is about 260 nm, and the length of the reproduction limit pitch is about 530 nm.
[0033]
The light detection unit 3 includes a condenser lens 36 and a split photo detector 37. The condensing lens 36 appropriately condenses the reflected light from the super-resolution optical disc 12 on the split photodetector 37. The divided photodetector 37 detects the light beam of the reflected light that is appropriately condensed as an optical signal as will be described later.
[0034]
The signal processing unit 4 includes a signal processing circuit (reproducing means) 40, processes the optical signal, and reproduces information recorded on the super-resolution optical disc 12.
[0035]
Next, the operation of each unit in the optical reproducing apparatus 10 when reproducing the super-resolution optical disk 12 will be described.
[0036]
First, in the optical recording medium driving unit 1, the super-resolution optical disk 12 is held by the spindle motor 11. The spindle motor 11 rotates the super-resolution optical disk 12 at a constant speed in a certain direction. In the present embodiment, the rotation is performed so that the linear velocity is 6 m / s.
[0037]
The super-resolution optical disc 12 is irradiated with laser light from the light irradiation unit 2. In the light irradiation unit 2, laser light having a wavelength λ is generated from the laser diode 21. This laser light is, for example, linearly polarized divergent light and has a wavelength of λ = 630 nm. This laser light is converted into parallel light by the collimator lens 22. This parallel light passes through the polarization beam splitter 23. At this time, only certain polarized light passes through the polarization beam splitter 23. The light transmitted through the polarizing beam splitter 23 is converted into circularly polarized light by the quarter wavelength plate 24. This circularly polarized light is condensed on the super-resolution optical disk 12 by the objective lens 25 focused by the drive unit 26. The numerical aperture (NA) of the objective lens 25 is 0.6. As a result, the super-resolution optical disc 12 is irradiated with a laser beam having a focused spot diameter of 1050 nm (λ / NA).
[0038]
The laser light irradiated onto the super-resolution optical disk 12 is irradiated onto pits and spaces formed on the super-resolution optical disk 12, and reflected light modulated thereby is used as reproduction light. The reproduction light is collimated by the objective lens 25, passes through the quarter-wave plate 24, and becomes linearly polarized light inclined by 90 ° from the first linearly polarized light. The reproduction light is reflected toward the light detection unit 3 by the polarization beam splitter 23.
[0039]
In the light detection unit 3, the light beam of the reproduction light is appropriately condensed by the condenser lens 36 so as to enter the detection unit of the split photodetector 37. The split photo detector 37 is disposed near the pupil plane of the light beam. In other words, the split photodetector 37 is arranged at a position where a spectrum with respect to the spatial frequency after Fourier transform of a signal composed of pits and spaces on the super-resolution optical disk 12 appears in the cross section of the light beam. Note that it is not necessary to be strictly a pupil plane, and the split photodetector 37 may be arranged on a cross section that is spectrally resolved to such an extent that super-resolution reproduction is possible. Further, since a spectrum cannot be obtained at a strict focal position, the split photodetector 37 is not placed at the focal point. At the position where the spectrum appears in the cross section of the light beam, the split photodetector 37 detects the reproduction signal from the reproduction light. This reproduction signal is processed by the signal processing unit 4 to reproduce the information on the super-resolution optical disk 12.
[0040]
Here, the operations of the divided photodetector 37 and the signal processing circuit (reproducing means) 40 of the signal processing unit 4 will be described with reference to FIG.
[0041]
As shown in FIG. 1, the split light detector 37 collects the reproduction light as a detection beam h (light beam) (a region surrounded by a chain line shown in FIG. 1). In the divided photodetector 37, the detection beam h is detected as an optical signal.
[0042]
In the present embodiment, the divided photo detector 37 includes a first end photo detector (end detection means or first detection unit) 45, a central partial photo detector (center detection means or second detection unit) 46, a second end. It is divided into three individual photo detectors, ie, partial photo detectors (end detection means or first detection unit) 47. Each of the photodetectors 45 to 47 is arranged with respect to the track direction in the detection beam h. That is, the first end photo detector 45 and the second end photo detector 47 are reflected at the end in the track direction in the reflected light beam (reproduced light) that has been reflected from the super-resolution optical disc 12 and has reached the vicinity of the pupil plane. An optical signal is detected, and the detection result is converted into an electric signal and output as an optical detection signal a · c. In addition, the central photo detector 46 detects the optical signal of the central portion in the track direction in the reflected light beam reflected from the super-resolution optical disc 12 and reaching the vicinity of the pupil plane, and converts the detection result into an electric signal to convert the optical signal. Output as detection signal b. Thereby, the spectrum decomposed | disassembled on the cross section of the light beam is detectable as a signal. In other words, the signals detected by the first end photo detector 45 and the second end photo detector 47 contain a lot of signals from pits (or marks) and spaces having a length corresponding to a length less than the reproduction limit. The signal detected by the central photodetector 46 includes many signals from pits (or marks) having a spatial frequency corresponding to a length longer than the reproduction limit and spaces.
[0043]
The width dimension along the track direction of the central portion photodetector 46 is preferably 50% to 95% with respect to the diameter of the detection beam h. Further, the width dimension along the track direction of the first end photo detector 45 and the second end photo detector 47 is such that the remaining part of the detection beam h detected by the center photo detector 46 can be detected. I just need it. For example, when the width dimension of the center portion photodetector 46 is 50% with respect to the diameter of the detection beam h, the width dimension of the first end photo detector 45 and the second end photo detector 47 is at least the detection beam, respectively. It may be 25% of the diameter of h. In the case where the width dimension of the central portion photodetector 46 is 95%, the width dimension of the first end photo detector 45 and the second end photo detector 47 may be at least 2.5%.
[0044]
The photodetection signal a output from the first end photodetector 45, the photodetection signal b output from the central portion photodetector 46, and the photodetection signal c output from the second end photodetector 47 are sent to the signal processing unit 4. The signal is input and processed (subtracted) by the signal processing circuit 40 of the signal processing unit 4. As a result, an optical reproduction signal g (subtraction signal) that is information of the super-resolution optical disk 12 is generated. Thereby, information on the super-resolution optical disk 12 is reproduced.
[0045]
The generation of the optical reproduction signal g will be described in detail as follows.
[0046]
The light detection signals a, b, and c are input to the signal processing circuit 40 as shown in FIG. The amount of signal of the light detection signal b is adjusted by the volume 43 and becomes an output f. This output f is a signal obtained only by changing the amplitude of the light detection signal b, and is also a detection result by the central portion photodetector 46. Such a process can be similarly applied to the light detection signals a and c. On the other hand, the photodetection signals a and c are input to the addition amplifier 42 and added. As a result, an addition output e is generated. The output f and the addition output e are input to the subtraction amplifier 44. The subtraction amplifier 44 performs a process of subtracting the output f from the addition output e, thereby generating a reproduction signal g. Each of the light detection signals a, b, and c may be input to a summing amplifier (not shown), and b immediately before the output f in FIG. Further, the subtracting amplifier 44 subtracts a signal obtained by adding the light detection signals a, b, and c from the addition output e when the width ratio of the central portion photodetector 46 is large, and when it is small. Is good. Alternatively, the optical reproduction signal g may be obtained by performing a process of subtracting the addition output e from the output f.
[0047]
Here, each signal waveform when reproducing the super-resolution optical disk 12 using the optical reproducing apparatus 10 will be described more specifically based on FIG. In reproduction at this time, processing is performed by the signal processing circuit 40 shown in FIG.
[0048]
3A shows pits continuously formed on the super-resolution optical disk 12 (ROM type). Here, an example of a mark row constituted by 200 nm and 400 nm marks and spaces having a length of 200 nm and 1000 nm will be described. The material of the reflective film of the super-resolution optical disk 12 is germanium or silicon, and the film thickness is 15 nm. The amount of laser light applied to the super-resolution optical disc 12 is 1.5 mW to 2.0 mW. B shows the waveform of the photodetection signal b output from the central portion photodetector 46. C indicates the waveform of the addition signal e output from the addition amplifier 42. D is a signal when the light detection signals a, b, and c are added, in other words, a signal when the photodetector 37 is not divided. E indicates the waveform of the optical reproduction signal g output from the addition amplifier 44. The optical reproduction signal g shows a waveform obtained by subtracting the light detection signal b (B waveform) whose signal amount is adjusted from the addition signal e (C waveform).
[0049]
From the signal waveform indicated by D, from the signal obtained by integrating all of the reproduction light detected by the divided photodetector 37 (all areas of the detection beam h shown in FIG. 1), spatial frequencies of 150 nm and 250 nm which are less than the reproduction limit. It can be seen that almost no pits (pits shorter than the reproduction limit) are detected. That is, even with a super-resolution optical disc, the conventional detection method can easily detect an optical signal (low frequency component) from a pit that is longer than the reproduction limit, but an optical signal from a pit that is less than the reproduction limit ( It can be seen that the high frequency component) is difficult to detect. This is because an optical signal from a pit shorter than the reproduction limit is small and buried in a large optical signal from a pit exceeding the reproduction limit. A pit above the reproduction limit represents a pit corresponding to a spatial frequency having a length longer than the reproduction limit, and a pit shorter than the reproduction limit represents a pit corresponding to a spatial frequency having a length less than the reproduction limit.
[0050]
On the other hand, when looking at the waveform of the addition signal e shown in C, from the luminous flux at the end in the track direction (the region on the first end photo detector 45 and the second photo detector 46 in the detection beam h shown in FIG. 1), It can be seen that an optical signal from a pit at 200 nm (a pit shorter than the reproduction limit) having a spatial frequency less than the reproduction limit is detected. That is, it can be seen that a high frequency component can be detected from the light flux at the end of the reproduction light with respect to the track direction, and pits shorter than the reproduction limit can be resolved and detected. By detecting the signal at the end of the light beam in this way, the signal from the pit (or mark) having a length less than the reproduction limit can be particularly enhanced and detected.
[0051]
An optical signal (high frequency component) having a high spatial frequency is considered to easily pass through the end of the light beam. Therefore, the end photo detectors 45 and 47 can detect an optical signal having a high spatial frequency more clearly. The summing amplifier 42 can emphasize the optical signal with a high spatial frequency detected by the end photo detectors 45 and 47. Therefore, as shown in FIG. 3C, the summing amplifier 42 can emphasize and output an optical signal from a short pit that is less than the reproduction limit, which is an optical signal having a high spatial frequency.
[0052]
Further, the light from which the light detection signal b (B in FIG. 3), which detects the reproduction signal having the spatial frequency corresponding to the length longer than the reproduction limit, is detected. By subtracting from the signal e (C in FIG. 3), the optical signal from a short pit that is relatively less than the reproduction limit can be increased. When subtracting, the light detection signal b is adjusted by the volume 43 in FIG. As a result, the reproduction signal from a short pit that does not reach the reproduction limit can be enhanced, and the signal-to-noise ratio can be improved by canceling the common-mode noise by the subtraction process. That is, information can be more reliably reproduced as compared with a conventional reproduction signal waveform (D in FIG. 3) that does not perform subtraction processing. In particular, this effect is remarkable in the reproduction of the super-resolution optical disk 12. Here, since the optical signal is detected using the individual photodetector as described above, two signals (addition output e and output f) to be subtracted can be easily generated.
[0053]
As described above, according to the optical reproducing apparatus 1, information can be reproduced with a high signal-to-noise ratio from the super-resolution optical disk 12 including pits or marks having a length less than the reproduction limit.
[0054]
[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIGS. For convenience of explanation, members having the same functions as those shown in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The optical regenerator 20 (FIG. 2) according to the present embodiment differs in the configuration of the split photodetector 37 and the signal processing circuit 40 of the optical regenerator 10 in the first embodiment. That is, in this embodiment, a divided photo detector 37a is provided instead of the divided photo detector 37, and a signal processing circuit (reproducing means) 40a is provided instead of the signal processing circuit 40.
[0055]
In the present embodiment, the divided photo detector (light detecting means) 37a includes end photo detectors (end detecting means, first detecting units) 51, 54, 55, 58, center partial photo detectors (center detecting means, second detecting units). ) 52, 53, 56 and 57, which are divided into 8 individual photodetectors. Each of the photodetectors 51 to 54 and each of the photodetectors 55 to 58 are aligned with respect to the track direction in the detection beam h, as in the first embodiment. Further, in the region including the central portion photodetectors 52, 53, 56, and 57, the width dimension along the track direction in the detection beam h is smaller than the diameter of the detection beam h as in the central portion photodetector 46 in the first embodiment. The ratio is preferably 50 to 95%. In addition, the reproduction limit (λ / (2 × NA)), the amount of light applied, and the like are the same as in the first embodiment.
[0056]
The end photo detectors 51, 54, 55, and 58 detect the optical signal at the end in the track direction in the reflected light (reproduced light) beam that has been reflected from the super-resolution optical disc 12 and has reached the vicinity of the pupil plane. The detection results are converted into electrical signals and output as light detection signals S1, S4, S5, and S8. The central portion photodetectors 52, 53, 56, and 57 detect the optical signal at the central portion in the track direction in the reflected light beam reflected from the super-resolution optical disc 12 and reaching the vicinity of the pupil plane, and the detection result is electrically detected. It converts into a signal and outputs it as photodetection signal S2, S3, S6, S7. Thereby, the spectrum decomposed | disassembled on the cross section of the light beam is detectable as a signal. That is, the signals detected by the end photo detectors 51, 54, 55, and 58 include a large number of signals from pits (or marks) and spaces having a length corresponding to a length less than the reproduction limit. The signals detected by the partial photodetectors 52, 53, 56, and 57 contain a large number of signals from pits (or marks) and spaces corresponding to lengths exceeding the reproduction limit.
[0057]
Each of the light detection signals S1 to S8 is input to the signal processing unit 4 and processed by the signal processing circuit 40a of the signal processing unit 4. As a result, the optical reproduction signal w, the focus error signal t for condensing the light beam on the super-resolution optical disc 12, and the track error signal u for causing the optical beam to follow the track of the super-resolution optical disc 12 are simultaneously generated. can do.
[0058]
Here, generation of the optical reproduction signal w, the focus error signal t, and the track error signal u from each of the light detection signals S1 to S8 input to the signal processing circuit 40a will be described.
[0059]
First, the generation of the optical reproduction signal w will be described.
The photodetection signals S1, S4, S5, and S8 output from the end photo detectors 51, 54, 55, and 58 are added by the addition amplifier 60, and an addition output l is generated. On the other hand, the respective photodetection signals S2, S3, S6, and S7 detected by the respective central part photodetectors 52, 53, 56, and 57 are added by the adding amplifier 61, and an added output m is generated.
[0060]
These addition outputs l · m are added by the addition amplifier 66 to generate an addition output n. Then, the amount of signal of the added output n is adjusted by the volume 70 to become an output v.
[0061]
Subtraction processing is performed on the output v and the addition output l in a form in which the output v is subtracted from the addition output l by the subtraction amplifier 67 to generate an optical reproduction signal (subtraction signal) w. The added output l is a detection signal at the end of the light beam, and the output v is a detection signal at a portion including at least the central portion of the light beam. As a result, a space corresponding to a length longer than the reproduction limit can be obtained from a signal including both a spatial frequency signal corresponding to a length longer than the reproduction limit and a spatial frequency signal corresponding to a length less than the reproduction limit. The frequency signal can be subtracted, and the subtraction result is the optical reproduction signal w. The optical reproduction signal w may be obtained by performing a process of subtracting the addition output l from the output v.
[0062]
Therefore, in the information recorded on the super-resolution optical disc 12, a signal from a short pit (high spatial frequency) less than the reproduction limit can be emphasized and detected and reproduced. By detecting the signal at the end of the light beam in this way, the signal from the pit (or mark) having a length less than the reproduction limit can be particularly enhanced and detected. Moreover, since the common-mode noise included in the two signals is reduced by subtraction, the signal-to-noise ratio in the detected signal can be improved. Here, since the optical signal is detected using the individual photodetector as described above, it is possible to easily generate two signals (addition output l and output v) to be subtracted.
[0063]
As a result, according to the optical reproducing device 20, information can be reproduced with a high signal-to-noise ratio from the super-resolution optical disc 12 including pits or marks having a length less than the reproduction limit.
[0064]
Next, generation of the focus error signal t will be described.
[0065]
The photodetection signals S1, S2, S5, and S6 output from the photodetectors 51, 52, 55, and 56 are added by the addition amplifier 62 to generate an addition output o. On the other hand, the photodetection signals S3, S4, S7, and S8 output from the photodetectors 53, 54, 57, and 58 are added by the addition amplifier 63 to generate an addition output p.
[0066]
The addition output o and the addition output p are input to the subtraction amplifier 68. By subtracting the addition output p from the addition output o by the subtraction amplifier 68, a focus error signal t of the astigmatism method is generated.
[0067]
Next, generation of the track error signal u will be described.
[0068]
The photodetection signals S1, S2, S3, and S4 output from the photodetectors 51, 52, 53, and 54 are added by the addition amplifier 64 to generate an addition output q. On the other hand, the photodetection signals S5, S6, S7, and S8 output from the photo detectors 55, 56, 57, and 58 are added by the addition amplifier 65 to generate an addition output r.
[0069]
The addition output q and the addition output r are input to the subtraction amplifier 69. The subtraction amplifier 69 subtracts the addition output r from the addition output q, thereby generating a push-pull tracking error signal u.
[0070]
As described above, in this embodiment, signal detection from a short pit that does not reach the reproduction limit and servo signal detection can be performed simultaneously.
[0071]
The first and second embodiments have been described above.
[0072]
Note that the optical regenerator of the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof. In particular, the super-resolution optical disc is not limited to the ROM type, and can be applied to other write-once or rewritable media. In the ROM type, information is recorded by continuation of pits and spaces, whereas in the write-once type or rewritable type, information is recorded by continuation of marks and spaces. Further, the detailed configuration of the light source unit and the optical system for detecting the reproduction light is arbitrary. The shape of the divided photodetector is not limited to a belt shape, and can be variously changed within the scope of the gist.
[0073]
In the optical reproducing apparatus according to the present invention, when the wavelength of the reproducing light is λ and the numerical aperture of the objective lens is NA, a mark (or pit) having a length of λ / (4 × NA) or less, a space, In a device for reproducing information from an optical recording medium including a high spatial frequency (length less than the reproduction limit) existing at the end of a light beam in an optical path of an optical system for detecting light from the optical recording medium It is expressed that a reproduction means for reproducing a signal is obtained by subtracting a signal component having a low spatial frequency (length longer than the reproduction limit) existing in the central portion of the light beam from the signal component (or vice versa). be able to.
[0074]
Furthermore, the optical reproducing apparatus according to the present invention performs first detection for reproducing an optical signal (a component having a high spatial frequency) from a mark (or pit) and a space shorter than approximately λ / (4 × NA). A second detection system for reproducing an optical signal (component having a low spatial frequency) from a system, a mark (or pit) longer than approximately λ / (4 × NA) and a space, and the first detection And a signal processing circuit that reproduces information by subtracting the signal detected by the second detection system from the signal detected by the system (or vice versa). It is preferable that the first detection system reproduces an end portion of the light beam, and the second detection system includes reproduction means for reproducing a central portion of the light beam.
[0075]
According to these, a signal from a pit or mark with a length less than the reproduction limit (wavelength of light) / (4 × numerical aperture) or less is reliably reproduced, and the recording density is improved as compared with the conventional case. be able to.
[0076]
By the way, the super-resolution phenomenon occurs due to the arrangement of detailed marks (or pits) and spaces. The spatial frequency of the reproduced signal exceeds the diffraction limit of the optical system. By increasing the power of the reproduction light, the degree of modulation of the reproduction signal increases, but the common-mode noise also increases as the amount of incident light increases. In order to improve the signal-to-noise ratio, it is important to suppress an increase in common-mode noise while increasing the modulation degree.
[0077]
Therefore, in the optical reproducing apparatus and optical reproducing method according to the present invention, since at least the central portion of the light beam of the reproduced light is subtracted, the common-mode noise is further enhanced while enhancing the signal having a length less than the reproduction limit. And the signal-to-noise ratio of the reproduced signal is increased.
[0078]
In a super-resolution optical disk, it is considered that an optical signal from a mark or pit having a high spatial frequency detected by the super-resolution effect is likely to pass toward the end of the pupil of the detection optical system. Therefore, in order to detect an optical signal from a mark or pit with a high spatial frequency, subtracting a light detection signal that detects a light beam that passes through the center of the pupil from a signal that detects only the light beam that passes through the edge of the pupil, Alternatively, by providing such an optical system, it is possible to emphasize and reproduce signals below the reproduction limit of the entire light beam. Then, signals from marks or pits having a length smaller than the reproduction limit and having a plurality of lengths can be reproduced. In particular, as in the first and second embodiments, when reproducing light is detected using a divided detector for reproduction of a super-resolution optical disc, a signal having a length less than the reproduction limit is enhanced at the same time. The effect of removing common mode noise is great.
[0079]
【The invention's effect】
As described above, the optical reproducing apparatus of the present invention includes an end detection means for detecting a signal at an end in the track direction in the reflected or transmitted light beam, and the track direction in the reflected or transmitted light beam. Generates a subtraction signal between the signal detected by the center detection means for detecting at least the center portion signal, the signal detected by the edge detection means and the signal detected by the center detection means, and reproduces the information from the subtraction signal And a reproducing means.
[0080]
Therefore, the space corresponding to the length exceeding the reproduction limit from the signal including both the spatial frequency signal corresponding to the length exceeding the reproduction limit and the spatial frequency signal corresponding to the length less than the reproduction limit. The frequency signal can be reduced. Therefore, in the information recorded on the optical recording medium, it is possible to emphasize and reproduce a signal having a spatial frequency corresponding to a length that does not satisfy the reproduction limit. Moreover, since the common-mode noise included in the two signals is reduced by subtraction, the signal-to-noise ratio in the detected signal can be improved.
[0081]
As a result, it is possible to provide an optical reproducing apparatus capable of reproducing information with a high signal-to-noise ratio from an optical recording medium including a pit or mark having a length less than the reproduction limit.
[0082]
As described above, the optical reproducing apparatus of the present invention has a configuration in which each of the end detection means and the center detection means is composed of individual photodetectors.
[0083]
Therefore, there is an effect that the two signals to be subtracted can be easily generated.
[0084]
As described above, the optical reproducing apparatus of the present invention reproduces information of pits or marks of an optical recording medium by detecting reflected light or transmitted light of light irradiated on the optical recording medium. A first detector for detecting a signal having a spatial frequency higher than the reproduction limit of the entire reflected or transmitted light beam; a second detector for detecting a signal having a spatial frequency lower than the reproduction limit; And a reproducing unit that generates a subtraction signal between the signal detected by the first detection unit and the signal detected by the second detection unit, and reproduces the information from the subtraction signal.
[0085]
Therefore, a spatial frequency signal longer than the reproduction limit is subtracted and reproduced. As a result, signals from pits or marks that are less than the reproduction limit are emphasized and reproduced. Moreover, since the common-mode noise included in the two signals is reduced by subtraction, the signal-to-noise ratio in the detected signal can be improved.
[0086]
As a result, it is possible to provide an optical reproducing apparatus capable of reproducing information with a high signal-to-noise ratio from an optical recording medium including a pit or mark having a length less than the reproduction limit.
[0087]
As described above, the optical reproducing apparatus of the present invention has a configuration in which the first detection unit includes an end detection unit that detects an end signal in the light flux of the reflected light or transmitted light.
[0088]
Therefore, there is an effect that a signal from a pit or mark having a length less than the reproduction limit can be further enhanced and detected.
[0089]
As described above, the optical reproducing apparatus of the present invention has a configuration in which the first detection unit and the second detection unit are configured by individual photodetectors.
[0090]
Therefore, there is an effect that the two signals to be subtracted can be easily generated.
[0091]
As described above, the optical reproducing apparatus of the present invention is configured to include the pit or mark whose length is equal to or less than (the wavelength of the light) / (4 × numerical aperture).
[0092]
Therefore, it is possible to reliably reproduce a signal from a pit or mark having a length less than the reproduction limit and improve the recording density as compared with the conventional case.
[0093]
As described above, the optical reproducing apparatus of the present invention uses, as the optical recording medium, a super-resolution optical recording medium including pits or marks having a length that is less than the reproduction limit of the entire reflected light or transmitted light. It is the structure to do.
[0094]
Therefore, it is possible to increase the signal-to-noise ratio by further enhancing and reproducing the pit or mark signal having a length less than the reproduction limit included in the reflected light or transmitted light from the super-resolution optical recording medium. Play.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a configuration of a divided photodetector and a signal processing circuit used in an optical reproducing apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing a configuration of an optical regenerator according to an embodiment of the present invention.
FIG. 3 is a detection waveform diagram showing a waveform type of a reproduction signal detected by the optical reproduction device corresponding to the length of a recording pit in the super-resolution optical disc used in the optical reproduction device of FIG. 2;
FIG. 4 is a circuit block diagram showing a configuration of a split photodetector and a signal processing circuit used in an optical reproducing apparatus according to another embodiment of the present invention.
[Explanation of symbols]
10 Optical regenerator
12 Super-resolution optical disk (optical recording medium)
20 Optical regenerator
40 Signal processing circuit (reproducing means)
40a Signal processing circuit (reproducing means)
45 First end photo detector (end detection means, first detection unit, photo detector)
46 Center part photo detector (center detecting means, second detecting unit, photo detector)
47 Second end photo detector (end detection means, first detection unit, photo detector)
51, 54, 55, 58
End photo detector (end detection means, first detection unit, photo detector)
52, 53, 56, 57
Center part photo detector (center detection means, second detection unit, photo detector)
g Optical regeneration signal (subtraction signal)
w Optical regeneration signal (subtraction signal)
h Detection beam (light flux)

Claims (6)

In an optical reproducing apparatus for reproducing information of pits or marks of an optical recording medium by detecting reflected light or transmitted light of light irradiated on the optical recording medium,
End detection means for detecting a signal at an end in the track direction in the light flux of the reflected light or transmitted light;
Center detecting means for detecting a signal of at least the central portion of the reflected light or transmitted light in the track direction;
A reproduction unit that generates a subtraction signal between the signal detected by the end detection unit and the signal detected by the center detection unit, and reproduces the information from the subtraction signal ;
An optical reproducing apparatus comprising a super-resolution optical recording medium including pits or marks having a length less than or equal to a reproduction limit of the whole reflected light or transmitted light as the optical recording medium .   2. The optical reproducing apparatus according to claim 1, wherein each of the end detection unit and the center detection unit includes individual photodetectors. In an optical reproducing apparatus for reproducing information of pits or marks of an optical recording medium by detecting reflected light or transmitted light of light irradiated on the optical recording medium,
A first detector that detects a signal having a spatial frequency higher than a reproduction limit of the entire reflected light or transmitted light;
A second detector for detecting a signal having a spatial frequency lower than the reproduction limit;
Reproduction means for generating a subtraction signal between the signal detected by the first detection unit and the signal detected by the second detection unit, and reproducing the information from the subtraction signal ;
An optical reproducing apparatus comprising a super-resolution optical recording medium including pits or marks having a length less than or equal to a reproduction limit of the whole reflected light or transmitted light as the optical recording medium .   4. The optical reproducing apparatus according to claim 3, wherein the first detection unit includes end detection means for detecting a signal at an end of the reflected light or transmitted light.   5. The optical reproducing apparatus according to claim 3, wherein each of the first detection unit and the second detection unit includes individual photodetectors. 6.   6. The optical reproducing apparatus according to claim 1, wherein the pit or mark has a length not greater than (wavelength of the light) / (4 × numerical aperture).

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