JP4024559B2 - Optical reproducing apparatus and optical reproducing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an optical reproducing method and an optical reproducing apparatus for reproducing an optical recording medium, and more particularly to an optical reproducing method and an optical reproducing apparatus for a super-resolution optical disc.
[0002]
[Prior art]
  In recent years, recording density has been increasing in the field of optical recording. Accordingly, there has been proposed an optical disc (super-resolution optical disc) capable of super-resolution reproduction with improved recording density using a recording medium that undergoes some structural change by condensing light.
[0003]
  The mark or pit pitch, which is the reproduction limit of a normal optical disk, is determined by the wavelength λ of the light for reproduction and the numerical aperture NA of the objective lens, and the reproduction limit is λ / 2NA. On the other hand, a super-resolution optical disc can reproduce minute marks or pits exceeding the reproduction limit.
[0004]
  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 partial liquid phase state is formed at a condensing point 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, Japanese Patent Laid-Open No. 2001-250274 describes an optical system (wavelength: 635 nm, NA: 0.6) in a ROM type optical disc in which minute pits are formed with a structure using Ge, Si, W, etc. as a reflective film ( This shows that a signal having a pit length of 200 nm can be super-resolution reproduced using a reproduction limit pit length of 270 nm. The above-described super-resolution optical disk can improve the recording density without greatly changing the optical system.
[0008]
[Problems to be solved by the invention]
  Super-resolution reproduction is achieved by reproducing a fine mark or pit arrangement. The spatial frequency of the signal reproduced at this time exceeds the diffraction limit of the optical system. For this reason, it is difficult to detect the reproduction light from fine marks and pits. Therefore, the degree of modulation of the reproduction signal can be increased by increasing the power of the reproduction light. However, since the incident light quantity increases, white noise increases. As the white noise increases, the signal-to-noise ratio (CNR) decreases. That is, in the super-resolution reproduction described above, it can be pointed out as a problem that the signal-to-noise ratio is low for a minute mark or pit.
[0009]
  Furthermore, in a ROM-type super-resolution optical disk with a reflective film such as Ge, Kikukawa et al. Lost part of the signal when a pit with a length shorter than the playback limit was sandwiched between pits longer than the playback limit. The problem of doing is found. (JJAP, 40, 2001, 1624)
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 minute pits or marks having a length less than the reproduction limit. It is to provide an optical regeneration method and an optical regeneration device that can perform.
[0010]
[Means for Solving the Problems]
  BookIn order to solve the above-described problems, an optical reproducing apparatus of the invention uses reflected light or transmitted light of light irradiated on the optical recording medium as information from pits or marks formed in the track direction of the optical recording medium. In an optical reproducing apparatus that reproduces by detecting, a first detection unit that detects a signal from a pit or mark that is longer than the reproduction limit in the reflected light or transmitted light, and shorter than the reproduction limit in the reflected light or transmitted light A second detector for detecting a signal from a pit or mark, and a reproducing means for reproducing information by combining the signal detected by the first detector and the signal detected by the second detector. It is characterized by having.
[0011]
  According to the above configuration, a signal from a pit or mark having a length longer than the reproduction limit and a signal from a pit or mark having a length less than the reproduction limit are combined and reproduced. Thereby, a signal from a pit or mark having a length less than the reproduction limit is emphasized and reproduced. That is, the information recorded on the optical recording medium can be reproduced while avoiding omission.
[0012]
  In addition to the above configuration, the optical reproducing apparatus of the present invention is characterized in that the second detection unit includes detection means for detecting an end portion of a light beam of reflected light or transmitted light.
[0013]
  According to the above configuration, since the end of the light beam of the reflected light or transmitted light is detected, a signal from a pit or mark having a length less than the reproduction limit can be detected more reliably.
[0014]
  In order to solve the above problems, the optical reproducing method of the present invention detects the reflected light or transmitted light of the light irradiated to the optical recording medium, thereby forming pits or marks formed in the track direction of the optical recording medium. In the light reproduction method for reproducing information according to the above, a first signal from a pit or mark having a length longer than the reproduction limit is detected from the reflected or transmitted light beam, and reproduced from the reflected or transmitted light beam. Information on an optical recording medium is reproduced by detecting a second signal from a pit or mark having a length less than the limit and combining the first signal and the second signal.
[0015]
  According to the above configuration, an optical signal from a pit or mark having a length longer than the reproduction limit and an optical signal from a pit or mark having a length less than the reproduction limit are combined and reproduced. Thereby, an optical signal from a pit or mark having a length less than the reproduction limit is emphasized and reproduced. That is, the information recorded on the optical recording medium can be reproduced while avoiding omission.
[0016]
  In addition to the above configuration, the optical reproduction method of the present invention is characterized in that the second signal is a signal obtained by removing at least a central portion of the light beam and detecting an end portion of the light beam.
[0017]
  According to the above configuration, since the end of the reflected or transmitted light beam is detected, a signal from a pit or mark having a length less than the reproduction limit can be detected more reliably.
[0018]
  In addition to the above configuration, the optical reproduction method of the present invention is characterized in that a servo signal is generated by combining the first signal and the second signal.
[0019]
  According to said structure, a servo signal can be easily produced | generated by synthesize | combining a 1st signal and a 2nd signal. Thereby, more stable optical reproduction can be performed.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
  [Embodiment 1]
  An embodiment of the present invention will be described with reference to FIGS. 1 to 3. As shown in FIG. 2, the optical regenerator according to the present embodiment (the present optical regenerator) is as follows. The optical recording medium driving unit 1, the light irradiation unit 2, the light detection unit 3, and a signal processing unit (reproducing means) 4 are included.
[0021]
  This optical reproducing apparatus reproduces information recorded on a super-resolution optical disc (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. The signal processing unit 4 processes (synthesizes) the signal detected by the light detection unit 3 to reproduce information recorded on the super-resolution optical disc 12.
[0022]
  Here, each part will be described in more detail. In the following, the case of detecting reflected light will be described. However, not only the reflected light but also transmitted light of the light irradiated on the super-resolution optical disc 12 may be detected as a signal.
[0023]
  The optical recording medium driving unit 1 includes a spindle motor (driving means) 11 as shown in FIG. The spindle motor 11 holds a super-resolution optical disk 12. The spindle motor 11 drives the super-resolution optical disk 12 so as to rotate in a constant direction at a predetermined speed.
[0024]
  Examples of the super-resolution optical disk 12 include a disk in which a Ge reflective layer is formed (film-formed) to a thickness of 15 nm on a polycarbonate substrate. A pitch composed of a pair of pits and spaces is formed on the polycarbonate substrate. This pitch is formed in a fixed direction in the super-resolution optical disk 12. This direction is the track direction. This track direction is the same as the rotation direction of the super-resolution optical disk 12. That is, this track direction is the same as the reproduction scan direction when information on the super-resolution optical disk 12 is reproduced. For example, the shortest pit length (pit length) is 290 nm and the shortest pitch is 580 nm.
[0025]
  The light irradiation unit 2 includes a laser diode (light irradiation means) 21, a collimator lens 22, a polarization beam splitter 23, a ¼ wavelength plate 24, and an objective lens 25. The laser diode 21 emits laser light having a wavelength λ. The objective lens 25 includes a drive unit 26. This drive unit 26 adjusts the focus of the light irradiated to the super-resolution optical disk 12. The objective lens 25 has a numerical aperture NA. In the present embodiment, for example, the wavelength λ is 680 nm and the numerical aperture NA is 0.55. In this case, the reproduction limit (λ / 2NA) is about 620 nm. The wavelength λ and the numerical aperture NA are appropriately changed according to the laser diode, objective lens, etc. used, and are not particularly limited.
[0026]
  The light detection unit 3 includes a condenser lens 36 and a divided photo detector (detection means) 37. The condensing lens 36 condenses the reflected light from the super-resolution disk 12 on the split photodetector 37. The split photodetector 37 detects the collected reflected light as an optical signal.
[0027]
  The signal processing unit 4 includes a signal processing circuit (reproducing means) 40, and processes the optical signal to reproduce information recorded on the super-resolution optical disc 12.
[0028]
  Next, the operation of each unit in the optical reproducing apparatus (the optical reproducing method) when reproducing the super-resolution optical disk 12 will be described.
[0029]
  First, in the optical 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 predetermined speed in a certain direction.
[0030]
  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 = 680 nm. This laser light is converted into parallel light by the collimator lens 22. This parallel light is incident on the polarization beam splitter 23. At this time, only predetermined 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. As a result, the super-resolution optical disc 12 is irradiated with laser light.
[0031]
  The laser light irradiated on the super-resolution optical disk 12 is reflected on the super-resolution optical disk 12. This reflected laser light is used as reproduction light. Further, when the laser light irradiated on the super-resolution optical disk 12 is irradiated on the pits formed on the super-resolution optical disk 12, the laser light is modulated by the pits.
[0032]
  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 linearly polarized light at the time of irradiation. Therefore, the reproduction light is reflected toward the light detection unit 3 by the polarization beam splitter 23.
[0033]
  In the light detection unit 3, the reproduction light is condensed on the divided photodetector 37 by the condenser lens 36. The split photo detector 37 is disposed so as to receive light in a defocused state. In the divided photodetector 37, the reproduction light is detected as an optical signal. This optical signal is processed in the signal processing unit 4 and information on the super-resolution optical disk 12 is reproduced.
[0034]
  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.
[0035]
  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.
[0036]
  In the present embodiment, the divided photo detector 37 includes a first end photo detector (detection means, first detection portion) 45, a central partial photo detector (center detection means, second detection portion) 46, and a second end photo detector (detection). The first detection unit 47 is divided into three parts. 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 detect reflected light (reproduced light) from both ends in the track direction in the light irradiated on the super-resolution optical disc 12. Further, the central photo detector 46 detects reflected light (reproduction light) at the central portion in the track direction in the light irradiated on the super-resolution optical disc 12.
[0037]
  Further, the width dimension of the central portion photodetector 46 in the track direction may be a ratio of 1/2 to 49/50 with respect to the diameter of the detection beam h, and preferably a ratio of 19/20. The center portion photodetector 46 detects the center portion of the detection beam h. Therefore, in other words, the central portion is a portion having a ratio of 1/2 to 49/50 with respect to the diameter of the detection beam h, and is preferably a portion having a ratio of 19/20.
[0038]
  Further, the width dimension of the end photo detectors 45 and 47 in the track direction is not particularly limited. However, according to the detection range of the central portion photo detector 46, the width dimension of the detection beam h is 1 /. The detection beams at a ratio of 100 to 1/4 are detected by the end photo detectors 45 and 47, respectively. Therefore, in other words, the end photo detectors 45 and 47 need only have a size capable of detecting a detection beam other than that detected by the central portion photo detector 46.
[0039]
  Also, the so-called reproduction limit (λ / 2NA) in the present optical reproducing apparatus is a 620 nm pitch. The power of the reproduction light is 3 mW, for example.
[0040]
  The first end photo detector 45 detects the optical signal a. In the central photo detector 46, the optical signal b is detected. The second end photo detector 47 detects the optical signal c. The optical signals a, b, and c are input to the signal processing unit 4 and processed (combined) by the signal processing circuit 40 of the signal processing unit 4. Thereby, the optical reproduction signal g (information of the super-resolution optical disk 12) is generated. Thereby, information on the super-resolution optical disk 12 is reproduced.
[0041]
  The generation of the optical reproduction signal g will be described in detail as follows.
[0042]
  Each of the optical signals a, b, and c is input to the signal processing circuit 40 as shown in FIG. The optical signals a, b, and c are input to the addition amplifier 41 and added. Thereby, the addition output d is generated. The added output d is adjusted in volume by the volume 43 and becomes an output f. On the other hand, the optical signals a and c are input to the addition amplifier 42 and added. As a result, an addition output e is generated. Then, the output f and the addition output e are input to the addition amplifier 44 and added by the addition amplifier 44 to generate a reproduction signal g.
[0043]
  Here, the case of reproducing the super-resolution optical disk 12 using the present optical reproducing apparatus will be described more specifically based on FIG. At this time, processing is performed by the signal processing circuit 40 shown in FIG.
[0044]
  FIG. 3A shows the pitch formed continuously on the super-resolution optical disc 12. Here, an example in which three pitches are arranged in the order of 580 nm, 580 nm, and 2320 nm in pitch length will be described. (B) shows the waveform of the optical signal d output from the addition amplifier 41. (C) shows the waveform of the optical signal e output from the addition amplifier 42. Further, (d) shows the waveform of the optical reproduction signal g output from the addition amplifier 44. The optical reproduction signal g shows a waveform obtained by synthesizing the optical signal d (waveform of (b)) with the signal amount adjusted and the optical signal e (waveform of (c)).
[0045]
  From the waveform of the optical signal d shown in (b), pits (reproduction) at a minimum pitch of 580 nm are obtained from all the luminous fluxes of the reproduction light detected by the split photodetector 37 (all the areas of the detection beam h shown in FIG. 1). It can be seen that pits shorter than the limit) are hardly detected. In other words, when all of this reproduction light is integrated, an optical signal (low frequency component) from a pit longer than the reproduction limit is detected, and an optical signal (high frequency component) from a pit whose length is less than the reproduction limit is detected. You can see that it was not done. In other words, when all of the reproduction light is integrated, it can be seen that the optical signal from the pit shorter than the reproduction limit is not decomposed and is missing. This is because an optical signal from a pit shorter than the reproduction limit has a low output and is buried in a high output optical signal from a pit above the reproduction limit. A pit that is longer than the reproduction limit (or shorter than the reproduction limit) represents a pit at a pitch that is longer than the reproduction limit (or less than the reproduction limit).
[0046]
  On the other hand, from the waveform of the optical signal e shown in (c), the luminous flux at the end of the reproduction light detected by the split photodetector 37 (the first end photo detector 45 and the second end at the detection beam h shown in FIG. 1). From the area on the photodetector 47, it can be seen that an optical signal from a pit (pit shorter than the reproduction limit) at 580 nm which is the minimum pitch is detected. That is, it can be seen that a high frequency component can be detected from the luminous flux at the end of the reproduction light, and pits shorter than the reproduction limit can be decomposed and detected. At this time, it can be seen that the edge of the pit can be emphasized and detected.
[0047]
  In this way, by removing the central portion of the light beam of the reproduction light guided to the split photodetector 37, the light amount can be cut without affecting the high-frequency component passing near the end of the light beam. Thereby, white noise can be reduced and the signal-to-noise ratio of the reproduced signal can be increased. Therefore, the high frequency component can be detected more clearly.
[0048]
  Further, it is considered that an optical signal (high frequency component) having a high spatial frequency easily passes through the end of the pupil of the detection optical system, that is, the end of the light beam. Therefore, it is considered that the edge photodetectors 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, 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.
[0049]
  Further, by combining the optical signal d that has detected a reproduction signal of a long pit that exceeds the reproduction limit and the optical signal e that has detected a reproduction signal of a short pit that is less than the reproduction limit, the reproduction limit is substantially satisfied. The optical signal from no short pit can be increased. Since the optical signal d is reduced by the volume 43 before being synthesized, the optical signal e is relatively more emphasized than the optical signal d. As a result, it is possible to avoid missing a reproduction signal from a short pit that does not reach the reproduction limit. That is, the information actually recorded on the super-resolution optical disk 12 can be reproduced more reliably. Further, since the optical signal b from the central portion of the light beam is reduced, the total light amount is reduced and white noise can be reduced.
[0050]
  [Embodiment 2]
  Another embodiment of the present invention will be described 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. In the present embodiment, the divided photodetector 37 and the signal processing circuit 40 in the first embodiment are different in configuration. That is, in the present embodiment, a divided photo detector 37 a is provided instead of the split photo detector 37, and a signal processing circuit (reproducing means) 40 a is provided instead of the signal processing circuit 40.
[0051]
  In the present embodiment, the divided photo detector (light detecting means) 37 a includes end photo detectors (detecting means, second detecting units) 51, 54, 55, and 58, and central partial photo detectors (center detecting means, first detecting unit) 52. It is divided into 8 parts 53, 56 and 57. 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. In addition, in the region including the central portion photodetectors 52, 53, 56, and 57, the width dimension of the detection beam h with respect to the track direction is equal to the diameter of the detection beam h, as in the central portion photodetector 46 in the first embodiment. On the other hand, the ratio may be 1/2 to 49/50, and preferably 19/20. The center portion photodetector 46 detects the center portion of the detection beam h. Therefore, in other words, the central portion is a portion having a ratio of 1/2 to 49/50 with respect to the diameter of the detection beam h, and is preferably a portion having a ratio of 19/20.
[0052]
  Further, the width dimension of the end photo detectors 45 and 47 in the track direction is not particularly limited. However, according to the detection range of the central portion photo detector 46, the width dimension of the detection beam h is 1 /. The detection beams at a ratio of 100 to 1/4 are detected by the end photo detectors 45 and 47, respectively. Therefore, in other words, the end photo detectors 45 and 47 need only have a size capable of detecting a detection beam other than that detected by the central portion photo detector 46. In addition, the reproduction limit (λ / 2NA), reproduction light power, and the like are the same as those in the first embodiment.
[0053]
  Each of the photodetectors 51 to 58 detects the optical signals S1 to S8 in order. The optical signals S1 to S8 are 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 (servo signal) t for condensing the light beam on the super-resolution optical disk 12, and the track error signal (for tracking the track of the super-resolution optical medium 12) Servo signal (u) can be generated simultaneously.
[0054]
  Here, generation of the optical reproduction signal w, the focus error signal t, and the track error signal u from each of the optical signals S1 to S8 input to the signal processing circuit 40a will be described.
[0055]
  First, the generation of the optical reproduction signal w will be described.
[0056]
  The optical signals S1, S4, S5, and S8 detected by the end photo detectors 51, 54, 55, and 58 are added by the adding amplifier 60, and an added output l is generated. On the other hand, the respective optical signals S2, S3, S6, and S7 detected by the respective central portion photodetectors 52, 53, 56, and 57 are added by the adding amplifier 61, and an added output m is generated.
[0057]
  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.
[0058]
  The output v and the addition output l are added by an addition amplifier 67, and an optical reproduction signal w is generated. As a result, a signal from a short pit that is less than the reproduction limit is emphasized and detected.
[0059]
  Next, generation of the focus error signal t will be described.
[0060]
  The optical signals S1, S2, S5, and S6 detected by the photodetectors 51, 52, 55, and 56 are added by the addition amplifier 62, and an addition output o is generated. On the other hand, the optical signals S3, S4, S7, and S8 detected by the photodetectors 53, 54, 57, and 58 are added by the addition amplifier 63 to generate an addition output p.
[0061]
  The addition output o and the addition output p are input to the subtraction amplifier 68 and subtracted to generate a focus error signal t of the well-known astigmatism method.
[0062]
  Next, generation of the track error signal u will be described.
[0063]
  The optical signals S1, S2, S3, and S4 detected by the photodetectors 51, 52, 53, and 54 are added by the adding amplifier 64 to generate an added output q. On the other hand, the optical signals S5, S6, S7, and S8 detected by the photodetectors 55, 56, 57, and 58 are added by the adding amplifier 65, and an added output r is generated.
[0064]
  The addition output q and the addition output r are input to a subtraction amplifier 69 and subtracted to generate a well-known push-pull tracking error signal u.
[0065]
  As described above, in the present embodiment, signal detection from a short pit that is less than the reproduction limit and servo signal detection can be simultaneously performed by the divided photodetector (light detection means) 37a.
[0066]
  The optical regeneration method and the optical regeneration apparatus of the present invention are not limited to the above embodiments, and can be variously modified within the scope of the gist. In particular, the super-resolution optical disk is not limited to the ROM type, and can be applied to various media. 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. For example, as shown in FIGS. 5A and 5C, the split photodetector includes a center part photodetector 80 having a quadrangular shape (rectangle or rhombus), and the other parts of the split photodetector are end detectors 81 to 84. It may be equally divided. Further, as shown in FIG. 5 (b), the central portion photodetector 80 may be circular. Even in these cases, the center partial photodetector 80 may have a width dimension in the track direction of the detection beam h that is a ratio of 1/2 to 49/50 with respect to the diameter of the detection beam h. A ratio of 20 is preferred.
[0067]
  In the first and second embodiments, the end of the light flux in the track direction is detected. However, the present invention is not limited to this, and it is only necessary to detect the end of the light flux. The photodetectors are aligned in the track direction. However, the present invention is not limited to this, and it is only necessary that the photodetectors are arranged so as to be able to detect the end portions of the light flux. Accordingly, by detecting the end portion in the direction perpendicular to the track, it is possible to increase not only the recording density of the pits or marks but also the track honeyness. That is, it is possible to more reliably detect a signal from a track with a short pitch, and thus a signal from a track pitch with a length less than the reproduction limit of the optical recording medium. In other words, tracks can be detected separately at a track pitch that is less than the reproduction limit.
[0068]
  In the above description, signals from the pits of the super-resolution disc are detected. However, not only the pits but also recording marks and the like on recordable media can be detected in the same manner.
[0069]
  In the above, the detection of the signal from the pit is described. However, when information is actually reproduced (read), the information is reproduced from the pitch composed of pits or marks and spaces formed on the optical recording medium. Will be read (read).
[0070]
  The optical reproducing apparatus according to the present invention reproduces information from an optical recording medium including marks or pits having a pitch of λ / 2NA or less, where NA is the wavelength λ of light for reproduction and NA is the numerical aperture of the objective lens. In the above, it can be expressed that the optical path of the optical system for detecting the light from the optical recording medium is provided with reproducing means for removing at least the central portion of the light beam.
[0071]
  Further, the optical reproducing apparatus according to the present invention includes a first detection system for reproducing an optical signal from a mark or pit having a pitch longer than approximately λ / 2NA, a mark having a pitch shorter than approximately λ / 2NA, A signal for reproducing information by combining a second detection system for reproducing an optical signal from a pit, a signal detected by the first detection system, and a signal detected by the second detection system And a processing circuit. The second detection system preferably includes a reproducing unit that reproduces a signal by removing at least the central portion of the light beam.
[0072]
  Furthermore, the optical reproducing method according to the present invention reproduces information from an optical recording medium including marks or pits having a pitch of λ / 2NA or less, where λ is the wavelength of light for reproduction and NA is the numerical aperture of the objective lens. A first signal corresponding to information from a mark or pit having a pitch longer than approximately λ / 2NA is reproduced from all of the light flux including information from the optical recording medium, and the information from the optical recording medium is reproduced. Removing at least the central portion of the included light beam, detecting a light beam positioned at an end with respect to the track direction, and reproducing a second signal including information from a mark or pit having a pitch shorter than approximately λ / 2NA; It can be expressed that information is reproduced from the first and second signals.
[0073]
  By the way, the super-resolution phenomenon occurs due to the arrangement of fine marks and pits. The spatial frequency of the reproduced signal exceeds the diffraction limit of the optical system. Increasing the power of the reproduction light increases the degree of modulation of the reproduction signal, but also increases white noise due to an increase in the amount of incident light. In order to improve the signal-to-noise ratio, it is important to suppress an increase in white noise while increasing the degree of modulation.
[0074]
  Therefore, in the optical reproducing apparatus and optical reproducing method according to the present invention, since at least the central part of the luminous flux of the reproduced light is removed, the luminous flux center is not affected to the vicinity of the luminous flux around which the signal component passes. Therefore, the white noise is reduced and the signal-to-noise ratio of the reproduction signal is increased.
[0075]
  Further, 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 light beam of the detection optical system. Therefore, in order to detect an optical signal from a mark or pit with a high spatial frequency, only the light beam passing through the end of the light beam is detected, or by providing such an optical system, the signal below the reproduction limit is emphasized. Can be played. A plurality of lengths included in the actual recording / reproduction information are formed by configuring this reproduction signal and a signal (a signal from a mark or pit larger than the reproduction limit) that detects the light beam including the central portion of the light beam. The signal from the mark or pit can be reproduced.
[0076]
  Furthermore, the low-frequency component against the so-called signal loss, in which the low-frequency high-frequency component from the mark or pit below the reproduction limit is buried in the high-power low-frequency component from the mark or pit above the reproduction limit. By preventing the passage of the low output signal from the mark or pit below the reproduction limit can be avoided. Similarly to the above, by detecting and synthesizing the light beam passing through the end and the center of the light beam with different detection systems, a signal including a plurality of marks or pits having a length less than the reproduction limit is eliminated. While avoiding this, the output can be increased.
[0077]
  In order to solve the above problems, an optical reproducing apparatus of the present invention uses reflected light or transmitted light of light irradiated on the optical recording medium as information from pits or marks formed in the track direction of the optical recording medium. An optical reproducing apparatus that reproduces by detecting includes a detecting means for detecting a signal at an end of the reflected light or transmitted light beam.
[0078]
According to the above configuration, it is considered that a signal from a pit or mark having a short length passes more around the light beam of the reproducing optical system than a signal from a pit or mark having a long length. Therefore, by detecting the end of the reflected or transmitted light beam with the above configuration, a signal from a pit or mark having a short length, and hence from a pit or mark having a length less than the reproduction limit of the optical recording medium. The signal can be detected more reliably. In other words, it is possible to avoid missing signals that are less than the reproduction limit. In addition, since the central portion of the light beam is reduced or removed, the amount of light to be detected is cut. Therefore, since white noise can be reduced, the signal-to-noise ratio in the detected signal can be improved.
[0079]
The optical reproducing apparatus of the present invention is characterized in that, in addition to the above-described configuration, a split photodetector including the detecting means is provided.
[0080]
According to the above configuration, the end of the reflected or transmitted light beam can be detected by the split photodetector, and the pit has a length less than the reproduction limit of the optical recording medium that is considered to pass many ends of the beam. Alternatively, the signal from the mark can be detected more reliably.
[0081]
In addition to the above-described configuration, the optical regenerator of the present invention includes a regenerating unit that regenerates at least the signal detected by the detection unit.
[0082]
According to the above configuration, a signal from a pit or mark having a length less than the reproduction limit from the optical recording medium can be more reliably reproduced. That is, it is possible to increase and reproduce signals from pits or marks having a length less than the reproduction limit.
[0083]
In addition to the above-described configuration, the optical reproducing apparatus of the present invention includes at least the reflected or transmitted light. Center detecting means for detecting a signal of the central portion of the bundle, wherein the reproducing means combines and reproduces the signal detected by the detecting means and the signal detected by the center detecting means; Yes.
[0084]
According to said structure, the signal of the center part in a light beam is detected, and the signal from the pit or mark of the length beyond a reproduction limit is detected. Then, by combining the signal at the center and the signal at the end of the luminous flux, both the signal from the pit or mark having a length longer than the reproduction limit and the signal from the pit or mark having a length less than the reproduction limit Can be reliably detected. Therefore, the information recorded on the optical recording medium can be reproduced while avoiding missing.
[0085]
In addition to the above configuration, the optical reproducing apparatus of the present invention is characterized by including a split photodetector having the center detecting means.
[0086]
According to said structure, the signal of the center part in a light beam can be isolate | separated and detected with a division | segmentation photodetector.
[0087]
In the optical reproducing apparatus of the present invention, in addition to the above configuration, the reproducing means further generates a servo signal by synthesizing the signal detected by the detecting means and the signal detected by the center detecting means. It is characterized by that.
[0088]
According to the above configuration, since the signals detected by the detection unit and the center detection unit are synthesized, the servo signal can be easily generated only by adding a circuit having a simple configuration. Therefore, it is possible to provide an optical reproducing apparatus that can perform optical reproduction more stably. In addition, it is not necessary to add a new device or the like for generating a servo signal, and space can be saved.
[0089]
【The invention's effect】
  BookAs described above, the optical reproducing apparatus of the present invention detects information reflected from the pits or marks formed in the track direction of the optical recording medium by detecting reflected light or transmitted light of the light irradiated on the optical recording medium. In the optical reproducing apparatus for reproducing, the first detection unit for detecting a signal from a pit or mark longer than the reproduction limit in the reflected light or transmitted light, and the pit or mark shorter than the reproduction limit in the reflected light or transmitted light. Comprising: a second detection unit for detecting the signal of the first signal; and a reproducing means for reproducing the information by combining the signal detected by the first detection unit and the signal detected by the second detection unit. It is.
[0090]
  According to the above configuration, a signal from a pit or mark having a length longer than the reproduction limit and a signal from a pit or mark having a length less than the reproduction limit are combined and reproduced. Thereby, a signal from a pit or mark having a length less than the reproduction limit is emphasized and reproduced. That is, there is an effect that information recorded on the optical recording medium can be reproduced while being omitted.
[0091]
  In addition to the above configuration, the optical reproducing apparatus of the present invention has a configuration in which the second detection unit includes a detection unit that detects an end of the reflected light or transmitted light.
[0092]
  According to the above configuration, since the end of the reflected or transmitted light beam is detected, it is possible to more reliably detect a signal from a pit or mark having a length less than the reproduction limit. Play.
[0093]
  In order to solve the above problems, the optical reproducing method of the present invention detects the reflected light or transmitted light of the light irradiated to the optical recording medium, thereby forming pits or marks formed in the track direction of the optical recording medium. In the light reproduction method for reproducing information according to the above, a first signal from a pit or mark having a length longer than the reproduction limit is detected from the reflected or transmitted light beam, and reproduced from the reflected or transmitted light beam. In this configuration, the second signal from a pit or mark having a length less than the limit is detected, and the information on the optical recording medium is reproduced by combining the first signal and the second signal.
[0094]
  According to the above configuration, an optical signal from a pit or mark having a length longer than the reproduction limit and an optical signal from a pit or mark having a length less than the reproduction limit are combined and reproduced. Thereby, an optical signal from a pit or mark having a length less than the reproduction limit is emphasized and reproduced. That is, there is an effect that information recorded on the optical recording medium can be reproduced while being omitted.
[0095]
  In the optical reproducing method of the present invention, in addition to the above configuration, the second signal is a signal obtained by removing at least a central portion of the light beam and detecting an end portion of the light beam.
[0096]
  According to the above configuration, since the end of the reflected light or transmitted light is detected, an optical signal from a pit or mark having a length less than the reproduction limit can be detected more reliably. Play.
[0097]
  The optical reproduction method of the present invention is configured to generate a servo signal by synthesizing the first signal and the second signal in addition to the above configuration.
[0098]
  According to said structure, a servo signal can be easily produced | generated by synthesize | combining a 1st signal and a 2nd signal. Thereby, there is an effect that more stable optical reproduction can be performed.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a split 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 configuration diagram showing an optical regenerator according to an embodiment of the present invention.
3A is a shape of a recording pit in a super-resolution optical disc used in the optical reproducing apparatus, and FIGS. 3B to 3D are waveforms of a reproduction signal detected by the optical reproducing apparatus. FIG.
FIG. 4 is a circuit diagram showing a split photodetector and a signal processing circuit used in an optical reproducing apparatus according to another embodiment.
FIGS. 5A to 5C are configuration diagrams showing another configuration example of the divided photodetector.
[Explanation of symbols]
12 Super-resolution optical disk (optical recording medium)
21 Laser diode (irradiation means)
23 Polarizing beam splitter
25 Objective lens
37-segment photo detector (light detection means)
40 Signal processing circuit (reproducing means)
45 First end photo detector (detection means, first detection unit)
46 Center part photodetector (center detection means, second detection unit)
47 Second end photo detector (detection means, first detection unit)
h Detection beam (light flux)

Claims (4)

In an optical reproducing apparatus for reproducing information from pits or marks formed in the track direction of an optical recording medium by detecting reflected light or transmitted light of the light irradiated on the optical recording medium,
A first detector for detecting a signal from a pit or mark longer than the reproduction limit in the reflected light or transmitted light;
A signal from a pit or mark having detection means for detecting an end portion of the reflected light or transmitted light beam, and shorter than the reproduction limit of the reflected light or transmitted light from the edge of the light beam detected by the detection means. A second detector for detecting
Reproducing means for reproducing the information by combining the signal detected by the second detection unit with a signal amount of the signal detected by the first detection unit being smaller than that at the time of detection;
An optical reproducing apparatus comprising: In an optical reproducing method for reproducing information of the optical recording medium by detecting reflected light or transmitted light of the light irradiated to the optical recording medium,
A first signal from a pit or mark longer than the reproduction limit is detected from the light flux from the reflected light or transmitted light,
A second signal from a pit or mark shorter than the reproduction limit is detected from the end of the luminous flux from the reflected or transmitted light,
An optical reproducing method for reproducing information on an optical recording medium by making the signal amount of the first signal smaller than that at the time of detection and combining it with the second signal.   The optical reproduction method according to claim 2, wherein the second signal is a signal obtained by removing at least a central portion of the light beam and detecting an end portion of the light beam.   4. The optical reproduction method according to claim 2, wherein a servo signal is generated by synthesizing the first signal and the second signal.

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