JPH04258814A - optical regeneration device - Google Patents

Abstract

PURPOSE:To excellently detect a signal even for information bit which is shorter than the spot diameter of reproducing laser beam by delaying the output of at least one photodetector part among several photodetector parts. CONSTITUTION:Light reflected by an optical disk 5 passes through an objective lens 4, a beam splitter 3 and an analyser 6 and made incident on two photodetectors 7 and 8. The photodetectors 7 and 8 are arranged in the direction of the information bit string of the disk 5, and the reflected light corresponding to the first half of a light spot is made incident on the detector 8 while the relfected light corresponding to the last half of the light spot is made incident on the detector 7. The detectors 7 and 8 detect the change in the direction of polarization as the change of light intensity, delay the output of the detector 8 via a delay line 9 by the amount of time corresponding to the movement of a half distance of the diameter of the light spot and add it with the output of the detector 7 in an adder 10. Thus, time required for the change of signal level can be halved and the excellent signal detection can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reproducing apparatus for reproducing information signals from an optical recording medium using a focused laser beam.

0002

[Prior Art] In an optical reproducing device that optically reproduces information, information signals are reproduced by focusing a laser beam onto an optical recording medium and detecting changes in reflected light from the optical recording medium. There is. When using an optical disk using a magneto-optical medium such as TbFeCo as an optical recording medium, when a linearly polarized laser beam is focused on the disk and the focused spot follows the information track of the disk, information is generated. Recorded information is detected by converting changes in the polarization direction of light reflected from the disk depending on the presence or absence of bits into changes in light intensity. An optical disk has, as an information track, an information bit string positioned by a continuous guide groove or a discontinuous pre-pit string, and information is magnetically recorded in the information bit.

FIG. 5 shows an example of a specific configuration of a conventional optical reproducing apparatus for reproducing such an optical disc. The light emitted from the laser light source 51 passes through the collimator lens 52.
The parallel light is converted into parallel light, reflected by a beam splitter 53, and then focused onto an optical disk 55 by an objective lens 54. Here, the light from the laser light source 51 is linearly polarized light (beam splitter 5
3), and the beam splitter 5
For example, the polarization characteristic of No. 3 is such that the transmission/reflection ratio is 1 for P-polarized light.
0:0 and 7:3 for S-polarized light. optical disc 55
The reflected light is converted into parallel light by the objective lens 54,
After passing through a beam splitter 53 and an analyzer 56, it reaches a photodetector 57. In the analyzer 56, the light passes selectively depending on the polarization direction, so a change in the polarization direction of the reflected light from the disk is converted into a change in light intensity. Here, the analyzer 56 has an analyzer angle (for example,
α=5°), and the incident light R+ with different polarization directions
and R- are passed as lights AR+ and AR-, respectively, in the direction of the polarization plane of the analyzer. Therefore, the photodetector 57 is
Changes in the polarization direction of reflected light are detected as changes in light intensity. The output of the photodetector 57 is sent to a signal processing device (not shown) via an amplifier 60, and an information signal is reproduced.

FIG. 7 shows an example of the relationship between the information bits on the optical disk in the conventional optical reproducing apparatus shown in FIG. 5 and changes in the intensity of the optical signal detected by the photodetector.

FIG. 7A shows a row of information bits 70 formed on a disk and a light spot 71 focused on the disk. When the light spot 71 moves relatively in the direction of the illustrated arrow, the intensity of the optical signal detected by the photodetector changes as shown in FIG. 7(b). In this case, the light intensity signal level changes from the light intensity signal level when the light spot 71 is located between one information bit 70 and the next information bit 70 to the light intensity signal level when the light spot 71 is located on the next information bit 70. It takes time for the light spot 71 to move a distance corresponding to its diameter.

FIG. 8 shows an example of a change in the intensity of an optical signal obtained from a disk in which the length of information bits is short. In Figure 8 (
If the length of the information bit 72 on the disk is shorter than the diameter of the optical spot 71 as shown in FIG.
), the amplitude A4 of the light intensity signal is smaller than the signal amplitude A3 (FIG. 7(b)) when the length of the information bit 72 is sufficiently long (FIG. 7).

[0007] Generally, MTF (Modulation
From the cutoff spatial frequency of n Transfer Function), the minimum detectable length L0 of the information bit 72 is given by L0=λ/(4·NA). Here, NA is the numerical aperture of the objective lens 54, and λ is the wavelength of the reproduction laser beam. Therefore, if the diameter d0 of the optical spot 71 is d0=0.82·λ/NA, then L0=d0/3.28. As described above, if the length of the information bit 72 is about 1/3 or less of the diameter of the reproduction light spot 71, it becomes impossible to detect the reproduction signal.

Another configuration of a conventional optical reproducing device is shown in FIG. In the optical regenerator shown in FIG. 9, light emitted from a laser light source 81 is made into parallel light by a collimator lens 82, reflected by a beam splitter 83, and then reflected by an objective lens 83.
4, the light is focused on the optical disk 85. Here, the light from the laser light source 81 is linearly polarized light (corresponding to S-polarized light with respect to the beam splitter 83) with a polarization plane perpendicular to the plane of the paper, and the polarization characteristics of the beam splitter 83 are such that, for example, the transmission/reflection ratio is P. 10:0 for polarized light, 7 for S-polarized light
:3. The light reflected by the optical disk 85 is made into parallel light by the objective lens 84 , passes through the beam splitter 83 , has its polarization direction rotated by 45 degrees by the 1/2 wavelength plate 86 , and then reaches the polarizing beam splitter 87 . The polarization characteristics of the polarization beam splitter 87 are transparent for P polarized light, and transparent for S polarized light.
It is a reflection of polarized light, and as shown in Figure 10, light R+ and R- with different polarization directions are transmitted as PR+ and PR- in the P polarization direction, and as SR+ and SR- in the S polarization direction. and will be reflected. The light transmitted by the polarizing beam splitter 87 reaches a photodetector 88, and the reflected light reaches a photodetector 90. The outputs of photodetectors 88 and 90 are input to a differential amplifier 92. The output of the differential amplifier 92 is sent to a signal processing device (not shown), and the information signal is reproduced.

[0009] Even in an optical reproducing device having such a configuration,
The relationship between the length of the information bit and the reproduced signal is the same as in the conventional example with the configuration shown in FIG. Become.

0010

[Problems to be Solved by the Invention] As mentioned above, since conventional optical reproducing devices directly detect changes in the light intensity of reflected light from an optical disk, the information bit length is small compared to the optical spot diameter. When it is short, the level of the reproduced signal detected becomes small, and there is a problem that the reproduced signal cannot be detected especially when the diameter of the reproduced light spot is about ⅓ or less.

[0011] This problem similarly occurs in reproducing apparatuses for optical discs using phase-change recording materials as optical recording media and optical discs in which information bits are constructed of convex protrusions or the like.

[0012] An object of the present invention is to provide an optical reproducing device that enables good signal detection even for information bits that are shorter than the spot diameter of the reproducing laser beam.

[0013]

[Means for Solving the Problems] The optical regeneration device of the present invention includes:
An optical reproducing device that reproduces information based on reflected light from an optical recording medium having an information bit string, and includes a light detection means for receiving the reflected light, the light detection means detecting the direction of the information bit string. The optical regeneration device further includes a delay means for delaying the output of at least one of the plurality of photodetectors. This achieves the above objectives.

The optical reproducing apparatus of the present invention reproduces information based on reflected light from an optical recording medium having an information bit string, and includes a plurality of photodetecting means each receiving polarized light in different directions of the reflected light. an optical reproducing device comprising: each of the optical detecting means comprising a plurality of optical detecting sections arranged in substantially the same direction as the direction of the information bit string; It may further include a delay means for delaying the output of at least one photodetector among the detectors.

Furthermore, each of the above configurations may further include adding means provided after the delay means and adding the outputs of the plurality of photodetectors.

[0016]

[Operation] In the above structure, the reflected light from the optical recording medium is divided in the direction of the information bit string and detected by the plurality of photodetectors. The output of each photodetector is delayed by a delay means, and the output timing of each is shifted. This delay is preferably such that the output of the photodetector that first receives the reflected light from the information bit is delayed. As a result, it is equivalent to dividing the light spot into multiple parts and each part of the divided light spot irradiating the same information bit at the same time. Therefore, the signal can be detected well even if the information bits are short.

[0017] Furthermore, since adding the delayed output signals corresponds to making the optical spot smaller, the resolution of optical reproduction is improved and signals can be detected even for short information bits. Become.

[0018]

EXAMPLES The present invention will be explained below with reference to examples.

An example of a specific configuration of the optical reproducing device of the present invention is shown in FIG. This embodiment uses CLV (Constant
This is a playback device for optical discs using the Linear Velocity method. Light emitted from a laser light source 1 is collimated by a collimator lens 2, reflected by a beam splitter or half prism 3, and then focused onto an optical disk 5 by an objective lens 4. Here, the light from the laser light source 1 is linearly polarized light with a polarization plane perpendicular to the paper (corresponding to S-polarized light with respect to the beam splitter 3), and the polarization characteristics of the beam splitter 3 are such that the transmission/reflection ratio is P-polarized light. 10:0 for S-polarized light and 7:3 for S-polarized light. The light reflected by the optical disk 5 is made into parallel light by the objective lens 4, passes through the beam splitter 3, passes through the analyzer 6, and then enters two photodetectors 7 and 8. The photodetectors 7 and 8 are arranged in the direction (
(in the direction of the arrow shown). In other words, the photodetectors 7 and 8 have a light spot 2 shown in FIG.
The reflected light based on the right half 21b of 1 enters the photodetector 7.
are arranged so that the reflected light from the left half 21a is incident thereon. Since light is selectively passed through the analyzer 6 depending on the polarization direction, a change in the polarization direction of the reflected light from the disk 5 is converted into a change in light intensity. That is, the analyzer 6 has an analyzer angle (α=5°) as shown in FIG.
Incident lights R+ and R- with different polarization directions are passed as lights AR+ and AR- in the polarization plane directions of the analyzer, respectively. Photodetectors 7 and 8 detect changes in the polarization direction of the reflected light as changes in light intensity.

The output of the photodetector 8 is inputted to one input terminal of the summing amplifier 10 via a delay line 9 which is a delay means, and the output of the photodetector 7 is inputted to the summing amplifier 10 via normal wiring. is input directly to the other input terminal. Delay line 9 is a lumped constant delay line for analog signal delay. The outputs of the photodetectors 7 and 8 are summed by a summing amplifier 10 and then sent to a signal processing device (not shown), where an information signal is reproduced.

FIG. 2 shows the relationship between the information bits on the optical disc 5 and the changes in the light intensity signals detected by the photodetectors 7 and 8 in this embodiment. FIG. 2A shows a row of information bits 20 on the disk 5 and a light spot 21 focused on the disk 5. FIG. When the light spot 21 moves relatively in the direction of the arrow shown in the figure, the output of the photodetector 8 into which the reflected light based on the right half 21b of the light spot 21 is incident changes as shown by the solid line in FIG. 2(b). do. On the other hand, the output of the photodetector 7 into which the reflected light from the left half 21a of the light spot is incident changes as shown in FIG. 2(c).

Here, assuming that the linear velocity is 1.2 m/sec and the diameter of the light spot 21 is 1.2 μm, the light spot 21
The time required for the particle to move a distance half its diameter (0.6 μm) is 0.5 μsec. If a delay line 9 with a delay amount of 0.5 μsec is used, the photodetector 8
The output of is delayed by the delay line 9 by a time corresponding to movement of the distance half the diameter of the optical spot 21 (ie, 0.5 μsec). Therefore, the output of the photodetector 8 obtained via the delay line 9 changes as shown by the broken line in FIG. 2(b). That is, the high period of the output of the photodetector 8 and the high period of the output of the photodetector 7 (FIG. 2(c)) substantially match. Output of photodetector 7 (light spot 2
1) and the photodetector 8 (a delayed signal based on the right half 21b of the light spot 21) are added by the adder 9, resulting in a signal as shown in FIG. 2(d). I get a signal. In this reproduced signal, the time T1 required for changing the signal level is half that of the conventional reproduced signal ((b) in FIG. 7).

FIG. 3 shows an example of the output of the adder 9 obtained when the above embodiment is used to reproduce information from an optical disc having short information bits 22. As shown in FIG. 3(a), even if the length of the information bit 22 on the disk is shorter than the diameter of the optical spot 21, the amplitude of the reproduced signal will change as shown in FIG. 3(b). A2 is equal to the amplitude A1 (FIG. 2(d)) of the above-mentioned reproduced signal. In this way, sufficient signal amplitude can be obtained even when the information bit length is short, so
Signals can be read even when the information bit length is about 1/3 of the optical spot diameter.

In the above embodiment, two arrayed photodetectors are used, but if three or more photodetectors are used, even shorter information bits can be accommodated. For example, if three photodetectors are used and arranged so that the reflected light from the light spot is divided into approximately three equal parts and received, the delay amount of each delay means is 1 part of the diameter of the light spot.
The time required to travel a distance of /3 and a distance of 2/3 may be selected as a guide. Further, a preamplifier or the like may be used between each of the plurality of detectors and the summing amplifier to adjust the signal level of each.

Another embodiment of the invention is shown in FIG. In the optical reproducing device of FIG. 4, the light emitted from the laser light source 31 is
The collimator lens 32 converts the light into parallel light, which is reflected by a beam splitter or half prism 33 , and then focused onto an optical disk 35 by an objective lens 34 . The light from the laser light source 31 is linearly polarized light with a polarization plane perpendicular to the plane of the paper (corresponding to S-polarized light with respect to the beam splitter 33), and the polarization characteristics of the beam splitter 33 are such that the transmission/reflection ratio is 10:0 and 7 for S polarized light.
:3. The light reflected by the optical disk 35 is converted into parallel light by the objective lens 34, and is converted into parallel light by the beam splitter 33.
After passing through the 1/2 wavelength plate 36 and rotating the polarization direction by 45 degrees, the light beam reaches the polarization beam splitter 37 . The polarization characteristic of the polarizing beam splitter 37 is that it transmits P-polarized light and reflects S-polarized light, and as shown in FIG. and PR-, and in the S polarization direction, it is transmitted and reflected as light such as SR+ and SR-.

The P-polarized light transmitted through the polarizing beam splitter 37 enters two photodetectors 38 and 39. On the other hand, the S-polarized light reflected by the polarizing beam splitter 37 enters two photodetectors 40 and 41. The photodetectors 38 to 41 receive the reflected light from the right half 21b of the light spot 21 shown in FIG. 2, respectively, and the photodetectors 39 and 41 receive the reflected light from the left half 21a. They are arranged so that each light can enter them.

The output of the photodetector 38 is connected to the non-inverting input terminal of the differential amplifier 42, and the output of the photodetector 40 is connected to the differential amplifier 42.
The output of the photodetector 38 and the output of the photodetector 40 are differentially amplified by the differential amplifier 42 . The output of the differential amplifier 42 is sent to the summing amplifier 45.
has been entered. Further, the output of the photodetector 39 is inputted to the non-inverting input terminal of the differential amplifier 43, and the output of the photodetector 41 is inputted to the inverting input terminal of the differential amplifier 43. Differential amplification of the output of the photodetector 41 and the output of the photodetector 41 is performed. The output of the differential amplifier 43 is input to an summing amplifier 45 via a delay line 44. In this embodiment as well, a lumped constant delay line for analog signal delay is used as the delay line 44. The output of the differential amplifier 42 and the delayed output of the differential amplifier 43 are added in an adding amplifier 45, and then sent to a signal processing device (not shown), where the information signal is reproduced.

In this embodiment as well, the relationship between the length of the information bit and the reproduced signal is the same as in the embodiment shown in FIG. , good signal detection is possible.

Since each of the embodiments described above is a reproducing apparatus for a CLV type optical disc, the relative speed between the information bit and the optical spot is constant, but the relative speed of the information bit and the optical spot is constant.
When reproducing an optical disc using the Angular Velocity method, the relative speed changes. For example, when the linear velocity of the optical disc changes from 5 m/sec to 12 m/sec, the distance of half the diameter of the optical spot (0.6
The time corresponding to the movement (μm) is 0.12 μsec to 0
．． The time is 05 μsec. In such a case, a delay means with a variable delay amount may be used, or a plurality of delay means having different delay amounts may be selectively used. An example of a delay means with variable delay amount is a CCD (charge coupled device) which is a delay element of a semiconductor device. When using CCD,
The amount of delay can be changed by changing the external clock frequency. Alternatively, the output of the photodetection may be A/D converted and the converted digital signal may be delayed by a shift register.

Furthermore, in each of the embodiments, the amount of delay is a time delay equivalent to moving a distance half the diameter of the light spot. The amount of delay may be adjusted so that an optimal reproduced signal can be obtained depending on the situation.

In the optical disc device to which the present invention is applied, the astigmatism method and push A pull method or the like may be used, but the photodetector used in each of the above embodiments may also be used to detect these error signals.

In each of the embodiments described above, a plurality of photodetectors are provided on the same optical path, but the light may be split by a beam splitter or the like and received by each individual detector. Alternatively, changes in light intensity may be detected after condensing the light onto the detector using a lens or the like in front of the photodetector.

It goes without saying that the present invention can also be applied to playback devices for optical discs using phase-change recording materials as optical recording media and for optical discs in which information bits are composed of convex protrusions, etc. It is.

[0034]

[Effects of the Invention] As explained above, according to the present invention,
By detecting the reflected light from the optical recording medium by dividing it in the direction of the information bit string using a plurality of optical detection means, and delaying each detected output using the delay means, each divided portion of the reflected light is detected at the same time. This is equivalent to reaching the same information bit at the same time. Therefore, the signal can be detected well even if the information bits are short. Here, since adding the respective delayed output signals corresponds to making the optical spot smaller, the resolution of optical reproduction is improved and signals can be detected even for short information bits. As a result, according to the present invention:
An optical reproducing device is provided that is capable of good signal detection even for information bits that are shorter than the spot diameter of the reproducing laser beam.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.

FIGS. 2(a) to 2(d) are diagrams showing the relationship between information bits, optical spots, and reproduction signals in the embodiment.

FIGS. 3(a) and 3(b) are diagrams showing the relationship among information bits, optical spots, and reproduction signals when the information bits are short in the embodiment.

FIG. 4 is a diagram showing the configuration of another embodiment of the present invention.

FIG. 5 is a diagram showing the configuration of a conventional optical reproducing device.

FIG. 6 is a diagram illustrating polarization characteristics of an analyzer.

FIGS. 7(a) and 7(b) are diagrams showing the relationship among information bits, optical spots, and reproduced signals in a conventional optical reproducing device.

FIGS. 8(a) and 8(b) are diagrams showing the relationship among information bits, optical spots, and reproduction signals when the information bits are short in a conventional optical reproducing device.

FIG. 9 is a diagram showing the configuration of another example of a conventional optical reproducing device.

FIG. 10 is a diagram illustrating polarization characteristics of a polarization beam splitter.

[Explanation of symbols]

1, 31 Laser light source 2, 32 Collimator lens 3, 33 Beam splitter 4, 34 Objective lens 5, 35 Optical disc 6 Analyzer 7, 8, 38-41 Photodetector 9, 44 Delay line 10, 45 Addition amplifier 20 Information bit 21. Light spot 36 1/2 wavelength plate 37 Polarizing beam splitter 42, 43 Differential amplifier

Claims (3)

[Claims] 1. An optical reproducing apparatus that reproduces information based on reflected light from an optical recording medium having an information bit string, and includes a light detection means for receiving the reflected light, the light detection means comprising: The optical reproducing device includes a plurality of photodetectors arranged in substantially the same direction as the direction of the information bit string, and the optical reproducing device delays the output of at least one photodetector among the plurality of photodetectors. An optical regeneration device further comprising delay means. 2. An optical reproducing device that reproduces information based on reflected light from an optical recording medium having an information bit string, and includes a plurality of light detection means each receiving polarized light in different directions of the reflected light. Each of the photodetecting means includes a plurality of photodetecting sections arranged in substantially the same direction as the direction of the information bit string, and the optical reproducing device detects at least one of the plurality of photodetecting sections. An optical regeneration device further comprising a delay means for delaying the output of one photodetector. 3. The optical reproducing apparatus according to claim 1, further comprising an adding means provided after the delay means and adding the outputs of the plurality of photodetecting sections.