JP7332246B2 - Playback device and playback method - Google Patents

Description

The present technology relates to a reproducing apparatus and a reproducing method that are applied to reproduce optical media such as optical discs.

For example, when reproducing a multi-layer optical disk, the amount of signal light decreases, which increases the possibility of errors occurring in signal reading. In order to solve this problem, a homodyne detection method that amplifies a detection signal using light interference is known (see Patent Documents 1 and 2).

In Patent Document 1, as a homodyne method for detecting light in which signal light and reference light interfere with each other, detection is performed for four sets of signal light and reference light whose phase differences are different by 90 degrees. has been Specifically, detection is performed for pairs of signal light and reference light with phase differences of 0 degrees, 90 degrees, 180 degrees, and 270 degrees, respectively. Each of these detections is performed by detecting the light intensity of light obtained by interfering the signal light and the reference light. Further, a servo is applied to correct the change in the optical path length due to surface wobbling of the optical disk. Patent Document 2 describes obtaining the optical path length difference between the signal light and the reference light by calculation.

In the homodyne method, a signal light component amplified according to the light intensity of the reference light can be obtained as a reproduced signal. By amplifying the signal light in this way, the SNR of the reproduced signal can be improved.

JP 2010-044832 A JP 2013-054801 A

In the homodyne system, if there is an optical path difference (phase offset) θ between the signal light and the reference light, the intended effect cannot be obtained. θ includes phase fluctuations at relatively low frequencies due to surface vibration of the optical disk and phase fluctuations at higher frequencies. High-frequency phase fluctuations are caused, for example, by minute irregularities (surface roughness) on the disk surface. In the case of the servo control described in Patent Document 1, phase fluctuations are higher than the servo band, and phase fluctuations in high frequencies cannot be completely removed.

Phase fluctuations in the high frequency range cannot be removed by a method in which the length of the optical path is changed by the displacement of the mirrors, so the phase fluctuations are removed by signal processing. When correcting the phase for this, phase unwrapping and filtering are applied to remove noise in the detected phase difference signal. However, due to the influence of noise, phase unwrapping may not be performed correctly, and a large error may be added to the filtering result.

Therefore, an object of the present technology is to provide a reproducing apparatus and a reproducing method that employ the homodyne detection method and prevent phase unwrapping from being performed correctly due to the influence of noise.

This technology obtains signal light by irradiating a recording medium with light emitted from a light source, generates reference light from the light emitted from the light source, and superimposes the signal light and the reference light. Optics for generating a set of first signal light and reference light with a phase difference of approximately 0° and a set of third signal light and reference light with a phase difference of approximately 90° with respect to the combined light. system and
a light-receiving unit that receives a set of the first signal light and the reference light by the first light-receiving element, and receives a set of the third signal light and the reference light by the third light-receiving element;
a phase correction unit to which the first light receiving signal obtained by the first light receiving element and the third light receiving signal obtained by the third light receiving element are supplied and which corrects the optical path length difference θ between the signal light and the reference light;
The phase corrector is
It consists of a phase correction circuit, a phase detection circuit that detects the phase correction residual from the output signal of the phase correction circuit, and a filtering circuit that filters the phase correction residual, and the output of the filtering circuit is fed back to the phase correction circuit. A playback device comprising a path and .
This technology obtains signal light by irradiating a recording medium with light emitted from a light source, generates reference light from the light emitted from the light source, and superimposes the signal light and the reference light. A set of the first signal light and the reference light giving a phase difference of about 0° to the combined light, a set of the second signal light and the reference light giving a phase difference of about 180° with respect to the combined light, and a set of the second signal light and the reference light giving a phase difference of about 90° an optical system for generating a third set of signal light and reference light having a phase difference of about 270° and a fourth set of signal light and reference light having a phase difference of approximately 270°;
A set of the first signal light and the reference light is the first light receiving element, a set of the second signal light and the reference light is the second light receiving element, a set of the third signal light and the reference light is the third light receiving element, and a fourth light receiving element is the set of the third signal light and the reference light. a light-receiving unit that receives a pair of the signal light and the reference light from the fourth light-receiving element, respectively;
A first difference signal a that is the difference between the first light receiving signal obtained by the first light receiving element and the second light receiving signal obtained by the second light receiving element, the third light receiving signal obtained by the third light receiving element and the fourth light receiving element A computing unit that obtains a second difference signal b that is a difference between the fourth light reception signals obtained in and has a phase relationship orthogonal to the first difference signal a;
a phase correction unit to which the first differential signal a and the second differential signal b are supplied and which corrects an optical path length difference θ between the signal light and the reference light;
The phase corrector is
It consists of a phase correction circuit, a phase detection circuit that detects the phase correction residual from the output signal of the phase correction circuit, and a filtering circuit that filters the phase correction residual, and the output of the filtering circuit is fed back to the phase correction circuit. A playback device comprising a path and .

According to at least one embodiment, the phase difference between the signal light and the reference light is sequentially updated, and the phase correction residual is approximately centered at 0 degrees, so that the correction phase can be calculated correctly without the need for phase unwrapping. Land/groove recording The optical recording medium of the system can be read well using the homodyne detection method. Note that the effects described here are not necessarily limited, and may be any effect described in the present technology or an effect different from them. Moreover, the contents of the present technology are not to be construed as being limited by the effects illustrated in the following description.

FIG. 1 is a diagram showing the configuration of an example of a conventional playback device. FIG. 2 is a diagram showing the configuration of another example of a conventional playback device. FIG. 3 is a block diagram showing the configuration of a phase detector in another example of a conventional reproducing device. 4A and 4B are schematic diagrams used to describe the phase unwrapping process. 5A, 5B, and 5C are schematic diagrams used to explain problems in phase unwrapping processing. FIG. 6 is a diagram showing the configuration of the first embodiment of the present technology. FIG. 7 is a block diagram showing the configuration of a phase correction unit according to the first embodiment of the present technology; FIG. 8 is a block diagram showing the configuration of a phase correction unit according to the second embodiment of the present technology; FIG. 9 is a diagram showing the configuration of still another example of a conventional playback device.

The embodiments described below are preferred specific examples of the present technology, and are subject to various technically preferable limitations. However, the scope of the present technology is not limited to these embodiments unless there is a description to the effect that the present technology is specifically limited in the following description.
In addition, description of this technique is made according to the following order.
<1. Reproduction device using conventional homodyne detection>
<2. First Embodiment>
<3. Second Embodiment>
<4. Variation>

<1. Reproduction device using conventional homodyne detection>
FIG. 1 shows the configuration of an example of a playback device using conventional homodyne detection. An optical recording medium (hereinafter referred to as an optical disk) 1 is rotated by a spindle motor when loaded into a reproducing apparatus. A recorded signal is reproduced by irradiating a laser beam onto the optical disk 1 which is rotationally driven. The optical disc 1 is a so-called write-once optical disc on which information is recorded by forming recording marks, for example.

The optical disc 1 is formed with a cover layer, a recording layer (reflective film), and a substrate in order from the upper layer side. Here, the “upper layer side” refers to the upper layer side when the surface on which laser light from the playback device side is incident is the upper surface. In other words, in this case, the laser beam is incident on the optical disc 1 from the cover layer side. The substrate is made of, for example, a resin such as polycarbonate, and has an uneven cross-sectional shape on its upper surface side. The cover layer is provided for protecting the recording layer. A mark row is formed on the optical disk 1 to be reproduced.

A laser (semiconductor laser) 10 serving as a laser light source for reproduction is provided in the optical system of the reproducing apparatus. A laser beam emitted from a laser 10 is collimated through a collimation lens 11 and then enters a polarizing beam splitter 12 .

The polarizing beam splitter 12 is configured, for example, to transmit P-polarized light and reflect S-polarized light. The laser beam that has passed through the polarization beam splitter 12 passes through the quarter-wave plate 8 and the objective lens 13 held by the biaxial actuator, and is irradiated onto the recording layer of the optical disk 1 so as to be condensed. A laser beam reflected by the recording layer of the optical disk 1 is incident on the polarization beam splitter 12 via the objective lens 13 and the quarter-wave plate 8 . By passing through the quarter-wave plate 8 twice, the plane of polarization is rotated by 90 degrees. Therefore, the return light from the disk 1 is reflected to the half beam splitter 16 without being transmitted by the polarization beam splitter 12 . In the figure, the optical path of the signal light is indicated by a dashed line.

Laser light emitted from the laser 10 and reflected by the polarization beam splitter 12 functions as reference light in the homodyne detection method. The reference light reflected by the polarization beam splitter 12 passes through the quarter-wave plate 9 and the lens 14, is reflected by the mirror 15, passes through the lens 14 and the quarter-wave plate 9 again, and reaches the polarization beam splitter 12. is incident. The light reflected by the polarizing beam splitter 12 from the laser 10 and directed to the mirror 15 passes through the quarter-wave plate 9 twice between the polarizing beam splitter 12 and the mirror 15, thereby rotating the plane of polarization by 90 degrees. do. Therefore, the reflected light from the mirror 15 is transmitted to the half beam splitter 16 without being reflected by the polarization beam splitter 12 . In the figure, the optical path of the reference light is indicated by a solid line. The mirror 15 is displaced by the reference beam servo, as indicated by the arrows, so that the optical path length of the reference beam can be expanded or contracted.

Signal light and reference light are incident on the polarization beam splitter 12 , the signal light is reflected by the polarization beam splitter 12 , and the reference light passes through the polarization beam splitter 12 . The polarizing beam splitter 12 emits the signal light and the reference light in the same direction while superimposing them. Specifically, in this case, the signal light and the reference light are emitted in the same direction while being superimposed so that their optical axes are aligned. Here, the reference light is so-called coherent light.

The combined light of the signal light and the reference light output from the polarization beam splitter 12 is incident on the half beam splitter 16 . Half beam splitter 16 splits incident light into reflected and transmitted light in a ratio of approximately 1:1.

The superimposed light of the signal light and the reference light transmitted through the half beam splitter 16 is incident on the polarization beam splitter 18 via the half-wave plate 17 . On the other hand, the combined light of the signal light and the reference light reflected by the half beam splitter 16 is incident on the polarization beam splitter 20 via the quarter-wave plate 19 .

The half-wave plate 17 and the quarter-wave plate 19 are capable of rotating the plane of polarization. Therefore, by combining the half-wave plate 17 and the polarizing beam splitter 18, the ratio of the amount of light split by the polarizing beam splitter 18 can be adjusted. Similarly, the quarter-wave plate 19 can adjust the ratio of the amount of light split by the polarizing beam splitter 20 .

The amount of light split by each of the polarizing beam splitters 18 and 20 is approximately 1:1. Light reflected by the polarizing beam splitter 18 enters a photodetector 21 (PD1) as a first light receiving element, and light transmitted through the polarizing beam splitter 18 enters a photodetector 22 (PD2) as a second light receiving element. ). The light reflected by the polarizing beam splitter 20 enters a photodetector 23 (PD3) as a third light receiving element, and the light transmitted through the polarizing beam splitter 20 enters a photodetector 24 (PD4) as a fourth light receiving element. ).

A first received light signal I outputted from the photodetector 21 and passed through a capacitor 25 and a second received light signal J outputted from the photodetector 22 and passed through a capacitor 26 are supplied to a subtractor 27a. Further, the third received light signal K output from the photodetector 23 and passed through the capacitor 28 and the fourth received light signal L output from the photodetector 24 and passed through the capacitor 29 are supplied to the subtractor 27b. . Capacitors 25-29 are provided for supplying each received light signal to a subtractor 27a or 27b with AC coupling. A subtractor 27a generates a first difference signal a of (a=I−J) and a subtractor 27b generates a second difference signal b of (b=KL). The first differential signal a and the second differential signal b are orthogonal to each other, the first differential signal a is called the 0° phase side signal, and the second differential signal b is called the 90° phase side signal.

The output signal (0° phase side) of the subtractor 27a is supplied to the decoding processing section 30, and the reproduction signal is output from the decoding processing section 30. FIG. Also, the output signal (0° phase side) of the subtractor 27 a and the output signal (90° phase side) of the subtractor 27 b are supplied to the phase detection circuit 31 . A servo error signal is output from the phase detection circuit 31 . A servo error signal is provided to the servo mechanism (not shown) of mirror 15 via servo filter 32 . A mirror 15 is displaced according to the servo error signal to control the optical path length of the reference light.

The reference beam servo mechanism as described above can correct relatively low-frequency phase fluctuations such as surface wobbling of the optical disc 1, but has the problem that it cannot eliminate high-frequency phase fluctuations. High-frequency phase fluctuations are caused, for example, by minute irregularities (surface roughness) on the disk surface.

FIG. 2 shows another example configuration of a playback device using conventional homodyne detection. The configuration for taking out the 0° phase side signal a (=I−J) as the output of the subtractor 27a and taking out the 90° phase side signal b (=KL) as the output of the subtractor 27b is the same as in FIG. Therefore, the same reference numerals are given to the corresponding constituent elements, and the description thereof is omitted.

The 0° phase side signal a and the 90° phase side signal b are supplied to the phase correction section 33 , and the phase-corrected signal is supplied to the decoding processing section 30 . Note that the above-described reference beam servo may be used together.

FIG. 3 shows the configuration of the phase corrector 33. As shown in FIG. The 0° phase side signal a and the 90° phase side signal b are supplied to the rotation processing circuit 41 and the phase detection circuit 42 . A phase correction output A is obtained from the rotation processing circuit 41 . The phase detection circuit 42 performs the following arithmetic processing when the detected phase is represented by θ.

sin(2θ)=2ab
cos(2θ)=a ² -b ²

These equations are used to determine the detected phase θ.
θ=0.5a tan {(a ² −b ² ), ab}

The obtained detection phase θ is supplied to the phase unwrapping circuit 43 . The phase unwrapping circuit 43 is a circuit that reproduces the original signal from the phase-wrapped signal. An unwrapped phase θu is obtained at the output of the phase unwrapping circuit 43 .

The phase θu is supplied to the filtering circuit 44 . The filtering circuit 44 is provided for noise reduction and is, for example, a low-pass filter. The corrected phase θa extracted from the filter processing circuit 44 is supplied to the rotation processing circuit 41 . In the rotation processing circuit 41, the following arithmetic processing is performed, and a phase correction output A in which the phase fluctuation is corrected is obtained.

A=a·cos(θa)+b·sin(θa)

The processing of the phase unwrapping circuit 43 will be described with reference to FIG. The phase unwrapping process is a process of obtaining a level difference between two consecutive samples, determining that the phase has been folded when the obtained level difference is larger than a predetermined value, and correcting this folding. For example, as shown in FIG. 4A, the detected phase θ obtained by the phase detection circuit 42 can only take values in the range of (+180° to −180°). is wrapped to

In the phase unwrapping circuit 43, as an example, since the difference between the sample near +180° and the sample near −180° exceeds a predetermined value, it is determined that phase wrapping has occurred, as shown in FIG. 4B. , performs phase unwrapping processing to correct folding. Note that in FIG. 4, the dotted line represents the average value of the detected phases.

Since the phase unwrapping process described above is based on the premise that the detected phase .theta. changes continuously, there is a problem that the phase unwrapping process cannot be performed correctly if noise exists. For example, as shown in FIG. 5A, two samples (Pi−1 and Pi) that are continuous in time and close to +180° may have values lower than +180° and higher than +180° due to the influence of noise. Possible.

For such data, the data wrapped at +180° would be sample Pi−1 with the original value and sample Pi wrapped at −180°, as shown in FIG. 5B. The difference between two consecutive samples Pi−1 and Pi is calculated, but since the difference does not become large, the folding cannot be detected, resulting in data after phase unwrapping as shown in FIG. 5C. . The data in FIG. 5C is different from the correct value of detected phase θ.

<2. First Embodiment>
A first embodiment of the present technology will be described. The present technology performs phase correction by arithmetic processing, and has a system configuration as shown in FIG. It has a homodyne detection configuration similar to the conventional reproducing apparatus shown in FIG. In order to avoid duplication of description, the same reference numerals are given to corresponding components and their description is omitted. The 0° phase side signal a (=I−J) and the 90° phase side signal b (=KL) are supplied to the phase corrector 50 according to the present technology to form a phase corrected output.

The phase corrector 50 will be described with reference to FIG. The 0° phase side signal a(n) and the 90° phase side signal b(n) are supplied to the rotation processing circuit 51 . Note that n represents discrete time. A rotation processing circuit 51 performs a rotation operation on two input signals. From the rotation processing circuit 51, the following phase-corrected outputs (phase-corrected outputs A(n) and B(n)) are taken out. Here, θa(n) is the correction phase fed back from the filter processing circuit 53 .

A(n)=a(n)cos(θa(n))−b(n)sin(θa(n))
B(n)=a(n) sin(θa(n))+b(n)cos(θa(n))

The phase corrected output A(n) is taken as an output and supplied to phase detection circuit 52 . A phase correction output B(n) is also supplied to the phase detection circuit 52, and the detected phase .theta.(n) is obtained by the following calculation.

sin(2θ(n))=2A(n)B(n)
cos(2θ(n))=A(n) ² -B(n) ²
From these equations, the detection phase θ(n) can be obtained as follows.

θ(n)=0.5a tan {(A(n) ² -B(n) ² ), A(n)B(n)}

The obtained detection phase θ(n) is obtained by detecting the phase after phase correction by the rotation processing circuit 51, and the obtained detection phase θ(n) is the phase correction residual. The detected phase θ(n) is supplied to the filtering circuit 53 . The filter processing circuit 53 is, for example, a low-pass filter that performs a double integration operation as shown in the following equation to form the correction phase θa. The corrected phase θa formed by the filter processing circuit 53 is fed back to the rotation processing circuit 51 . θt is the output of the first integration and θa is the output of the second integration. In the formula, k1-k4 are constants.

θt(n+1)=k1θt(n)+k2θ(n)
θa(n+1)=k3θa(n)+k4θt(n+1)

In the first embodiment, by repeating the feedback process, the phase correction residual is approximately centered at 0°, so the phase unwrapping process becomes unnecessary. In this manner, since the phase correction unit 50 does not perform phase unwrapping processing, it is possible to prevent errors in phase unwrapping processing due to noise as described above. Further, by repeating the phase correction feedback loop, the corrected phase θa converges to a correct value.

<3. Second Embodiment>
A second embodiment of the present technology will be described. It has the same system configuration as the first embodiment (see FIG. 6). Also, the phase corrector 60 of the second embodiment has the configuration shown in FIG. A feedback path from the filter processing circuit 63 to the rotation processing circuit 61 is provided in the same manner as the phase correction unit 50 of the first embodiment.

The phase corrector 60 will be described with reference to FIG. The 0° phase side signal a(n) and the 90° phase side signal b(n) are supplied to the rotation processing circuit 61 . Note that n represents discrete time. A rotation processing circuit 61 performs a rotation operation on two input signals. The following phase correction outputs A(n) and B(n) are taken out from the rotation processing circuit 61 . Here, θa(n) is the corrected phase fed back from the filter processing circuit 63 .

A(n)=a(n)cos(θa(n))−b(n)sin(θa(n))
B(n)=a(n) sin(θa(n))+b(n)cos(θa(n))

These phase correction outputs A(n) and B(n) are supplied to phase detection circuit 62 . In the phase detection circuit 62, as shown below, two phase-corrected signals having a phase relationship orthogonal to each other are multiplied to obtain the correlation between the two, and the detected phase θ(n) (phase corrected residual).

θ(n)=A(n)B(n)

The detected phase θ(n) obtained by the phase detection circuit 62 is supplied to the filter processing circuit 63 . The filter processing circuit 63 is configured to perform two integrations as in the first embodiment. The corrected phase θa formed by the filter processing circuit 63 is fed back to the rotation processing circuit 61 .

In the second embodiment, since the phase unwrapping process is not performed, it is possible to prevent the phase unwrapping process from being erroneous due to noise as described above. Further, by repeating the phase correction feedback loop, the corrected phase θa converges to a correct value. Furthermore, since it is not necessary to perform trigonometric functions as in the first embodiment, the configuration of the phase detection circuit 62 can be simplified.

<5. Variation>
Although the embodiments of the present technology have been specifically described above, the present technology is not limited to the above-described embodiments, and various modifications are possible based on the technical idea of the present technology.

Also, the configurations, methods, steps, shapes, materials, numerical values, etc. of the above-described embodiments can be combined with each other without departing from the gist of the present technology.

For example, the present invention can also be applied to a configuration that does not perform differential operation, as shown in FIG. Elements in FIG. 9 that correspond to those in FIG. 2 are given the same reference numerals.

Note that the present technology can also take the following configuration.
(1)
Signal light is obtained by irradiating a recording medium with light emitted from a light source, reference light is generated from the light emitted from the light source, and the signal light and the reference light are superimposed. An optical system for generating a first set of signal light and reference light having a phase difference of approximately 0° and a third set of signal light and reference light having a phase difference of approximately 90°. and,
a light-receiving unit that receives the set of the first signal light and the reference light with a first light-receiving element and the set of the third signal light and the reference light with a third light-receiving element;
a phase correction unit to which a first light receiving signal obtained by the first light receiving element and a third light receiving signal obtained by the third light receiving element are supplied and which corrects an optical path length difference θ between the signal light and the reference light; ,
The phase corrector is
A phase correction circuit, a phase detection circuit for detecting a phase correction residual from an output signal of the phase correction circuit, and a filtering circuit for filtering the phase correction residual, wherein the output of the filtering circuit is subjected to the phase correction. A playback device comprising: a circuit feedback path;
(2)
Signal light is obtained by irradiating a recording medium with light emitted from a light source, reference light is generated from the light emitted from the light source, and the signal light and the reference light are superimposed. A pair of the first signal light and the reference light giving a phase difference of approximately 0° to the light, a pair of the second signal light and the reference light giving a phase difference of approximately 180°, and a pair of the light having a phase difference of approximately 90° an optical system for generating a third set of signal light and reference light with a phase difference and a fourth set of signal light and reference light with a phase difference of approximately 270°;
A set of the first signal light and the reference light is a first light receiving element, a set of the second signal light and the reference light is a second light receiving element, and a set of the third signal light and the reference light is a third light receiving element. , a light-receiving unit that receives the set of the fourth signal light and the reference light with a fourth light-receiving element, respectively;
A first difference signal a that is a difference between a first light receiving signal obtained by the first light receiving element and a second light receiving signal obtained by the second light receiving element; a third light receiving signal obtained by the third light receiving element; a computing unit that obtains a second difference signal b that is a difference between the fourth light receiving signals obtained by the fourth light receiving element and that has a phase relationship orthogonal to the first difference signal a;
a phase correction unit to which the first differential signal a and the second differential signal b are supplied and correcting an optical path length difference θ between the signal light and the reference light;
The phase corrector is
A phase correction circuit, a phase detection circuit for detecting a phase correction residual from an output signal of the phase correction circuit, and a filtering circuit for filtering the phase correction residual, wherein the output of the filtering circuit is subjected to the phase correction. A playback device comprising: a circuit feedback path;
(3)
The phase correction circuit forms outputs A(n) and B(n) after the phase correction by the following calculation when the corrected phase fed back is θa and the discrete time is n (1) or (2) 3. The playback device according to .
A(n)=a(n)cos(θa(n))−b(n)sin(θa(n))
B(n)=a(n) sin(θa(n))+b(n)cos(θa(n))
(4)
The reproducing apparatus according to (3), wherein the phase detection circuit forms the phase correction residual θ(n) by the following calculation when the corrected phase fed back is θa and the discrete time is n.
θ(n)=0.5atan{(A(n) ² -B(n) ² ), A(n)B(n)}
(5)
The reproducing apparatus according to (3), wherein the phase detection circuit forms the phase correction residual θ(n) by the following calculation when the corrected phase fed back is θa and the discrete time is n.
θ(n)=A(n)B(n)
(6)
The reproducing apparatus according to any one of (1) to (5), wherein the reference light is generated by reflecting the light emitted from the light source with a mirror.
(7)
Signal light is obtained by irradiating a recording medium with light emitted from a light source, reference light is generated from the light emitted from the light source, and the signal light and the reference light are superimposed. generating a first set of signal light and reference light with a phase difference of approximately 0° and a third set of signal light and reference light with a phase difference of approximately 90°;
receiving a set of the first signal light and the reference light by a first light receiving element and a set of the third signal light and the reference light by a third light receiving element;
a first light-receiving signal obtained by the first light-receiving element and a third light-receiving signal obtained by the third light-receiving element are supplied, and a phase correction unit corrects an optical path length difference θ between the signal light and the reference light;
The phase corrector is
A reproducing method comprising detecting a phase correction residual from a phase correction output signal, filtering the phase correction residual, and feeding back the filtered output to a phase correction circuit.
(8)
Signal light is obtained by irradiating a recording medium with light emitted from a light source, reference light is generated from the light emitted from the light source, and the signal light and the reference light are superimposed. A pair of the first signal light and the reference light giving a phase difference of approximately 0° to the light, a pair of the second signal light and the reference light giving a phase difference of approximately 180°, and a pair of the light having a phase difference of approximately 90° generating a third set of signal light and reference light with a phase difference and a fourth set of signal light and reference light with a phase difference of approximately 270°;
A set of the first signal light and the reference light is a first light receiving element, a set of the second signal light and the reference light is a second light receiving element, and a set of the third signal light and the reference light is a third light receiving element. , receiving the set of the fourth signal light and the reference light by a fourth light receiving element, respectively;
A first difference signal a that is a difference between a first light receiving signal obtained by the first light receiving element and a second light receiving signal obtained by the second light receiving element; a third light receiving signal obtained by the third light receiving element; Obtaining a second difference signal b, which is a difference of the fourth light receiving signal obtained by the fourth light receiving element and has a phase relationship orthogonal to the first difference signal a,
the first difference signal a and the second difference signal b are supplied, and a phase correction unit corrects an optical path length difference θ between the signal light and the reference light;
The phase corrector is
A reproducing method comprising detecting a phase correction residual from a phase correction output signal, filtering the phase correction residual, and feeding back the filtered output to the phase correction circuit.

Reference Signs List 1 optical disk 12, 20 polarizing beam splitter 15 mirror
21, 22, 23, 24... Photodetector, 27a, 27b... Subtractor,
30... signal processing section, 33, 50, 60... phase detection section,
41, 51, 61... rotation processing circuit, 43... phase unwrapping circuit,
44, 53, 63... filter processing circuit

Claims (8)

Signal light is obtained by irradiating a recording medium with light emitted from a light source, reference light is generated from the light emitted from the light source, and the signal light and the reference light are superimposed. An optical system for generating a first set of signal light and reference light having a phase difference of approximately 0° and a third set of signal light and reference light having a phase difference of approximately 90°. and,
a light-receiving unit that receives the set of the first signal light and the reference light with a first light-receiving element and the set of the third signal light and the reference light with a third light-receiving element;
a phase correction unit to which a first light receiving signal obtained by the first light receiving element and a third light receiving signal obtained by the third light receiving element are supplied and which corrects an optical path length difference θ between the signal light and the reference light; ,
The phase corrector is
A phase correction circuit, a phase detection circuit for detecting a phase correction residual from an output signal of the phase correction circuit, and a filtering circuit for filtering the phase correction residual, wherein the output of the filtering circuit is subjected to the phase correction. A playback device comprising: a circuit feedback path; Signal light is obtained by irradiating a recording medium with light emitted from a light source, reference light is generated from the light emitted from the light source, and the signal light and the reference light are superimposed. A pair of the first signal light and the reference light giving a phase difference of approximately 0° to the light, a pair of the second signal light and the reference light giving a phase difference of approximately 180°, and a pair of the light having a phase difference of approximately 90° an optical system for generating a third set of signal light and reference light with a phase difference and a fourth set of signal light and reference light with a phase difference of approximately 270°;
A set of the first signal light and the reference light is a first light receiving element, a set of the second signal light and the reference light is a second light receiving element, and a set of the third signal light and the reference light is a third light receiving element. , a light-receiving unit that receives the set of the fourth signal light and the reference light with a fourth light-receiving element, respectively;
A first difference signal a that is a difference between a first light receiving signal obtained by the first light receiving element and a second light receiving signal obtained by the second light receiving element; a third light receiving signal obtained by the third light receiving element; a computing unit that obtains a second difference signal b that is a difference between the fourth light receiving signals obtained by the fourth light receiving element and that has a phase relationship orthogonal to the first difference signal a;
a phase correction unit to which the first differential signal a and the second differential signal b are supplied and correcting an optical path length difference θ between the signal light and the reference light;
The phase corrector is
A phase correction circuit, a phase detection circuit for detecting a phase correction residual from an output signal of the phase correction circuit, and a filtering circuit for filtering the phase correction residual, wherein the output of the filtering circuit is subjected to the phase correction. A playback device comprising: a circuit feedback path; 3. The phase correction circuit forms phase-corrected outputs A(n) and B(n) by the following calculation when the corrected phase fed back is θa and the discrete time is n. 3. The playback device according to .
A(n)=a(n)cos(θa(n))−b(n)sin(θa(n))
B(n)=a(n) sin(θa(n))+b(n)cos(θa(n)) 4. The reproducing apparatus according to claim 3, wherein the phase detection circuit forms the phase correction residual .theta.(n) by the following calculation when the corrected phase fed back is .theta.a and the discrete time is n.
θ(n)=0.5a tan {(A(n) ² -B(n) ² ), A(n)B(n)} 4. The reproducing apparatus according to claim 3, wherein the phase detection circuit forms the phase correction residual .theta.(n) by the following calculation when the corrected phase fed back is .theta.a and the discrete time is n.
θ(n)=A(n)B(n) 3. The reproducing apparatus according to claim 1, wherein the reference light is generated by reflecting the light emitted from the light source with a mirror. Signal light is obtained by irradiating a recording medium with light emitted from a light source, reference light is generated from the light emitted from the light source, and the signal light and the reference light are superimposed. generating a first set of signal light and reference light with a phase difference of approximately 0° and a third set of signal light and reference light with a phase difference of approximately 90°;
receiving a set of the first signal light and the reference light by a first light receiving element and a set of the third signal light and the reference light by a third light receiving element;
a first light-receiving signal obtained by the first light-receiving element and a third light-receiving signal obtained by the third light-receiving element are supplied, and a phase correction unit corrects an optical path length difference θ between the signal light and the reference light;
The phase corrector is
A reproducing method comprising detecting a phase correction residual from an output signal of a phase correction circuit , filtering the phase correction residual , and feeding back the filtered output to the phase correction circuit.
Signal light is obtained by irradiating a recording medium with light emitted from a light source, reference light is generated from the light emitted from the light source, and the signal light and the reference light are superimposed. A pair of the first signal light and the reference light giving a phase difference of approximately 0° to the light, a pair of the second signal light and the reference light giving a phase difference of approximately 180°, and a pair of the light having a phase difference of approximately 90° generating a third set of signal light and reference light with a phase difference and a fourth set of signal light and reference light with a phase difference of approximately 270°;
A set of the first signal light and the reference light is a first light receiving element, a set of the second signal light and the reference light is a second light receiving element, and a set of the third signal light and the reference light is a third light receiving element. , receiving the set of the fourth signal light and the reference light by a fourth light receiving element, respectively;
A first difference signal a that is a difference between a first light receiving signal obtained by the first light receiving element and a second light receiving signal obtained by the second light receiving element; a third light receiving signal obtained by the third light receiving element; Obtaining a second difference signal b, which is a difference of the fourth light receiving signal obtained by the fourth light receiving element and has a phase relationship orthogonal to the first difference signal a,
the first difference signal a and the second difference signal b are supplied, and a phase correction unit corrects an optical path length difference θ between the signal light and the reference light;
The phase corrector is
A reproducing method comprising detecting a phase correction residual from an output signal of a phase correction circuit , filtering the phase correction residual , and feeding back the filtered output to the phase correction circuit.

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