阅读说明：本技术 再现装置以及再现方法 (Reproduction device and reproduction method ) 是由 堀笼俊宏 于 2019-09-04 设计创作，主要内容包括：一种再现装置,具有：运算部,求出第1差分信号a和与第1差分信号a相位关系正交的第2差分信号b；以及相位校正部,被供给第1差分信号a及第2差分信号b,校正信号光和参照光的光路长度差θ,相位校正部由相位校正电路、从相位校正电路的输出信号检测相位校正残差的相位检测电路以及对相位校正残差进行滤波处理的滤波处理电路构成,具备将滤波处理电路的输出反馈给相位校正电路的路径。(A reproduction apparatus has: a calculation unit that obtains a 1 st differential signal a and a 2 nd differential signal b orthogonal in phase relation to the 1 st differential signal a; and a phase correction unit to which the 1 st and 2 nd differential signals a and b are supplied and which corrects an optical path length difference θ between the signal light and the reference light, the phase correction unit being composed of a phase correction circuit, a phase detection circuit which detects a phase correction residual from an output signal of the phase correction circuit, and a filter processing circuit which performs filter processing on the phase correction residual, and including a path which feeds back an output of the filter processing circuit to the phase correction circuit.)

1. A reproduction apparatus has:

an optical system that 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 generates a group of 1 st signal light and reference light to which a phase difference of substantially 0 ° is applied and a group of 3 rd signal light and reference light to which a phase difference of substantially 90 ° is applied, respectively, for superimposed light obtained by superimposing the signal light and the reference light;

a light receiving unit for receiving the 1 st group of signal light and reference light by a 1 st light receiving element and receiving the 3 rd group of signal light and reference light by a 3 rd light receiving element; and

a phase correction unit to which a 1 st light reception signal obtained by the 1 st light receiving element and a 3 rd light reception signal obtained by the 3 rd light receiving element are supplied and which corrects an optical path length difference theta between the signal light and the reference light,

the phase correction unit includes 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 filter processing circuit for performing filter processing on the phase correction residual, and includes a path for feeding back an output of the filter processing circuit to the phase correction circuit.

2. A reproduction apparatus has:

an optical system that 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 generates a group of 1 st signal light and reference light to which a phase difference of substantially 0 ° is applied, a group of 2 nd signal light and reference light to which a phase difference of substantially 180 ° is applied, a group of 3 rd signal light and reference light to which a phase difference of substantially 90 ° is applied, and a group of 4 th signal light and reference light to which a phase difference of substantially 270 ° is applied, respectively, for superimposed light obtained by superimposing the signal light and the reference light;

a light receiving unit for receiving the 1 st group of signal light and reference light by a 1 st light receiving element, receiving the 2 nd group of signal light and reference light by a 2 nd light receiving element, receiving the 3 rd group of signal light and reference light by a 3 rd light receiving element, and receiving the 4 th group of signal light and reference light by a 4 th light receiving element;

a calculation unit that calculates a 1 st differential signal a and a 2 nd differential signal b, the 1 st differential signal a being a difference between a 1 st light-receiving signal obtained by the 1 st light-receiving element and a 2 nd light-receiving signal obtained by the 2 nd light-receiving element, the 2 nd differential signal b being a difference between a 3 rd light-receiving signal obtained by the 3 rd light-receiving element and a 4 th light-receiving signal obtained by the 4 th light-receiving element, the 2 nd differential signal b being orthogonal in phase relation to the 1 st differential signal a; and

a phase correction unit to which the 1 st differential signal a and the 2 nd differential signal b are supplied and which corrects an optical path length difference θ between the signal light and the reference light,

the phase correction unit includes 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 filter processing circuit for performing filter processing on the phase correction residual, and includes a path for feeding back an output of the filter processing circuit to the phase correction circuit.

3. The reproduction apparatus according to claim 1 or 2, wherein,

when the feedback correction phase is theta a and the dispersion time is n, the phase correction circuit forms phase-corrected outputs A (n) and B (n) by the following operation,

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 reproduction apparatus according to claim 3, wherein,

when the feedback correction phase is represented by θ a and the dispersion time is represented by n, the phase detection circuit forms a phase correction residual θ (n) by the following operation,

θ(n)＝0.5atan{(A(n)²-B(n)²),A(n)B(n)}。

5. the reproduction apparatus according to claim 3, wherein,

when the feedback correction phase is represented by θ a and the dispersion time is represented by n, the phase detection circuit forms a phase correction residual θ (n) by the following operation,

θ(n)＝A(n)B(n)。

6. the reproduction apparatus according to claim 1 or 2, wherein,

the reference light is generated by reflecting light emitted from the light source by a mirror.

7. A method of reproducing a video signal includes the steps of,

a first step of obtaining signal light by irradiating a recording medium with light emitted from a light source, and generating reference light from the light emitted from the light source, and a second step of generating a group of 1 st signal light and reference light to which a phase difference of substantially 0 DEG is applied and a group of 3 rd signal light and reference light to which a phase difference of substantially 90 DEG is applied, respectively, for superimposed light obtained by superimposing the signal light and the reference light,

the 1 st light receiving element receives the 1 st set of signal light and reference light, the 3 rd light receiving element receives the 3 rd set of signal light and reference light,

supplying a 1 st light receiving signal obtained by the 1 st light receiving element and a 3 rd light receiving signal obtained by the 3 rd light receiving element, correcting an optical path length difference theta between the signal light and the reference light by a phase correcting section,

the phase correction section performs:

a phase correction residual is detected from the phase corrected output signal, the phase correction residual is subjected to filtering processing, and the output of the filtering processing is fed back to the phase correction circuit.

8. A method of reproducing a video signal includes the steps of,

a signal light is obtained by irradiating a recording medium with light emitted from a light source, a reference light is generated from the light emitted from the light source, and a group of a 1 st signal light and the reference light to which a phase difference of substantially 0 DEG is applied, a group of a 2 nd signal light and the reference light to which a phase difference of substantially 180 DEG is applied, a group of a 3 rd signal light and the reference light to which a phase difference of substantially 90 DEG is applied, and a group of a 4 th signal light and the reference light to which a phase difference of substantially 270 DEG is applied are generated for superimposed light obtained by superimposing the signal light and the reference light,

receiving the set of the 1 st signal light and the reference light by a 1 st light receiving element, receiving the set of the 2 nd signal light and the reference light by a 2 nd light receiving element, receiving the set of the 3 rd signal light and the reference light by a 3 rd light receiving element, and receiving the set of the 4 th signal light and the reference light by a 4 th light receiving element,

obtaining a 1 st differential signal a and a 2 nd differential signal b, the 1 st differential signal a being a difference between a 1 st light-receiving signal obtained by the 1 st light-receiving element and a 2 nd light-receiving signal obtained by the 2 nd light-receiving element, the 2 nd differential signal b being a difference between a 3 rd light-receiving signal obtained by the 3 rd light-receiving element and a 4 th light-receiving signal obtained by the 4 th light-receiving element, the 2 nd differential signal b being orthogonal in phase relation to the 1 st differential signal a,

supplying the 1 st differential signal a and the 2 nd differential signal b, correcting the optical path length difference theta between the signal light and the reference light by a phase correction unit,

the phase correction section performs:

a phase correction residual is detected from the phase corrected output signal, the phase correction residual is subjected to filtering processing, and the output of the filtering processing is fed back to the phase correction circuit.

Technical Field

The present technology relates to a reproduction apparatus and a reproduction method suitable for reproducing an optical medium such as an optical disc.

Background

For example, when a multilayer optical disc is reproduced, the amount of signal light decreases, and there is a high possibility that an error occurs in reading a signal. In order to solve this problem, a homodyne (homodyne) detection method is known in which a detection signal is amplified by interference of light (see patent documents 1 and 2).

In patent document 1, as a homodyne method for detecting light obtained by interfering signal light and reference light, 4 signal light/reference light groups obtained by shifting the phase difference by 90 degrees are detected. Specifically, the detection is performed for each of the signal light/reference light groups having the phase differences of 0 degrees, 90 degrees, 180 degrees, and 270 degrees. These detections are performed by detecting the light intensities of the light obtained by interfering the signal light and the reference light, respectively. Further, a servo that corrects a change in the optical path length due to surface vibration of the optical disc is applied. Patent document 2 describes that the optical path length difference between the signal light and the reference light is obtained by calculation.

In the homodyne system, a component of the signal light 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.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2010-044832

Patent document 2: japanese patent laid-open publication No. 2013-054801

Disclosure of Invention

Problems to be solved by the invention

In the homodyne method, when there is a difference (phase shift) θ in optical path length between the signal light and the reference light, a desired effect cannot be obtained. There are phase fluctuations of a relatively low frequency and phase fluctuations of a higher frequency due to surface vibration of the optical disc in θ. The phase fluctuation of the high frequency is caused by, for example, minute irregularities (surface roughness) on the disk surface. In the case of the servo control described in patent document 1, the phase fluctuation is higher than the servo band, and the high-frequency phase fluctuation cannot be completely eliminated.

Since the phase fluctuation of a high frequency cannot be eliminated by changing the length of the optical path by the displacement of the mirror, the phase fluctuation is eliminated by signal processing. In the case of correcting the phase therefor, in order to eliminate noise of the detected phase difference signal, a phase expansion process and a filtering process are applied. However, there are cases where the expansion of the phase cannot be performed correctly due to the influence of noise and a large error is added to the filtering processing result.

Therefore, an object of the present technology is to provide a playback device and a playback method that employ a homodyne detection scheme and can prevent phase expansion from being affected by noise and being unable to be performed correctly.

Means for solving the problems

The present technology provides a playback device having:

an optical system that 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 generates a group of 1 st signal light and reference light to which a phase difference of substantially 0 ° is applied and a group of 3 rd signal light and reference light to which a phase difference of substantially 90 ° is applied, respectively, for superimposed light obtained by superimposing the signal light and the reference light;

a light receiving unit for receiving the 1 st group of signal light and reference light by the 1 st light receiving element and receiving the 3 rd group of signal light and reference light by the 3 rd light receiving element; and

a phase correction unit to which the 1 st light receiving signal obtained by the 1 st light receiving element and the 3 rd light receiving signal obtained by the 3 rd light receiving element are supplied and which corrects the optical path length difference theta between the signal light and the reference light,

the phase correction unit includes 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 filter processing circuit for performing filter processing on the phase correction residual, and includes a path for feeding back an output of the filter processing circuit to the phase correction circuit.

The present technology provides a playback device having:

an optical system that obtains signal light by irradiating a recording medium with light emitted from a light source and generates reference light from the light emitted from the light source, and generates a group of 1 st signal light and reference light to which a phase difference of substantially 0 ° is applied, a group of 2 nd signal light and reference light to which a phase difference of substantially 180 ° is applied, a group of 3 rd signal light and reference light to which a phase difference of substantially 90 ° is applied, and a group of 4 th signal light and reference light to which a phase difference of substantially 270 ° is applied, respectively, for superimposed light obtained by superimposing the signal light and the reference light;

a light receiving unit for receiving the 1 st group of signal light and reference light by the 1 st light receiving element, receiving the 2 nd group of signal light and reference light by the 2 nd light receiving element, receiving the 3 rd group of signal light and reference light by the 3 rd light receiving element, and receiving the 4 th group of signal light and reference light by the 4 th light receiving element;

a calculation unit that calculates a 1 st differential signal a and a 2 nd differential signal b, the 1 st differential signal a being a difference between a 1 st light-receiving signal obtained by a 1 st light-receiving element and a 2 nd light-receiving signal obtained by a 2 nd light-receiving element, the 2 nd differential signal b being a difference between a 3 rd light-receiving signal obtained by a 3 rd light-receiving element and a 4 th light-receiving signal obtained by a 4 th light-receiving element, and being orthogonal in phase relation to the 1 st differential signal a; and

a phase correction unit to which the 1 st and 2 nd differential signals a and b are supplied and which corrects the optical path length difference theta between the signal light and the reference light,

the phase correction unit includes 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 filter processing circuit for performing filter processing on the phase correction residual, and includes a path for feeding back an output of the filter processing circuit to the phase correction circuit.

ADVANTAGEOUS EFFECTS OF INVENTION

According to at least one embodiment, since the phase difference between the signal light and the reference light is sequentially updated and the phase correction residual is centered at substantially zero degrees, the correction phase can be accurately calculated without phase expansion, and the land/groove (land/groove) recording type optical recording medium can be satisfactorily reproduced by the homodyne detection method. The effects described herein are not necessarily limited, and may be any effects described in the present technology or effects different from them. The content of the present technology should not be interpreted as being limited to the exemplary effects described in the following description.

Drawings

Fig. 1 is a diagram showing a configuration of an example of a conventional playback apparatus.

Fig. 2 is a diagram showing another example of the conventional playback apparatus.

Fig. 3 is a block diagram showing the configuration of a phase detection unit of another example of the conventional playback apparatus.

Fig. 4A and 4B are schematic diagrams for explaining the phase unwrapping process.

Fig. 5A, 5B, and 5C are schematic diagrams for explaining a problem point of the phase unwrapping process.

Fig. 6 is a diagram showing the configuration of embodiment 1 of the present technology.

Fig. 7 is a block diagram showing the configuration of the phase correction section according to embodiment 1 of the present technology.

Fig. 8 is a block diagram showing the configuration of the phase correction section according to embodiment 2 of the present technology.

Fig. 9 is a diagram showing another example of the conventional playback apparatus.

Detailed Description

The embodiments described below are preferable specific examples of the present technology, and various limitations that are preferable in the art are added. However, the scope of the present technology is not limited to these embodiments unless otherwise specified in the following description.

The present technology is described in the following order.

<1. reproducing apparatus using conventional homodyne detection >

<2 > embodiment 1 >

<3 > embodiment 2 >

<4. modified example >

<1. reproducing apparatus using conventional homodyne detection >

Fig. 1 shows a configuration of an example of a playback apparatus using conventional homodyne detection. When loaded in a playback device, an optical recording medium (hereinafter referred to as an optical disc) 1 is driven to rotate by a spindle motor. The recording signal is reproduced by irradiating the optical disk 1 driven by rotation with laser light. The optical disc 1 is, for example, a so-called write-once type optical disc in which information is recorded by forming a recording mark.

In the optical disc 1, a cover layer, a recording layer (reflective film), and a substrate are formed in this order from the upper layer side. Here, the "upper layer side" refers to the upper layer side when the surface on which the laser light from the playback device side is incident is defined as the upper surface. That is, in this case, the laser light enters the optical disc 1 from the cover layer side. The substrate is made of a resin such as polycarbonate, for example, and has a cross-sectional shape with irregularities provided on the upper surface side thereof. The cover layer is provided to protect the recording layer. In the optical disc 1 to be reproduced, a mark train is formed.

In the optical system of the reproduction apparatus, a laser (semiconductor laser) 10 serving as a laser light source for reproduction is provided. The laser light emitted from the laser 10 is collimated by the collimator lens 11 and then enters the polarization beam splitter 12.

The polarization beam splitter 12 is configured to transmit P-polarized light and reflect S-polarized light, for example. The laser light transmitted through the polarization beam splitter 12 is condensed on the recording layer of the optical disc 1 via the 1/4 wavelength plate 8 and the objective lens 13 held by the 2-axis actuator, and is irradiated. The laser light reflected by the recording layer of the optical disc 1 is incident on the polarization beam splitter 12 via the objective lens 13 and the 1/4 wavelength plate 8. The plane of polarization is rotated 90 degrees due to the 2 passes through the 1/4 wavelength plate 8. Therefore, the return light from the disk 1 is not transmitted by the polarization beam splitter 12 but reflected and directed toward the half beam splitter 16. In the figure, the optical path of the signal light is shown by broken lines.

The 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 1/4 wavelength plate 9 and the lens 14, is reflected by the mirror 15, passes through the lens 14 and the 1/4 wavelength plate 9 again, and enters the polarization beam splitter 12. The light reflected by the polarization beam splitter 12 from the laser 10 toward the mirror 15 passes through the 1/4 wavelength plate 9 2 times in the round trip between the polarization beam splitter 12 and the mirror 15, and the polarization plane is rotated by 90 degrees. Therefore, the reflected light from the mirror 15 is transmitted toward 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 can be displaced by the reference light servo as indicated by an arrow, thereby extending and shortening the optical path length of the reference light.

The signal light and the reference light enter 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. These signal light and reference light are emitted in the same direction in a superimposed state by the polarization beam splitter 12. Specifically, in this case, the signal light and the reference light are emitted in the same direction in a state where they are overlapped so that their optical axes coincide. Here, the reference light is so-called coherent light.

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

The overlapped light of the signal light and the reference light transmitted through the half beam splitter 16 is incident to the polarization beam splitter 18 via the 1/2 wavelength plate 17. On the other hand, the superimposed 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 1/4 wavelength plate 19.

The 1/2 wavelength plates 17 and 1/4 wavelength plate 19 can rotate the polarization plane. Therefore, by combining 1/2 the wavelength plate 17 and the polarization beam splitter 18, the ratio of the amounts of light split by the polarization beam splitter 18 can be adjusted. Similarly, the 1/4 wavelength plate 19 can be used to adjust the ratio of the amounts of light split by the polarization beam splitter 20.

The light quantity of the light split by each of the polarization beam splitter 18 and the polarization beam splitter 20 is made to be substantially 1: 1. the light reflected by the polarization beam splitter 18 enters the photodetection section 21 as the 1 st light receiving element (PD1), and the light transmitted through the polarization beam splitter 18 enters the photodetection section 22 as the 2 nd light receiving element (PD 2). The light reflected by the polarization beam splitter 20 is incident on the photodetection section 23 as the 3 rd light receiving element (PD3), and the light transmitted through the polarization beam splitter 20 is incident on the photodetection section 24 as the 4 th light receiving element (PD 4).

The 1 st received light signal I output from the light detection unit 21 via the capacitor 25 and the 2 nd received light signal J output from the light detection unit 22 via the capacitor 26 are supplied to the subtractor 27 a. The 3 rd received light signal K output from the light detection unit 23 via the capacitor 28 and the 4 th received light signal L output from the light detection unit 24 via the capacitor 29 are supplied to the subtractor 27 b. The capacitors 25 to 29 are provided to supply the respective light reception signals to the subtracter 27a or the subtracter 27b even in the case of ac coupling. Subtractor 27a generates 1 st differential signal a (a-I-J), and subtractor 27b generates 2 nd differential signal b (b-K-L). The 1 st differential signal a and the 2 nd differential signal b are in a quadrature relationship, and the 1 st differential signal a is referred to as a 0 ° phase side signal, and the 2 nd differential signal b is referred to as a 90 ° phase side signal.

The output signal (on the 0 ° phase side) of the subtractor 27a is supplied to the decoding processing unit 30, and the decoding processing unit 30 outputs a reproduction signal. The output signal of the subtractor 27a (on the 0 ° phase side) and the output signal of the subtractor 27b (on the 90 ° phase side) are supplied to the phase detection circuit 31. The phase detection circuit 31 outputs a servo error signal. The servo error signal is supplied to a servo mechanism (not shown) of the mirror 15 via a servo filter 32. The mirror 15 is displaced in accordance with the servo error signal to control the optical path length of the reference light.

The reference optical servo mechanism as described above can correct phase fluctuations of a relatively low frequency such as surface vibrations of the optical disc 1, but has a problem that phase fluctuations of a high frequency cannot be eliminated. The phase fluctuation of the high frequency is caused by, for example, minute irregularities (surface roughness) on the disk surface.

Fig. 2 shows another example of a playback apparatus using conventional homodyne detection. The configuration for extracting the 0 ° phase side signal a (═ I-J) from the output of the subtractor 27a and extracting the 90 ° phase side signal b (═ K-L) from the output of the subtractor 27b is the same as that in fig. 1, and therefore the same reference numerals are assigned 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 unit 33, and the phase-corrected signals are supplied to the decoding processing unit 30. In addition, the above-described reference light servo may be used in combination.

Fig. 3 shows the structure of the phase correcting section 33. 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. The phase correction output a is obtained from the rotation processing circuit 41. The phase detection circuit 42 performs the following operation when the detection phase is represented by θ.

sin(2θ)＝2ab

cos(2θ)＝a²-b²

The detection phase θ is obtained using these equations.

θ＝0.5atan{(a²-b²),ab}

The detected phase θ thus obtained is supplied to the phase unwrapping circuit 43. The phase unwrapping circuit 43 is a circuit for reproducing an original signal from the phase-wrapped signal. The phase expanded θ u is obtained as an output of the phase expansion circuit 43.

The phase θ u is supplied to the filter processing circuit 44. The filter processing circuit 44 is provided for reducing noise, and is, for example, a low-pass filter. The correction phase θ a extracted from the filter processing circuit 44 is supplied to the rotation processing circuit 41. The rotation processing circuit 41 performs the following operation processing to obtain a phase correction output a in which the phase fluctuation is corrected.

A＝a·cos(θa)+b·sin(θa)

The processing of the phase unwrapping circuit 43 is explained with reference to fig. 4. The phase unwrapping process is a process of finding a level difference between 2 consecutive samples, determining that a phase is wrapped and correcting the wrapping when the found level difference is larger than a predetermined value. For example, as shown in fig. 4A, the detected phase θ obtained by the phase detection circuit 42 can take only a value in the range of (+180 ° to-180 °), and thus, for example, a value exceeding +180 ° is folded back to the-180 ° side.

In the phase development circuit 43, as an example, since the difference between the sample in the vicinity of +180 ° and the sample in the vicinity of-180 ° exceeds a predetermined value, it is determined that the phase folding occurs, and as shown in fig. 4B, a phase development process of correcting the folding is performed. In fig. 4, broken lines indicate the average values of the detection phases.

The phase expansion process is premised on the detection phase θ continuously changing, and therefore there is a problem that the phase expansion process cannot be accurately performed in the presence of noise. For example, as shown in fig. 5A, 2 samples (Pi-1 and Pi) which are continuous in time and are close to a value of +180 ° may have a value lower than +180 ° and a value higher than +180 ° due to the influence of noise.

In the case of such data, as shown in fig. 5B, with respect to data wound at +180 ° (wrapping), sample Pi-1 is the original value and sample Pi is the folded value at-180 °. The difference between 2 consecutive samples Pi-1 and Pi is calculated, but the difference is not large, so that the fold cannot be detected, and data after the phase unwrapping process shown in fig. 5C is generated. The data of fig. 5C is different from the correct value of the detection phase θ.

<2 > embodiment 1 >

Embodiment 1 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. 6. The configuration of the homodyne detection is similar to that of the conventional playback apparatus shown in fig. 2. In order to avoid redundant description, the same reference numerals are assigned to corresponding constituent elements, and the description thereof is omitted. The 0 ° phase side signal a (═ I-J) and the 90 ° phase side signal b (═ K-L) are supplied to the phase correction unit 50 according to the present technology, and phase correction outputs are formed.

The phase correction section 50 is explained with reference to fig. 7. The 0 ° phase side signal a (n) and the 90 ° phase side signal b (n) are supplied to the rotation processing circuit 51. Further, n represents a discrete time. The rotation processing circuit 51 performs rotation operation of the two input signals. The phase-corrected outputs (phase correction outputs a (n) and b (n)) shown below are extracted from the rotation processing circuit 51. Here, θ a (n) is a 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 correction output a (n) is extracted as an output and supplied to the phase detection circuit 52. The phase detection circuit 52 is also supplied with a phase correction output b (n) to calculate a detection phase θ (n) 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) is obtained as follows.

θ(n)＝0.5atan{(A(n)²-B(n)²),A(n)B(n)}

The obtained detection phase θ (n) is a result of detecting the phase after the phase correction by the rotation processing circuit 51, and the obtained detection phase θ (n) is a phase correction residual. The detected phase θ (n) is supplied to the filter processing circuit 53. The filter processing circuit 53 is, for example, a low-pass filter that performs an operation of 2-time integration as shown in the following expression to form the correction phase θ a. The corrected phase θ a formed by the filter processing circuit 53 is fed back to the rotation processing circuit 51. θ t is the output of the 1 st integration, and θ a is the output of the 2 nd integration. In the formula, k1 to k4 are constants.

θt(n+1)＝k1θt(n)+k2θ(n)

θa(n+1)＝k3θa(n)+k4θt(n+1)

In embodiment 1, since the phase correction residual is centered at approximately 0 ° by repeating the feedback process, the phase development process becomes unnecessary. In this way, since the phase correction unit 50 does not perform the phase expansion process, it is possible to prevent the phase expansion process from being mistaken by noise as described above. Further, by repeating the feedback loop of the phase correction, the corrected phase θ a converges to a correct value.

<3 > embodiment 2 >

Embodiment 2 of the present technology will be described. The system has the same configuration as that of embodiment 1 (see fig. 6). The phase correction unit 60 according to embodiment 2 has the configuration shown in fig. 8. As in the phase correction unit 50 of embodiment 1, a feedback path from the filter processing circuit 63 to the rotation processing circuit 61 is provided.

The phase correction section 60 is explained with reference to fig. 8. The 0 ° phase side signal a (n) and the 90 ° phase side signal b (n) are supplied to the rotation processing circuit 61. Further, n represents a discrete time. The rotation processing circuit 61 performs rotation calculation of the two input signals. The phase correction outputs a (n) and b (n) shown below are extracted from the rotation processing circuit 61. Here, θ a (n) is a correction 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 the phase detection circuit 62. The phase detection circuit 62 obtains a correlation between two signals after phase correction, which have orthogonal phase relationships, by using a value obtained by multiplying the two signals as described below, and uses the correlation as a detected phase θ (n) (phase correction 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 integration 2 times as in embodiment 1. The corrected phase θ a formed by the filter processing circuit 63 is fed back to the rotation processing circuit 61.

In embodiment 2, since the phase expansion process is not performed, it is possible to prevent the phase expansion process from being mistaken by noise as described above. Further, by repeating the feedback loop of the phase correction, the corrected phase θ a converges to a correct value. Further, since it is not necessary to perform the operation of the trigonometric function as in embodiment 1, the configuration of the phase detection circuit 62 can be simplified.

<5. modified example >

The embodiments of the present technology have been described above specifically, but the present technology is not limited to the above embodiments, and various modifications based on the technical idea of the present technology can be made.

The structures, methods, steps, shapes, materials, numerical values, and the like of the above embodiments can be combined with each other without departing from the gist of the present technology.

For example, as shown in fig. 9, the present invention can be applied to a configuration in which differential operation is not performed. The same reference numerals are given to the constituent elements in fig. 9 corresponding to fig. 2.

The present technology can also adopt the following configuration.

(1)

A reproduction apparatus has:

an optical system that 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 generates a group of 1 st signal light and reference light to which a phase difference of substantially 0 ° is applied and a group of 3 rd signal light and reference light to which a phase difference of substantially 90 ° is applied, respectively, for superimposed light obtained by superimposing the signal light and the reference light;

a light receiving unit for receiving the 1 st group of signal light and reference light by a 1 st light receiving element and receiving the 3 rd group of signal light and reference light by a 3 rd light receiving element; and

a phase correction unit to which a 1 st light reception signal obtained by the 1 st light receiving element and a 3 rd light reception signal obtained by the 3 rd light receiving element are supplied and which corrects an optical path length difference theta between the signal light and the reference light,

the phase correction unit includes 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 filter processing circuit for performing filter processing on the phase correction residual, and includes a path for feeding back an output of the filter processing circuit to the phase correction circuit.

(2)

A reproduction apparatus has:

an optical system that 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 generates a group of 1 st signal light and reference light to which a phase difference of substantially 0 ° is applied, a group of 2 nd signal light and reference light to which a phase difference of substantially 180 ° is applied, a group of 3 rd signal light and reference light to which a phase difference of substantially 90 ° is applied, and a group of 4 th signal light and reference light to which a phase difference of substantially 270 ° is applied, respectively, for superimposed light obtained by superimposing the signal light and the reference light;

a light receiving unit for receiving the 1 st group of signal light and reference light by a 1 st light receiving element, receiving the 2 nd group of signal light and reference light by a 2 nd light receiving element, receiving the 3 rd group of signal light and reference light by a 3 rd light receiving element, and receiving the 4 th group of signal light and reference light by a 4 th light receiving element;

a calculation unit that calculates a 1 st differential signal a and a 2 nd differential signal b, the 1 st differential signal a being a difference between a 1 st light-receiving signal obtained by the 1 st light-receiving element and a 2 nd light-receiving signal obtained by the 2 nd light-receiving element, the 2 nd differential signal b being a difference between a 3 rd light-receiving signal obtained by the 3 rd light-receiving element and a 4 th light-receiving signal obtained by the 4 th light-receiving element, the 2 nd differential signal b being orthogonal in phase relation to the 1 st differential signal a; and

a phase correction unit to which the 1 st differential signal a and the 2 nd differential signal b are supplied and which corrects an optical path length difference θ between the signal light and the reference light,

the phase correction unit includes 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 filter processing circuit for performing filter processing on the phase correction residual, and includes a path for feeding back an output of the filter processing circuit to the phase correction circuit.

(3)

The reproduction apparatus according to (1) or (2), wherein,

when the feedback correction phase is theta a and the dispersion time is n, the phase correction circuit forms phase-corrected outputs A (n) and B (n) by the following operation,

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 reproduction apparatus according to (3), wherein,

when the feedback correction phase is represented by θ a and the dispersion time is represented by n, the phase detection circuit forms a phase correction residual θ (n) by the following operation,

θ(n)＝0.5atan{(A(n)²-B(n)²),A(n)B(n)}。

(5)

the reproduction apparatus according to (3), wherein,

when the feedback correction phase is represented by θ a and the dispersion time is represented by n, the phase detection circuit forms a phase correction residual θ (n) by the following operation,

θ(n)＝A(n)B(n)。

(6)

the reproduction apparatus according to any one of (1) to (5), wherein,

the reference light is generated by reflecting light emitted from the light source by a mirror.

(7)

A method of reproducing a video signal includes the steps of,

a first step of obtaining signal light by irradiating a recording medium with light emitted from a light source, and generating reference light from the light emitted from the light source, and a second step of generating a group of 1 st signal light and reference light to which a phase difference of substantially 0 DEG is applied and a group of 3 rd signal light and reference light to which a phase difference of substantially 90 DEG is applied, respectively, for superimposed light obtained by superimposing the signal light and the reference light,

the 1 st light receiving element receives the 1 st set of signal light and reference light, the 3 rd light receiving element receives the 3 rd set of signal light and reference light,

supplying a 1 st light receiving signal obtained by the 1 st light receiving element and a 3 rd light receiving signal obtained by the 3 rd light receiving element, correcting an optical path length difference theta between the signal light and the reference light by a phase correcting section,

the phase correction section performs:

a phase correction residual is detected from the phase corrected output signal, the phase correction residual is subjected to filtering processing, and the output of the filtering processing is fed back to the phase correction circuit.

(8)

A method of reproducing a video signal includes the steps of,

a signal light is obtained by irradiating a recording medium with light emitted from a light source, a reference light is generated from the light emitted from the light source, and a group of a 1 st signal light and the reference light to which a phase difference of substantially 0 DEG is applied, a group of a 2 nd signal light and the reference light to which a phase difference of substantially 180 DEG is applied, a group of a 3 rd signal light and the reference light to which a phase difference of substantially 90 DEG is applied, and a group of a 4 th signal light and the reference light to which a phase difference of substantially 270 DEG is applied are generated for superimposed light obtained by superimposing the signal light and the reference light,

receiving the set of the 1 st signal light and the reference light by a 1 st light receiving element, receiving the set of the 2 nd signal light and the reference light by a 2 nd light receiving element, receiving the set of the 3 rd signal light and the reference light by a 3 rd light receiving element, and receiving the set of the 4 th signal light and the reference light by a 4 th light receiving element,

obtaining a 1 st differential signal a and a 2 nd differential signal b, the 1 st differential signal a being a difference between a 1 st light-receiving signal obtained by the 1 st light-receiving element and a 2 nd light-receiving signal obtained by the 2 nd light-receiving element, the 2 nd differential signal b being a difference between a 3 rd light-receiving signal obtained by the 3 rd light-receiving element and a 4 th light-receiving signal obtained by the 4 th light-receiving element, the 2 nd differential signal b being orthogonal in phase relation to the 1 st differential signal a,

supplying the 1 st differential signal a and the 2 nd differential signal b, correcting the optical path length difference theta between the signal light and the reference light by a phase correction unit,

the phase correction section performs:

a phase correction residual is detected from the phase corrected output signal, the phase correction residual is subjected to filtering processing, and the output of the filtering processing is fed back to the phase correction circuit.

Description of the symbols

1. optical disk, 12, 20. polarization beam splitter, 15. mirror,

21. 22, 23, 24. DEG.light detection part, 27a, 27 b. DEG.subtracter,

a 30. signal processing part, 33, 50, 60. phase detecting part,

41. 51, 61. rotation processing circuit, 43. phase unwrapping circuit,

44. 53, 63. filter processing circuit