JP5043049B2 - Optical information reproducing method and optical disc apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detecting an interference-type optical information signal capable of easily adjusting an optical path difference between signal light and reference light, providing a high signal amplification effect, and stably maintaining the effect, and suited to the miniaturization of an optical system. <P>SOLUTION: The optical disk device for interfering light used as reference light without being applied to an optical disk 109 with reflected light from the optical disk, and obtaining an amplifying signal by calculation based on a plurality of interference signal outputs includes, in its signal processing circuit 25, a calculation adjustment mechanism for monitoring one or both of ongoing calculation and a calculation output and adjusting calculation so as to stabilize the output. Thus, variations of device components or an influence of a change of characteristics with time or the like is prevented, and an amplifying effect is stably obtained. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a high S / N ratio of a reproduction signal of an optical disc apparatus.

  Optical discs have reached the limit of the resolution of the optical system, resulting in the commercialization of a blue-ray disc using a blue semiconductor laser and a high NA objective lens. To further increase the capacity, the recording layer will be multilayered in the future. It is thought to be influential. In such a multi-layer optical disc, the reflectance from a specific recording layer must be reduced because the amount of light detected from each recording layer needs to be substantially equal. However, since the optical disk needs to have a large capacity and a high dubbing speed for video and the like, the data transfer speed is also increasing, and the S / N ratio of the reproduced signal cannot be secured sufficiently. Therefore, in order to simultaneously advance the multilayering and speeding up of the recording layer in the future, it is essential to increase the S / N of the detection signal.

  Techniques related to increasing the S / N ratio of the reproduction signal of the optical disk are described in Patent Documents 1 to 3, for example. In Patent Documents 1 and 2, regarding the increase in the S / N ratio of the reproduction signal of the magneto-optical disk, the light from the semiconductor laser branches before irradiating the optical disk, and the light not irradiated to the optical disk is combined with the reflected light from the optical disk. The aim is to amplify the amplitude of a weak signal by increasing the amount of light that does not irradiate the optical disk by causing interference with waves. The differential detection of the transmitted light and reflected light of the polarization beam splitter conventionally used for magneto-optical disk signal detection is essentially the incident polarization direction caused by the original incident polarization component and the polarization rotation by the magneto-optical disk. Is detected by amplifying the orthogonal polarization component with the incident polarized light. Therefore, if the original incident polarization component is increased, the signal can be increased, but the intensity of the light incident on the optical disk must be kept below a certain level in order not to erase or overwrite the data. There is. On the other hand, in the above conventional technique, the light to be interfered with the signal light is separated in advance, and this is interfered with the signal light without condensing it on the disk, and the intensity of the light to be interfered for signal amplification is This makes it possible to increase the intensity regardless of the light intensity on the disk surface. Thus, in principle, the S / N ratio compared to the noise of the amplifier that converts the photocurrent from the photodetector into a voltage can be increased as the intensity is increased within the range allowed by the light intensity. Patent Document 3 relates to a high S / N ratio of a reproduction signal of an optical disk using a photochromic medium, and similarly to Patent Documents 1 and 2, signal amplification is performed by causing light that does not irradiate the optical disk to interfere with reflected light from the optical disk. Aiming. Also for an optical disk using a photochromic medium, the higher the incident light intensity for signal reproduction, the faster the medium is deteriorated. Therefore, similarly to the magneto-optical disk, the intensity of light applied to the recording medium is limited.

  In Patent Document 1, interference light intensity is detected by causing two lights to interfere with each other. At this time, the optical path length of the reflected disk light to be interfered is made variable so as to secure the interference signal amplitude. In Patent Documents 2, 3, and 4, differential detection is also performed in addition to interference light intensity detection. As a result, the intensity component of each light that does not contribute to the signal is canceled and the signal amplitude is doubled to achieve a high S / N ratio.

  In general, an interference signal obtained by interference between two lights depends on an interference phase (optical path length difference) between the two lights to be interfered. On the other hand, Patent Document 1 stabilizes the optical path length difference by making a triangular prism inserted in the optical path movable in the direction of the incident optical axis. Similarly, in Patent Document 4, the entire optical interference system is caused to follow the optical disc, thereby canceling the optical path length difference caused by the surface blur caused by the rotation of the optical disc. Further, the optical path length difference is stabilized by making the position of the mirror that reflects the light not hitting the optical disc movable in the optical axis direction. In Patent Document 5, a plurality of interference signals having different interference states are generated, and a signal is generated by calculating them, thereby outputting an amplified signal that does not depend on the interference phase.

Japanese Patent Laid-Open No. 5-342678 JP-A-6-223433 JP-A-6-68470 JP 2007-317284 A JP 2008-65961 A

  In the above prior art, in order to keep the optical path length difference stable, the movable target is made to follow the current optical disc surface deviation of about 600 μm, and the positioning is performed with an accuracy of several nanometers which is sufficiently smaller than the wavelength of the light source. Need to do. However, it is difficult to achieve a stroke and positioning accuracy that meet this requirement with current actuators. Furthermore, unevenness in the thickness of the cover layer provided on the optical disk also causes the optical path length difference to be disturbed. However, the above-described prior art does not particularly describe a method for controlling the optical path length corresponding to the uneven thickness.

  On the other hand, Patent Document 5 employs a method of obtaining an output that does not depend on the optical path length difference, so the above problem does not occur. However, when the optical system is deviated from an ideal state, the dependency on the interference phase is present. It will occur and the original effect cannot be obtained. The main causes of the dependency on the interference phase include the branching ratio of the half beam splitter in the optical system for generating a plurality of interference lights, the difference in the delay amount with respect to the polarization, the λ / 2 plate and the λ / 4 plate. Examples include errors such as the set angle, delay amount, and detector quantum efficiency. However, it is generally difficult to suppress all of these errors to a negligible level, and even if errors can be suppressed during assembly of the optical system, errors will occur again due to temperature changes and changes over time. It is difficult to obtain a stable effect.

  The first object of the present invention is to easily adjust the optical path difference between two lights, to have a high signal amplification effect, to maintain the effect stably, and to an interference type light suitable for downsizing an optical system. It is to provide a method for detecting an information signal.

  The second object of the present invention is to adjust the optical path difference between two lights, to have a high signal amplification effect, to maintain the effect stably, and to an interference type light suitable for downsizing of an optical system. An object of the present invention is to provide an optical disc apparatus provided with an information signal detection system.

In the present invention, the following means are used to achieve the first object.
The light beam emitted from the light source is divided into a first light beam and a second light beam, the first light beam is condensed and irradiated on the optical information recording medium, and a plurality of signal lights reflected from the optical information recording medium are emitted. The light is guided to the detector, the second light beam is not collected on the optical information recording medium, but is guided to a plurality of detectors as reference light, and the signal light and the reference light are optically optically different from each other on the plurality of detectors. The reproduced signal is obtained by performing an operation using the outputs from a plurality of detectors as inputs. At that time, based on the output in the middle of multiple interference phases, the final calculation output, or both, the calculation content of the calculation is variably set so that the dependence of the calculation result on the interference phase is minimized. The calculation adjustment to be set was performed. Once the calculation content is variably set, it is fixed to that setting.

  Thus, by performing calculations based on the outputs of a plurality of detectors, even if the optical interference state at each detector changes, it is possible to always obtain the same reproduced signal as in the optimally matched phase. it can. Further, by adjusting the calculation, it is possible to obtain a reproduction signal that does not depend on the interference state even when the optical system is incomplete or unstable.

  Specifically, when there are four detectors that acquire interference signals, the phase relationship between the reference light and the signal light is 180 degrees different between the first detector and the second detector, The third detector and the fourth detector are different from each other by 180 degrees, and the first detector and the third detector are different from each other by 90 degrees. Thereby, four phase states shifted by 90 degrees out of the 360 degree phase relationship can be detected simultaneously. Since the reproduction signal changes in a sine wave shape in response to a change in the phase state of light of 360 degrees, the signal state in an arbitrary phase state can be calculated by observing four signals that are shifted in phase state by 90 degrees. It becomes possible to reproduce. That is, stable reproduction / detection in an arbitrary phase state is realized.

  As the calculation, a quadratic polynomial of a differential signal of the first detector and the second detector and a differential signal of the third detector and the fourth detector is used. Here, since the phases of the first and second detector sets and the third and fourth detector sets are shifted by 90 degrees, either one of the differential signals has a sufficient amplitude regardless of the interference phase. Therefore, it becomes possible to always obtain a constant maximum output signal. Even when the optical system for acquiring the four interference signals deviates from the ideal state, the interference phase dependence of the output signal is monitored, and the coefficients of the second-order polynomial are appropriately selected so that this is minimized. This makes it possible to obtain a constant output signal that does not depend on the interference phase.

  As another means, in addition to the above means, the optical phase difference (optical path length difference) between the signal light and the interference light was modulated. As a result, even when the fluctuation of the optical path length is small and the interference phase dependency of the output signal cannot be measured sufficiently, the interference phase can be intentionally modulated, so that the above interference phase dependency can be stably obtained. it can. Furthermore, the interference phase dependency of the output signal can be accurately measured by setting the interference phase to a constant frequency and detecting the frequency component in the output signal.

  As another means, the calculation is performed by excluding a direct current component of each of the two differential signals, the first differential signal square, the second differential signal square, and the first difference. The product of the dynamic signal and the second differential signal was added by multiplying by an appropriate coefficient. As a result, the number of coefficients to be searched is reduced, so that the calculation can be adjusted at high speed.

  As another means, the above operation is to add the sum of the squares of these two products and a predetermined coefficient to the two differential outputs, which are obtained by multiplying a predetermined coefficient by removing the DC component, respectively. It was. As a result, the adjustment is uniquely determined and the search for one coefficient is performed, so that the adjustment of the calculation becomes faster.

  As another means, the calculation is a quadratic polynomial of the two differential signals, and the calculation adjustment is three values obtained by reading the coefficients of the quadratic polynomial from one differential signal in different interference phase states. And the calculation using two values read out from the other differential signal in different interference phase states. As a result, the adjustment can be performed only by a uniquely determined operation, so that the adjustment becomes faster. More specifically, the values to be read are the maximum value and the minimum value of the two differential signals, and the value of the other differential signal in the interference phase state in which one of the differential signals is maximum.

  In order to achieve the second object, the optical disk apparatus preferably includes an optical head, a control unit, and a signal processing unit, and the following means can be used.

  The optical head condenses the semiconductor laser, the first optical element that branches the light beam from the semiconductor laser into the first light beam and the second light beam, and the first light beam on the recording film surface of the optical information recording medium. An objective lens for receiving the reflected light, a reference light beam reflecting means provided in the optical path of the second light beam, a first light detector, a second light detector, and a third light detector, And a fourth photodetector. Further, the first light detector and the second light detection are performed by branching a light beam obtained by combining the first light beam reflected by the optical information recording medium and the second light beam reflected by the reference light beam reflecting means. The second optical element to be incident on the device, the first light beam and the second light beam are combined in a state where the phase relationship is 90 degrees different from the combination by the second optical element, and the combined light beam is A third optical element branched and incident on the fourth optical detector, and the phase relationship between the first and second light fluxes is the same as that on the first detector. And 180 on the second detector, 180 degrees on the third detector and the fourth detector, and 90 degrees on the first detector and the third detector. Configured to be.

  The control unit controls the positions of the optical head and the objective lens and the light emission state of the semiconductor laser. The signal processing unit generates a reproduction signal by a predetermined calculation from the output signals of the first to fourth photodetectors, outputs during the calculation of the above calculation at a plurality of interference phases, outputs of the final calculation, or Based on both, the calculation contents of the calculation are variably set, and the calculation adjustment is performed so that the dependence on the interference phase of the calculation result is minimized by the fixed setting.

  As a result, the first, second, third, and fourth detectors can synthesize the reference light and the signal light reflected by the optical disk and amplify and reproduce it by the interference effect. Can be detected with high S / N. That is, it is possible to significantly improve the S / N ratio during multi-layer media with low reflectivity and a small signal amount, and high-speed playback that is greatly affected by broadband noise.

  In addition, the adjustment function of the calculation makes it possible to widen the tolerance of the characteristics of the components of the optical head and the error in assembling, thereby reducing the cost of manufacturing the apparatus.

  According to the present invention, an optical disc provided with an interference type optical disc signal detection system that can output a stable amplified signal without being affected by variations in various characteristics generated in an actual optical system and is suitable for downsizing of the optical system. The device can be provided at low cost. As a result, when the signal light intensity has to be lower than before, such as a multilayer optical disk with multiple recording layers, or when the signal reproduction speed is higher than before, noise increases. It is possible to improve the reproduction signal quality by signal amplification.

  According to the present invention, it can be produced in the same size as a conventional disk device, can generate a stable output signal without being affected by variations in various characteristics of the built-in interference optical system, and has a signal amplification effect. An interference type optical disc apparatus can be provided.

1 is a schematic diagram showing an example of an optical disc apparatus according to the present invention. The figure showing the detail of the detector for servo detection. The block diagram of a signal processing circuit. The figure which shows the external shape of a corner cube. Explanatory drawing of the polarization disturbance correction of a corner cube. The block diagram of a calculation circuit and a calculation adjustment circuit. The figure which shows an optical head in case the detector which detects an interference signal is three. The figure which shows another embodiment which modulates an optical path length difference with a piezo element. The figure which shows another embodiment which adjusts and modulates an optical path length difference with the inclination of an actuator. The figure which shows another embodiment which simplified calculation adjustment. The figure which shows another embodiment which further simplified calculation adjustment. The figure which shows another embodiment which performs calculation adjustment by the calculation of a differential output. The figure which shows another embodiment which performed calculation adjustment by the calculation of differential output, and simplified the calculation. The figure showing the drive voltage to a piezo element in the Example which changes an optical path length difference by a fixed frequency.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of an optical disc apparatus according to the present invention.
The light from the semiconductor laser 101 is converted into parallel light by the collimator lens 102, transmitted through the λ / 2 plate 103, and incident on the polarization beam splitter 104. The polarization beam splitter 104 has a function of transmitting almost 100% of p-polarized light (hereinafter referred to as horizontal polarization) incident on the separation surface and reflecting almost 100% of s-polarized light (hereinafter referred to as vertical polarization). At this time, the intensity ratio between the transmitted light and the reflected light can be adjusted by adjusting the rotation angle of the λ / 2 plate 103 around the optical axis. The transmitted light first enters the special polarization beam splitter 105. The special polarizing beam splitter 105 has a property of transmitting 100% of horizontally polarized light, reflecting part of vertically polarized light, and partially transmitting. Therefore, the incident light is 100% transmitted, is transmitted through the λ / 4 plate 106, is converted into circularly polarized light, passes through the beam expander 129 that corrects spherical aberration, and passes through the objective lens 108 mounted on the two-dimensional actuator 107. Thus, the light is condensed on the recording layer on the optical disk 109. The reflected light from the optical disk returns along the same optical path, is converted into parallel light by the objective lens 108, and becomes linearly polarized light whose 90 ° polarization direction is rotated from the first incident time by the λ / 4 plate 106. Next, the light is incident on the special polarization beam splitter 105, and a part of the light is transmitted and a part of the light is reflected by the above properties. The reflected light is incident on the detector 111 by the cylindrical lens 110.

  Here, the detector 111 is divided into four detectors 201, 202, 203, and 204 as shown in FIG. 2. If the respective output signals are set as A, B, C, and D as shown in the figure, the calculation is performed. A−B−C + D is fed back as a current to the voice coil motor of the two-dimensional actuator 107 as a defocus signal (FES) and a calculation A−B + C−D as a track shift signal (TES).

  On the other hand, the light transmitted through the special polarization beam splitter 105 enters the polarization beam splitter 104. Then, since the polarized light is rotated by 90 degrees, it is reflected and enters the condenser lens 113. On the other hand, the light emitted from the semiconductor laser 101 and reflected by the polarizing prism 104 is reflected by the reflecting prism 115 mounted on the movable portion 114 and enters the corner cube prism 116 mounted on the two-dimensional actuator 107. The corner cube prism is an element that reflects incident light in the opposite direction. Here, the incident light is incident on the vertex formed by the three reflecting surfaces of the corner cube prism 116. The light reflected thereby returns along the same optical path and enters the polarization beam splitter 104. Here, since the polarization and wavefront of the light are disturbed by the corner cube prism, the disturbance is compensated by the compensation element 117 inserted in the middle of the optical path, and the polarization of the return light is 90% with respect to the forward light. I try to rotate it. For this reason, the reflected light from the corner cube prism passes through the polarization beam splitter 104 and enters the condensing lens 113 in a state of being coaxial with the reflected light from the optical disk in a state in which the polarization is orthogonal to each other.

The two lights incident on the condenser lens 113 are reflected and transmitted by the non-polarizing beam splitter 118 at a ratio of 1: 1, respectively. The transmitted light is transmitted through the λ / 2 plate 119 and the polarization is rotated by 45 degrees, and then separated by the polarization beam splitter 120 into a horizontal polarization component and a vertical polarization component, and the separated lights are detected by the detectors 121 and 122. Detected by. The light reflected from the non-polarizing beam splitter 118 passes through the λ / 4 plate 123 and then separated into a horizontal polarization component and a vertical polarization component by the polarization beam splitter 124, and the separated lights are detected by the detectors 125 and 126. Is done. The output signal of the detector 121 and 122 are input to a differential circuit 127, the differential signal D ₁ is output. Similarly, the output signal of the detector 125 and 126 are input to a differential circuit 128, the differential signal D ₂ is output.

Here, D ₁ and D ₂ are input to the signal processing circuit 25 in the reproduction block 2. Here, at the time of input, the signal processing circuit 25 samples and digitizes D ₁ and D ₂ and performs the subsequent processing by digital calculation.

A specific example of the circuit block configuration of the signal processing circuit 25 is shown in FIG. D ₁ and D ₂ are digitized by the AD conversion circuits 301 and 302 and input to the arithmetic circuit 303 to obtain a digital signal output S. The sampling timing of the AD converter is such that the output of the arithmetic circuit 303 and the output of the voltage controlled variable frequency oscillator (VCO) 304 are phase-compared by the phase comparator 305 and the output of the phase comparator is output by the low-pass filter (LPF) 306. It is generated by averaging and feeding back to the control input of the VCO. That is, a clock output (CK) whose phase is controlled by a phase-locked loop (PLL) circuit configured by the phase comparator 305, the VCO 304, and the LPF 306 is obtained, and the AD conversion timing is controlled. Inside the arithmetic circuit, a quadratic polynomial calculation relating to D ₁ and D ₂ is performed, and an arithmetic expression is determined by a coefficient given from the arithmetic adjustment circuit 307.

  The arithmetic adjustment circuit 307 stores the arithmetic output obtained by dropping the reproduction signal component through the low-pass filter 308 in a memory for a certain period, and calculates the magnitude of fluctuation of the arithmetic output as the difference between the maximum value and the minimum value from the stored data. Then, the value of the coefficient is changed at regular intervals so as to minimize the calculated value and fed back to the arithmetic circuit 303 to obtain an optimum coefficient. Since the lower limit of the frequency of a normal optical disk reproduction signal is two or more orders of magnitude higher than the upper limit of the fluctuation frequency of the calculation output, the cut-off frequency of the low-pass filter may be set between the two. For example, the reproduction signal frequency when reproducing the current Blu-ray disc at 1 × speed (linear velocity: 4.917 m / s) is several hundred kHz or more, while the fluctuation frequency of the calculation output due to the fluctuation of the optical path length difference is several kHz. Therefore, the cut-off frequency of the low-pass filter may be set to about 10 kHz.

  After the optimum coefficient is determined, the digital signal output S is input to the demodulating circuit 24 and the address detecting circuit 23 after appropriate digital equalization processing, and is decoded by the decoding circuit 26 as user data into the memory 29 and the microprocessor 27. Sent to. The microprocessor controls an arbitrary servo circuit 79 and automatic position control means 76 according to an instruction from the host device 99, and positions the light spot 37 at an arbitrary address. The microprocessor 27 controls the laser driver 28 depending on whether the instruction from the host device is reproduction or recording, and causes the laser 101 to emit light with an appropriate power / waveform. The servo circuit 79 controls the two-dimensional actuator 107 based on the servo signals FES and TES. Furthermore, the microprocessor 27 controls the movable portion 114 based on the signal quality or the disk information, and adjusts the position of the movable portion 114 to a place where the optical path length difference is minimized, that is, the signal output is maximized.

  In this optical system, in order to obtain a sufficient interference signal output, the optical path length difference between the signal light and the reference light needs to be set within about the coherence length of the light source. For this reason, the movable unit 114 is set so that the optical path length difference between the signal light and the reference light becomes zero by moving the reflecting prism 115 in the optical axis direction of the incident light according to the reading layer of the multilayer optical disk or the type of the disk. To do. The position where the optical path length difference is zero is searched or learned as a position where the amplitude of the interference signal output is maximized. Or it is good also as a position where the jitter of a reproduction signal becomes the minimum. In addition, the change in the optical path length difference due to the surface blur of the optical disk is canceled by the corner cube prism 116 being integrally mounted on the actuator 107 together with the objective lens 108.

  The polarization compensation of the corner cube prism will be described in detail. As shown in FIG. 4A, the corner cube prism is formed by cutting out a medium such as glass to form three surfaces of a cube. Incident light to the corner cube prism is reflected by these three surfaces and is emitted as return light in the opposite direction to the incident light. Here, since the reflection at each reflecting surface satisfies the total reflection condition, a phase difference corresponding to a predetermined incident angle occurs between the p-polarized light and the s-polarized light with respect to the incident surface. For this reason, the return light is disturbed in polarization and wavefront. In addition, the order of reflecting the three reflecting surfaces differs depending on the position where the light is incident, so that the polarization disturbance is different. FIG. 4B is a view when the corner cube is viewed from the direction of incident light. Different polarization disturbances in the regions (1), (2), (3), (4), (5), and (6) shown here. Will occur. However, the bold line in the figure represents the boundary line between the reflecting surfaces.

  In order to correct this, as shown in FIG. 5, a compensation element 117 composed of a three-divided phase plate 501, a λ / 4 plate 502, and a six-divided λ / 2 plate 503 may be inserted. The λ / 4 plate and the 6-divided λ / 2 plate not only compensate for the polarization, but also have a function of rotating the polarization of the return light by 90 degrees with respect to the incident light. The three-divided phase plate generates a predetermined phase difference φp−φs (φp and φs are phases generated in horizontal polarization and vertical polarization, respectively) between horizontal polarization and vertical polarization in a specific region. It has the role of compensating for the phase difference between the region that passes through the element and the region that does not pass through, and aligning the wavefront of the return light. As an example, Table 1 shows set values of a three-divided phase plate, a λ / 4 plate, and a six-divided λ / 2 plate when the wavelength of light is 405 nm and the medium of the corner cube prism is BK7. As shown in FIG. 4, the angle is defined such that the vertical polarization direction 504 is 0 degree and the counterclockwise direction is positive when viewed from the incident light direction.

  Next, the process of obtaining an amplified signal by light interference will be described in detail. First, consider a case where the optical system is in an ideal state. The light incident on the condenser lens 113 is obtained by coaxially combining the return light from the corner cube 116 that is horizontally polarized light and the return light from the optical disk 109 that is vertically polarized light. Therefore, when the polarization state of light is expressed by a Jones vector, Equation (1) is obtained.

Here, E _s is the electric field of the return light from the optical disc 4, and E _r is the electric field of the return light from the corner cube prism 116. The first component of the vector represents horizontal polarization, and the second component represents vertical polarization.

  This light is divided into two by a non-polarizing beam splitter 118, and the transmitted light passes through a λ / 2 plate 119 having a fast axis in the direction of 22.5 degrees when viewed from the horizontal polarization direction. At this time, the Jones vector is expressed by the following equation (2).

  Next, since the horizontal polarization component is transmitted by the polarization beam splitter 120 and the vertical polarization component is reflected, the electric fields of the transmitted light and the reflected light are expressed by equations (3) and (4), respectively.

  On the other hand, the light reflected by the non-polarizing beam splitter 118 passes through the λ / 4 plate 123 having a fast axis in the direction of 45 degrees as viewed from the horizontal polarization direction. At this time, the Jones vector is expressed by Equation (5).

  Next, since the horizontal polarization component is transmitted by the polarization beam splitter 124 and the vertical polarization component is reflected, the electric fields of the transmitted light and the reflected light are expressed by equations (6) and (7), respectively. Therefore, the detection signals of the four detectors 121, 122, 125, and 126 are expressed by equations (8) to (11), respectively.

η is the conversion efficiency of the detector. Δφ is a phase relationship between the signal light and the reference light, that is, an interference phase. If these are set as A ₁ , A ₂ , A ₃ , and A ₄ , respectively, the differential signals D ₁ and D ₂ are expressed as Expression (12) and Expression (13), respectively.

At this time, in the arithmetic circuit, an output that does not depend on the interference phase is obtained when calculating the sum of squares of D ₁ and D ₂ (one of the quadratic expressions), as in the following expression.

This output has a form in which the electric field of light reflected from the optical disk (hereinafter referred to as signal light) is amplified by the electric field of return light from the corner cube (hereinafter referred to as reference light). Thus small E _s the reason of low reflectance, etc. of the optical disk, even when the signal properly be detected directly signal light can not be played, it is possible to correctly reproduce amplifies the signal. Note that the square root of this output may be treated as a reproduction signal. This improves the linearity of the signal and simplifies data demodulation.

Next, it will be shown that the arithmetic adjustment circuit 307 works effectively when the optical system is incomplete. In actually manufacturing the optical head, various parameters of the optical system, such as reflectance, transmittance, delay amount of the half beam splitter 118, delay amounts of the λ / 2 plate 119 and λ / 4 plate 123, set angle, or The conversion efficiencies and offsets of the detectors 121, 122, 125, 126 cause errors from ideal values. Due to these errors, the detector outputs A ₁ , A ₂ , A ₃ , and A ₄ can no longer be described by equations such as equations (8), (9), (10), and (11). In general, the differential outputs D ₁ and D _{2 in the} case where there is such an error are expressed by the equations (15) and (16), respectively. a, r, b ₁ , b ₂ , and δ are constants.

If the same sum-of-squares calculation as in the ideal case is output, a term that depends on the interference phase generally remains. However, if the equations (17), (18), and (19) are used, D ₁ ′ and D ₂ ″ have the same form as D ₁ and D _{2 in} the ideal case, and the sum of squares of these is the equation (20). Thus, the output does not depend on the phase.

When Expression (20) is expressed using D ₁ and D ₂ , Expression (21) is obtained, which is a quadratic polynomial of D ₁ and D ₂ (where s = sin δ).

Therefore, by setting the calculation output to a quadratic polynomial of D ₁ and D ₂ and setting the coefficient of each term to the value of equation (21), an output signal that does not depend on the interference phase as in the ideal state can be obtained. Obtainable. However, in order to equal the ideal case the amplitude of the output signal, in fact as the following equation, a material obtained by dividing equation (21) by the square of 1 / cos [delta] and the target value of each coefficient, the D ₁ The coefficient of the square term is fixed at 1.

Note that since the square of 1 / cos δ changes only by about ± 3% in a practical fluctuation range of about ± 10 degrees, the above division hardly affects the amplitude of the output signal. Further, the constant term c ₅ in the equation (22) is irrelevant to the dependency on the interference phase, but is uniquely determined from the coefficients c ₁ , c ₂ , c ₃ , and c ₄ of other terms as follows.

To summarize the above, the optimal calculation adjustment is represented by a block diagram as shown in FIG. First, input signal D ₁ , D ₂ to D ₁ square, D ₂ square, product of D ₁ and D ₂ are generated using square circuits 601, 602, etc., and coefficient c ₁ given from optimization circuit 603 is given. , C ₂ , c ₃ , c ₄ , and c ₅ , a signal output S is generated. Here, the coefficient of the square term of D ₁ is fixed to ₁ , and the coefficient values c ₁ , c ₂ , c ₃ , c ₄ , and c ₅ of terms other than the constant term are searched as parameters. The constant term c ₅ is generated by the constant term generation circuit 604 from the search parameters c ₁ , c ₂ , c ₃ , and c ₄ using equation (23). The output signal S is dropped in the reproduction signal component by the low-pass filter 308 and stored in the memory 605 for a certain period. The data processing circuit 606 generates the maximum value and the minimum value, and the differential circuit 607 outputs the difference between them. Is done. However, the low-pass filter may be omitted. The same applies to all the low-pass filters described below. This output is a parameter representing the degree of dependence on the interference phase, and the optimization circuit 603 adjusts the values of c ₁ , c ₂ , c ₃ , and c ₄ so that this value is minimized. Since the optimized parameter is set to the value shown in Expression (22), the signal output S independent of the interference phase is obtained. Note that the parameters to be searched are not limited to the above coefficient values. For example, r, b ₁ , b ₂ , and sin δ may be used as search parameters, and the coefficients of the quadratic expression may be calculated from these values according to the equation (22). .

  Note that the dependency index of the calculation output on the interference phase is not limited to the difference between the maximum value and the minimum value of the output as described above. For example, a value obtained by normalizing this value with the magnitude of the reproduction signal amplitude or the DC component may be used instead.

  After the above-described calculation adjustment is completed, a stable reproduction signal can be acquired with a fixed set value. That is, after the adjustment is completed, it is not necessary to perform adjustment when the reproduction signal is acquired. However, there is a possibility that the ideal setting value shifts due to changes in the status of the device over time or changes in the environmental temperature, and interference phase dependence may gradually occur. It is necessary to do. In this embodiment, a parameter indicating the magnitude of the interference dependency is constantly monitored, and the above-described calculation adjustment is started when the parameter exceeds a certain value. In addition to this, the adjustment may be performed periodically when the apparatus is activated and after a predetermined period has elapsed since the latest adjustment.

Note that the number of detectors for obtaining this effect and the phase difference between the signal light and the reference light on each detector are not necessarily as described above, and in principle, each of three or more detectors Detection may be performed so that the phase difference between the signal light and the reference light on the detector is different from each other. As an example, FIG. 7 shows a configuration of an optical head unit in which three detectors are used and the phase difference between the signal light and the reference light is 0 degree, 120 degrees, and 240 degrees on each detector, respectively. The light that has passed through the condenser lens 113 is divided into three light beams by non-polarizing beam splitters 701 and 702, and after passing through polarizers 703, 704, and 705 that respectively transmit 45-degree polarized light, detectors 706, 707, 708 is detected. Of these three luminous fluxes, one phase plate 709 generates a phase difference of 60 degrees between the signal light and the reference light, and the other has a phase difference of 300 degrees between the signal light and the reference light. Each of the phase plates 710 to be generated is inserted. Further, the non-polarizing beam splitter 701 has a ratio of transmittance to reflectance of 1: 2, and the non-polarizing beam splitter 702 has the same transmittance and reflectance so that the amount of light on each detector is equal. Use things. At this time, the intensities I ₁ , I ₂ , and I ₃ of the light incident on each detector can be expressed by the following equations, respectively.

However, here, it is considered that a phase difference of 180 degrees occurs between the signal light and the reference light when reflected by the non-polarizing beam splitters 701 and 702. Next, these output signals are input to the arithmetic circuit 711 to generate the following outputs D ₁ and D ₂ .

Then, they have the same shape as the differential signals D ₁ and D ₂ in the above four detector examples. Therefore, an amplified signal that does not depend on the phase difference between the signal light and the reference light can be obtained by the calculation of the following equation.

If the optical system is incomplete, D ₁ and D ₂ are in the form of equations (15) and (16) as in the case of the above four detectors. Adjustment may be performed.

  This embodiment is premised on reproduction of a normal optical disc such as a DVD or a Blu-ray disc, but the form is not particularly limited as long as the incident light and the modulated signal light are coherent and have the same wavelength. For example, the present invention can be applied to a large capacity memory such as a hologram memory or a near field memory.

  FIG. 8 shows a case where a mechanism for modulating the optical path length difference is mounted as another embodiment. In order to accurately perform the calculation adjustment described in the first embodiment, the interference phase needs to change in a range of 2π or more. In the first embodiment, the fluctuation of the interference phase caused by the instability of the optical system is used. However, in this embodiment, the mirror 802 that drives the voltage to the piezo element 801 and reflects the signal light by the command from the microprocessor is moved back and forth. Since the optical path length difference is modulated by modulating in the direction, even if the optical system is stable and the interference phase hardly fluctuates, it is possible to reliably perform calculation adjustment by intentionally modulating the interference phase. .

  Note that the mechanism for modulating the optical path length difference may be the same as the optical path length difference adjusting mechanism, and the optical path length difference may be modulated around the position set by the optical path length difference adjustment. In FIG. 8, these adjusting mechanisms are inserted in the middle of the signal optical path, but the same effect can be obtained even if they are inserted in the middle of the reference optical path. The modulation speed may be about several hundred Hz to several kHz, and it is sufficient to use a stepping motor or the like as the movable mechanism. As another movable mechanism, an actuator equipped with an objective lens and a corner cube prism as shown in FIG. 9 may be a three-dimensional actuator 901, and the optical path length difference may be generated by tilting in the optical axis direction.

Further, the modulation of the interference phase may be performed at a constant frequency f. In general, the calculation output when the interference phase dependency remains is expressed as shown in Expression (30) (Δφ is a phase difference, k ₁ , k ₂ , k ₃ , k ₄ , k ₅ , k ₆ , k ₇ , k ₈ , δ ₁ and δ ₂ are constants).

Here, when the voltage for driving the piezo element is linearly changed so that the optical path length difference Δl is changed at the speed v represented by the equation (31) (λ is the wavelength of the light source), the equation (32) is obtained. Therefore (t is time, l ₀ is the optical path length difference at time 0), a frequency f component and a 2f component are generated in the calculation output.

  Therefore, the magnitude of these modulation frequency components is set to the magnitude of the dependency on the interference phase, and calculation adjustment may be performed so that these are the minimum (zero). Note that the driving voltage of the piezo element may not be a voltage that changes linearly in one direction but may be a triangular wave as shown in FIG.

FIG. 10 is a signal processing block diagram in a case where calculation adjustment is simplified in Example 1 as another embodiment. In this case, the differential signals D ₁ and D ₂ first pass through the high-pass filters 1001 and 1002, and the DC component is removed. Then, since b ₁ = b ₂ = 0 in the equations (15) and (16), the equation (22) in the first embodiment becomes the following equation (33), which is the sum of only three components. Therefore, in this embodiment, if the differential signal D ₁ , D _{2 from} which the DC component is removed is used to perform the calculation of the form (34), and the optimization circuit 603 optimizes c ₁ , c _2. Good.

  In this case, the arithmetic expression is simplified as compared with the first embodiment, and the number of coefficients to be searched is reduced from four to two, so that the adjustment can be performed at higher speed.

FIG. 11 shows a case where the calculation adjustment of Example 3 is further simplified as another embodiment. In the above-described embodiments, calculation adjustment is performed based only on the final result of the calculation. In this embodiment, values in the middle of calculation (between differential calculation and second-order polynomial calculation) are also used for calculation adjustment. . In this case, one (here, D ₂ ) of the differential signals from which the DC component has been removed is input to the gain adjustment circuit 1101. Here, adjustment is performed to equalize the magnitudes of fluctuations of D ₁ and D ₂ . Specifically, D ₁ and D ₂ are respectively passed through the low-pass filters 1102 and 1103 and the reproduced signal components are dropped and stored in the memories 1104 and 1105 for a certain period of time, and the data processing circuits 1106 and 1107, the differential circuit 1108, In 1109, the amplitudes of D ₁ and D ₂ (the difference between the maximum value and the minimum value in a certain period) are output, and a ratio between them is generated by a division circuit 1110, and this is multiplied by D ₂ . As a result, since r = 1, the expression (22) in the first embodiment becomes the expression (35). Therefore, in this embodiment, after removing the DC component and passing through the gain adjustment circuit, the calculation in the form of Expression (36) is performed, and the optimization circuit 603 may optimize the coefficient c ₁ .

  In this embodiment, since only one coefficient is searched for, adjustment can be performed at higher speed.

FIG. 12 shows a case where the calculation adjustment of Example 1 is performed by calculation processing as another embodiment. In this case, the coefficient of calculation is determined from the maximum value and the minimum value of each of the differential signals D ₁ and D ₂ and the value of D _{2 in} the interference phase where D ₁ takes the maximum value. Specifically, D ₁ and D ₂ are passed through the low-pass filters 1201 and 1202, respectively, and the reproduction signal component is dropped and stored in the memories 1203 and 1204 for a certain period, and the maximum value of D ₁ is obtained by the data processing circuits 1205 and 1206. The value a ₅ of D _{2 in} the interference phase where the maximum value a ₃ , minimum value a ₄ , and D _{1 of} a ₁ , minimum value a ₂ , and D ₂ take the maximum value is output. These values are input to the arithmetic circuit 1207, and the values of r, b ₁ , b ₂ and sin δ are determined by the following calculation.

Next, each coefficient of the quadratic equation may be determined from these values according to equation (22). In this embodiment, since the coefficient can be uniquely determined by the calculation process without searching for the coefficient value as in the above embodiment, the calculation can be performed at high speed. As shown in FIG. 13, the same processing may be performed after the DC components of D ₁ and D ₂ are dropped by the high-pass filters 1001 and 1002 as in the fourth embodiment. In this case, since b ₁ = b ₂ = 0, the arithmetic circuit 1207 calculates only the expressions (37) and (40), and calculates the coefficients c ₁ and c ₂ of the expression (34) according to the expression (33). Just decide.

  According to the present invention, it becomes possible to detect a reproduction signal of a large-capacity multilayer high-speed optical disk stably and with high quality, and a wide range of industrial applications such as a large-capacity video recorder, a hard disk data backup device, and a stored information archive device can be expected.

2 ... Reproduction signal processing block, 23 ... Address detection circuit, 24 ... Demodulation circuit, 25 ... Signal processing circuit, 26 ... Decoding circuit, 27 ... Microprocessor, 28 ... Laser driver, 29 ... Memory, 79 ... Servo circuit, 76 ... Automatic position control means, 77 ... motor, 37 ... light spot, 99 ... host device, 1501: optical head, 101: semiconductor laser, 102: collimating lens, 103: λ / 2 plate, 104: polarizing prism, 105: special polarization Beam splitter, 106: λ / 4 plate, 107: two-dimensional actuator, 108: objective lens, 109: optical disk, 110: condenser lens, 111: detector, 112: arithmetic circuit, 113: condenser lens, 114: movable 115: Prism mirror 116: Corner cube prism 117: Polarization compensator 118: Non-polarized light Half beam splitter, 119: λ / 2 plate, 120: polarization beam splitter, 121, 122: detector, 123: λ / 4 plate, 124: polarization beam splitter, 125, 126: detector, 127: arithmetic circuit, 128 : Differential circuit, 129: beam expander, 201, 202, 203, 204: light receiving unit, 205: incident beam, 301, 302: AD converter circuit, 303: arithmetic circuit, 304: voltage control oscillator, 305: phase Comparator, 306: Low-pass filter, 307: Arithmetic adjustment circuit, 308: Low-pass filter, 501: Three-division phase plate, 502: λ / 4 plate, 503: Six-division wavelength plate, 504: Vertical polarization direction, 601, 602: Square circuit, 603: Optimization circuit, 604: Constant term generation circuit, 605: Memory, 606: Data processing circuit, 607: Differential circuit 701, 702: Unpolarized beam splitter, 703, 704, 705: Polarizer, 706, 707: Phase plate, 708, 709, 710: Detector, 711: Arithmetic circuit, 801: Piezo element, 802: Mirror, 901: Three-dimensional actuator, 1001, 1002: high-pass filter, 1101: gain adjustment circuit, 1102, 1103: low-pass filter, 1104, 1105: memory, 1106, 1107: data processing circuit, 1108, 1109: differential circuit, 1110: division circuit 1201, 1202: low-pass filter, 1203, 1204: memory, 1205, 1206: data processing circuit, 1207: arithmetic circuit

Claims (18)

Splitting the light beam emitted from the light source into a first light beam and a second light beam;
Condensing and irradiating the first light flux on an optical information recording medium;
Signal light reflected from the optical information recording medium is guided to a plurality of detectors,
Guiding the second light flux to the plurality of detectors as reference light without irradiating the optical information recording medium;
Optically interfering the signal light and the reference light on the plurality of detectors in a state in which their optical phase relationships are different from each other;
Performing an operation with the outputs from the plurality of detectors as inputs,
An optical information reproduction method for obtaining a result of the calculation as a reproduction signal,
Based on the output during the calculation of the plurality of interference phases, the output of the final calculation, or both, the calculation content of the calculation is variably set, and the dependency of the calculation result on the interference phase is minimized. An adjustment step for fixing the calculation content as described above,
An optical information reproducing method, wherein a reproduction signal is obtained with the fixed calculation content.   2. The optical information reproducing method according to claim 1, wherein the calculation content is variably set while modulating an optical phase difference between the signal light and the reference light.   3. The optical information reproducing method according to claim 2, wherein the optical phase difference is modulated at a predetermined frequency, and the magnitude of the component of the predetermined frequency and a component of the frequency twice that in the result of the calculation are calculated. An optical information reproducing method characterized by having a large dependence on an interference phase. The optical information reproducing method according to claim 1,
The number of the detectors is 4,
The interference phases on the four detectors differ from each other by an integral multiple of 90 degrees;
In the calculation, a differential signal between the first detector and the second detector in which the interference phases of the detected signal light and the reference light are different from each other by 180 degrees is used as a first differential signal, and Among them, the differential signal of the remaining third detector and the fourth detector is used as a second differential signal, and a second-order polynomial operation result of the first differential signal and the second differential signal is obtained. The playback signal,
In the adjusting step, a coefficient of each term of the polynomial calculation that minimizes the dependence of the calculation result on the interference phase is searched and set, wherein the optical information reproducing method is characterized in that: The optical information reproducing method according to claim 1,
The number of the detectors is 4,
The interference phases on the four detectors differ from each other by an integral multiple of 90 degrees;
In the calculation, the first differential is obtained by removing the DC component of the differential signal of the first detector and the second detector in which the interference phases of the detected signal light and the reference light are 180 degrees different from each other. A signal obtained by removing the DC component of the differential signals of the remaining third detector and the fourth detector from among the detectors as a second differential signal, and the square of the first differential signal. And the sum of the square of the second differential signal and the product of the first differential signal and the second differential signal multiplied by a predetermined coefficient, respectively. And
In the adjusting step, the coefficient is searched and set so that the dependence of the calculation result on the interference phase is minimized. The optical information reproducing method according to claim 1,
The number of the detectors is 4,
The interference phases on the four detectors differ from each other by an integral multiple of 90 degrees;
In the calculation, the first coefficient is obtained by removing a direct current component from the differential signal of the first detector and the second detector in which the interference phases of the detected signal light and the reference light are 180 degrees different from each other. The product obtained by multiplying is the first differential signal, and the differential signal of the remaining third detector and the fourth detector among the detectors is obtained by multiplying the second coefficient by excluding the DC component. As the second differential signal, the sum of squares of the first differential signal and the second differential signal, and the product of the first differential signal and the second differential signal, respectively. What is obtained by multiplying the third coefficient and the fourth coefficient and then adding them is the reproduction signal,
In the adjustment step, the first differential signal and the second differential signal have the same magnitude of fluctuation when the interference phase on the four detectors fluctuates. An optical system characterized in that a coefficient and the second coefficient are set, and further, the third coefficient and the fourth coefficient are set so that the dependence of the calculation result on the interference phase is minimized. Information reproduction method. The optical information reproducing method according to claim 1,
The number of the detectors is 4,
The interference phases on the four detectors differ from each other by an integral multiple of 90 degrees;
In the calculation, a differential signal between the first detector and the second detector in which the interference phases of the detected signal light and the reference light are different from each other by 180 degrees is used as a first differential signal, and Among them, the differential signal of the remaining third detector and the fourth detector is used as a second differential signal, and a second-order polynomial operation result of the first differential signal and the second differential signal is obtained. The playback signal,
In the adjustment step, the maximum value and the minimum value of the first differential signal, the maximum value and the minimum value of the second differential signal, and the first differential when the interference phase is changed. A value of the second differential signal in an interference phase state in which the signal takes a maximum value is read, and a coefficient of the second-order polynomial calculation is determined and set based on the read value. Optical information reproduction method.   2. The optical information reproducing method according to claim 1, wherein the degree of dependence on the interference phase is monitored, and the adjusting step is performed when the dependency exceeds a predetermined value. .   2. The optical information reproducing method according to claim 1, wherein the adjusting step is performed when the apparatus is activated and when a predetermined time has elapsed since the previous adjustment. An optical head, a control unit, and a signal processing unit;
The optical head includes a semiconductor laser, a first optical element that divides a light beam emitted from the semiconductor laser into a first light beam and a second light beam, and condenses the first light beam on an optical information recording medium. An objective lens that receives reflected light reflected from the optical information recording medium as signal light, and reference light reflecting means that is provided in the optical path of the second light flux and reflects the second light flux as reference light And a plurality of detectors, and the signal light and the reference light are combined and guided to the plurality of light detectors, and the signal light and the reference light interfere with each other with different phase relationships on each detector. Interference light detection optical system
The control unit controls the position of the optical head and the objective lens and the light emission state of the semiconductor laser,
The signal processing unit performs an operation with the outputs of the plurality of detectors as inputs and obtains a result of the operation as a reproduction signal, an output in the middle of the operation at a plurality of interference phases, and finally And an arithmetic adjustment unit that variably sets the content of the calculation by the arithmetic circuit so that the magnitude of the dependence on the interference phase of the result of the calculation is minimized based on the output of the simple calculation or both. An optical disk device. 11. The optical disk device according to claim 10 , further comprising a modulation element that modulates an optical phase difference between the signal light and the reference light in an optical path of the signal light or the reference light. apparatus. 12. The optical disk apparatus according to claim 11 , further comprising a circuit that modulates the optical phase difference at a predetermined frequency by the modulation element, wherein a component of the modulation frequency and a component of a frequency twice that in the result of the calculation are obtained. An optical disc apparatus characterized in that a magnitude is a magnitude of dependence on the interference phase. The optical disk apparatus according to claim 10 , wherein
Having four detectors as the plurality of detectors;
The phase relationship between the signal light and the reference light on the four detectors differs from each other by an integer multiple of 90 degrees,
The arithmetic circuit outputs a first differential signal as a differential signal of a first detector and a second detector in which interference phases of the detected signal light and the reference light are different from each other by 180 degrees, A second differential signal is output as a differential signal between the remaining third detector and the fourth detector of the detectors, and a second order of the first differential signal and the second differential signal is output. The calculation adjustment unit searches for and sets the coefficient of each term of the polynomial calculation that minimizes the dependency of the output of the calculation circuit on the interference phase. Optical disk device to perform. The optical disk apparatus according to claim 10 , wherein
Having four detectors as the plurality of detectors;
The interference phases on the four detectors differ from each other by an integral multiple of 90 degrees;
The arithmetic circuit has a first difference obtained by removing a DC component of a differential signal of the first detector and the second detector in which the interference phases of the detected signal light and the reference light are 180 degrees different from each other. Output as a moving signal, and outputs a signal obtained by removing the DC component of the differential signal of the remaining third detector and the fourth detector from among the detectors as a second differential signal. A product of a square of a differential signal, a square of the second differential signal, and a product of the first differential signal and the second differential signal multiplied by a predetermined coefficient, respectively, and added. Output as a playback signal,
The optical disk apparatus characterized in that the calculation adjustment unit searches for and sets the coefficient that minimizes the dependency of the output of the calculation circuit on the interference phase. The optical disk apparatus according to claim 10 , wherein
Having four detectors as the plurality of detectors;
The interference phases on the four detectors differ from each other by an integral multiple of 90 degrees;
The arithmetic circuit obtains a first coefficient excluding a direct current component with respect to a differential signal of the first detector and the second detector in which interference phases of the detected signal light and the reference light are 180 degrees different from each other. The multiplied product is output as a first differential signal, and the differential signal of the remaining third detector and the fourth detector among the detectors is multiplied by the second coefficient except for the DC component. Output as a second differential signal, and a product of the sum of squares of the first differential signal and the second differential signal, and the first differential signal and the second differential signal. And the result obtained by multiplying and adding the third coefficient and the fourth coefficient, respectively, is output as the reproduction signal,
The arithmetic adjustment unit is configured to make the first differential signal and the second differential signal have the same magnitude of fluctuation when the interference phase on the four detectors fluctuates. The coefficient of 1 and the second coefficient are set, and the third coefficient and the fourth coefficient are set so that the dependence of the calculation result on the interference phase is minimized. Optical disk device. The optical disk apparatus according to claim 10 , wherein
Having four detectors as the plurality of detectors;
The interference phases on the detector differ from each other by an integer multiple of 90 degrees;
The arithmetic circuit outputs a first differential signal as a differential signal of a first detector and a second detector in which interference phases of the detected signal light and the reference light are different from each other by 180 degrees, A second differential signal is output as a differential signal between the remaining third detector and the fourth detector of the detectors, and a second order of the first differential signal and the second differential signal is output. The result of the polynomial operation is output as the reproduction signal,
The calculation adjustment unit is configured such that the maximum value and the minimum value of the first differential signal, the maximum value and the minimum value of the second differential signal, and the first difference when the interference phase is changed. A value of the second differential signal in an interference phase state in which a moving signal takes a maximum value is read, and a coefficient of the second-order polynomial calculation is determined and set based on the read value. Optical disk device to perform. 11. The optical disc apparatus according to claim 10 , wherein the magnitude of the dependence on the interference phase is monitored, and the calculation adjustment unit is activated when the dependency exceeds a predetermined value. 11. The optical disc apparatus according to claim 10 , wherein the calculation adjustment unit is activated when the apparatus is started up and when a predetermined time has elapsed after variably setting the previous calculation contents.

Images