JP5778624B2 - Optical information reproducing apparatus and optical information reproducing method - Google Patents

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 as a result of commercialization of a blue-ray disc using a blue semiconductor laser and a high NA objective lens. As a method for simultaneously realizing further increase in capacity and increase in data transfer speed, multi-layer recording in which data is recorded on a plurality of recording layers is promising, and up to three-layer discs have already been commercialized.

  In order to further improve the recording capacity, it is desired to increase the number of recording layers. However, as the number of recording layers increases, the manufacturing yield of the disk deteriorates, making it difficult to realize. For this reason, the recording layer is not provided with the groove structure found in the conventional recording type optical disk, but is provided with a reflection surface having a groove structure for track servo operation separately (servo surface servo optical disk, Non-Patent Document 1). In addition, a volume type optical disc without a recording layer structure has been proposed and has become a promising candidate for the next generation optical disc. The volume type optical disc has a micro-hologram method (Non-Patent Document 2) for recording data by minute interference fringes of light, and a void recording method for recording data by a multi-photon absorption process that occurs when a high peak power laser is focused. (Non-Patent Document 3) is known.

  In the servo surface servo optical disk and volume type optical disk described above, focus servo and track servo operations are performed using a light beam (servo light) focused on a reflective surface (servo surface) having a groove structure at the time of data recording. Data recording is performed using another light beam (recording light) focused on a predetermined position of the recording medium. During data playback, in order to perform servo control with high accuracy, the focus servo and track servo operations are performed using the reflected light of the light beam collected on the recording layer, and the playback signal is simultaneously acquired, as with conventional optical disks. To do. As a method of track servo operation, a push-pull method or a modified push-pull method, an advanced push-pull method, or the like is used as a known method. In addition, a method of enhancing a differential push-pull method signal by light interference (Patent Document 1) is known.

JP 2009-15944 A

M. Ogasawara, K. Takahashi, M. Nakano, M. Inoue, A. Kosuda and T. Kikukawa, 16 Layers Write Once Disc with a Separated Guide Layer, ISOM Tech. Dig., ThL07, Taiwan, Oct. 2010. H. Miyamoto, H. Yamatsu, K. Saito, N. Tanabe, T. Horigome, G. Fujita, S. Kobayashi and H. Uchiyama, “Direct Servo Error Signal Detection Method from Recorded Micro-Reflectors,” Jpn. J. Appl. Phys. 48, 03A054, Mar. 2009. D. Ueda et al., “Dynamic Recording of 200 Gbytes in Three-Dimensional Optical Disk by a 405 nm Wavelength Picosecond Laser,” Jpn. J. Appl. Phys. 50, 032704, 2010.

  The track servo operation at the time of reproduction basically uses the intensity difference between the left and right areas of the reflected light (corresponding to the radial direction of the disk, that is, the radial direction) as a track error signal. This difference in intensity is caused by the diffracted light caused by the structure in which the difference in reflectance / phase between the recorded portion (mark) and the unrecorded portion in the recording layer is periodically repeated. The amplitude of the error signal varies depending on the difference between the two and the shape of the recording mark. For this reason, the amplitude of the track error signal varies greatly due to variations in recording conditions, the material composition of the recording medium, etc., and there is a problem that stable track servo operation is difficult.

  In view of the above problems, an object of the present invention is to provide an optical information reproducing apparatus and an optical information reproducing method capable of stable track servo control.

In order to achieve the object of the present invention, the following means were used.
(1) a light source such as a semiconductor laser; a light splitting means such as a non-polarizing beam splitter that splits a light beam from the light source into a first light beam and a second light beam; A focusing unit such as an objective lens that focuses light on a position; a drive unit such as an electromagnetic actuator that drives the focusing unit in a direction perpendicular to the optical axis direction of the first light beam; The reflected light is combined with the second light flux, and there are three types for each of the two areas, that is, the area A including the + 1st order diffracted light of the first light flux and the area B including the −1st order diffracted light of the first light flux. An interference optical system that generates the above interference light, such as a hologram element, a non-polarization beam splitter, a polarization beam splitter, a λ / 2 plate, and a λ / 4 plate, a detector that detects the interference light, and an output of the detector To at least the first luminous flux in region A and the first luminous flux. A signal processing unit that generates the phase difference of the light beam in the region B of one light beam and a servo circuit that inputs the phase difference as a track error signal to the drive unit are provided.
This makes it possible to perform stable track servo control even when variations in characteristics of recording marks and recording media occur.

(2) a light source such as a semiconductor laser; a light splitting means such as a non-polarizing beam splitter that splits a light beam from the light source into a first light beam and a second light beam; A focusing unit such as an objective lens that focuses light on a position; a drive unit such as an electromagnetic actuator that drives the focusing unit in a direction perpendicular to the optical axis direction of the first light beam; An interference optical system composed of a hologram element, a polarization beam splitter, a λ / 2 plate, a λ / 4 plate, etc. that multiplexes the reflected light with the second light beam to generate two or more types of interference light, and the first light beam From the optical path length difference adjusting means such as an electromagnetic actuator and a piezo element that adjusts the optical path length difference of the second light beam, the detector that detects the interference light, and the output of the detector, the first-order diffracted light of the first light beam is converted. The first-order diffracted light of the first region A signal processing unit for generating a phase difference from the light flux in the region B including the phase and a phase of the first light flux reflected from the recording medium based on the phase of the second light flux, and driving the phase difference as a track error signal And a servo circuit for inputting the phase of the first light flux as a phase error signal to the optical path length difference adjusting means.
Thereby, track servo control similar to (1) can be performed with a small number of detectors, which contributes to downsizing of the apparatus.

(3) In (1) or (2), the interference optical system includes a region A including the + 1st order diffracted light, a region B including the −1st order diffracted light, and a region C including only the 0th order light in the first light flux. Each of the interference optical systems generates three or more types of interference light, and the phase difference is a phase difference based on the phase of the region C of the first light flux.
Thereby, even when the optical path lengths of the first light flux and the second light flux fluctuate, it is possible to stably acquire a track error signal equivalent to (1) or (2).

(4) In (3), the phase difference is the difference between the imaginary part of the electric field in region A and the imaginary part of the electric field in region B when the phase of region C of the first light flux is zero. .
This makes it possible to perform stable track servo control even when a focusing means such as an objective lens shifts in the radial direction.

(5) In (1), the interference optical system has a central portion of at least the region A including the + 1st order diffracted light, the region B including the −1st order diffracted light, and the region including only the 0th order light in the first light flux. An interference optical system that generates three or more types of interference light for each of the four areas of the area C and the peripheral area D. The signal processing unit determines the phase difference between the areas C and D as a focus error. The servo circuit is generated as a signal and performs focus control of the light collecting means by a focus error signal.
This makes it possible to simultaneously acquire the focus error signal in the process of acquiring the track error signal, contributing to simplification and miniaturization of the apparatus.

(6) In (1), there are two regions of the first light flux in which interference light is generated.
Thereby, track servo control equivalent to (1) can be performed with a simpler configuration.

According to the present invention, it is possible to provide an optical information reproducing apparatus capable of performing track servo control regardless of the characteristics of recording marks and recording media.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

The block diagram of one Example of the optical information reproducing | regenerating apparatus by this invention. Detailed view of electromagnetic actuator. The figure showing the area | region division pattern of a hologram element. Schematic of a detector and a signal processing circuit. The block diagram of a signal processing circuit. Schematic of the reflected light from an optical disk. The figure showing the electric field of each field of signal light. The figure showing the electric field of each field of signal light. The figure explaining the generation principle of the track error signal of the present invention. The figure explaining the generation principle of the track error signal of the present invention. The figure which shows the simulation result of a track error signal. The figure showing the phase of the signal photoelectric field at the time of on-track when there is no phase difference between a recording mark and a space. The figure showing the phase of the signal photoelectric field at the time of off-track when there is no phase difference between a recording mark and a space. The figure which shows the example of another area division | segmentation pattern of a hologram element. The figure which shows the example of another area division | segmentation pattern of a hologram element. The figure which shows the example of the arrangement pattern of the light-receiving part of the detector when not using a hologram element. The block diagram of another optical system which detects the interference light of signal light and reference light. The block diagram of the detector in another optical system which detects the interference light of signal light and reference light. The schematic diagram of the optical system in the case of producing | generating three types of interference light. The figure which shows the example of another area division pattern of the hologram element in the case of removing the offset of a track error signal. FIG. 6 is a schematic diagram of a detector and a signal processing unit circuit for another area division pattern of a hologram element when removing an offset of a track error signal. The block diagram of embodiment which performs feedback control of the optical path length of signal light and reference light. FIG. 5 is a detailed diagram of a detector and a signal processing circuit in an embodiment that performs feedback control of optical path lengths of signal light and reference light. The figure showing the electric field of each field of signal light in an embodiment which performs feedback control of the optical path length of signal light and reference light. The block diagram in the case of performing feedback control of the optical path length of signal light and reference light, and acquiring a reproduction signal from interference light of signal light and reference light. FIG. 3 is a detailed diagram of a detector and a signal processing circuit when feedback control is performed on the optical path lengths of signal light and reference light and a reproduction signal is acquired from interference light of the signal light and reference light. The block diagram of embodiment which acquires a focus error signal from the interference light of signal light and reference light. The figure which shows the example of the area | region division pattern of a hologram element in embodiment which acquires a focus error signal from the interference light of signal light and reference light. The block diagram of the signal processing circuit in embodiment which acquires a focus error signal from the interference light of signal light and reference light. The figure which shows the example of another area division | segmentation pattern of a hologram element in embodiment which acquires a focus error signal from the interference light of signal light and reference light. The figure which shows the example of another area division | segmentation pattern of a hologram element in embodiment which acquires a focus error signal from the interference light of signal light and reference light. The figure which shows the example of the area | region division pattern of a hologram element in embodiment which reduced the number of the area | regions detected separately. The block diagram of the signal processing circuit in embodiment which reduced the number of the area | regions detected separately. The block diagram of another signal processing circuit in embodiment which reduced the number of the area | regions detected separately.

[Example 1]
(Outline of operation)
FIG. 1 is a block diagram showing an embodiment of an optical information reproducing apparatus according to the present invention. The optical disk 112 is a grooveless medium having no groove structure in the recording layer, such as a servo surface servo optical disk or a volume type optical disk. In the present specification, a virtual surface constituted by tracks of a volume optical disc is also called a recording layer.

  First, the operation during reproduction of the apparatus of the present embodiment will be described. The laser driver 101 causes the semiconductor laser 104 to emit light according to an instruction from the microprocessor 102. The light beam emitted from the semiconductor laser 104 passes through the λ / 2 plate 105. Here, the light beam from the semiconductor laser 104 is vertically polarized light (s-polarized light), the optical axis direction of the λ / 2 plate 105 is set to 22.5 degrees with respect to the horizontal direction, and the polarization direction of the light beam is 45 degrees. Rotated. The polarized light is split by the polarization beam splitter 106 into a vertically polarized light beam that is reflected and a horizontally polarized light beam that is transmitted. The reflected light beam is converted into parallel light by the first collimating lens 107, and then passes through a relay lens 108 that corrects spherical aberration and a λ / 4 plate (axial direction: 45 degrees with respect to the horizontal polarization direction) 109. Then, the light is condensed on the recording layer inside the optical disc 112 by the objective lens 111 with NA of 0.85 mounted on the electromagnetic actuator 110.

  FIG. 2 is a diagram illustrating a configuration example of the electromagnetic actuator 110. The electromagnetic actuator 110 includes a mounting portion 2901 on which the objective lens 111 is mounted, an electromagnet 2902, and a permanent magnet 2903. The position of the mounting portion 2901 is displaced by a current flowing through the electromagnet 2902. A plurality of electromagnets 2902 are provided, and the objective lens 111 can be displaced in the optical axis direction and in the horizontal direction by a combination of currents flowing through them.

  Reflected light from the optical disk 112 (hereinafter referred to as signal light) follows an optical path opposite to that at the time of irradiation, passes through the λ / 4 plate 109 again, becomes horizontal polarized light, and enters the polarization beam splitter 106. On the other hand, a light beam that has passed through the polarization beam splitter 106 (hereinafter referred to as reference light) is converted into a parallel light beam by the collimator lens 118, and then reflected by the mirror 119 in the opposite direction, and the λ / 4 plate 120 (axial direction: The polarization direction is changed to vertical polarization by reciprocating through 45 degrees with respect to the horizontal polarization direction, and is incident on the polarization beam splitter 106 again.

  Here, since both the signal light and the reference light are emitted in the direction in which the special polarization beam splitter 113 is arranged, the signal light and the reference light are combined in the polarization beam splitter 106 in a state where the polarizations are orthogonal to each other. This combined beam enters a special polarization beam splitter (transmits 50% of horizontally polarized light, reflects 50%, and transmits 100% of vertically polarized light) 113, and only the horizontally polarized light component, which is a signal light component, is recorded. As with time, it is reflected at a rate of 50% and the rest is transmitted. The reflected light passes through the cylindrical lens 114 and is collected and detected by the quadrant detector 115. A focus error signal is generated from the output signal of the quadrant detector 115 and fed back as a drive current of the electromagnetic actuator 110 via the servo circuit 116. Thereby, the spot 117 of the light beam condensed by the objective lens 111 is controlled to be formed on the recording surface. In this embodiment, the astigmatism method is used as focus servo control.

  The transmitted light beam from the special polarization beam splitter 113 passes through the hologram element 121, and a plurality of regions in the light beam are diffracted in different directions. The hologram element is divided into three regions A, B, and C as shown in FIG. 3, where A includes the + 1st order diffracted light of the reflected light from the optical disc, B includes the −1st order diffracted light, and C includes the 0th order light. Contains only. These diffracted lights are divided into two by the non-polarizing beam splitter 122 into transmitted light and reflected light.

  The transmitted light passes through the λ / 2 plate 123 whose optical axis is set to 22.5 degrees with respect to the horizontal direction, and the polarization is rotated 45 degrees, and is separated into a p-polarized component and an s-polarized component by the polarizing beam splitter 124. Is done. The separated light beams respectively enter the detectors 125 and 126, and are detected by separate light receiving portions for each area of the hologram element in each detector, and an electric signal proportional to the intensity is output.

  Similarly, the light beam reflected by the non-polarization beam splitter 122 is separated by the polarization beam splitter 128 after passing through the λ / 4 plate 127 whose optical axis is set to 45 degrees with respect to the horizontal direction, and is detected by the detectors 129 and 130. Is detected. As will be described later, each of the light beams received by the detector is interference light in which the signal light and the reference light interfere with each other.

  The outputs of the detectors 125, 126, 129 and 130 are sent to the signal processing circuit 131. As described above, each detector has a light receiving unit that detects the light beams from the regions A, B, and C, respectively, and outputs from each of the three channels are input to the signal processing circuit 131 as shown in FIG. The signal processing circuit 131 outputs a reproduction signal and a track error signal based on the input signal. The obtained reproduction signal is demodulated by the demodulation circuit 132, sent to the decoding circuit 133, converted into user data, and sent to the host device 103 through the microprocessor 102. The track error signal is fed back as a drive current for the electromagnetic actuator 110 via the servo circuit 116, and the radial position of the spot 117 is controlled to be the center of the recording track.

(Reproduction principle)
Here, the principle of generating the reproduction signal and the track error signal by generating the interference light by the above-described operation will be described. Since the light beam incident on the non-polarizing beam splitter 122 includes reproduction light as a p-polarized component and reference light as an s-polarized component, this polarization state is represented by the Jones vector as follows.

Here E _s is the electric field of the signal light, which is the electric field of E _r reference light. However, E _s and E _r may be considered as an electric field in any region of the hologram element 121. The first component of this vector represents p-polarized light, and the second component represents s-polarized light.

  The Jones vector after this light beam passes through the non-polarizing beam splitter 122 and passes through the λ / 2 plate 123 is as follows.

となり、信号光と参照光の重ね合わせ、すなわち干渉光となっている。一方、無偏光ビームスプリッタ１２２を反射した光がλ／４板１２７を通過した後のジョーンズベクトルは

となる。次に偏光ビームスプリッタ１２８によってｐ偏光成分とｓ偏光成分に分離されるため、分離された光束の電場はそれぞれ

となり、やはり信号光と参照光の重ね合わせ、すなわち干渉光となっている。 Since the polarization beam splitter 124 separates the p-polarized component and the s-polarized component, the electric fields of the separated light beams are respectively

Thus, the signal light and the reference light are superimposed, that is, interference light. On the other hand, the Jones vector after the light reflected by the non-polarizing beam splitter 122 passes through the λ / 4 plate 127 is

It becomes. Next, since the polarization beam splitter 128 separates the p-polarized component and the s-polarized component, the electric field of the separated light flux is respectively

Thus, the signal light and the reference light are superimposed, that is, interference light.

  Accordingly, the intensities of the four interference lights are respectively expressed by the following equations, and electric signals proportional to these are output from the detectors 125, 126, 129, and 130, respectively.

  Actually, three detector outputs corresponding to the regions A, B, and C of the hologram element 121 are obtained at each detector, and a total of twelve output signals are input to the signal processing circuit 131. The outputs of the expressions (8), (9), (10), and (11) for the region A are respectively expressed as the expressions (8), (9), and (10) for the areas A1, A2, A3, A4, and B. ), And the output of expression (11) are respectively output from expression (8), expression (9), expression (10), and expression (11) for B1, B2, B3, B4, and region C, respectively. C4. In Equation (8), Equation (9), Equation (10), and Equation (11), the first term and the second term represent the intensity components of the signal light and the reference light, respectively, and the third term represents the signal light and the reference light. This is a term representing interference. φ is the phase of the signal light based on the phase of the reference light.

となり、上記の干渉を表す項に比例した出力となっている。領域Ｂ，Ｃについても同様の信号Ｂ_I，Ｂ_Q，Ｃ_I，Ｃ_Qが得られる。これらの信号から、領域Ａ，Ｂ，Ｃにおける信号光の電場に対応する信号

が得られる。これらの出力が信号光の電場に対応することは、簡単のために参照光電場Ｅ_rを１とすると、例えば領域Ａについて

と表されることから確認できる。再生信号は信号光電場の強度の変調信号のため、これらの電場より

として出力される。トラックエラー信号は、信号光の左右の領域（領域Ａ，Ｂ）の位相差に相当する信号として

が出力される。 A block diagram of signal processing in the signal processing circuit 131 is shown in FIG. First, the difference between the outputs of the detectors 125 and 126 and the difference between the outputs of the detectors 129 and 130 are calculated, and these are converted into digital signals by the AD converter. These represent, for example, the output related to region A

Thus, the output is proportional to the term representing the interference. Similar signals B _I , B _Q , C _I , and C _Q are obtained for the regions B and C. From these signals, signals corresponding to the electric field of the signal light in the regions A, B, and C

Is obtained. These outputs correspond to the electric field of the signal light. For the sake of simplicity, if the reference photoelectric field _Er is 1, for example, for the region A

It can be confirmed from this. Since the reproduction signal is a modulated signal of the intensity of the signal photoelectric field,

Is output as The track error signal is a signal corresponding to the phase difference between the left and right regions (regions A and B) of the signal light.

Is output.

  Here, the principle of obtaining the track error signal by the phase difference between the left and right regions of the signal light will be described in detail. The reflected light from the optical disc includes the + 1st order light and the −1st order light displaced to the left and right in addition to the 0th order light which is the regular reflected light because the recording marks are aligned as tracks with a predetermined interval. It is. Since this reflected light has zero light quantity outside the range where the 0th order light exists due to the aperture limitation of the objective lens, as shown in FIG. 6, the + 1st order light and − There is a region where primary light overlaps.

Here, if the electric fields of the 0th order light, the + 1st order light, and the −1st order light are expressed as E ₀ , E ₊₁ , and E ₋₁ , the signal photoelectric fields in the regions A, B, and C are E ₀ + E _+1, respectively. , E ₀ + E ₋₁ , E ₀ . This is illustrated on the complex plane as shown in FIG. The + 1st order light and the −1st order light are the same when the spot 117 is at the center of the track formed by the recording marks, and the electric fields in the areas A and B are equal as shown in FIG. When the spot 117 is displaced in the radial direction from the track center, the + 1st order light and the −1st order light have phases opposite to each other, resulting in a phase difference between the regions A and B. In this embodiment, the imaginary part of the electric field is treated as a value reflecting the phases of the regions A and B. However, since the phase value is based on the 0th order light, the imaginary part is taken after dividing E _A and E _B by E _C. These values are expressed as shown in FIG. 9 with respect to the amount of displacement of the spot from the track center (off-track), and the output of equation (19), which is the difference between these values, is when the off-track is zero as shown in FIG. 0, which is an ideal output as a track error signal.

(Track error signal simulation)
FIG. 11 shows a simulation result in which the amplitude of the track error signal in this embodiment and the amplitude of the track error signal by the conventional push-pull method are compared for various recording marks. In this simulation, the NA of the objective lens is 0.85, the wavelength of the light source is 405 nm, the track pitch is 0.32 μm, the rim intensity (ratio of the intensity of the peripheral part to the intensity of the central part of the light beam) is 40%, and the mark The shape was a continuous mark having a rectangular shape (mark width 0.16 μm).

  Among these results, when the phase difference between the mark and space is 0 or half wavelength (0.5λ), the amplitude of the conventional push-pull method is 0, whereas in this embodiment, there is no mark. Except for the case where the relative reflectance of the mark corresponding to is 100%, a sufficient amplitude was obtained. This is explained as follows.

  When the phase difference between the mark and the space is 0 or half wavelength (0.5λ), the phase of the 0th order light, the + 1st order light, and the −1st order light at the time of on-track becomes equal, as shown in FIG. The phases of the signal photoelectric fields in the regions A, B, and C are all equal. For this reason, the electric fields in the regions A and B at the time of off-track are opposite in phase to each other and have the same magnitude (that is, intensity) as shown in FIG. Since the error signal by the conventional push-pull method is a difference in intensity between the left and right areas of the signal light (areas A and B in this embodiment), in such a situation where there is no difference in intensity between the left and right areas, push-pull is performed. No signal is generated. On the other hand, since the error signal of this embodiment corresponds to the left and right phase difference, the error signal can be acquired because the sign of the phase is reversed even if the intensity is the same on the left and right.

  Due to this property, as can be seen from FIG. 11, the error signal of this embodiment has a smaller amplitude variation with respect to the mark / space phase difference and the reflectance variation than the conventional push-pull method. Therefore, the error signal is stabilized under actual conditions, and stable track servo control is possible. The push-pull method, such as the differential push-pull method, the advanced push-pull method, and the new advanced push-pull method, is essentially the same as the push-pull method in that it acquires the intensity difference between the left and right signal light. It is. In contrast to these conventional methods, the method of acquiring the left and right phase difference of the signal light in this embodiment is essentially a different method.

  In Patent Document 1, the track error signal is acquired from the interference signal between the signal light and the reference light as in the present embodiment. However, since the signal to be acquired corresponds to the difference in intensity between the left and right signal lights, and is essentially the same signal as the conventional differential push-pull method, it is different from the method of this embodiment.

  The track error signal of this embodiment has a property that it is robust against a radial position shift of the objective lens due to the eccentricity of the optical disk. This is understood as follows. When the objective lens is shifted in the radial direction, the amount of zero-order light in the areas A and B changes. However, the track error signal of this embodiment is irrelevant to the magnitude of the 0th-order light, as is apparent from FIG. On the other hand, the light amounts of the + 1st order light and the −1st order light are constant as long as they do not protrude from the areas A and B. As a result, even if the radial position shift of the objective lens occurs, an offset or amplitude change occurs in the track error signal. Does not occur.

  In this embodiment, the hologram element 121 is divided into regions as shown in FIG. 3, but the setting of each region is not limited to this example, and the region including all + 1st order light and the region including all −1st order light. , It is sufficient that there are three regions including only the 0th-order light. For example, you may use the hologram element by which the area | region was divided | segmented like FIG. 14, FIG. In addition, the hologram element 121 is not necessarily required to obtain a signal output separately for each region. For example, the detectors 125, 126, 129, and 130 are shifted in the optical axis direction from the focusing positions of the signal light and the reference light. The same operation can be realized even if the light receiving units are arranged at positions and each light receiving unit is divided into three as shown in FIG.

  In this embodiment, the non-polarizing beam splitter 122, the polarizing beam splitters 124 and 128, the λ / 2 plate 123, the λ / 4 plate 127, and the like are used as means for generating the interference light of the signal light and the reference light. It is not limited to this. For example, as described in Hideharu Mikami et al., “Ultra-Compact Optical Module of Homodyne Detection,” ISOM / ODS Tech. Dig., OMC3, Hawaii, Jun. 2011, the configuration shown in FIG. . In this case, the light beam obtained by combining the signal light and the reference light is first branched into ± first-order diffracted light by the non-polarization diffraction grating 2601 (corresponding to a non-polarization beam splitter). Next, these diffracted lights pass through the phase plate 2602, and the phase difference between the signal light and the reference light between the two diffracted lights changes by π / 2 (corresponding to λ / 2 plate and λ / 4 plate), Thereafter, these light beams are branched by ± 45 degree polarization components by the Wollaston prism 2603, and as a result, four interference lights are generated for each of the regions A, B, and C. These light beams are detected by the same detector 2604. The detector 2604 provides a light receiving unit for each branched light beam as shown in FIG. 18, and outputs signals of different channels.

  In this embodiment, four types of interference light are generated for each signal light region, and a reproduction signal and a track error signal are obtained from these. The parameters that determine the interference light between the signal light and the reference light are signal light intensity and reference light. Since the intensity and the phase difference between the signal light and the reference light are three, in principle, the same operation is possible if three or more types of interference light are acquired.

 FIG. 19 is a schematic diagram of the optical system after passing through the hologram element 121 when three types of interference light are acquired. With respect to the combined light beam of the signal light and the reference light, the incident light beam is divided into three light beams by non-polarizing beam splitters 1201 and 1202, and one of the light beams has a phase difference of 120 degrees with respect to the p-polarized light. Another light beam passes through the phase plate 1203 through which the s-polarized light causes a phase difference of 240 degrees with respect to the p-polarized light, and then the polarizer 1205 transmits only 45-degree polarized light in all three light beams. 1206 and 1207 are transmitted and detected by detectors 1208, 1209 and 1210. Each of these detectors includes three detectors that detect the light fluxes in the regions A, B, and C. The outputs for region A are expressed as follows.

  From these outputs, an output corresponding to the signal photoelectric field is obtained by the following calculation.

  Similar outputs can be obtained for regions B and C. From these outputs, a reproduction signal and a track error signal are obtained in the same manner as in the above embodiment.

  In this embodiment, the track error signal and the reproduction signal are acquired from the signal light and the interference light of the reference light. However, the method for acquiring the reproduction signal is not limited to the method of this embodiment. For example, the sum of the output signals from the four light receiving units (corresponding to the total signal light amount) in the quadrant detector 115 may be used as the reproduction signal. In this case, the calculation for obtaining the reproduction signal in the signal processing circuit 131 is omitted.

  In this embodiment, Equation (19) is used as a track error signal as a signal corresponding to the phase difference between the left and right of the signal light, but the type of signal is not limited to this. For example, the following equation for directly calculating the phase difference between the + 1st order light and the −1st order light may be used as the track error signal.

  Here, k is a predetermined coefficient, and the zero-order photoelectric field is zero in each of the numerator and denominator of the division in the equation (24) from the average value of the zero-order photoelectric fields included in the regions A, B, and C. Calculated. Actually, the reproduction signal quality is optimized so that the track servo is driven. In this case, the numerator in arg is the electric field of + 1st order light, the denominator is the electric field of −1st order light, and the declination of these divisions is the phase difference between + 1st order light and −1st order light.

In the present embodiment, as described above, even if the radial position shift of the objective lens occurs, the track error signal is not offset. However, the configuration for removing the track error signal offset is not limited to this. Absent. For example, the hologram element 121 is divided into four parts as shown in FIG. That is, the areas A and B are the same as in this embodiment, and the areas where the + 1st order light and the −1st order light are all accommodated, and the other areas are further divided into left and right areas C and D. These regions are received by the detectors 125, 126, 129, and 130, respectively, as shown in FIG. 21, and generate different output signals. Similarly to this embodiment, signals E _A , E _B , E _C , E _D corresponding to the electric fields in the regions A, B, C, _D are output, and a track error signal is obtained by the following calculation.

However, k is a predetermined coefficient, and the numerator and denominator of the division in the equation (25) are calculated from the average values of the zero-order photoelectric fields included in the regions A, B, C, and D as in the case of the equation (24). Is calculated so that the zero-order photoelectric field becomes zero. Actually, the reproduction signal is optimized so that the quality of the reproduction signal is best when the track servo is driven. In this case, when the radial position shift of the objective lens occurs, the zero order light components of E _A and E _C decrease, and the zero order light components of E _B and E _D increase. Alternatively, the zero order light components of E _A and E _C decrease, and the zero order light components of E _B and E _D increase. In either case, since the subtraction is performed in the numerator and denominator of the calculation of Expression (25), the increase / decrease in the 0th-order light component is canceled, and as a result, the offset and the amplitude are hardly changed.

  Compared with such a configuration, the configuration of this embodiment is advantageous because the number of divisions of the hologram element 121 and the number of light receiving portions of the detectors 125, 126, 129, and 130 are small. In this configuration, the reproduction signal is obtained as the following equation because of the total amount of signal light.

  In the above simulation results, the track error signal of this embodiment is obtained for most combinations of the relative reflectivity and phase difference of the mark and space (the track error signal cannot be obtained because the reflection of the mark and space Since there is no rate difference and the phase difference is an integral multiple of the wavelength, that is, only when there is substantially no mark / space structure), the recording medium to which the present embodiment is applicable is not particularly limited, for example, Japanese Patent Application Laid-Open No. 2011-076665. In the case of recording by phase multi-level modulation in the micro-hologram method as shown in Japanese Patent Publication No. 2, or using the one in which the interface of the reflective layer is deformed according to the light intensity at the time of recording as in Japanese Patent No. 2705330 May be. Of course, the present invention can also be applied to a conventional recording medium such as a recordable BD or a BD-ROM. The following embodiments can also be applied to similar recording media.

  In this embodiment, the electromagnetic actuator 110 is movable in two directions (incident optical axis direction and radial direction) in order to perform both the focus servo operation and the track servo operation. Needless to say, in order to perform the track servo operation, an electromagnetic actuator movable only in the radial direction may be used.

[Example 2]
This embodiment is another embodiment in which signal processing is simple. FIG. 22 shows a configuration diagram of the optical information reproducing apparatus of this example.

  In this embodiment, the reference light is reflected by the mirror 1502 mounted on the piezo element 1501 before and after being reflected by the mirror 119, and the mirror 119 is mounted on the electromagnetic actuator 1503. Further, the non-polarizing beam splitter 122 and the optical system for detecting the reflected light are omitted. In this embodiment, the optical axis direction position of the objective lens 111 is controlled by the focus error signal, and at the same time, the optical axis direction position of the mirror 119 is displaced by the same focus error signal, so that the optical path lengths of the signal light and the reference light are approximately equal. It is controlled to become. Further, the piezo element 1501 is driven by the phase error signal PES, and is controlled so that the phases of the signal light and the reference light are constant. Further, the reproduction signal is output as the total light amount of the quadrant detector 115 and input to the demodulation circuit 132 without passing through the signal processing circuit 131.

  The configurations of the detectors 125 and 126 and the signal processing circuit 131 of this embodiment are shown in FIG. First, difference signals A2-A1, B2-B1, C2-C1 are calculated for the output signals from the detectors 125, 126 in the same manner as in the first embodiment, and the difference signal C2-C1 is passed through the servo circuit 116 as a phase error signal. It is fed back as a driving voltage for the piezo element 1501. Further, the difference between the difference signals A 2 -A 1 and B 2 -B 1, that is, A 2 -A 1 -B 2 + B 1 is calculated and becomes a track error signal, which is fed back as a drive signal for the objective lens 110 via the servo circuit 116.

  The operation principle of this embodiment will be described below. The difference signal C2-C1, which is a phase error signal, is expressed by Expression (12), and is proportional to the cosine of the zero-order light component of the signal light and the phase difference φ of the reference light. Therefore, by controlling the phase difference between the signal light and the reference light using this signal as an error signal, φ can be maintained at π / 2 or −π / 2 (so that the cosine becomes 0). This means that the real part of the zero-order component of the signal light (electric field in region C) with reference light as a reference is zero, and is represented by a vector in the imaginary axis direction on the complex plane. . This is shown in FIG. Here, since the reference light signals A2-A1 and B2-B1 represent the real part components of the electric fields in the regions A and B, respectively, these difference signals A2-A1-B2 + B1 are apparent when FIG. 24 and FIG. 7 are compared. Thus, it is the same as the track error signal in the first embodiment. In this way, it is possible to perform track servo control using the left and right phase differences of the signal light as in the first embodiment by simple calculation.

  In the present embodiment, a signal corresponding to the total light amount of the signal light is directly generated by the quadrant detector as a reproduction signal. However, as in the first embodiment, it can also be generated from the interference light with the reference light. The configuration in this case is shown in FIG. In this case, the non-polarizing beam splitter 122 is not omitted, and the detectors 129 and 130 receive only the light flux in the region C and output a signal. The signal processing circuit in this case is as shown in FIG. 26, and in addition to the configuration of the present embodiment, a signal obtained by A / D converting the difference signal C3-C4 of the signals from the detectors 129 and 130 is output as a reproduction signal. Is done. The difference signal C3-C4 corresponds to the imaginary axis component of the electric field in the region C in FIG. 24, that is, the length (intensity) of the electric field, and thus can be used as a reproduction signal.

  In this embodiment, the electromagnetic actuator 1503 and the piezo element 1501 are used as a control mechanism for the optical path length of the reference light. However, the electromagnetic actuator 1503 secures a stroke (control range) necessary for the optical path length control. This is used for the purpose of precise optical path length control in the wavelength order. However, the electromagnetic actuator 1503 can be omitted if the stroke of the piezo element is equal to or greater than the surface deflection of the optical disk.

  Reexplaining the optical information reproducing method of this embodiment, the light beam is divided into a first light beam and a second light beam, the first light beam is condensed at a predetermined position on the recording medium, and the first light beam The region A including the + 1st order diffracted light in the first light flux from the output of the detection signal that detects the interference light by combining the reflected light from the recording medium with the second light flux to generate two or more types of interference light. And the phase of the first light beam reflected from the recording medium based on the phase difference between the first light beam and the light beam in the region B including the −1st order diffracted light and the phase of the second light beam. The feedback control of the condensing position of the first light beam using the phase difference as a track error signal, and the feedback control of the optical path length difference between the first light beam and the second light beam using the phase of the first light beam as the phase error signal It is.

[Example 3]
In this embodiment, in addition to the track error signal of the first embodiment, a focus error signal is acquired from interference light of signal light and reference light. FIG. 27 shows a configuration diagram of the optical information reproducing apparatus of the present embodiment.

Compared with the configuration of the first embodiment shown in FIG. 1, the configuration of the present embodiment omits the special polarization beam splitter 113, the cylindrical lens 114, and the quadrant detector 115 that are prepared for acquiring the focus error signal. Instead, the focus error signal is output from the signal processing circuit 131 instead. Further, as shown in FIG. 28, the hologram element is divided into a region C in the central portion of the light beam and a region D in the upper and lower portions of the light beam in addition to the regions A and B as in the first embodiment. In 125, 126, 129, and 130, light is received by separate light receiving sections, and signals of separate channels are output. The configuration of the signal processing circuit 131 is shown in FIG. In addition to the configuration of the first embodiment, the electric field E _{D of the} region D is calculated, and a focus error signal is generated as the following calculation output together with the value of the electric field E _C of the region C.

  Here, the reason why Expression (27) becomes a focus error signal will be described. When the spot is at a position different from the recording surface, the signal light includes defocus aberration, so that a phase difference occurs between the central portion and the peripheral portion. This phase difference becomes 0 when the spot is on the recording surface, and the sign is reversed depending on whether the spot is in the back or in front of the recording surface. That is, the phase difference between the central portion and the peripheral portion of the signal light can be used as a focus error signal. However, since regions A and B contain diffracted light from the recording track, an extra phase is added. Accordingly, a focus error signal can be obtained by acquiring the phase difference between the region D that is the peripheral portion not including the diffracted light and the region C that is the central portion.

  In the present embodiment, similarly to the first embodiment, the shape of the region division of the hologram element 121 is not limited to this, and the region including the + 1st order diffracted light, the region including the −1st order diffracted light, and the 0th order including many central portions. The same operation can be realized if there are four areas, that is, a light-only area and a zero-order light-only area including many peripheral portions. For example, a divided shape as shown in FIGS. 30 and 31 may be used.

をトラックエラー信号とする。また、再生信号はＥ_Cが省略された

が出力として用いられる。 [Example 4]
The present embodiment is another embodiment in which the number of light flux areas to be detected separately is reduced. The configuration diagram of the optical information reproducing apparatus of the present embodiment is shown in FIG. However, as shown in FIG. 32, the hologram element 121 is only divided into two on the left and right sides of the incident light beam, and these left and right regions A and B are separated by detectors 125, 126, 129, and 130 by separate light receiving sections. Detected. The configuration of the signal processing circuit 131 is shown in FIG. In the calculation for generating the track error signal, instead of the electric field E _{C in} the region C of the first embodiment, the sum E _A + E _B of the regions A and _B is used.

Is a track error signal. Also, E _C is omitted from the playback signal.

Is used as output.

This embodiment is effective when the phase difference between the recording mark and the space (unrecorded) portion of the optical disk 112 is 0 or very small. The operation principle will be described below. When the phase difference between the recording mark and the space (unrecorded) portion of the optical disk 112 is 0 or very small, as described in the first embodiment, the electric fields E _A and E _B in the left and right regions are out of phase with each other on the complex plane. Represented as a vector of opposite magnitude in equal direction. In this case, the sum of E _A and E _B always points in the direction of the 0th order light. That is, E _A + E _B has the same phase as the 0th order light. This property is the same as the electric field E _C in the region C, which is an electric field including only the 0th-order light in the first embodiment, and it becomes possible to replace E _C with E _A + E _B in the calculation of the track error signal. Also in the present embodiment, the property that the track error signal does not change with respect to the radial position shift of the objective lens is maintained.

  In the same way, it is possible to reduce the number of divided areas in the second and third embodiments. For example, in the second embodiment, the hologram element is divided into left and right as shown in FIG. 32 as in the present embodiment, and as shown in FIG. 34, the signal processing circuit calculates the phase error signal as A2-A1 and B2. It can be used as the sum signal A2-A1 + B2-B1 of -B1.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  Each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files for realizing each function can be stored in a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

  According to the present invention, a large-capacity optical information recording / reproducing apparatus can be provided, and a wide range of industrial applications such as a large-capacity video recorder, a hard disk data backup apparatus, and a stored information archive apparatus can be expected.

101: laser driver, 102: microprocessor, 103: host device, 104: semiconductor laser, 105: λ / 2 plate, 106: polarization beam splitter, 107: collimating lens, 108: relay lens, 109: λ / 4 plate, 110: Electromagnetic actuator, 111: Objective lens, 112: Optical disk, 113: Special polarization beam splitter, 114: Cylindrical lens, 115: Quadrant detector, 116: Servo circuit, 117: Spot, 118: Collimating lens, 119: Mirror 120: λ / 4 plate, 121: hologram element, 122: non-polarization beam splitter, 123: λ / 2 plate, 124, 128: polarization beam splitter, 125, 126, 129, 130: detector, 127: λ / 4 plates, 131: signal processing circuit, 132: demodulation circuit, 1 33: Decoding circuit, 1201, 1202: Non-polarizing beam splitter, 1203, 1204: Phase plate, 1205, 1206, 1207: Polarizer, 1208, 1209, 1210: Detector, 1501: Piezo element, 1502: Mirror, 1503: Electromagnetic actuator, 2601: diffraction grating, 2602: phase plate, 2603: Wollaston prism, 2604: detector, 2901: mounting portion, 2902: electromagnet, 2903: permanent magnet

Claims (13)

A light source;
A light splitting means for splitting a light beam from the light source into a first light beam and a second light beam;
Condensing means for condensing the first light flux at a predetermined position on the recording medium;
A drive unit that drives the light collecting means in a direction perpendicular to the optical axis direction of the first light flux;
The reflected light from the recording medium of the first light flux is combined with the second light flux, and the region A including at least the + 1st order diffracted light of the first light flux and the −1st order diffracted light of the first light flux are obtained. An interference optical system that generates three or more types of interference light for each of the two regions B including the region B;
A detector for detecting the interference light;
A signal processing unit that generates a phase difference between at least the light flux in the region A of the first light flux and the light flux in the region B of the first light flux from the output of the detector;
A servo circuit that inputs the phase difference as a track error signal to the drive unit;
An optical information reproducing apparatus comprising: A light source;
A light splitting means for splitting a light beam from the light source into a first light beam and a second light beam;
Condensing means for condensing the first light flux at a predetermined position on the recording medium;
A drive unit that drives the light collecting means in a direction perpendicular to the optical axis direction of the first light flux;
An interference optical system for combining reflected light from the recording medium of the first light flux with the second light flux to generate two or more types of interference light;
An optical path length difference adjusting unit for adjusting an optical path length difference between the first light flux and the second light flux;
A detector for detecting the interference light;
From the output of the detector, the phase difference between the luminous flux in the region A including the + 1st order diffracted light in the first luminous flux and the luminous flux in the region B including the −1st order diffracted light in the first luminous flux, and the first A signal processing unit that generates a phase of the first light beam reflected from the recording medium based on a phase of the second light beam;
A servo circuit that inputs the phase difference as a track error signal to the drive unit;
A servo circuit that inputs the phase of the first light flux to the optical path length difference adjustment unit as a phase error signal;
An optical information reproducing apparatus comprising: The optical information reproducing apparatus according to claim 1 or 2,
The interference optical system generates three or more types of interference light for each of the three areas of the area A, the area B, and the area C including only the 0th-order light of the first light flux. And
The optical information reproducing apparatus according to claim 1, wherein the phase difference is a phase difference based on a phase of a light beam in the region C of the first light beam. The optical information reproducing apparatus according to claim 3,
The phase difference is defined as the imaginary part of the electric field of the first light beam in the region A and the electric field of the first light beam in the region B when the phase of the first light beam in the region C is 0. An optical information reproducing apparatus characterized by being a difference from an imaginary part. The optical information reproducing apparatus according to claim 1,
The interference optical system has at least four regions, namely, the region A, the region B, and the region C including the central portion of the region including only the 0th-order light of the first light beam and the region D of the peripheral portion. Are interference optical systems that generate three or more types of interference light,
The signal processing unit generates a phase difference between the light flux in the region C and the light flux in the region D as the focus error signal in the first light flux,
An optical information reproducing apparatus, comprising: a servo circuit that performs focus control of the light collecting means according to the focus error signal.   2. The optical information reproducing apparatus according to claim 1, wherein the first light beam has two regions where interference light is generated. The optical information reproducing apparatus according to claim 1 or 2,
An optical information reproducing apparatus for reproducing a recording medium having a recording surface without a groove structure. Split the luminous flux into a first luminous flux and a second luminous flux,
Condensing the first light flux at a predetermined position on the recording medium;
The reflected light from the recording medium of the first light flux is combined with the second light flux, and the region A including at least the + 1st order diffracted light of the first light flux and the −1st order diffracted light of the first light flux are obtained. Generate three or more types of interference light for each of the two regions B including the region B,
From the output of the detection signal that detects the interference light, generate a phase difference between at least the light flux in the region A of the first light flux and the light flux in the region B of the first light flux,
An optical information reproducing method, wherein feedback control is performed on the condensing position of the first light flux using the phase difference as a track error signal. The optical information reproducing method according to claim 8,
Three or more types of interference light are generated for each of the region A, the region B, and the region C including only the 0th-order light of the first light flux,
The optical information reproducing method, wherein the phase difference is a phase difference based on a phase of a region C of the first light flux. The optical information reproducing method according to claim 9, wherein
The phase difference is defined as the imaginary part of the electric field of the first light beam in the region A and the electric field of the first light beam in the region B when the phase of the first light beam in the region C is 0. An optical information reproducing method characterized in that the difference is an imaginary part. The optical information reproducing method according to claim 8,
At least three types for each of the four areas of the area A, the area B, and the area C including only the 0th-order light of the first light flux, the central area C and the peripheral area D Produces interference light
A phase difference between the light flux in the region C and the light flux in the region D of the first light flux is generated as a focus error signal.
An optical information reproducing method, wherein the focus position of the first light flux is feedback controlled by the focus error signal.   9. The optical information reproducing method according to claim 8, wherein the first light flux has two regions where interference light is generated. The optical information reproducing method according to claim 8,
An optical information reproducing method, wherein the recording medium has a recording surface without a groove structure.

Images