JP2007066492A - Optical information reproducing apparatus and method, and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information reproducing apparatus and method, and an optical pickup device in which a high transfer rate of information can be obtained. <P>SOLUTION: An output beam from a semiconductor laser 12 is switched to a condensed spot of an almost circular shape irradiating one information track or a condensed spot of an almost linear shape irradiating a plurality of information tracks by an optical element 14, so as to control irradiating output of the semiconductor laser 12 in accordance with a shape of the condensed spot. Then, reflected light in accordance with a shape of the condensed spot is received from an optical disk 11 by a light receiving element 28 divided in the direction corresponding to the condensed spot of almost linear shape, an error signal and/or a reproduced signal are generated based on this reflected light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical information reproducing apparatus and method for reproducing information recorded on a disk-shaped recording medium by illuminating a light spot on the disk-shaped recording medium, and an optical pickup apparatus.

  A conventional optical disc recording / reproducing apparatus performs signal recording and signal reproduction by illuminating an information track formed in advance on an optical disc with a single spot focused by an objective lens. Normally, the information track is formed in a spiral shape from the innermost periphery to the outer periphery or from the outermost periphery to the inner periphery, so that the optical disk recording / reproducing apparatus performs tracking control on the track. The signals are sequentially written or read.

  As a known method for improving the information transfer rate of reading and writing of an optical disc, there is a method of increasing the rotational speed of the disc. On the other hand, an optical disk substrate using a polycarbonate material is considered to have an upper limit of rotation speed of about 10,000 rpm from the viewpoint of safety, and the transfer speed at the outermost circumference of the disk compared with the reference transfer rate (standard speed) is CD ( The upper limit is about 50 × speed for Compact Disc, about 16 × speed for DVD (Digital Versatile Disc), and about 12 × speed for BD (Blu-ray Disc). In addition, the information transfer rate at the same rotational speed increases in accordance with the bit density (linear recording density). For example, when a BD having a capacity of 25 GB (Giga Byte) is recorded / reproduced at a rotational speed of 10,000 rpm, A transfer rate of about 430 Mbps can be realized in the unit.

  However, higher rotation of the optical disc requires wider bandwidth for focus control and track control, and in BD, along with the improvement in recording density brought about by shorter wavelength of light source and higher numerical aperture of objective lens. Therefore, higher precision control is required. Further, the transfer rate that can be realized becomes lower in the innermost circumference of the disk, and in the case of BD, the value is limited to about 180 Mbps.

  As a technique for improving the information transfer rate of the optical disk reproducing apparatus, a technique for reading information on a plurality of tracks in parallel by simultaneously irradiating a plurality of beams has been proposed in addition to the above technique for increasing the disk rotation speed.

  For example, Japanese Patent No. 2667998 (hereinafter referred to as Patent Document 1) reports an optical disc apparatus using a multi-beam semiconductor laser as a light source as a method of irradiating a plurality of spots onto an optical disc medium. In Japanese Translation of PCT International Publication No. 2002-504734 (hereinafter referred to as Patent Document 2), a single semiconductor laser is used as a light source, and by combining diffraction elements, beams generated from a plurality of diffraction orders are condensed, and an optical disk is collected. A method for forming a plurality of illumination spots on a medium has been proposed.

  Further, for example, in Japanese Patent Laid-Open No. 04-123331 (hereinafter referred to as Patent Document 3), a semiconductor laser and a cylindrical lens are combined as a method of simultaneously reading a plurality of information tracks using a single focused spot. Describes a method of reading a signal by forming a linear beam. Japanese Patent Laid-Open No. 08-249720 (hereinafter referred to as Patent Document 4) proposes a method using an LED (Light Emitting Diode) as a wide range illumination light source.

  Japanese Patent Application Laid-Open No. 02-183430 (hereinafter referred to as Patent Document 5) discloses a method of obtaining an oval beam shape by combining a concave cylindrical lens and a convex cylindrical lens and changing the positional relationship between the two. Proposed.

Japanese Patent No. 2667998 JP-T-2002-504734 Japanese Patent Laid-Open No. 04-123331 Japanese Patent Laid-Open No. 08-249720 Japanese Patent Laid-Open No. 02-183430

  Although the method of forming a plurality of focused spots described in Patent Document 1 and Patent Document 2 is considered to be an effective method for a CD having only a single signal layer, there are two or more signal layers. In DVDs and BDs that are assumed to be used, since a plurality of illumination lights are affected by unnecessary reflected light (interlayer stray light) generated by reflection on other signal layers, servo error signals and reproduction signals are deteriorated. Concerned. In particular, with regard to BD, expandability up to eight layers is expected, and reflected light in a large number of signal layers may interfere with each other in a complicated manner and have a great influence.

  In addition, any of the methods described in Patent Document 3 and Patent Document 4 is intended to increase the transfer rate at the time of signal reading, but does not realize compatibility with signal recording.

  Further, since the above-mentioned Patent Document 5 does not describe a specific signal processing method or servo error signal detection method, the technique of Patent Document 5 may move the objective lens as the information track follows. It is impossible to read signals from a plurality of information tracks at the same time.

  The present invention has been made in view of these problems, and an object thereof is to provide an optical information reproducing apparatus and method, and an optical pickup apparatus that can realize a high information transfer rate.

  In order to solve the above-described problems, an optical information reproducing apparatus according to the present invention irradiates one information track with a laser light source for irradiating an information track of an optical information recording medium and output light of the laser light source. A focused spot shape control means for switching to a substantially circular focused spot or a substantially linear focused spot that irradiates a plurality of information tracks, and the irradiation output of the laser light source is controlled according to the shape of the focused spot. An output control means and a light detection means having a light receiving region divided in a direction corresponding to the substantially linear light collecting spot, and receiving reflected light corresponding to the shape of the light collecting spot from the optical information recording medium And signal generation means for generating an error signal and / or a reproduction signal based on the reflected light received by the light detection means.

  Also, the optical information reproducing method according to the present invention provides the output light of the laser light source for irradiating the information track of the optical information recording medium as the substantially circular condensing spot or the plurality of information tracks for irradiating one information track. A converging spot shape control step for switching to a substantially linear condensing spot for irradiating light, an output control step for controlling the irradiation output of the laser light source in accordance with the shape of the condensing spot, and the substantially linear condensing point Based on the light detection step of receiving reflected light according to the shape of the focused spot from the optical information recording medium by the light receiving region divided in the direction corresponding to the spot, and the reflected light received by the light detection step And a signal generation step of generating an error signal and / or a reproduction signal.

  An optical pickup device according to the present invention includes a laser light source for irradiating an information track of an optical information recording medium, and a substantially circular condensing spot for irradiating one information track with the output light of the laser light source. Condensed spot shape control means for switching to a substantially linear focused spot that irradiates a plurality of information tracks, output control means for controlling the irradiation output of the laser light source in accordance with the shape of the focused spot, and the approximate line And a light detection unit that has a light receiving region divided in a direction corresponding to the light-condensing spot and receives reflected light corresponding to the shape of the light-converging spot from the optical information recording medium. .

  Since the present invention can simultaneously read a plurality of information tracks during reproduction, for example, when three tracks are reproduced in parallel, a high transfer rate exceeding 1 Gbps at the maximum can be realized at the outermost periphery of the disk. Further, when switching the shape of the focused spot, the S / N can be prevented from decreasing by controlling the irradiation output onto the optical information recording medium. Further, since the rotation speed of the optical information recording medium can be kept low, the power consumption can be reduced. Further, it is possible to avoid signal degradation due to interlayer interference, which is a concern when a plurality of focused spots are simultaneously irradiated in a multilayer optical information recording medium.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of an optical system to which the present invention is applied. In this example, a BD (Blu-ray Disc) is used as the optical disc 11 for recording and reproducing information. However, the present invention is not limited to this.

  The optical system includes a semiconductor laser 12, a collimator lens 13, an optical element 14 for limiting aperture, a half-wave plate 15, a polarization beam splitter 16, a condensing lens 17, and a light-receiving output detection light-receiving element. 18, a correction element 19 for correcting spherical aberration, a quarter-wave plate 20, and an objective lens 21 are provided.

  The optical system also includes a half-wave plate 22, a polarizing beam splitter 23, a condensing lens 24, a multi lens 25, a light receiving element 26 for detecting a servo error signal, a condensing lens 27, and a light receiving device. An element 28 is provided.

  In this optical system, it is preferable to apply an aperture limiting element enclosing a liquid crystal material to the optical element 14. For example, as shown in FIG. 2, the size of the focused spot that illuminates the optical disk 11 is controlled by switching the operation / non-operation of the aperture restriction according to the drive voltage. In this optical element 14, a uniform voltage is applied to the electrodes 141 to 142 shown in FIG. 2A, whereby a light shielding region 143 shown in FIG. 2B is formed, and the direction crossing the information track is formed. Is given an opening restriction.

  When the numerical aperture of the objective lens 21 is NA and the wavelength is λ, the diameter d of the focused spot on the optical disk can be obtained by the equation (1).

  Therefore, for example, when the semiconductor laser 12 that emits light with λ = 405 nm and the objective lens 21 with NA = 0.85 are used, the spot diameter is 0.48 μm. Here, when an aperture limit of 1/5 is added in the direction crossing the information track by the aperture limiting element, the value of NA in the equation (1) is equivalently reduced to 1/5, and the spot size is about the same direction. The linear illumination has a length five times (about 2.4 μm). In BD, since the information track interval is defined as 0.32 μm, it is possible to simultaneously illuminate a plurality of information tracks by this linear illumination.

  The correction element 19 includes, for example, M. Iwasaki, M. Ogasawara, and S. Ohtaki, “A New Liquid Crystal Panel for Spherical Aberration Compensation,” Technical Digest of Optical Data Storage Topical Meeting, Santa Fe, pp. 103. -105 (2001), a liquid crystal phase plate can be used. This liquid crystal phase plate has concentric electrodes (a), (b) and (c) having different diameters as shown in FIG. 3, and the difference in the thickness of the cover layer (light transmission protective film layer) of the BD The wavefront substantially equivalent to the correction amount of the spherical aberration generated by the above can be generated according to the voltage applied to each electrode. In addition to the liquid crystal phase plate described above, the spherical aberration may be corrected by moving an expander lens or a collimator.

  The light emitted from the blue-violet semiconductor laser 12 as the light source is converted into parallel light by the collimator lens 13, and then passes through the optical element 14 and the half-wave plate 15 that limit the aperture in a one-dimensional direction. 16 is led.

  A part of the light that has passed through the optical element 14 is reflected by the polarization beam splitter 16 and then guided to the light-emitting output detection light-receiving element 18 by the condenser lens 17. The amount of light incident on the light-emitting output detecting light-receiving element 18 is adjusted by rotating the half-wave plate 15. The output from the semiconductor laser 12 is controlled by an automatic light emission output value control (APC) circuit, which will be described later, based on the amount of light incident on the light receiving element 18 for detecting the light emission output.

  On the other hand, the spherical aberration of the light transmitted through the polarization beam splitter 16 is corrected by the correction element 19. Further, the linearly polarized light of the semiconductor laser 12 is changed to circularly polarized light by the quarter wavelength plate 20 and the information track on the optical disk 11 is illuminated via the objective lens 21.

  The reflected light from the optical disk 11 is reflected by the beam splitter 16 and then guided to the detection optical path. This detection optical path is divided into two optical paths by a polarization beam splitter 23 via a half-wave plate 22. One optical path is guided to the light receiving element 26 for servo error signal detection via the condenser lens 24 and the multi lens 25, and the other optical path is guided to the light receiving element 28 via the condenser lens 27.

  Next, processing of signals received by the servo error signal detecting light receiving element 26 and the light receiving element 28 will be described. These processes are performed by a signal processing circuit described later. Here, the astigmatism method is used to obtain the focus error signal (FES), and the push-pull method (PP) or the phase difference method (DPD) is used to obtain the track error signal (TES). Will be described.

  For example, as shown in FIG. 4, the servo error signal detecting light receiving element 26 is constituted by a light receiving element having light receiving areas A to H divided into eight. Light incident on the light receiving element is photoelectrically converted into signals A to H in the respective light receiving regions A to H. Since the spot received by this light receiving element shows an intensity distribution of a circle a at the time of focusing and an ellipse b otherwise, the calculation result at the time of focusing of the light receiving areas A to H is zero level. As described above, the servo error signal detecting light receiving element 26 outputs a so-called S-shaped error signal.

  In the case of a substantially circular focal spot, the signal processing circuit can obtain a focus error signal (FES) by the servo error signal detection light receiving element 26 according to the equation (2). Note that c in the parentheses indicates that the focused spot is substantially circular.

  Further, when the track error signal (TES) is obtained, the push-pull method (PP) is used in the case of a recordable disc, and in the case of a read-only optical disc (ROM) in which an information pit row is formed in advance, The phase difference method (DPD) is mainly used and is calculated as follows. In equation (3), k represents a coefficient, and in equation (4), φ represents a signal phase operator.

In addition, the light receiving element 28 includes, for example, 28 divided light receiving regions I to T, U _{1 to} U ₈ , and V _{1 to} V ₈ as shown in FIG. T, U _{1 to} U ₈ , and V _{1 to} V ₈ are output. For example, when the signal track B is irradiated with a substantially circular focused spot a, the light receiving element is configured to receive the reflected light in the light receiving regions I to T, and the reproduction signal (RF) is ( 5) It is obtained by adding the output signals from I to T as shown in the equation.

  Note that the reproduction signal (RF) can be obtained from the equation (6) when the eight-divided light receiving element shown in FIG. 4 is used.

  Next, a case where the optical element 14 is operated and a substantially linear focused spot is irradiated onto the optical disc will be described. FIG. 6 shows the relationship between the spot shape when three information tracks are illuminated simultaneously and the corresponding multi-divided detection elements. This light receiving element has the same configuration as the light receiving element described in FIG.

  When the optical element 14 becomes a horizontally elongated condensing spot b and illuminates three signal tracks A to C, the focus error signal (FES) is based on the signal received in the servo error signal detection optical path. It can be obtained from equation (7). Note that l in the parenthesis indicates that the focused spot is substantially linear.

  The astigmatism focus error signal (FES1) obtained by the equation (7) is a signal with a slight offset due to astigmatism applied by the operation of the optical element 14. By correcting the offset amount and performing focus control during signal reproduction, accurate focus control is possible.

  Further, when the track error signal (TES) is obtained by the push-pull method using the eight-divided light receiving element shown in FIG. 4, it can be obtained by the equation (8). In the equation (8), l represents a coefficient.

  Further, when the 28-divided light receiving element shown in FIG. 6 is used, it can be obtained by the equation (9). In equation (9), m represents a coefficient.

  Alternatively, the error signal detection range may be changed and calculated by the following equation. In the equation (9 '), n represents a coefficient.

  When the track error signal (TES) is obtained by the phase difference method, it can be obtained by the following equation using the light receiving element shown in FIG. 4 or FIG.

  The reproduction signal is output from the illuminated three information tracks A, B, and C by the following calculation.

  In addition, the reproduction signal detection range may be changed and calculated by the following equation.

  Thus, when reading a plurality of information tracks at the same time, it is necessary to rearrange the data string for sequentially demodulating the reproduction signal. In this case, as described in Japanese Patent Application Laid-Open No. 06-89440 and Japanese Translation of PCT International Publication No. 2002-525770, the read-out signal is temporarily stored in a buffer memory or the like, and then the data string is rearranged. A plurality of information tracks can be easily reproduced.

  Next, the voltage application to the optical element 14 is stopped to form a substantially circular condensing spot, or a driving voltage having the same amplitude is applied to all the electrodes to form a substantially circular condensing spot. The output control of the semiconductor laser 12 when recording a signal on the optical disk 11 or when illuminating a plurality of information tracks by spreading the light-converging spot substantially linearly will be described.

  FIG. 7 is a block diagram of an output control circuit that controls the output value of the semiconductor laser 12. This output control circuit includes a mark & space length determination unit 31 that analyzes a modulation signal, a RAM 32, a semiconductor laser drive unit 33 that controls the irradiation output of the semiconductor laser 12, and input terminals 301 to 306 to which various signals are input. I have.

  The mark & space length determination unit 31 detects the length of the modulation signal input from the input terminal 301 in synchronization with the channel clock input from the input terminal 302 and outputs the detection result to a RAM (Random Access Memory) 32. The modulation signal given together with the channel clock is supplied as an NRZI (Non Return-to-Zero Inverse) signal encoded by the 17PP modulation method in the BD, and becomes high for a time corresponding to the length in the mark portion. In the space part, it is Low for the time corresponding to the length.

  The RAM 32 stores in advance recording pulse generation timings corresponding to the recording mark length, the immediately preceding space length, and the immediately following space length. As a result, it is possible to generate a pulse according to any combination and control the output of the semiconductor laser 12. The recording pulse generation timing is updated by reading medium information stored in advance at a predetermined position in the optical disc 11.

  The output from the RAM 32 is, for example, three output values of a peak level (Pw), a bias level (Pb), and a cooling level (Pc), and three corresponding driving signals are supplied to the semiconductor laser driving unit 33.

  The semiconductor laser drive unit 33 includes a high-speed switching circuit 33a, a drive current generation circuit 33b, and an APC circuit 33c, and arbitrarily controls the irradiation power of the recording pulse in accordance with the three drive signals. As a result, the optical disk 11 can be irradiated in a pulsed manner with a high-power laser beam during recording.

  At the time of signal reproduction, a condensing spot having a desired irradiation beam width is formed by applying a driving voltage to the aperture-limiting optical element 14. The APC circuit unit 33 c sets the irradiation power on the optical disk 11 to an arbitrary value based on the signal from the light emission output detection element 18 for light emission value monitoring obtained via the input terminal 306, and the irradiation output of the semiconductor laser 12. To control.

  When the beam width is widened, the intensity of light that illuminates each information track decreases, which may reduce the S / N of the read signal. Therefore, when reading signals simultaneously from multiple information tracks, Control is performed so that the reproduction power on the board per irradiation area is substantially equal. Specifically, in each case, switching is performed according to the mode signal (Mode 0 to Mode 2) such as recording, reproduction, and OFF, which is input from the input terminals 303 to 305, and the shape of the focused spot at the time of reading. Outputs the optimal emission value.

  As described above, the present invention can dramatically increase the transfer rate during signal reproduction by changing the shape of the focused spot. For example, in the case of a polycarbonate material used as a substrate material for the optical disk 11, about 10,000 rpm is considered as the upper limit of the disk rotation speed from the viewpoint of safety. Although only a signal transfer rate of about 300 Mbps can be realized on average, according to the present invention, since a plurality of information tracks can be read simultaneously during reproduction, for example, when three tracks are reproduced in parallel, the maximum is at the outermost periphery of the disc. A transfer rate exceeding 1 Gbps can be realized.

  Further, the present invention uses a single semiconductor laser 12 as a light source and is equipped with an aperture-limiting optical element, so that a substantially circular focused spot for recording and reproducing a single information track, Since it is possible to arbitrarily switch between the substantially linear condensing spots that simultaneously illuminate the information track, when realizing the same transfer rate, the rotation speed of the optical disk 11 can be kept low. Power consumption of the mobile device can be reduced.

  Further, it is possible to avoid signal degradation caused by interlayer interference, which is a concern when a plurality of focused spots are simultaneously irradiated onto the multilayer optical disk 11, and to effectively increase the reproduction transfer rate of the multilayer optical disk 11.

  In addition, when the shape of the focused spot is switched, the light emission output value of the semiconductor laser is controlled so that the irradiation output per unit area on the optical disk is substantially the same, thereby illuminating multiple tracks simultaneously and reading the signal. Even in this case, it is possible to prevent the signal-to-noise ratio from decreasing and to perform good signal reproduction.

  In the present embodiment, the aperture-limiting optical element 14 is used, but a liquid crystal element having a one-dimensional condensing characteristic can be used. This liquid crystal element has, for example, linear electrode patterns (a), (b), (c), and (d) as shown in FIG. 8, and high resistance characteristics and light transmittance are provided between the electrodes. An ITO (Indium Tin Oxide) film is disposed. When no driving voltage is applied to the electrodes or when the same driving voltage is applied to all the electrodes, the liquid crystal element outputs incident parallel light as it is. On the other hand, when an appropriate different voltage amplitude is given to each electrode, a phase distribution corresponding to the applied voltage is generated on the outgoing wavefront, and a gentle convergent light or divergent light is generated in one direction (horizontal direction in this example). Output.

  When such a liquid crystal element is used, a method for obtaining a focus error signal (FES) from a substantially oval spot size described in Japanese Patent Laid-Open No. 04-123331 can be applied. In the equations (15) and (15 ′), α and β represent coefficients.

  Further, the focus error signal (FES) detection range may be changed and calculated by the following equation.

  In addition, as an optical element having a one-dimensional condensing characteristic, S. Kuiper, BHW Hendriks, “Variable-Focus Liquid Lens for Miniature Cameras,” Appl. Phys. Lett., Vol. 85, pp. 1128 to 1130 ( 2004)) may be used. In this case, it is preferable to drive integrally with the objective lens 21 so as to always maintain the same positional relationship with respect to the movement of the objective lens 21 accompanying the tracking of the information track. For example, the correction element 19 and the quarter wavelength plate are driven. It is preferable to arrange between 20.

  In addition, a multi-lens that has condensing power in the direction crossing the track and an optical component such as an aperture that restricts aperture are mounted on a movable stage and driven by a stepping motor, etc. It may be realized.

  In the present embodiment, a 28-divided light receiving element having an element density four times the track density is used as a light receiving element for simultaneously reading reproduction signals from a plurality of information tracks. It is not limited. The light receiving element only needs to have an element density of 2 times or more with respect to the direction crossing the information track. For example, a light receiving element having a high density of 6 times or 8 times may be used. In addition, in order to simultaneously read out a plurality of information tracks exceeding three tracks, the voltage applied to the liquid crystal element is changed to illuminate a wider range and to receive all signals from the corresponding information tracks. A split light receiving element may be used.

  In the above embodiment, the push-pull method (PP) or the phase difference method (DPD) is used to obtain the track error signal (TES). In the case of an optical disk (ROM), a three-track method (3TR) may be used. The track error signal (TES) by the three-track method (3TR) can be generated by a signal processing circuit described later.

  In an optical system that illuminates a plurality of information tracks with a substantially linear spot, unlike a substantially circular illumination, it is likely to receive signal leakage from adjacent tracks due to crosstalk. Therefore, in order to obtain a stable track error signal (TES), the presence or absence of a signal on an adjacent track is determined. For example, there is no signal pit in the central information track (Tr2), and both sides It is desirable to sample the reproduction signal by detecting the condition that a signal pit exists in at least one of the information tracks (Tr1, Tr3). Thereby, the influence from an adjacent track can be reduced.

The track error signal (TES) by the three-track method (3TR) is composed of, for example, 28 divided light receiving areas I to T, U _{1 to} U ₈ , and V _{1 to} V ₈ as shown in FIG. When the signals I to T, U _{1 to} U ₈ , and V _{1 to} V ₈ are output from the respective light receiving areas, they can be generated by performing the following calculation.

  Further, the detection range of the error signal may be changed, and the calculation may be performed using the equations (17) to (19).

  Similarly, the reproduction signal is sampled by detecting the condition that the signal pit exists in the central information track (Tr2) and at least one of the information tracks (Tr1, Tr3) on both sides does not exist. By doing so, a push-pull tracking error signal can also be calculated.

  Further, the error signal detection range may be changed and calculated by the equation (21).

  The reproduction signals RF1 to RF3 of the optical disk are output from the three information tracks by the following calculation, similarly to the equations (14) to (16) or (14 ') to (16').

  In addition, the reproduction signal detection range may be changed and calculated by the following equation.

  Next, a signal processing circuit that performs the above-described calculation will be described with reference to a block diagram shown in FIG. The signal processing circuit includes terminals 401 to 408 for inputting signals A to H output from the eight-divided light receiving elements shown in FIG. 4, addition amplifiers 41 and 42, and a differential amplifier 43. For example, according to the configuration example shown in FIG. 9, the focus error signal (FES) obtained by the equation (7) can be calculated.

  Further, the signal processing circuit includes terminals 409 to 420 for inputting signals I to S output from the 28-divided light receiving elements shown in FIG. 6, addition amplifiers 44 and 45, sample hold circuits (SH) 46 and 47, and so on. , Differential amplifier 48, terminals 421 to 423 for inputting reproduction signals RF1 to RF3 from three information tracks, equalizers (EQ) 49 to 51, level comparators (LC) 52 to 54, and a logical operation circuit (FPGA) 55.

  The reproduction signals (RF1 (l) to RF3 (l)) of the three information tracks are subjected to waveform equalization processing by an equalizer (EQ149 to EQ3 51). The reproduced signal after waveform equalization is output to a decoding circuit (not shown) (for example, PRML Detector), decoded, and binarized by a level comparator (LC1 52 to LC3 54) to determine the presence or absence of a pit. Is done. The binarized signal is input to the logical operation circuit 55. For example, there is no signal pit in the central information track (Tr2), and at least one of the information tracks (Tr1, Tr3) on both sides. Detects the condition in which a signal pit exists.

  In the BD-ROM, the reflectivity is reduced at the signal pit portion. Therefore, when the binarized output signals (101 to 103) are at a high level, there is a pit on each corresponding light receiving element. In addition, if it is Low Level, there is a pit.

  Therefore, for example, the condition that the signal pit does not exist in the central information track (Tr2) and the signal pit exists in at least one of the information tracks (Tr1, Tr3) on both sides is the binarization described above. Of the subsequent output signals 101 to 103, this corresponds to the output signal 102 being High and either the output signal 101 or the output signal 103, or both, being Low.

  That is, the track error signal (TES) by the three-track method (3TR) can be obtained by using, for example, TES_3TR1 (l ), The signals (I + L + M + P + Q + T and J + K + N + O + R + S) described in parentheses on the right side are sampled, and each signal is held under other conditions, so that the influence from adjacent tracks can be reduced.

  Further, when there is an information pit in Tr1 (that is, the output signal 101 is low and the output signal 102 is high), and when there is an information pit in Tr3 (that is, the output signal 102 is high and the output signal 103 is low). Are preferably determined independently, and the sampling pulses 104 and 105 are preferably applied. In order to optimize the sampling position, generally, the binarized output signals 101 to 103 are input to a logic operation circuit 55 such as an FPGA, and the positions and time widths of the sampling pulses 104 and 105 are optimized. It is preferable.

  In FIG. 10, the reproduction signal was sampled on the condition that the central track has no pits and the pits exist on either side of the track, and the track error signal (TES) was measured by the calculation of equation (16). Is. Here, the signals 10A, 10B, and 10C are a reproduction signal RF2, a sampling signal, and a track error signal (TES), respectively. Further, in FIG. 10B, a waveform having a time length of 1000 times the measurement result of FIG. 10A is recorded.

  In FIG. 11, the reproduction signal is sampled on the condition that there is a pit in the center track and no pit is present on either side of the track, and the track error signal (TES) calculated by the equation (20) is obtained. It is measured. Here, the signals 11A, 11B, and 11C are a reproduction signal RF2, a sampling signal, and a track error signal (TES), respectively. In FIG. 11B, a waveform having a time length of 1000 times the measurement result of FIG. 11A is recorded.

  FIG. 12 is a diagram illustrating a measurement result (a) of the track error signal (TES) when the track control is off and a measurement result (b) of the track error signal (TES) when the track control is on. . Here, the signals 12A and 12B are the reproduction signal RF2 and the track error signal (TES) that has passed through the low-pass filter after the calculation of the equation (16), respectively. Thus, the track control operation can be confirmed from the measurement result of FIG. 12B in which the track control is turned on.

It is a figure which shows an example of the optical system to which this invention is applied. It is a figure which shows the example of the aperture limiting element using the liquid crystal applied to this invention. It is a figure which shows the example of the liquid crystal spherical aberration correction element applied to this invention. It is a figure which shows the example of the 8 division | segmentation light receiving element for the servo error signal detection applied to this invention. It is a figure which shows typically the light reception intensity distribution on the multi-segment light receiving element at the time of substantially circular beam irradiation. It is a figure which shows typically the light reception intensity distribution on the multi-segment light receiving element at the time of linear beam irradiation. It is a block diagram which shows the output control circuit which performs output value control of a semiconductor laser. It is a figure which shows the example of the liquid crystal element which produces | generates a linear beam. It is a block diagram which shows the structural example of the signal processing circuit applied to this invention. It is a figure which shows the measurement result (the 1) of a track error signal. It is a figure which shows the measurement result (the 2) of a track error signal. It is a figure which shows the measurement result of the track error signal by track control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Optical disk, 12 Semiconductor laser, 13 Collimator lens, 14 Optical element, 15 1/2 wavelength plate, 16 Polarizing beam splitter, 17 Condensing lens, 18 Light receiving output detection light receiving element, 19 Correction element, 20 1/4 wavelength plate , 21 Objective lens, 22 1/2 wavelength plate, 23 Polarizing beam splitter, 24 Condensing lens, 25 Multi lens, 26 Light receiving element for servo error signal detection, 27 Condensing lens, 28 Light receiving element

Claims (13)

A laser light source for irradiating an information track of an optical information recording medium;
A condensing spot shape control means for switching the output light of the laser light source to a substantially circular condensing spot that irradiates one information track or a substantially linear condensing spot that irradiates a plurality of information tracks;
Output control means for controlling the irradiation output of the laser light source according to the shape of the focused spot;
A light detecting means having a plurality of light receiving regions divided in a direction corresponding to the substantially linear focused spot, and receiving reflected light corresponding to the shape of the focused spot from the optical information recording medium;
An optical information reproducing apparatus comprising: a signal generating unit that generates an error signal and / or a reproduction signal based on the reflected light received by the light detection unit.   The condensing spot shape control means switches to a substantially circular condensing spot when recording a signal on the optical information recording medium, and substantially circular or substantially linear when reproducing a signal from the optical information recording medium. The optical information reproducing apparatus according to claim 1, wherein the optical information reproducing apparatus is switched to a condensing spot.   2. The optical information reproducing apparatus according to claim 1, wherein the light detecting means has an element density at least twice as large as an information track interval.   The condensing spot shape control means switches the shape of the condensing spot by means of a liquid crystal element having a condensing characteristic in a one-dimensional direction or a variable focus lens enclosing a liquid transparent material. 1. An optical information reproducing apparatus according to 1.   2. The optical information according to claim 1, wherein the condensing spot shape control means switches the shape of the condensing spot by a liquid crystal element or an aperture element that limits an aperture in a one-dimensional direction with respect to an illumination light beam. Playback device.   The condensing spot shape control means controls the length of the substantially linear condensing spot shape in the direction traversing the information track according to the number of information tracks to be irradiated during signal reproduction. The optical information reproducing apparatus according to claim 1.   The liquid crystal element having the light condensing characteristic in the one-dimensional direction or the variable focus lens enclosing the liquid transparent material has the objective so as to maintain a predetermined positional relationship with respect to the movement of the objective lens following the information track. 5. The optical information reproducing apparatus according to claim 4, wherein the optical information reproducing apparatus is driven integrally with the lens.   The liquid crystal element or aperture element that restricts the aperture of the illumination light beam in a one-dimensional direction is arranged at a position where the aperture restriction is not applied to the reflected light from the optical information recording medium. The optical information reproducing apparatus according to claim 5.   2. The optical information reproducing apparatus according to claim 1, wherein the signal generating means generates a track error signal based on reproduction signals from at least three information tracks when the focused spot is substantially linear.   When the focused spot is substantially linear, the signal generating means samples a reproduction signal based on a signal pit position on an information track on which the focused spot is illuminated, and generates a track error signal. The optical information reproducing apparatus according to claim 1.   When the focused spot is substantially linear, the signal generating means has no signal pit at the center on the information track on which the focused spot is illuminated, and the signal pit is located at least on either side of the signal track. Or a signal pit is present in the center of the information track illuminated with the focused spot, and a signal pit is not present on at least one of the sides, and the reproduction signal is sampled. 11. The optical information reproducing apparatus according to claim 10, wherein a track error signal is generated. The output light of the laser light source for irradiating the information track of the optical information recording medium is switched to a substantially circular condensing spot for irradiating one information track or a substantially linear condensing spot for irradiating a plurality of information tracks. A focused spot shape control step;
An output control step for controlling the irradiation output of the laser light source according to the shape of the focused spot;
A light detection step of receiving reflected light according to the shape of the focused spot from the optical information recording medium by a light receiving region divided in a direction corresponding to the substantially linear focused spot;
And a signal generation step of generating an error signal and / or a reproduction signal based on the reflected light received by the light detection step. A laser light source for irradiating an information track of an optical information recording medium;
A condensing spot shape control means for switching the output light of the laser light source to a substantially circular condensing spot that irradiates one information track or a substantially linear condensing spot that irradiates a plurality of information tracks;
Output control means for controlling the irradiation output of the laser light source according to the shape of the focused spot;
A light detection area having a light receiving area divided in a direction corresponding to the substantially linear light collection spot, and receiving reflected light corresponding to the shape of the light collection spot from the optical information recording medium. A characteristic optical pickup device.

Images