JP2010205353A - Optical information reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information reproducing device and an optical information reproducing method, for properly eliminating interference of background light to always performing excellent super-resolution reproduction by subtracting a detection signal of a second beam from that of a first beam with a proper ratio in accordance with characteristics of a super-resolution medium and a state of super-resolution reproduction. <P>SOLUTION: An excellent super-resolution reproduction waveform is always obtained by properly eliminating interference of the background light in accordance with characteristics of the super-resolution medium and in accordance with the state of the super-resolution reproduction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical information reproducing apparatus and optical information reproducing method for reproducing information using a laser beam, and more particularly to an optical information reproducing apparatus and an optical information reproducing method for reproducing information recorded at high density.

  An example of an optical information recording medium that reproduces information using laser light is an optical disk. An optical disc has a large capacity and is widely used as a medium for distributing and storing images, music, or computer information.

  The capacity of the optical disc is determined by the size of the mark to be recorded. That is, the smaller the recording mark, the larger the capacity per optical disc. The size of the recording mark basically depends on the condensing spot size of the laser beam used for reproducing information. That is, the smaller the spot size, the higher density information can be reproduced with better reproduction quality. A spot obtained by condensing the laser beam by the objective lens does not converge to one point even at the condensing point due to the diffraction effect of the light, and has a finite area. This is generally called the diffraction limit. When the wavelength of the laser beam is λ and the numerical aperture of the objective lens is NA (Numerical Aperture), the limit of the mark length that can be reproduced is λ / (4NA).

  For example, in an optical system with λ = 405 nm and NA = 0.85, 119 nm is the mark length reproduction limit. That is, in this example, a mark having a length of 119 nm or less cannot be accurately read. In order to increase the capacity per optical disc, there are methods of shortening the wavelength of the laser beam or increasing the NA of the objective lens. However, when manufacturing optical components, it is difficult to shorten the laser wavelength and increase the NA of the objective lens.

  On the other hand, a medium super-resolution technique is known as a technique for improving the reproduction resolution beyond the diffraction limit. In the medium super-resolution technique, a medium using a super-resolution film whose optical characteristics change nonlinearly with temperature or light intensity is used. Here, for example, a case where a super-resolution film whose reflectivity changes sharply at a certain temperature as described in Patent Document 1 (Japanese Patent Laid-Open No. 05-89511) is used with reference to FIG. explain. Here, a phase change material is used as the super-resolution film, and the difference in reflectance between the crystalline state (solid phase) and the molten state (liquid phase) above the melting point is used.

  FIG. 1 is an enlarged view of a recording mark row of one track among recording marks formed in advance along a spiral track on a transparent substrate of a super-resolution optical disk. The laser beam that has passed through the objective lens is irradiated as a focused spot 51 on the medium. Due to the absorption of the irradiated laser light, the temperature rises in the vicinity of the focused spot 51, and a high temperature region is generated. In the high temperature region, particularly in the melting region 52 that exceeds the melting point of the super-resolution film, the super-resolution film changes from the solid phase state to the liquid phase state. This change increases the reflectivity of the melted area 52, and the melted area 52 serves as an opening for reproducing the recording mark. As a result, the size of the aperture contributing to reproduction can be made smaller than the focused spot size determined by the diffraction limit. Therefore, information on a minute recording mark 54 below the reproduction limit can be read as a super-resolution reproduction signal.

  In the medium super-resolution technique, if the reflectance of the opening (melting region 52) is sufficiently higher than the reflectance of other than the opening (non-melting region 53), ideal super-resolution reproduction using only the opening can be performed. However, in practice, the reflectances other than the aperture cannot be made so small that they can be ignored. For this reason, the reflected light (background light) from other than the aperture interferes with the reflected light from the aperture, and the quality of the super-resolution reproduction signal is degraded.

  On the other hand, Patent Document 2 (Japanese Patent Application Laid-Open No. 2006-244597) describes an optical head device that irradiates two beams at different positions on the same data track. The purpose is to reduce the low-frequency noise of a Super RENS disk which is a kind of super-resolution medium. This optical head device includes a first beam for super-resolution reproduction and a second beam. The intensity of the second beam is 1/5 to 1/20 of the intensity of the first beam. Either one of the first beam and the second beam is given a delay. This optical head device reduces low-frequency noise by subtracting the detection signal of the first beam and the detection signal of the second beam.

  In addition, about PRSNR (Partial Response Signal to Noise Ratio) mentioned later in order to demonstrate this invention, nonpatent literature 1 (Japan Journal of Applied Physics, Vol.43, No.7B, 2004, pp.48). Is disclosed in detail.

JP 05-89511 A JP 2006-244597 A

Japan Journal of Applied Physics, Vol. 43, no. 7B, 2004, pp. 4863-4866

  The optical head device described in Patent Document 2 can be applied to prevent deterioration of the quality of a super-resolution reproduction signal due to background light interference. At this time, in order to remove the interference of the background light, an appropriate ratio of the detection signal of the second beam to the detection signal of the second beam in accordance with the characteristics of the super-resolution medium and the state of the super-resolution reproduction. It is necessary to subtract with. However, the optical head device of Patent Document 2 has a problem that the background light interference cannot be sufficiently removed because the ratio between the detection signal of the first beam and the detection signal of the second beam is fixed. .

  An object of the present invention is to provide an optical information reproducing apparatus capable of appropriately removing background light interference and always performing excellent super-resolution reproduction in accordance with the characteristics of the super-resolution medium and the state of super-resolution reproduction. It is to provide an optical information reproducing method.

  An optical information reproducing apparatus according to the present invention includes a first light receiving unit, a second light receiving unit, a time difference correction unit, a signal amplitude correction unit, a calculation unit, and a signal amplitude correction amount adjustment circuit unit. Here, the first light receiving unit is a first laser beam irradiated and reflected on a track on which information is recorded in an optical information recording medium having a super resolution layer and corresponding to a super resolution reproduction method. Is received, and a first detection signal corresponding to the first laser beam is output. The second light receiving unit is located at the same time as the first laser at a position spaced apart by a predetermined distance along the track from the position where the first laser is irradiated on the optical information recording medium. The second laser beam irradiated and reflected with an intensity different from that of the first laser is received, and a second detection signal corresponding to the second laser beam is output. The time difference correction unit gives a predetermined delay to the first detection signal. The signal amplitude correcting unit corrects and outputs the signal amplitude of at least one of the first and second detection signals. The calculation unit is connected to a subsequent stage of the signal amplitude correction unit, and calculates and outputs a difference between the first and second detection signals. The signal amplitude correction amount adjustment circuit unit adjusts the signal amplitude correction amount in the signal amplitude correction unit based on the output signal of the calculation unit.

  The optical information reproducing method according to the present invention includes: (a) a first information which is irradiated and reflected on a track on which information is recorded in an optical information recording medium having a super-resolution layer and corresponding to a super-resolution reproduction method. A step of receiving the first laser beam and outputting a first detection signal corresponding to the first laser beam, and (b) along the track from the position irradiated with the first laser in the optical information recording medium. The second laser beam irradiated and reflected at a position separated backward by a predetermined distance at the same time as the first laser and with an intensity different from that of the first laser is received, and the second laser beam is received. Outputting a second detection signal corresponding to the laser beam; (c) providing a predetermined delay to the first detection signal; and (d) at least one of the first and second detection signals. Correcting the signal amplitude and outputting, e) after step (d), calculating and outputting the difference between the first and second detection signals; and (f) based on the signal output in step (e), in the signal amplitude correction unit. Adjusting a correction amount of the signal amplitude.

  The effect of the optical information reproducing apparatus of the present invention is that a minute recording mark below the reproduction limit can always be super-resolution reproduced with a good bit error rate, and the recording density can be remarkably increased. The reason is that a good super-resolution reproduction waveform can always be obtained by appropriately removing background light interference in accordance with the characteristics of the super-resolution medium and the state of super-resolution reproduction.

FIG. 1 is an enlarged view of a recording mark row of one track among recording marks formed in advance along a spiral track on a transparent substrate of a super-resolution optical disk. FIG. 2 is a block diagram for explaining the configuration of the optical system of the optical information reproducing apparatus according to the embodiment of the present invention. FIG. 3A is a conceptual cross-sectional view of a medium for explaining a configuration example of an optical information recording medium (recording medium) 20 having a super-resolution effect. FIG. 3B is a conceptual cross-sectional view of the medium for explaining the configuration of an optical information recording medium (ROM medium) 20 ′ having a super-resolution effect. FIG. 4 is a diagram for explaining the arrangement of two beam spots collected on the recording surface of the optical information recording medium 20. FIG. 5 is a block diagram for explaining the configuration of the light receiving unit of the detector 19 and a part of the signal processing circuit in the present embodiment. FIG. 6 is a graph showing the relationship between the correction amount Kr and the bit error rate (bER) of the reproduction signal in this embodiment. FIG. 7 is a graph showing the relationship between the correction amount Kr and the bit error rate (bER) of the reproduction signal in this embodiment.

  With reference to the accompanying drawings, a mode for carrying out an optical information reproducing apparatus and an optical information reproducing method according to the present invention will be described below.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 2 is a block diagram for explaining the configuration of the optical system of the optical information reproducing apparatus according to the embodiment of the present invention. This optical information reproducing apparatus includes a laser oscillator 11, a collimator lens 12, a diffraction grating 13, a beam splitter 14, a quarter wavelength plate 15, a rising mirror 16, an objective lens 17, and a condenser lens. 18 and a detector 19.

  The optical axis of the laser oscillation device 11, the optical axis of the collimator lens 12, the optical axis of the diffraction grating 13, the first optical axis of the beam splitter 14, and the optical axis of the quarter-wave plate 15 are the same. It arrange | positions so that it may become an optical axis. The raising mirror 16 is arranged so that the optical axis of the quarter-wave plate 15 is reflected and becomes the same as the optical axis of the objective lens 17. The second optical axis of the beam splitter 14, the optical axis of the condenser lens 18, and the optical axis of the detector 19 are arranged to be the same optical axis.

An operation in the optical system of the optical information reproducing apparatus in this embodiment will be described.
First, the laser oscillation device 11 emits light. The collimator lens 12 makes the light emitted from the laser oscillation device 11 parallel light. The diffraction grating 13 separates the parallel light transmitted through the collimator lens 12 into two beams. These two beams have different intensities and slightly different exit angles. The beam splitter 14 transmits the two beams that have passed through the diffraction grating 13. The quarter wavelength plate 15 converts the polarization of each of the two beams transmitted through the modified beam splitter 14 from linearly polarized light to circularly polarized light. The rising mirror 16 reflects the two beams transmitted through the quarter-wave plate 15 toward the optical information recording medium 20. The objective lens 17 condenses the two beams reflected by the rising mirror 16 at two different positions on the recording surface of the optical information recording medium 20. The optical information recording medium 20 reflects a part of each of the two condensed beams.

  Next, the objective lens 17 transmits the two beams reflected by the optical information recording medium in opposite directions. The rising mirror 16 reflects the two beams transmitted in the opposite directions through the objective lens 17 toward the quarter-wave plate 15. The quarter-wave plate 15 converts the polarization from circularly polarized light to linearly polarized light for each of the two beams reflected by the rising mirror 16.

  At this time, the two beams reciprocate on the quarter-wave plate 15. That is, the polarization planes of the two beams are rotated 90 degrees from the first polarization plane. Therefore, the beam splitter 14 reflects the two beams transmitted through the quarter-wave plate 15 in the opposite directions.

  The two beams reflected by the beam splitter 14 go to the condenser lens 18. The condensing lens 18 condenses the two beams reflected by the beam splitter 14 toward the detector 19. The detector 19 detects the received light intensity of each of the two beams collected by the condenser lens 18.

  FIG. 3A is a conceptual cross-sectional view of a medium for explaining a configuration example of an optical information recording medium (recording medium) 20 having a super-resolution effect. The optical information recording medium 20 is a recording medium, and includes a transparent substrate 21, a first dielectric film 22, a super-resolution film 23, a second dielectric film 24, a recording film 25, A third dielectric film 26 and a reflective film 27 are provided.

  The transparent substrate 21, the first dielectric film 22, the super-resolution film 23, the second dielectric film 24, the recording film 25, the third dielectric film 26, and the reflective film 27 are: They are stacked in this order.

  FIG. 3B is a conceptual cross-sectional view of the medium for explaining the configuration of an optical information recording medium (ROM medium) 20 ′ having a super-resolution effect. The optical information recording medium 20 is a ROM medium, and includes a transparent substrate 21 ′, a first dielectric film 22, a super-resolution film 23, a second dielectric film 24, and a reflective film 27. It has.

  The transparent substrate 21 ′, the first dielectric film 22, the super-resolution film 23, the second dielectric film 24, and the reflective film 27 are stacked in this order.

  Here, the super-resolution film 23 is, for example, a thin film whose complex refractive index changes sharply and reversibly at a predetermined temperature. Examples of the sharp reversible change of the complex refractive index include a change from the solid phase to the liquid phase accompanying the melting of the phase change material and a change from the liquid phase to the solid phase accompanying the solidification.

  The recording film 25 is a thin film whose complex refractive index changes at a predetermined temperature, for example. Examples of the change in the complex refractive index include an oxidation reaction of a metal oxide film.

  FIG. 4 is a diagram for explaining the arrangement of two beam spots collected on the recording surface of the optical information recording medium 20. A data track 31 is spirally formed on the recording surface of the optical information recording medium 20.

  The two beams are collected on the same data track 31. At this time, the main beam spot 32 and the sub beam spot 33 are arranged in this order as viewed from the direction of rotation of the optical information recording medium 20. That is, when the optical information recording medium is rotated, the same beam on the data track is irradiated first by a beam located behind the rotation traveling direction. That is, the sub beam becomes the preceding beam and the main beam becomes the subsequent beam.

  The main beam is set to a high intensity that excites the super-resolution effect, and the sub-beam is set to a low intensity that does not excite the super-resolution effect. In terms of signal quality, it is desirable that the intensity of the sub beam is as strong as possible within a range that does not excite the super-resolution effect and does not deteriorate the recording signal. The intensity ratio between the main beam and the sub beam can be set by forming the diffraction grating 13 with appropriate optical characteristics.

  The arrangement of the main beam spot 32 and the sub beam spot 33 is not limited to this order. For example, the main beam may be a preceding beam and the sub beam may be a following beam. However, as will be described later, since it is necessary to correct the received light intensity signal of the reflected light of the preceding beam by giving a delay or the like, the preceding beam is preferably a sub beam.

  FIG. 5 is a block diagram for explaining the configuration of the light receiving unit of the detector 19 and a part of the signal processing circuit in the present embodiment.

  The detector 19 includes a main beam light receiving unit 41 and a sub beam light receiving unit 42.

  5 includes a low-pass filter (LPF) 43, a time difference correction unit 44, an amplitude correction unit 45, a subtraction unit 46, and a phase synchronization circuit (PLL: Phase Locked). (Loop) 47, a decoding circuit 48, a signal quality evaluation unit 49, and a correction amount adjustment unit 50.

  The output unit of the sub beam light receiving unit 42 is connected to the input unit of the low pass filter 43. The output unit of the low-pass filter 43 is connected to the first input unit of the time difference correction unit 44. The output unit of the time difference correction unit 44 is connected to the first input unit of the amplitude correction unit 45. The output unit of the amplitude correction unit is connected to the minus (−) side input unit of the subtraction unit 46. The output unit of the main beam light receiving unit 41 is connected to the plus (+) side input unit of the subtracting unit 46. The output unit of the subtracting unit 46 is connected to the input unit of the phase synchronization circuit 47. The first output unit of the phase synchronization circuit is connected to the second input unit of the time difference correction unit 44. The second output unit of the phase synchronization circuit is connected to the input unit of the decoding circuit 48. The output unit of the decoding circuit 48 is connected to the input unit of the signal quality evaluation unit 49. The output unit of the signal quality evaluation unit 49 is connected to the input unit of the correction amount adjustment unit 50. The output unit of the correction amount adjustment unit 50 is connected to the second input unit of the amplitude correction unit 45.

  The main beam light receiving unit 41 receives the reflected light of the main beam among the two reflected beams collected by the condenser lens 18 and outputs a signal corresponding to the received light intensity. The main beam light receiving unit 41 includes a region divided into four. By calculating using the received light intensity in each region of the main beam light receiving unit 41, a focus error signal and a track error signal are obtained.

  The sub beam light receiving unit 42 receives the reflected light of the sub beam of the two reflected beams collected by the condenser lens 18 and outputs a signal corresponding to the received light intensity.

  The low-pass filter 43 receives the received light intensity signal of the sub beam output from the sub beam light receiving unit 42, removes the high frequency component from the received light intensity signal, and outputs the signal.

  The time difference correction unit 44 receives the low-frequency signal output from the low-pass filter 43, and outputs the signal with a predetermined delay. Details of this operation will be described later.

  The amplitude correction unit 45 receives the signal to which the delay is added by the time difference correction unit 44, multiplies the signal by a predetermined correction amount, and outputs the result. The predetermined correction amount corresponds to the output signal of the correction amount adjusting unit 50, as will be described later.

  The subtracting unit 46 receives the received light intensity signal of the main beam output from the main beam receiving unit 41 and the signal whose amplitude is corrected by the amplitude correcting unit 45. The subtracting unit 46 subtracts and outputs a signal obtained by removing the high frequency component of the sub-beam received light intensity signal and adding a delay to correct the amplitude from the received light intensity signal of the main beam.

  The phase synchronization circuit 47 receives the output signal of the subtractor 46, generates a signal whose phase is synchronized based on this signal, and outputs it.

  The decoding circuit 48 receives the output signal of the phase synchronization circuit 47, equalizes and decodes this signal, and outputs a reproduction signal.

  The signal quality evaluation unit 49 receives the output signal of the decoding circuit 48, calculates a bit error rate (bit ER) from this signal, and outputs it.

  The correction amount adjustment unit 50 receives the bit error rate output from the signal quality evaluation unit 49, and generates and outputs a signal for adjusting the correction amount of the amplitude correction unit 45 based on the bit error rate.

  Here, the operation of the time difference correction unit 44 will be described in more detail. As described above, the time difference correction unit 44 adds a predetermined delay to the received light intensity signal of the sub beam. The predetermined delay is a delay time in which the distance between the main beam spot 32 and the sub beam spot 33 on the recording surface of the optical information recording medium 20 is converted into time.

When the distance between the main beam spot 32 and the sub beam spot 33 is L (m) and the linear velocity of the data track 31 collecting the beam is V (m / s), the delay time ΔT (s) is
ΔT = L / V
It becomes. Actually, since the linear velocity fluctuates due to the influence of eccentricity or the like, it does not necessarily match the set linear velocity. However, by using the clock frequency synchronized with the PLL, the accurate delay time can be obtained by removing the influence of the linear velocity fluctuation due to the eccentricity or the like. Specifically, when the clock frequency synchronized with the PLL is fc (Hz) and the channel bit length is Lc (m), the delay time ΔT (s) is ΔT = L / (fc · Lc)
Is required.

  Here, the output subtracted by the subtractor 46 is used to synchronize the clock frequency for obtaining the delay time. However, the present invention is not limited to this. For example, a received light intensity signal of the main beam may be used.

  Here, the correction amount in the amplitude correction unit 45 described above will be described in more detail. The correction amount multiplied by the input signal in the amplitude correction unit 45 is obtained as the product of Ki and Kr (Ki · Kr). Here, Ki is a term for correcting the ratio of the two irradiation beam intensities irradiated to the optical information recording medium 20. Kr is a term for correcting the ratio of the two received light intensity signals in accordance with the characteristics of the super-resolution medium and the state of super-resolution reproduction. The term Ki for correcting the ratio of the irradiation beam intensity is obtained as Ki = Pm / Ps from the main beam intensity Pm and the sub beam intensity Ps. On the other hand, the term Kr for correcting the ratio of the received light intensity signal is adjusted as needed by the correction amount adjusting unit 50 so that the bit error rate is minimized.

  The timing for performing amplitude correction differs depending on a plurality of methods. For example, a method that performs adjustment only at the time of first playback after replacement of an optical information recording medium, a method that performs adjustment when switching from recording to playback, a method that performs adjustment when the bit error rate exceeds a predetermined value, and a constant adjustment during playback There is a method to do. In the present invention, in consideration of non-uniformity of characteristics over the entire surface of the optical information recording medium and changes in laser characteristics due to temperature, a system in which adjustment is always performed during reproduction is preferable.

  As the signal quality evaluated by the signal quality evaluation unit 49, the bit error rate is used. However, the present invention is not limited to this, and another index representing the signal quality can be used. For example, instead of the bit error rate, there is a method of using a PRSNR (Partial Response Signal to Noise Ratio) correlated with the bit error rate or a jitter amount.

  When PRSNR is used, the correction amount is adjusted under the condition that PRSNR is maximized.

  When the jitter amount is used, the signal quality evaluation unit 49 evaluates the jitter amount of the signal subtracted by the subtraction unit 46, and adjusts the correction amount under the condition that the jitter amount is minimized.

  Note that PRSNR is disclosed in detail in Non-Patent Document 1 (Japan Journal of Applied Physics, Vol. 43, No. 7B, 2004, pp. 4863-4866).

(First embodiment)
As a first example of the present embodiment, the optical information reproducing apparatus and the optical information reproducing method according to the present invention were evaluated according to the change in the film thickness of the first dielectric film of the optical information recording medium. Here, the recording medium of FIG. 3A is used.

The prepared optical information recording medium includes a first dielectric film made of ZnS—SiO ₂ , a super-resolution film made of InSb, and a ZnS—SiO ₂ layer on a polycarbonate substrate having a thickness of 0.6 mm in order from the bottom. _{A second} dielectric film made of 2, a recording film made of Co ₃ O ₄ , a _third dielectric film made of ZnS—SiO _2, and a reflective film made of an Ag alloy, respectively, are formed by sputtering. It is. Here, three types of optical information recording media having different thicknesses of the first dielectric film were prepared.

  Table 1 is a table showing the film thickness of each layer (film) in each of the three types of optical information recording media. Each column corresponds to each layer (film) of the optical information recording medium in order from the left. Each row corresponds to three types of media. The unit of each numerical value is nm.

  In order to record and reproduce information on this optical information recording medium, an optical system having a laser wavelength λ = 405 nm and a numerical aperture NA = 0.65 was used. Note that the reproduction limit pit length of this optical system is 156 nm from the values of λ and NA.

  With this optical system, information was first recorded on three types of optical information recording media. At this time, the irradiation beam intensity of the main beam and the sub beam was set to a ratio of 1: 016. Also, the mark speed of the shortest 100 nm was recorded by setting the linear velocity to 6.6 m / s and the recording power of the main beam to 5.5 mW. The recorded mark sequence was (1-7) modulation, the shortest mark length was 100 nm, the longest mark length was 400 nm, and the track pitch was 400 nm.

Next, the recorded signal was reproduced, and the bit error rate as signal quality was evaluated using PRML (Partial Response Maximum Likelihood). In this reproduction, the linear velocity is 6.6 m / s, the reproduction power of the main beam is 1.5 mW, and the term Kr for correcting the ratio of the two received light intensity signals in the correction amount is between 0 and 0.6. I went while changing. Further, the term Ki for correcting the ratio of the two irradiation beam intensities of the correction amount is Ki = Pm / Ps = 1 / 0.16 = 6.25.
It was.

  FIG. 6 is a graph showing the relationship between the correction amount Kr and the bit error rate (bER) of the reproduction signal in this embodiment. In this graph, the horizontal axis represents the correction amount Kr, and the vertical axis represents the bit error rate.

  As can be seen from FIG. 6, a suitable correction amount Kr varies depending on the configuration of the optical information recording medium. The correction amount Kr is adjusted by the correction amount adjustment unit so that the bit error rate is minimized. As a result, the correction amount Kr converges to about 0.2 for the medium A, about 0.25 for the medium B, and about 0.3 for the medium C.

  As described above, even if the configuration of the optical information recording medium is different, good super-resolution reproduction that always minimizes the bit error rate can be performed by adjusting the correction amount at any time in the correction amount adjustment unit. . The range of the correction amount Kr after adjustment is 0.1 to 0.5, and a more preferable range is 0.22 to 0.5.

(Second embodiment)
As a second example of the present invention, an optical information recording medium and an optical information reproducing method according to the present invention were evaluated by preparing one type of optical information recording medium and changing the reproducing power. Here, the ROM medium of FIG. 3B is used.

  In the optical information recording medium used here, a ROM substrate was formed by forming pits on a polycarbonate substrate having a thickness of 0.6 mm. That is, an electron beam method was used for pit recording of the ROM master, and the ROM master was stamped to form pit rows on the polycarbonate substrate.

The optical information recording medium used in this example has a first dielectric film made of ZnS—SiO _{2 with a} thickness of 20 nm and a thickness of 15 nm made of Bi ₂ Te ₃ on this polycarbonate substrate in order from the bottom. Each of the super-resolution film, the second dielectric film made of ZnS—SiO ₂ and having a thickness of 30 nm, and the reflective film made of Ag alloy and having a thickness of 50 nm are formed by sputtering.

  The pit train formed on the ROM substrate is recorded by (1-7) modulation, the shortest pit is 100 nm, the longest pit is 400 nm, the track pitch is 400 nm, and the pit depth is 40 nm. It was.

  In order to reproduce information from this optical information recording medium, an optical system having a laser wavelength λ = 405 nm and a numerical aperture NA = 0.65 was used. Note that the reproduction limit pit length of this optical system is 156 nm from the values of λ and NA.

With this optical system, the linear velocity was 6.6 m / s, and the main beam reproduction power was 1 mW, 1.2 mW, and 1.4 mW. The irradiation beam intensity of the main beam and the sub beam was set to a ratio of 1: 0.2. Further, the bit error rate during super-resolution reproduction was evaluated using PRML as the signal quality while changing the term Kr for correcting the ratio of the two received light intensity signals among the correction amounts between 0 and 10. Of the correction amount, the term Ki for correcting the ratio of the two irradiation beam intensities is:
Ki = Pm / Ps = 1 / 0.2 = 5
It was.

  FIG. 7 is a graph showing the relationship between the correction amount Kr and the bit error rate (bER) of the reproduction signal in this embodiment. In this graph, the horizontal axis represents the correction amount Kr, and the vertical axis represents the bit error rate.

  As can be seen from FIG. 7, a suitable correction amount Kr varies depending on the reproduction power. The correction amount Kr is adjusted by the correction amount adjustment unit so that the bit error rate is minimized, and is about 0.3 at a reproduction power of 1 mW, about 0.22 at a reproduction power of 1.2 mW, and about 0.2 at a reproduction power of 1.4 mW. Each converges to 35.

  As described above, even when the reproduction power is different from the optimum power, the correction amount adjustment unit adjusts the correction amount as needed to achieve good super-resolution reproduction that always minimizes the bit error rate. It can be carried out. The range of the correction amount Kr after adjustment is 0.1 to 0.5, and a more preferable range is 0.25 to 0.5.

  The preferred embodiments of the optical information reproducing apparatus according to the present invention have been described above. However, the optical information reproducing apparatus and the optical information reproducing method according to the present invention are not limited only to the configuration of the above embodiment or the above example. What carried out various correction | amendment and change from the structure of the said embodiment or Example is also contained in the scope of the present invention.

DESCRIPTION OF SYMBOLS 11 Laser oscillator 12 Collimator lens 13 Diffraction grating 14 Polarization beam splitter 15 1/4 wavelength plate 16 Rising mirror 17 Objective lens 18 Condensing lens 19 Detector 20 Optical information recording medium (recording type medium)
20 'Optical information recording medium (ROM medium)
DESCRIPTION OF SYMBOLS 21 Transparent substrate 21 'Transparent substrate 22 1st dielectric film 23 Super-resolution film 24 2nd dielectric film 25 Recording film 26 3rd dielectric film 27 Reflective film 31 Data track 32 Main beam spot 33 Sub beam spot 41 Main beam light receiving unit 42 Sub beam light receiving unit 43 Low-pass filter 44 Time difference correction unit 45 Amplitude correction unit 46 Subtraction unit 47 Phase synchronization circuit 48 Decoding circuit 49 Signal quality evaluation unit 50 Correction amount adjustment unit 51 Condensing spot 52 Melting region 53 Non-melting region 54 Record mark

Claims (14)

In the optical information recording medium having a super-resolution layer and corresponding to the super-resolution reproduction system, the first laser beam received on the track on which information is recorded and reflected is received, and the first laser A first light receiving unit that outputs a first detection signal corresponding to the light;
In the optical information recording medium, at the same time as the first laser and the first laser at a position spaced rearward by a predetermined distance along the track from the position irradiated with the first laser. Receiving a second laser beam irradiated and reflected at a different intensity and outputting a second detection signal corresponding to the second laser beam;
A time difference correction unit that gives a predetermined delay to the first detection signal;
A signal amplitude correction unit for correcting and outputting a signal amplitude of at least one of the first and second detection signals;
A calculation unit connected to a subsequent stage of the signal amplitude correction unit to calculate and output a difference between the first and second detection signals;
An optical information reproducing apparatus comprising: a signal amplitude correction amount adjustment circuit unit that adjusts a correction amount of the signal amplitude in the signal amplitude correction unit based on an output signal of the arithmetic unit. The optical information reproducing apparatus according to claim 1,
The signal amplitude correction amount adjustment circuit unit is
A decoding circuit for decoding information recorded on the optical recording medium and outputting a decoded signal based on an output signal of the arithmetic unit;
A signal quality evaluation unit that evaluates the quality of the decoded signal and outputs an evaluation result signal;
An optical information reproducing apparatus comprising: a correction amount adjustment unit that outputs a signal for adjusting the correction amount of the signal amplitude based on the evaluation result signal. The optical information reproducing apparatus according to claim 1 or 2,
The second laser light has an intensity that produces a super-resolution effect when irradiated to the optical information recording medium,
The optical information reproducing apparatus has an intensity that does not produce the super-resolution effect even when the first laser light is irradiated on the optical information recording medium. In the optical information reproducing device according to any one of claims 1 to 3,
The correction amount of the signal amplitude is integrated with a term for correcting the ratio of the irradiation intensity in the first and second laser beams and a term for correcting the ratio of the received light intensity in the first and second light receiving units. Optical information playback device. In the optical information reproducing device according to any one of claims 1 to 4,
The predetermined delay is set based on the predetermined distance. In the optical information reproducing device according to claim 5,
A phase synchronization unit connected to the preceding stage of the time difference correction unit and generating and outputting a phase synchronization signal synchronized with the phase of the output signal of the arithmetic unit or the phase of the second detection signal;
The time difference correction unit adjusts an amount of the predetermined delay based on the phase synchronization signal. The optical information reproducing apparatus according to claim 6, wherein
The predetermined amount of delay is:
Place the predetermined amount of delay as ΔT;
Place the predetermined distance as L,
The clock frequency of the phase synchronization signal is set as fc,
When the channel bit length of the phase synchronization signal is set to Lc,
ΔT = L / (fc · Lc)
An optical information reproducing device that satisfies the requirements. (A) receiving a first laser beam irradiated and reflected on a track on which information is recorded in an optical information recording medium having a super-resolution layer and corresponding to a super-resolution reproduction method; Outputting a first detection signal corresponding to the first laser beam;
(B) In the optical information recording medium, at the same time as the first laser and at a position spaced backward at a predetermined distance along the track from the position irradiated with the first laser. Receiving a second laser beam irradiated and reflected at an intensity different from that of the first laser, and outputting a second detection signal corresponding to the second laser beam;
(C) providing a predetermined delay to the first detection signal;
(D) correcting the signal amplitude of at least one of the first and second detection signals and outputting the corrected signal;
(E) after the step (d), calculating and outputting a difference between the first and second detection signals;
(F) Adjusting the correction amount of the signal amplitude in the signal amplitude correction unit based on the signal output in the step (e). An optical information reproducing method. The optical information reproducing method according to claim 8, wherein
The step (f)
(F-1) decoding the information recorded on the optical recording medium based on the signal output in step (e) and outputting a decoded signal;
(F-2) evaluating the quality of the decoded signal and outputting an evaluation result signal;
(F-3) An optical information reproducing method comprising: outputting a signal for adjusting a correction amount of the signal amplitude based on the evaluation result signal. The optical information reproducing method according to claim 8 or 9,
The step (b)
(B-1) irradiating the optical information recording medium with the second laser beam having an intensity that produces a super-resolution effect;
The step (a)
(A-1) An optical information reproducing method comprising a step of irradiating the optical information recording medium with the first laser beam having an intensity that does not produce the super-resolution effect. In the optical information reproducing method according to any one of claims 8 to 10,
The step (f)
(F-4) integrating the term for correcting the ratio of the irradiation intensity in the first and second laser beams and the term for correcting the ratio of the received light intensity in the first and second detection units, An optical information reproducing method comprising a step of obtaining a signal amplitude correction amount. The optical information reproducing method according to any one of claims 8 to 11,
In step (c),
(C-1) An optical information reproducing method comprising the step of setting the predetermined delay based on the predetermined distance. The optical information reproducing method according to claim 12,
The step (c)
(C-2) generating and outputting a phase synchronization signal synchronized with the phase of the output signal of the arithmetic unit or the phase of the second detection signal;
(C-3) adjusting the amount of the predetermined delay based on the phase synchronization signal; and an optical information reproducing method. The optical information reproducing method according to claim 13,
The step (c-3)
(C-3-1) The predetermined delay amount is set as ΔT, the predetermined distance is set as L, the clock frequency of the phase synchronization signal is set as fc, and the channel bit length of the phase synchronization signal is set as Lc. An optical information reproducing method comprising the step of setting the predetermined amount of delay as ΔT = L / (fc · Lc) when placing.

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