JP2009301653A - Optical head apparatus and information recording/reproducing apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording/reproducing apparatus for recording information in a recording medium using a pulse laser beam of a sub nano class generated with relaxation vibration as a recording pulse recording information, and an optical head apparatus used for the same, wherein output of a recording pulse is stabilized. <P>SOLUTION: The optical head apparatus includes a laser driving circuit (9) supplying, to a laser element (20), a driving current regulated so that light output from the laser element includes continuous two or more peaks and each interval between two peaks is 200 ps (picosecond) or less, wherein the temperature of an information recording layer of an optical disk is increased in a short time to form a recording mark. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an information recording / reproducing apparatus that records information on a recording medium using sub-nano class pulse laser light and an optical head apparatus used therefor.

  An optical disk is widely used as a recording medium suitable for recording, reproducing, and erasing (repeating recording) information. Optical discs are classified into CD standards and DVD (digital versatile discs) standards when distinguished by recording capacity. In addition, optical discs that are further developed from the DVD standard capable of recording video and audio (music data) with higher density have already been put into practical use.

  As a method for recording on an optical disc, which is a further development of the above-mentioned DVD standard, a method for increasing the recording density by utilizing a steep pulse whose recording pulse length is smaller than 1 ns (nanosecond) has been developed. This recording method is called, for example, a sub-nanopulse recording method or a recording method using relaxation oscillation.

Patent Document 1 discloses an optical disk recording device / semiconductor laser driving method using relaxation oscillation. Note that Document 1 describes that when a recording laser beam is output, the current injected into the semiconductor laser element is reduced and the period is approximately 2 GHz to 4 GHz.
JP 2002-123963 A

  However, in the recording apparatus / semiconductor laser driving method described in Patent Document 1, only the relaxation oscillation is used in order to improve the rising and falling characteristics of the recording laser beam. There is no mention of stabilizing the output and using a steep pulse generated by relaxation oscillation for information recording.

  An object of the present invention is to provide a peak power in an information recording / reproducing apparatus for recording information on a recording medium using a sub-nanoclass pulsed laser beam generated by relaxation oscillation as a recording laser beam for recording information, and an optical head device used therefor. That is, the output of the recording pulse is stabilized.

  The present invention has been made on the basis of the above problems, and a light source that outputs light of a predetermined wavelength and the light output from the light source includes two or more peaks, and there is an interval between the peaks. An optical head comprising: a drive circuit that supplies a drive current defined to be 200 ps (picoseconds) or less; and a lens that focuses light from the light source onto an information recording layer of an information recording medium. Device.

  According to the present invention, the output of a sub-nano class pulsed laser beam generated with relaxation oscillation, that is, the output of a recording pulse is stabilized. As a result, stable recording of information on an optical disc having a high recording density, which is a further development of the DVD standard, can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an example of the configuration of an information recording / reproducing apparatus (optical disc apparatus) to which an embodiment of the present invention can be applied.

  The information recording / reproducing apparatus, that is, the optical disc apparatus 1 shown in FIG. 1 has a central wavelength of 405 nm and can output light in a violet wavelength band in the range of 400 to 410 nm, that is, a laser beam (hereinafter abbreviated as laser light). An element (light source) 20 is included. The semiconductor laser element 20 is, for example, a laser diode (hereinafter abbreviated as LD), and the resonator length is 0.8 mm.

  A laser beam 100 emitted from the LD 20 is collimated by a collimator lens (hereinafter abbreviated as CL) 21, passes through a polarization beam splitter 22 and a λ / 4 plate 23, and is objective lens (hereinafter abbreviated as OL). ) Guided to 24.

  The laser beam 100 guided to the OL 24 is given a predetermined convergence by the OL 24, passes through an information recording medium, that is, a transparent substrate (light incident side substrate) not described in detail of the optical disc D, and is collected on a target information recording layer. To be lighted. That is, the laser light that has passed through the OL 24 exhibits a minimum light spot at the focal position of the OL 24. Therefore, the OL 24 is sequentially changed by focus control so that the distance between the OL 24 and the information recording layer of the optical disc D coincides with the focal position of the OL 24, so that the optical disc can be obtained by the minimum light spot of the laser beam converged by the OL 24. Information recorded in the information recording layer D is reproduced. Further, when information is recorded on the optical disc D, a recording mark, that is, a pit is formed by locally raising the temperature of the information recording layer of the optical disc D by a laser beam that exhibits a minimum light spot. The OL 25 is made of plastic, for example, and the numerical aperture NA is, for example, 0.65.

  The reflected light (reflected laser light) 101 reflected by the information recording layer of the optical disc D passes through the substrate of the optical disc D, passes through the OL 24 and the λ / 4 plate 23, and returns to the polarization beam splitter 22.

  Although not described in detail, the reflected laser beam 101 returned to the polarization beam splitter 22 is reflected on the polarization beam split surface and given a predetermined convergence by an imaging lens (hereinafter abbreviated as “FL”) 25 to detect light. An image is formed on the light receiving portion (light receiving surface) of the detector 26.

  Although not described in detail, the light receiving surface of the photodetector 26 has a plurality of detection areas divided by, for example, two straight lines orthogonal to each other, and outputs a current corresponding to the light intensity in each detection area.

  The current output from the photodetector 26 is converted into a voltage by an I / V amplifier (not shown), and is reproduced as information (data) recorded in the information recording layer of the optical disc D via the arithmetic circuit 3. A signal, a focus error signal for controlling the interval between the information recording layer of the optical disc D for focus control and the OL 24, and a pit which is information recorded on the information recording layer of the optical disc D for track control Track error signal for controlling the position between the center of a guide groove (often referred to as a groove or a track) formed in a row or the same information recording layer and the light spot collected by the OL 24 And so on.

  The OL 24 passes through the actuator 27 in a direction perpendicular to the information recording layer of the optical disc D (the optical axis direction of the OL 24, that is, the focus control direction) and the disc radial direction (direction that crosses the guide groove, that is, the track / groove), that is, the track control direction. It is moved from time to time. That is, the OL 24 held by the actuator 27 is controlled by the actuator 27 by the control signal (focus control signal / track control signal) supplied from the servo driver 5 to the actuator 27, and the focus control direction and the track control direction (radial tilt ( In the on-focus state (minimum light spot) where the size of the light spot is smaller than a predetermined size at the center of the pit row or track / groove of the information recording layer of the optical disk D. It is moved from time to time to collect light.

  Regarding the waveform and intensity of the recording laser beam used for writing information (data) to the information recording layer of the optical disc D among the signals calculated by the arithmetic circuit 3, the write strategy portion (recording waveform) of the control portion 7 is used. Through the stabilization part), the strategy, ie the write waveform, is optimized.

  The write waveform optimized by the control unit 7 is a laser drive circuit (Laser diode driving) that outputs each of the recording laser beam, the reproduction laser beam, and the erasing laser beam output from the LD 20 with an optimal waveform and intensity. circiut (hereinafter abbreviated as LDD) 9. Thereby, a laser beam having a waveform and light intensity suitable for recording, erasing and reproducing information is output from the LD 20.

  As the optical disk D, for example, an optical disk capable of recording at a higher density than that of the current DVD standard optical disk can be used. Further, it is a DVD standard optical disc, and a DVD-RAM disc and a DVD-RW disc capable of recording and erasing information, a DVD-R disc capable of writing only new information (additional recording / recording once), or It goes without saying that various well-known types of discs such as DVD-ROM discs on which information has already been recorded can also be used.

  The LDD 9 will be described below with reference to FIGS. 2 and 5. In particular, when information is recorded on the optical disc D, the LDD 9 has a predetermined period and a relaxation oscillation of a waveform in order to output a sub-nanoclass short-period laser beam from the LD 20. A pulse can be output.

  First, a recording pulse generation method (laser driving method) that can be used to record information on a recording film (not shown) of the optical disc D (recording medium) will be described with reference to FIGS. 2 (a) to 2 (d). To do.

  FIGS. 2A and 2B show a relationship between a general laser driving current and laser light emission (laser output) when a laser driving current is supplied in an LD (semiconductor laser element). FIG. 2C shows an example of supplying a laser driving current that can obtain a relaxation oscillation pulse (a characteristic laser output used in the present invention). FIG. 2D shows that such a laser current is driven. The laser output (intensity of laser light) is shown.

  As shown in FIGS. 2A and 2C, the drive current is controlled to two levels, that is, a bias current Ibi and a peak current Ipe. In some cases, the bias current may be further subdivided into two levels or three levels to be controlled. Here, for simplification of explanation, the case where the bias current and the peak current are one level each is shown. It explains using.

  In the case of normal recording pulse generation, the LDD 9 first generates a bias current Ibi set to a level slightly higher than the threshold current Ith at which the LD 20 starts laser oscillation, as shown in FIG. Drive preliminarily. Thereafter, a peak current Ipe for obtaining a desired peak power is applied at time A until it is lowered to bias current Ibi at time B. Thus, by applying the peak current Ipe from time A to time B, a laser output (time change in laser emission light intensity) as shown in FIG. 2B is obtained.

  That is, until the time A when the magnitude of the laser drive current is the bias current Ibi, the intensity of the emitted light is such that the laser light output from the LD 20 cannot record data on the optical disk D. However, the peak current Ipe is applied, and the intensity of the laser beam is increased to the recording power. Needless to say, after time B, the intensity of the emitted light again becomes low power.

  When the intensity of the emitted light is observed in more detail, in FIG. 2B, when the intensity is raised to the recording power at time A, the intensity instantaneously increases until the steady recording power is stabilized. You can see how it falls (arrow C in the figure). This is due to the relaxation oscillation of the LD 20, and in normal recording pulse generation, control is performed so that this relaxation oscillation is minimized.

  In this way, relaxation oscillation is a transient oscillation phenomenon that occurs when the drive current suddenly increases from a certain level to a certain level that greatly exceeds the threshold current in the semiconductor laser.

  Note that the relaxation vibration becomes smaller every time the vibration is repeated, and the vibration is eventually stopped.

  In the optical recording apparatus of the present invention, this relaxation vibration is actively used for recording.

  That is, although it is originally a relaxation vibration that should be suppressed, the “pulse length is short” and “energy amount (integrated value of laser power as optical output) peculiar to the relaxation vibration are recorded on the recording film of the optical disk D. It is an object of the present invention to obtain “stable” a steep recording pulse having a short pulse length by utilizing the fact that “the recording level may be changed”.

  As shown in FIG. 2 (c), when a drive current having a predetermined characteristic is supplied to the LD 20 from the LDD 9, a laser output accompanied by vibration but having a high peak level can be obtained only for a short time, as is apparent from FIG. 2 (d). can get.

  More specifically, the bias current Ibi set to a level lower than the threshold current Ith is supplied to the LD 20, and at a predetermined timing, that is, at time A, the drive current is suddenly increased with a rise time earlier than normal recording pulse generation. Is raised to a peak current level Ipe higher than the threshold current Ith, and returned to the bias current Ibi at time D after a short time of nanosecond level shorter than normal recording pulse generation.

  In this case, as can be seen in FIG. 2 (d), laser output (time change in laser emission light intensity) can be obtained.

  That is, in FIG. 2D, the LD 20 does not start laser oscillation until time A when it is driven by the bias current Ibi lower than the threshold current Ith, and is at a negligible level. As a result, there is a certain amount of light emission. After that, when current is suddenly applied at time A, laser oscillation accompanied by relaxation oscillation occurs, and the emitted light intensity also rises rapidly.

  Hereinafter, the amplitude of the relaxation oscillation gradually converges to a steady level, but by setting a predetermined time, that is, time D, and setting the drive current to Ibi lower than the threshold current Ith, a laser beam having a certain energy amount can be obtained. . Note that the time D is the timing at which the pulse of the second period of the relaxation oscillation is generated, as is apparent from FIGS. 2 (c) and 2 (d).

  As described above, the pulse due to relaxation oscillation has a feature that the emitted light intensity increases in a very short time compared to a normal recording pulse, and the emitted light intensity decreases at a certain period determined by the structure of the semiconductor laser. ing. Therefore, by using a pulse due to relaxation oscillation as a recording pulse, it is possible to obtain a short pulse having a short rise / fall time and a strong peak intensity, which cannot be obtained by a normal recording pulse. Although an example is shown in the latter stage, the period of relaxation oscillation used in the present application is the laser output period defined by the time when the peak output is 10% and the time when the peak output is 90% (half value). Full width), when two or more pulses are continuous, the period between the full widths at half maximum of adjacent laser beams is shown, which is about 230 ps (picoseconds).

  FIG. 3 shows an example of the waveform of laser light emitted from an LD (semiconductor laser element) based on the principle described with reference to FIGS. 2 (a) to 2 (d).

  As already described, relaxation oscillation is a transient oscillation phenomenon that occurs when the drive current suddenly rises from a certain level to a certain level that greatly exceeds the threshold current in an LD (semiconductor laser device or oscillation system). Therefore, it occurs when a fast rising current is passed through the LD. On the other hand, when the rise time is long, this transient phenomenon is small, so that the peak output of the relaxation oscillation is significantly reduced. Therefore, in order to use it as a recording pulse for recording information on the information recording layer of the optical disc D, the peak output (maximum value of the laser beam) is scheduled as well as the pulse width (recording pulse length) is stable. It is essential to reach the level.

  The laser beam shown in FIG. 3 has a second output having a magnitude of about 60% after the elapse of a predetermined period (period of relaxation oscillation) T when the peak magnitude of the first output is “100”. Accompany. In the example shown in FIG. 3, the period between the first output and the second output, that is, the period T of the relaxation oscillation is approximately 230 ps as the period between the full widths at half maximum described above.

The period T of the relaxation oscillation is generally

Where A is the optical confinement factor, dg / dn is the differential gain, S is the photon density, and τp is the photon lifetime.
Indicated by.

  The parameter value that determines the period of relaxation oscillation in the above equation (1) is usually difficult to measure, but is generated when a current having a sufficiently short rise time as shown in FIG. The period T of relaxation oscillation can be measured based on the waveform of the laser beam.

  By the way, as to the intensity (peak output) of the laser beam generated by the relaxation oscillation, as shown in FIG. 4, the rise of the laser drive current supplied from the LDD (laser drive circuit) 9 to the LD (semiconductor laser element) 20 It is recognized that there is also a relationship with time. The rise time of the laser drive current shown in FIG. 4 will be described with reference to FIG. 5. “Time when the magnitude of the laser drive current is increased from 0 mA to a steady current value I1 (for example, 100 mA)” Fluctuates according to. The rise time of the laser drive current can be arbitrarily set by changing the resistance value of the transmission path (electric circuit) between the LDD 9 and the LD 20.

  That is, in FIG. 4, when the rise time of the laser drive current described with reference to FIG. 5 is 50 ps, the intensity (peak output) of the laser beam is “1” and the peak output is “0.9 (rise time is 50 ps). When the rise time for obtaining “90% of the output” is obtained, it is recognized that it is approximately 200 ps.

  From such a background, when information is recorded on the information recording layer of the optical disc D using relaxation vibration, information is recorded by laser light up to the first output and the second output of the relaxation vibration (second order). Assuming that the information recording film is heated by the energy up to the pulsed laser beam and a recording mark is formed), the second output of the laser beam is a period in which the period T is within 200 ps from the first output. It is necessary to be output within.

  6A to 6C, the time evolution of the laser drive current supplied from the laser drive circuit (LDD) 9 to the semiconductor laser element (LD) 20 (a), the laser emitted from the LD. The shape of the mark (recording mark) formed on the recording film of the optical disc D by the waveform (b) and the output laser waveform is shown (c).

  In FIG. 6A, the power of the laser beam emitted from the LD 20 is the optical disc D in the section of the region (A) where the condensing point of the laser beam on the recording film of the optical disc D is in the place where the recording mark is not formed. In order to read the upper position information and to apply the servo, the reproduction power used when reproducing the information from the optical disk D is controlled. That is, a drive current having a magnitude of I2 larger than Ith, which is a threshold value of a drive current capable of laser oscillation, is supplied to the LD 20.

  In the section (C), a laser drive current of I3 larger than I2 is supplied to the LD 20, and relaxation oscillation pulsed laser light (see FIG. 6B) whose maximum value reaches P1 is output.

  During the predetermined time T1 immediately before the region (C) where the relaxation oscillation pulse light is output, that is, during the region (B), a laser driving current having a magnitude I1 smaller than the threshold value Ith is supplied to the LD 20. The

  Further, the magnitude of the laser drive current after the end of the relaxation oscillation, that is, in the region (D) is again set to the aforementioned I2 that is larger than the threshold value Ith.

  Therefore, in the LDD (laser drive circuit) 9, the pulsed laser light accompanying the relaxation oscillation is output from the LD (semiconductor laser element) 20 to the second peak output (the second pulsed laser beam within the relaxation oscillation period). It is preferable that a resistance value of the transmission line that can be output within at least 200 ps is given up to the timing when the light is emitted.

  As described above, when laser light for recording is obtained using a laser diode (semiconductor laser element), pulsed laser light is generated by inducing relaxation vibration, compared with the case where relaxation vibration is not used. Thus, the intensity (peak output) of the laser beam can be increased. Also, by using up to the second peak output, which is output as relaxation vibration, for increasing the temperature of the information recording layer of the optical disk as a recording medium, that is, for recording information, it takes less time than when relaxation vibration is not used. Recording of information becomes possible.

  As a result, a large amount of energy can be applied to the optical disc in a relatively short time. In this way, when the optical disk is irradiated with a large amount of laser light in a short time, it is difficult for heat to escape within the time during which the laser light is irradiated, and the optical disk can be heated efficiently. The energy of the laser beam irradiated for forming becomes smaller than that in the case of using a long duration laser beam that does not use relaxation oscillation.

  Therefore, the power consumption by the LD (semiconductor laser element) is reduced, and the heat rise of the PUH (optical pickup head) can be suppressed. At the same time, it is possible to reduce the occurrence of aberrations due to the change in the wavelength of the laser light and the change in the refractive index of the OL (objective lens) as the temperature of the LD rises, and it is possible to suppress the deterioration of the quality of the recording mark. .

  Note that the present invention is not limited to any of the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in any of the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows an example of the information recording / reproducing apparatus (optical disk apparatus) with which one Embodiment of this invention is applied. FIG. 2 is a schematic diagram for explaining the relationship between light output from a semiconductor laser element incorporated in the optical disc apparatus shown in FIG. 1 and a laser drive current. FIG. 3 is a schematic diagram illustrating an example of a waveform of laser light emitted from an LD (semiconductor laser element) based on the principle described with reference to FIG. 2. Schematic explaining the relationship between the rise time of the laser drive current supplied to the LD (semiconductor laser element) and the light intensity of the emitted laser light. Schematic explaining the rise time of the laser drive current shown in FIG. FIG. 2 is a schematic diagram for explaining the relationship between light output from a semiconductor laser element incorporated in the optical disc apparatus shown in FIG. 1 and recording marks (formation process) formed on a recording film.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical disk apparatus (information recording / reproducing apparatus), 3 ... Arithmetic circuit, 5 ... Server driver, 7 ... Control part, 9 ... Laser drive circuit (LDD), 20 ... Laser diode (semiconductor laser element, light source), 21 ... Collimate Lens, 22 ... Polarizing beam splitter, 23 ... 1/4 wavelength plate, 24 ... Objective lens, 25 ... Imaging lens, 26 ... Photo detector, 27 ... Actuator.

Claims (7)

A light source that outputs light of a predetermined wavelength;
A drive circuit for supplying to the light source a drive current defined such that light output from the light source includes two or more peaks and an interval between the peaks is 200 ps (picoseconds) or less;
A lens that focuses light from the light source on an information recording layer of an information recording medium;
An optical head device comprising:   2. The optical head device according to claim 1, wherein light including two or more peaks output from the light source is generated by relaxation oscillation of the light source.   3. The optical head device according to claim 1, wherein the light including two or more peaks output from the light source is output by a driving current supplied from the driving circuit and having a rise time of 200 ps or less.   The rise time of the drive current supplied from the drive circuit to the light source is arbitrarily set according to a resistance value of a transmission path of the drive current supplied from the drive circuit to the light source. 4. The optical head device according to any one of 3. A laser element that outputs light of a predetermined wavelength;
A laser drive circuit that supplies a drive current having a rise time shorter than a predetermined rise time so that two or more continuous pulsed lights accompanied by relaxation oscillation can be output to the laser element;
A lens that focuses light from the laser element on an information recording layer of an information recording medium;
A signal processing circuit for reproducing the information recorded on the information recording medium from the reflected light from the information recording layer of the information recording medium obtained by the lens;
An information recording / reproducing apparatus comprising:   The rising time of the drive current supplied from the drive circuit to the laser element is arbitrarily set by a resistance value of a transmission path of the drive current supplied from the drive circuit to the laser element. 5. The information recording / reproducing apparatus according to 5. A laser element that outputs light of a predetermined wavelength is caused to output continuous pulsed light having two or more peaks due to relaxation oscillation by a drive current having a rise time of 200 ps or less,
An information recording / reproducing method, wherein information is recorded by heating an information recording layer of a recording medium with continuous pulsed light having two or more peaks.

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