JP4377944B2 - Optical recording head device, optical recording device, and recording method - Google Patents

Description

  The present invention relates to an optical recording head device, an optical recording device, and a recording method.

  As is well known, there is a DVD (Digital Versatile Disc) as an optical disc for storing digital video, and it is widely used all over the world mainly for storing and distributing movie contents (digital work publications). Further, compared with the above-mentioned DVD (referred to as an existing DVD), a disk having a larger capacity is realized.

  In optical discs, there is a strong demand for high transfer rates along with an increase in capacity, and even with HD DVD-R and HD DVD-RW, there is already a standard for double speed compared to standard single speed (linear speed 6.61 m / s). Has been issued. In the future, higher speeds such as 4 times speed and 8 times speed are expected.

  When recording data on an optical disc, if a peak current for obtaining a desired peak power is applied to the laser light source for a certain period of time, the intensity of the emitted light from the laser light source is increased to the recording power as well as the peak current is applied. . When the emitted light intensity of the laser light source is raised to the recording power, the intensity increases and decreases momentarily until the recording power becomes stable. This is due to the relaxation oscillation of the laser light source. In normal recording pulse generation, the relaxation oscillation is controlled to be as small as possible.

Conventionally, a laser driving method for recording a mark row on an optical disk using the above-described relaxation vibration and an optical disk apparatus using the laser driving method have been described (see Patent Document 1).
JP 2002-123963 A

  However, the recording method described in Patent Document 1 records a mark row on an optical disk using both a normal recording pulse and relaxation oscillation, and the period of relaxation oscillation is about 2 GHz. Only 4 GHz is described, and the relationship with the physical specifications of the laser light source is not mentioned.

  The present invention has been made in view of the above problems, and relates to an information recording apparatus for recording a data mark string corresponding to a bit string using relaxation oscillation of a laser light source. An object of the present invention is to provide an optical recording head device, an optical recording device, and a recording method that determine conditions (optical resonator length) and realize high-speed recording.

The optical recording head device according to the first aspect of the present invention includes a light source that outputs a relaxation oscillation pulse having a full width at half maximum of a single pulse of 820 ps or less, drive means for driving the light source, and light emitted from the light source. An objective lens that collects light reflected on the recording layer of the recording medium and captures the reflected light reflected by the recording layer of the recording medium, and a distribution unit that is disposed between the light source and the objective lens and distributes the incident light A light detecting means for receiving the reflected light reflected by the recording layer of the recording medium through the distributing means, and an optical recording head device in which the resonator length of the light source is 6560 μm or less, wherein the relaxation oscillation The optical recording head device records a single mark by raising the recording layer of the recording medium to a melting point or higher by one recording pulse composed of a pulse train of 1 cycle to 3 cycles .

The optical recording apparatus according to the second aspect of the present invention records a light source that outputs a relaxation oscillation pulse in which the full width at half maximum of a single pulse is 820 ps or less, drive means for driving the light source, and light emitted from the light source. An objective lens that collects light on the recording layer of the medium and captures the reflected light reflected by the recording layer of the recording medium; and a distribution means that is disposed between the light source and the objective lens and distributes incident light. An optical recording head device comprising: a light detecting means for receiving reflected light reflected by the recording layer of the recording medium through the distributing means; and a reproduction based on a signal output from the light detecting means An optical recording apparatus comprising: a calculating means for calculating a signal; and a control means for controlling the driving means and the calculating means, wherein the resonator length of the light source is 6560 μm or less, wherein one cycle of the relaxation oscillation Min. To 3 cycles By one of the recording pulses composed of pulse train, the recording layer of the recording medium is raised above the melting point, which is an optical recording apparatus for recording a single mark.

A recording method according to a third aspect of the present invention is a recording method by an optical recording apparatus having a light source having a resonator length of 6560 μm or less, and generates a drive current set at a level lower than the threshold current of the light source. A generation step; a driving step of driving the light source by inputting the driving current to the light source; and raising the driving current to a peak current level for a predetermined time so that the full width at half maximum of a single pulse is 820 ps or less. An output step for outputting a relaxation oscillation pulse , wherein the output step outputs a single recording pulse composed of a pulse train of not less than 1 period and not more than 3 periods of relaxation oscillation to the light source. The recording method of recording a single mark by raising the recording layer of the recording medium above the melting point .

  According to the present invention, for an information recording apparatus that records a data mark string corresponding to a bit string using relaxation oscillation of a laser light source, a physical condition (optical resonator length) required for the laser of the light source is determined, An optical recording head device, an optical recording device, and a recording method that realize high-speed recording can be provided.

  An optical recording apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration example of an optical recording apparatus according to an embodiment of the present invention. In the optical recording apparatus according to this embodiment, a short wavelength semiconductor laser 20 is used as a light source. The wavelength of the emitted light is, for example, in the violet wavelength band in the range of 400 nm to 410 nm.

  The emitted light 100 from the semiconductor laser light source 20 becomes parallel light by the collimating lens 21 and passes through the polarization beam splitter 22 and the λ / 4 plate 23. Then, the light enters the objective lens 24. Thereafter, the light passes through the substrate of the optical disc 1 and is focused on the target information recording layer. The reflected light 101 from the information recording layer of the optical disc 1 passes through the cover layer 4 of the optical disc 1 again, passes through the objective lens 24 and the λ / 4 plate 23, and is reflected by the polarization beam splitter 22. And enters the photodetector 26.

  The light receiving part of the photodetector 26 is usually divided into a plurality of parts, and a current corresponding to the light intensity is output from each light receiving part. The output current is converted into a voltage by an I / V amplifier (not shown), and then an arithmetic circuit 27 performs an HF signal for reproducing user data information and a focus error for controlling a beam spot position by a light source on the optical disc 1. Signals and track error signals are arithmetically processed. The arithmetic circuit 27 is controlled by the controller CTR.

  The objective lens 24 can be driven in the vertical direction and the disk radial direction by an actuator 28, and is controlled to follow the information track on the optical disk 1 by a servo driver SD. The optical disk 1 is a recordable disk on which information can be written, and information is recorded by the emitted light 100 of the semiconductor laser 20. The semiconductor laser 20 can be controlled by the semiconductor laser driving circuit 29 so that the amount of emitted light 100 can be controlled, and when the information is recorded on the optical disc 1, the relaxation oscillation pulse of the semiconductor laser 20 is emitted. The semiconductor laser drive circuit 29 is controlled by the controller CTR. The recording pulse at the time of recording information on the optical disc 1 will be described in detail later.

  Next, FIG. 2 shows an example of a cross-sectional view of the optical disc 1 used in the optical recording apparatus according to the present embodiment. For example, a recording layer 13 which is a phase change recording film is formed on a substrate 11 made of polycarbonate via a protective layer 12 made of a dielectric. A protective layer 12 made of a dielectric is further formed thereon, and a conductive reflective layer 14 is further formed thereon. Furthermore, another substrate 11 made of polycarbonate is formed on this with an adhesive layer 15 in between.

  In terms of the overall structure, the optical disc 1 is obtained by bonding two discs each having an information recording layer including a recording film on at least one substrate in opposite directions. The thickness of one substrate is about 0.6 mm, for example, and the entire thickness of the optical disc 1 is about 1.2 mm.

  In this embodiment, an example of an optical disk having four information recording layers is shown. However, the present invention is also applied to an optical disk having five or more information recording layers, such as providing interface layers above and below the recording layer 13. Is applicable. In this embodiment, the information recording layer is a single layer. However, the present invention can also be applied to an optical disc having two or more information recording layers. Furthermore, in the present embodiment, a disk-shaped optical disk is used as a recording medium. However, the present invention can also be applied to, for example, a card-shaped recording medium.

  FIG. 3 shows an example of a semiconductor laser 20 used as a light source in the optical recording apparatus according to this embodiment. FIG. 3 shows only a semiconductor chip portion that becomes a light emitting body of a semiconductor laser, and this chip portion is usually fixed to a metal block that becomes a heat sink, and further includes a base material and a cap with a glass window. Is done.

  Here, description will be made using only the semiconductor chip portion directly related to laser emission. As an example, the semiconductor laser chip is a micro block having a thickness (up and down direction in the figure) of 0.15 mm, a length (L in the figure) of 0.5 mm, and a lateral width (depth direction in the figure) of about 0.2 mm. . The upper end 31 and the lower end 32 of the laser chip are electrodes, the upper end 31 is a − (minus) electrode, and the lower end 32 is a + (plus) electrode.

  The central active layer 33 emits laser light, and an upper clad layer 34 and a lower clad layer 35 are formed on the upper and lower sides of the active layer 33. The upper clad layer 34 is an n-type clad layer having many electrons, and the lower clad layer 35 is a p-type clad layer having many holes.

  When a voltage is applied in a forward direction from the electrode 32 to the electrode 31 between the electrode 32 and the electrode 31, that is, when a current is passed from the electrode 32 toward the electrode 31, a large number of holes excited in the active layer 33 The electrons recombine, and light corresponding to the energy lost at that time is emitted. The material of the upper clad layer 34 and the lower clad layer 35 is selected so that the refractive index of the upper clad layer 34 and the lower clad layer 35 is lower than the refractive index of the active layer 33 (for example, 5% lower). The light wave travels left and right in the drawing while reflecting the boundary with the cladding layers 34 and 35 in the active layer 33.

  The left and right end faces in the figure are mirror surfaces M, and the active layer 33 itself forms an optical resonator. The light wave that travels left and right in the active layer 33 and is reflected by the mirror surfaces at the left and right ends is amplified in the active layer 33 and finally emitted from the right end (and left end) of the figure as laser light. At this time, the resonator length of the semiconductor laser 20 is the length L in the left-right direction in the drawing.

  The emission waveform of the semiconductor laser 20 is controlled by a drive current generated by a semiconductor laser (LD: Laser Diode) drive circuit 29. A state in which a recording pulse used for recording on the optical disc 1 is generated by the driving current of the LD driving circuit 29 will be described with reference to FIGS. 4A to 4D.

  4A and 4B show a normal LD drive current and an LD emission waveform, and FIGS. 4C and 4D show an LD drive current and an LD emission waveform when a relaxation oscillation pulse is generated. The drive current is controlled to two levels of the bias current Ibi and the peak current Ipe shown in FIGS. 4A and 4C. In some cases, the bias current is further subdivided into two levels or three levels to be controlled. Here, for simplification of explanation, the bias current Ibi and the peak current Ipe are each one level. The case will be described.

  In the case of normal recording pulse generation, the LD drive circuit 29 first generates a bias current Ibi set at a level slightly higher than the threshold current Ith at which the semiconductor laser 20 starts laser oscillation, as shown in FIG. 4A. The semiconductor laser 20 is driven. Thereafter, at time A, a peak current Ipe for obtaining a desired peak power is applied, and after the peak current Ipe is applied for a certain period of time, it is again lowered to the bias current Ibi at time B. FIG. 4B shows the change over time in the intensity of emitted light from the semiconductor laser 20 at this time.

  As shown in FIG. 4B, until the time A driven by the bias current Ibi, the emitted light intensity is extremely low power that data cannot be recorded on the optical disc 1, but the peak current Ipe is applied and the recording is performed. The strength is increased to power, and this level is maintained until the drive current is reduced to the bias current Ibi level at time B. After time B, the emitted light intensity becomes low power again. In this way, the semiconductor laser 20 is controlled so that the recording pulse is emitted during the period from time A to time B.

  When the intensity of the emitted light is observed in more detail, it can be seen that when the intensity is increased to the recording power at time A, the intensity instantaneously increases and decreases until it stabilizes to the steady recording power (in the figure). Broken line circle). This is due to the relaxation oscillation of the semiconductor laser 20, and in normal recording pulse generation, control is performed so that this relaxation oscillation is minimized.

  The 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. The relaxation vibration is reduced every time the vibration is repeated, and the vibration is eventually reduced.

  In the optical recording apparatus according to the present embodiment, this relaxation vibration is actively used for recording. When the relaxation oscillation is used as a recording pulse, the LD drive circuit 29 first generates a bias current Ibi set to a level lower than the threshold current Ith of the semiconductor laser 20 to drive the semiconductor laser 20 as shown in FIG. 4C. To do.

  Thereafter, at time A, the drive current is suddenly raised to the peak current level Ipe at a rise time earlier than normal recording pulse generation. After a shorter time than normal recording pulse generation, again at time C, Pulled down to bias current Ibi. FIG. 4D shows the change over time in the intensity of emitted light from the semiconductor laser 20 at this time.

  As shown in FIG. 4D, the semiconductor laser 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 the light emission as a light emitting diode of a negligible level is to some extent. It is. After that, with the rapid application of current at time A, relaxation oscillation is started, and the emitted light intensity rapidly increases. Thereafter, light emission by relaxation oscillation continues until time C at which the applied current is returned again below the threshold current. In this example, the time C is reached at the timing when the second pulse of the relaxation oscillation is generated, and the recording pulse generation is completed.

  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 with a normal recording pulse. .

  As a generally known relationship, there is the following relationship between the resonator length L of the LD and the relaxation oscillation period T.

T = k · {2 nL / c} (1)
Here, k is a constant, n is the refractive index of the active layer of the semiconductor laser, and c is the speed of light (3.0 × 10 ⁸ (m / s)). Therefore, it can be seen that the LD resonator length L and the relaxation oscillation period T, and hence the relaxation oscillation pulse width, are in a proportional relationship.

  For this reason, when it is desired to increase the relaxation oscillation pulse width, the LD resonator length L may be increased, and when the relaxation oscillation pulse width is desired to be decreased, the LD resonator length L may be decreased. That is, it can be said that the relaxation oscillation pulse width can be controlled by the LD resonator length L.

  FIG. 5 shows the measurement result of the relaxation oscillation waveform by a semiconductor laser having a resonator length L of 650 μm. It can be seen that the relaxation oscillation pulse width is about 81 ps at the full width at half maximum. From the above equation (1), it is known that the cavity length L of LD and the relaxation oscillation pulse width are in a proportional relationship. Therefore, the cavity length L of the semiconductor laser and the relaxation oscillation pulse width (FWHM) Wr obtained. The following relationship is obtained as the conversion formula.

Wr (ps) = L (μm) /8.0 (μm / ps) (2)
Next, data recording on the optical recording medium in the optical recording apparatus according to the present embodiment will be described. The optical disc 1 is a rewritable disc such as a DVD-RAM, DVD-RW, HD DVD-RW, or HD DVD-RAM, and uses a phase change material for the recording layer. In the phase change type optical disc, data bits are recorded and erased by controlling the intensity of pulsed laser light focused on the recording layer.

  Recording means forming an amorphous mark in a region initialized to a crystalline state of the recording layer. The amorphous mark is formed by melting the phase change material and quenching immediately thereafter. For this purpose, a relatively short and high-power pulsed laser beam is condensed on the phase change recording layer, and the local temperature is raised to a temperature exceeding the melting point Tm of the phase change material, thereby causing local melting. Must be generated. Thereafter, when the recording pulse is interrupted, the molten local region is rapidly cooled, and a solid amorphous mark is formed through a melting-quenching process.

  On the other hand, the recorded data bit is erased by recrystallizing the amorphous mark. Crystallization is now achieved by local annealing. By condensing the laser beam on the recording layer and controlling it to a level slightly lower than the recording power, the local temperature of the phase change recording layer is increased to the crystallization temperature Tg or higher, and the temperature is lower than the melting point Tm. keep.

  At this time, by maintaining the local temperature between the crystallization temperature Tg and the melting point Tm for a certain period of time, the amorphous mark can be phase-changed into a crystalline state. In this way, the recording mark can be erased.

  Note that the time required for crystallization at this time to be maintained between the crystallization temperature Tg and the melting point Tm is called crystallization time. To reproduce the recorded data bits, the information recording layer is irradiated with a DC laser beam having a low power that does not change the phase of the recording layer, that is, a reproducing power.

  The optical recording apparatus according to this embodiment is characterized in that a recording pulse used for recording a data bit is a short pulse such as a relaxation oscillation pulse. When the amorphous mark formed by the conventional recording pulse is formed through the process of melting and quenching the phase change material as described above, as shown in FIG. Crystallizing ring).

  This is because the region once melted at the peripheral portion of the amorphous mark is recrystallized by passing through the temperature region between the crystallization temperature Tg and the melting point Tm in the cooling process for the crystallization time or longer. Although this has the effect of reducing the size of the amorphous mark (self-sharpening effect) as a result, the jitter (fluctuation) of the reproduced signal at the mark periphery, thermal interference between the front and rear marks on the track, In some cases, the mark formed on the adjacent track may be partially erased (cross erase).

  On the other hand, the amorphous mark formed by a short pulse such as the relaxation oscillation pulse of the optical recording apparatus according to the present embodiment does not cause a recrystallization ring at the peripheral portion of the amorphous mark as shown in FIG. 6B. By irradiating a high-power laser beam in a short time with a short pulse, the phase-change layer is melted immediately after the laser beam irradiation, and the irradiation is terminated before the molten region spreads significantly to the peripheral part due to heat conduction. As a result, only the melted part immediately after laser beam irradiation is formed into an amorphous mark.

  As described above, in an amorphous mark that does not cause a recrystallization ring due to a short pulse, jitter at the peripheral edge of the mark is reduced, mark deformation or edge shift due to thermal interference between front and rear marks on the track, and adjacent tracks. There is an advantage that the cross-erasing of the mark formed on the substrate does not occur.

  Of course, recording with a short pulse has the advantage of improving the quality of the recording mark as described above, and since it can record the mark in a short time, it is needless to say that it is suitable for high transfer rate recording. .

  In optical discs, there is a strong demand for high transfer rates along with an increase in capacity, and the standard for double speed is already available for HD DVD-R and HD DVD-RW compared to the standard single speed (linear speed 6.61 m / s). Has been issued. In the future, it is expected that higher speeds such as 4 times speed and 8 times speed will be expected.

  In order to achieve a high transfer rate, it is necessary to record the recording mark at a high speed, that is, in a short time. In the phase change disk, this means that the amorphous mark is recorded by a short pulse. For example, in HD DVD, the channel clock rate is 518.4 Mbps at 8 × speed, and the time corresponding to one channel bit is 1.929 ns.

  The pulse width required for short pulse recording in the optical recording apparatus according to this embodiment is a pulse width that does not cause a recrystallization ring when an amorphous mark is formed. The region that becomes the recrystallization ring when the amorphous mark is formed is a region that is once melted at the periphery of the amorphous mark as described above, that is, the region that exceeds the melting point of the phase change material. At this time, only the region slightly exceeding the melting point is recrystallized.

This is because a region where the temperature has been raised to a temperature greatly exceeding the melting point has a large temperature decrease gradient and is cooled relatively steeply, and thus becomes amorphous. This is because the temperature gradient δT / δx and the heat flow density q (W / m ² ) are well known (Fourier's heat conduction law) q = K · δT / δx This is because the heat flow from the high temperature region to the low temperature region increases. Here, K (W / m · K) is the thermal conductivity, and x is the distance in the direction of thermal conduction (interface normal vector direction) at the interface having a temperature difference.

  In the case of short pulse recording, high-power laser light is irradiated so that the center of the light spot exceeds the melting point immediately after laser light irradiation. FIG. 7 is a view for explaining the temperature distribution on the recording track. The upper part is the melting point excess region on the track immediately after the recording pulse irradiation, the middle part is the melting point excess region at the end of the recording pulse, and the lower part is AA ′. The temperature distribution in the cross section is shown.

  FIG. 7A shows a case of short pulse recording, and FIG. 7B shows a case of recording by a conventional recording pulse. Originally, the recording beam spot (the area indicated by the broken line in FIG. 7A) moves in the vertical direction in the figure during pulse irradiation. However, in this example, it is assumed that it does not move for the sake of simplicity of explanation.

  In any recording pulse, the region beyond the melting point at the center of the light spot is enlarged by heat transfer immediately after the pulse irradiation until the end of the pulse. However, in the case of a short pulse, since the pulse irradiation time is short, it hardly expands.

  In the case of short pulse recording, the temperature distribution in the cross section including the center of the light spot at the end of the pulse has almost the same Gaussian distribution as that immediately after the light beam irradiation, and a steep temperature gradient before and after the boundary between the melting point and the melting point It has become. For this reason, a region to be recrystallized, that is, a region slightly exceeding the melting point (in the figure, a region having a temperature between the melting point Tm and the temperature Tm2) has almost no spread in the planar direction. Therefore, if the laser power becomes zero within a time period in which expansion of the region above the melting point at the center of the light spot due to heat transfer is negligible, the recrystallization ring is limited to a very narrow region.

  On the other hand, in the case of mark formation by a conventional recording pulse, since a relatively low power is irradiated for a long time, the region exceeding the melting point at the center of the light spot is gradually enlarged (from the upper stage to the middle stage in FIG. 7B). At this time, the temperature distribution in the cross section including the center of the light spot is no longer a Gaussian distribution but a shape having a gentler temperature gradient (lower part of FIG. 7B).

  For this reason, the region to be recrystallized has a relatively large extent in the plane direction. The broken line in the middle of FIG. 7B indicates the recrystallization limit, and the inside of this broken line is an area where an amorphous mark is formed. Thus, the conventional recording pulse is accompanied by a large recrystallization ring during mark formation.

The width in the planar direction of the recrystallization ring is considered to be substantially the same as the diffusion distance in the planar direction of the melting point region during the pulse irradiation time. As a general phase change material, assuming that thermal conductivity K = 0.005 J / cm / s / ° C. and specific heat C = 1.5 J / cm ³ / ° C., the thermal diffusion distance within the pulse irradiation time is estimated. I can do it. That is, during time t, heat is considered to diffuse by the distance L = (Kt / C) ^1/2 .

  On the other hand, the upper limit of the pulse irradiation time required for short pulse recording is determined from the fact that the width in the plane direction of the recrystallization ring is so small that there is no practical problem.

  FIG. 9 shows the relationship between the asymmetry of the playback signal of the HD DVD-RW and the mark length variation (the negative sign is the direction in which the mark becomes shorter) of the shortest mark (2T; T is the channel bit length = 0.102 μm). FIG. Asymmetry is obtained by dividing the difference between the signal center levels of the sparsest signal (11T) and the sparsest signal (2T) included in the reproduction signal by the sparsest signal amplitude.

  It is known that when the absolute value of the asymmetry is large, the error rate of the reproduction signal data becomes large. In HD DVD-RW, the limit value of the asymmetry is ± 0.10. As can be seen from FIG. 9, the asymmetry increases in the negative direction when the mark length of the shortest mark fluctuates (in this case, the mark length becomes shorter), and the lower limit of the asymmetry when the mark length fluctuates by 0.325T (becomes shorter). Which is -0.10. Since 1T (channel bit length) is 0.102 μm, the fluctuation of 0.325T corresponds to the fluctuation of 33 nm.

  In short pulse recording, since it is assumed that the recrystallization ring is generated only to a level where there is no practical problem, the mark length variation due to the recrystallization ring is required to be at most 33 nm or less.

  In addition, since it may be considered that the mark length shortening due to the recrystallization ring occurs uniformly in the front-rear direction of the mark, it can be said that the width of the recrystallization ring is required to be 16.5 nm or less. The pulse irradiation time corresponding to the thermal diffusion distance of 16.5 nm is 0.82 ns from the above relationship, and this can be said to be the upper limit pulse width required for short pulse recording.

As already described, since the equation (2) is obtained as the relationship between the resonator length L of the semiconductor laser and the obtained relaxation oscillation pulse width Wr, a pulse width of 820 ps or less should be used for short pulse recording. That is, it was found that it was necessary to use a semiconductor laser having a resonator length of 6560 μm or less.

The above-described conditions are examples where the mark length is shortened only by forming the recrystallization ring. Actually, in addition to the disk recording film factor of recrystallization ring formation, the factors causing the mark length fluctuation are the electric fluctuation of the driving pulse width generated by the LD driving circuit and the fluctuation of the disk moving speed (disk rotation speed). (Motor speed fluctuation)). Considering that these three elements are equal fluctuation elements, and the situation where the fluctuation due to the square sum of squares corresponds to the above asymmetry absolute value limit value of 0.10, it occurs only by recrystallization ring formation. The condition for the mark length variation is more severe than the above example. When the square root sum of the three elements corresponds to 0.10, the fluctuation due to one fluctuation element is ((0.1 ² ) / 3) ^1/2 = 0.06. From FIG. 9, the mark length variation that causes asymmetry variation with an absolute value of 0.06 is -0.2T. Therefore, it can be said that the mark length variation is desirably limited to 10% or less of the shortest mark length 2T = 0.204 μm of HD DVD-RW, that is, limited to 10.2 nm or less in one direction. In order to be limited to shortening the mark length of 10.2 nm or less in one direction, the pulse irradiation time is 0.31 ns from the above-described relationship between the thermal diffusion distance and the pulse irradiation time. That is, it is desirable to perform short pulse recording during this pulse irradiation time.

  In this case, as already described, since the equation (2) is obtained as the relationship between the cavity length L of the semiconductor laser and the obtained relaxation oscillation pulse width Wr, a pulse width of 310 ps or less is used for short pulse recording. That is, it is necessary to use a semiconductor laser having a resonator length of 2480 μm or less.

  On the other hand, from the viewpoint of reducing the recrystallization ring, the shorter the pulse irradiation time, the better. However, in reality, it is difficult to give energy for raising the temperature of the phase change material above the melting point. That is, it is necessary to irradiate extremely high power in a short time. Therefore, in reality, it may be considered that the pulse irradiation time is required to be about 50 ps or more. This corresponds to the need for a semiconductor laser having a resonator length of 400 μm or more when using the relationship of equation (2).

  As can be seen from Equation (2), when the relaxation oscillation pulse is used for information recording on the optical disc 1, the relaxation oscillation pulse width is uniquely determined when the resonator length of the semiconductor laser 20 used in the optical recording apparatus is determined. . As described above, when the pulse width is short, the phase change material is heated to the melting point or higher by irradiating high power. However, even if the semiconductor laser 20 is irradiated at the highest power, it reaches the melting point or higher. Sometimes not. In such a case, it is useful to irradiate the relaxation oscillation pulse a plurality of times.

  FIG. 8 shows an optical pulse waveform when the driving pulse of the semiconductor laser 20 is controlled so that the relaxation oscillation pulse is generated three times. By generating the relaxation oscillation pulse three times, the irradiation energy by the pulse (time integration value by the pulse in the figure) is increased, so that the phase change material can be raised above the melting point. However, as can be seen from the figure, the second and third pulse intensities gradually decrease compared to the first relaxation oscillation pulse. For this reason, irradiation of a plurality of pulses more than this is not very effective.

  As described above, in the optical recording apparatus that records data on the optical recording medium using the relaxation oscillation pulse of the semiconductor laser 20, it is necessary to adjust the number of relaxation oscillation pulses according to the resonator length of the laser. . Even when a laser having a low rated output of the semiconductor laser is used, it is useful to use a plurality of relaxation oscillation pulses.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. For example, in the above-described embodiments, a rewritable optical disk using a phase change material is used as an example. However, the present invention can be applied even to a one-time recording (recordable) optical disk.

  Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

1 is a diagram schematically showing a configuration example of an optical recording apparatus according to an embodiment of the present invention. The figure which shows an example of sectional drawing of the optical disk used in one Embodiment of this invention. 1 is a diagram showing an example of a semiconductor laser used as a light source in an optical recording apparatus according to an embodiment of the present invention. The figure which shows an example of the waveform of the drive current of the semiconductor laser at the time of performing normal recording. The figure which shows an example of the emitted waveform of the semiconductor laser at the time of performing normal recording. The figure which shows an example of the waveform of the drive current of a semiconductor laser at the time of producing | generating a relaxation oscillation pulse. The figure showing an example of the outgoing waveform of a semiconductor laser at the time of generating relaxation oscillation pulse. The figure which shows an example of the measurement result of the relaxation oscillation waveform by the semiconductor laser whose resonator length is 650 micrometers. The figure for demonstrating the amorphous mark formed of the conventional recording pulse. The figure for demonstrating the amorphous mark formed of the short pulse. The figure for demonstrating an example of the temperature distribution on the recording track in the case of short pulse recording. The figure for demonstrating an example of the temperature distribution on the recording track in the case of the recording by the conventional recording pulse. The figure which shows an example of the optical pulse waveform at the time of controlling the drive pulse of a semiconductor laser so that a relaxation oscillation pulse may generate | occur | produce 3 times. The figure for demonstrating an example of the tolerance | permissible_range of a recrystallization ring.

Explanation of symbols

  Ibi ... bias current, Ipe ... peak current, Ith ... threshold current, L ... resonator length, 1 ... optical disk (recording medium), 20 ... semiconductor laser light source, 21 ... collimator lens, 24 ... objective lens, 26 ... photodetector 27 ... arithmetic circuit, 29 ... semiconductor laser driving circuit

Claims (9)

A light source that outputs a relaxation oscillation pulse having a full width at half maximum of a single pulse of 820 ps or less;
Driving means for driving the light source;
An objective lens that collects the light emitted from the light source on the recording layer of the recording medium and captures the reflected light reflected by the recording layer of the recording medium;
A distribution means disposed between the light source and the objective lens, for distributing incident light;
Light detecting means for receiving reflected light reflected by the recording layer of the recording medium through the distributing means;
An optical recording head device having a resonator length of the light source of 6560 μm or less,
An optical recording head device for recording a single mark by raising the recording layer of the recording medium to a melting point or higher by one recording pulse composed of a pulse train of 1 cycle to 3 cycles of the relaxation oscillation . A light source that outputs a relaxation oscillation pulse having a full width at half maximum of a single pulse of 310 ps or less;
Driving means for driving the light source;
An objective lens that collects the light emitted from the light source on the recording layer of the recording medium and captures the reflected light reflected by the recording layer of the recording medium;
A distribution means disposed between the light source and the objective lens, for distributing incident light;
Light detecting means for receiving reflected light reflected by the recording layer of the recording medium through the distributing means;
An optical recording head device in which a resonator length of the light source is 2480 μm or less,
An optical recording head device for recording a single mark by raising the recording layer of the recording medium to a melting point or higher by one recording pulse composed of a pulse train of 1 cycle to 3 cycles of the relaxation oscillation . 3. The optical recording head device according to claim 1, wherein a full width at half maximum of a single pulse of the relaxation oscillation pulse is 50 ps or more. A light source that outputs a relaxation oscillation pulse with a full width at half maximum of a single pulse of 820 ps or less, a driving means that drives the light source, and light emitted from the light source is condensed on a recording layer of the recording medium, An objective lens that captures reflected light reflected by the recording layer, a distribution unit that is disposed between the light source and the objective lens, distributes incident light, and a recording layer of the recording medium via the distribution unit An optical recording head device comprising: a light detection unit that receives the reflected light reflected by the light detection unit; a calculation unit that calculates a reproduction signal based on a signal output from the light detection unit;
Control means for controlling the driving means and the computing means,
An optical recording apparatus in which a resonator length of the light source is 6560 μm or less,
An optical recording apparatus for recording a single mark by raising the recording layer of the recording medium to a melting point or higher by one recording pulse composed of a pulse train of 1 cycle to 3 cycles of the relaxation oscillation . A light source that outputs a relaxation oscillation pulse with a full width at half maximum of a single pulse of 310 ps or less, a driving means that drives the light source, and light emitted from the light source is condensed on a recording layer of the recording medium, An objective lens that captures reflected light reflected by the recording layer, a distribution unit that is disposed between the light source and the objective lens, distributes incident light, and a recording layer of the recording medium via the distribution unit An optical recording head device comprising: a light detection unit that receives the reflected light reflected by the light detection unit; a calculation unit that calculates a reproduction signal based on a signal output from the light detection unit;
Control means for controlling the driving means and the computing means,
An optical recording apparatus in which a resonator length of the light source is 2480 μm or less,
An optical recording apparatus for recording a single mark by raising the recording layer of the recording medium to a melting point or higher by one recording pulse composed of a pulse train of 1 cycle to 3 cycles of the relaxation oscillation . 6. The optical recording apparatus according to claim 4, wherein a full width at half maximum of a single pulse of the relaxation oscillation pulse is 50 ps or more. A recording method by an optical recording apparatus having a light source having a resonator length of 6560 μm or less,
Generating step for generating a drive current set at a level lower than the threshold current of the light source;
A drive step of driving the light source by inputting the drive current to the light source;
An output step of raising the drive current to a peak current level for a predetermined time and outputting a relaxation oscillation pulse having a full width at half maximum of a single pulse of 820 ps or less to the light source,
In the output step, the recording layer of the recording medium is raised above the melting point by causing the light source to output one recording pulse composed of a pulse train of one period or more and three periods or less of relaxation oscillation, and a single mark Recording method to record. A recording method by an optical recording apparatus having a light source having a resonator length of 2480 μm or less,
Generating step for generating a drive current set at a level lower than the threshold current of the light source;
A drive step of driving the light source by inputting the drive current to the light source;
An output step of raising the drive current to a peak current level for a predetermined time and outputting a relaxation oscillation pulse having a full width at half maximum of a single pulse of 310 ps or less to the light source,
In the output step, the recording layer of the recording medium is raised above the melting point by causing the light source to output one recording pulse composed of a pulse train of one period or more and three periods or less of relaxation oscillation, and a single mark Recording method to record. The recording method according to claim 7 or 8, wherein a full width at half maximum of a single pulse of the relaxation oscillation pulse output from the light source in the output step is 50 ps or more.

Images