JP4328006B2 - Optical recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention,lightThe present invention relates to a recording medium.
[0002]
[Prior art]
One recording medium for recording data is an optical recording medium (optical disk) that records data using light and reproduces the recorded data. As an example of a typical optical disk, an optical disk using a thin film of an amorphous alloy made of a rare earth metal and a transition metal as a recording layer can be cited. When data is recorded on this optical disc, light is applied to the optical disc while applying a magnetic field to locally heat the recording layer. The heated portion of the recording layer is heated to a temperature equal to or higher than the Curie point or the compensation point, and the magnetization direction changes to become a recording mark.
[0003]
The above-described light is laser light emitted from a semiconductor laser or the like. The laser light is condensed by the lens optical system and is irradiated as a spot light onto the recording layer. The laser beam can form a smaller recording mark as the spot diameter is smaller. For this reason, in recording data on the optical disc, the spot diameter of the laser beam is an important parameter for determining the recording density of the optical disc.
[0004]
The spot diameter of the laser beam cannot be made less than the wavelength of the laser beam because of the diffraction limit of the light. In recent years, near-field light has been used for recording and reproduction of optical disks in order to reduce the spot diameter of laser light and increase the recording density of optical disks. As an example of using near-field light for recording and reproduction of an optical disc, an optical fiber whose tip is processed is mounted on a precision actuator that is driven by a piezoelectric element, and a recording mark with a diameter of 60 nm is formed on a multilayer of platinum / cobalt while controlling the position. There have been reports of experiments on recording on a film and reproducing the recorded mark. In the probe used in the experiment, the tip was processed into a cone shape and coated with metal except for a region of several tens of nanometers in the processed tip (Applied Physics Letters, Vol. 62, No. 2, pp. 142-144, 1992).
[0005]
Some conventional optical discs include a nonlinear optical material layer made of a nonlinear optical material on the substrate side of the recording layer. An optical disc including a nonlinear optical material layer records data on the recording layer by irradiating the recording layer with light from the substrate side (nonlinear optical material layer side). At this time, in the nonlinear optical material layer, only a portion irradiated with light becomes a minute opening that transmits light. For this reason, the light that has passed through the aperture becomes near-field light and can form a smaller spot diameter on the recording layer of the spot light (Applied Physics Letters, Vol. 73, No. 15, pp. 2078-2080, 1998). Note that such a configuration is also expressed as a mask using a non-linear optical material in this specification.
[0006]
In the experiment described in the above-mentioned document, an SiN protective layer, a GeN layer, and an optical disk substrate made of polycarbonate are used.₂Sb₂Te_FiveThis was carried out using an optical disk laminated by depositing a thin recording layer and a protective layer of Sb. According to this experiment, it has been reported that a recording mark having a diameter of 90 nm can be formed by irradiating a laser beam from the substrate side.
[0007]
In addition, a recording / reproducing apparatus (recording / reproducing apparatus) that records data on an optical disc or reproduces data recorded on an optical disc accurately scans a laser beam on a track of the optical disc. It is detected whether it is not off. The detection is performed by irradiating a tracking mark on the optical disc with a laser beam and detecting a signal based on the reflected light. The fact that the laser beam deviates from the track center is called a tracking error, and the tracking error is detected by a tracking signal. In this specification, a signal indicating the occurrence of a tracking error in the tracking signal is particularly referred to as a tracking error signal.
[0008]
There is a sample servo method as a typical method for examining a tracking error. The sample servo system is a system applied to an optical disc in which sample servo areas (hereinafter simply referred to as servo areas) are discretely provided on a track and a pair of tracking marks are provided in the servo area. The pair of tracks are formed with an equal distance from each other in the radial direction of the optical disc with respect to the track center. Such a tracking mark is called a wobble tracking mark.
[0009]
The tracking error for the wobble tracking mark is examined by a so-called operation push-pull method (far field method). Specifically, each of the two tracking marks constituting the wobble tracking mark is irradiated with light, a difference in light intensity of reflected light reflected by each tracking mark is obtained, and the obtained value is used as a tracking signal. In the operation push-pull method, the laser beam is servoed in the radial direction of the optical disc so that the tracking signal obtained in the region where there is no wobble tracking mark becomes 0 in the sample-and-hold circuit (optical disc technology, radio technology company, 1990). ).
[0010]
FIG. 27 is a diagram for explaining the method for detecting the tracking error described above, and shows a servo region in which a wobble tracking mark is formed. In FIG. 27, the tracking marks m1 and m2 of the wobble tracking marks are shifted from each other by a quarter track pitch from the track center Tc in the radial direction of the optical disc.
[0011]
FIG. 28 is a diagram showing reflected light (denoted as detection light) detected by irradiating the wobble tracking mark shown in FIG. 27 with laser light. The vertical axis indicates the intensity of the detection light, and the horizontal axis indicates the detection light. The detection time is shown. In the figure, P1 indicates detection light obtained from the tracking mark m1, and P2 indicates detection light obtained from the tracking mark m2. When the laser beam scans the tracking mark through the course Tc ′ shifted from the track center Tc, the difference in the light detection intensity as shown in FIG. 28 occurs between P1 and P2. At this time, the tracking signal is represented by a difference between a value obtained by integrating the waveform of P1 with time and a value obtained by integrating the waveform of P2 with time.
[0012]
Conventionally, as shown in FIG. 29, when a plurality of recording mark rows are written in one groove, wobble tracking marks larger than the recording marks for actually writing data are provided by the track pitch of the mark row. A sample servo is applied.
[0013]
[Problems to be solved by the invention]
However, not only data recording on an optical disk but also near field light is applied to various fields, a probe produced by sharpening the tip of an optical fiber is used. When recording data using such a probe, it is necessary to precisely control the distance between the optical disk and the probe using a scanning focus microscope. For this reason, the conventional technique of recording data on an optical disk using a probe has a problem that when the optical disk is rotated at a high speed, the distance between the optical disk and the probe varies periodically due to the eccentricity of the optical disk, which makes control difficult. May occur.
[0014]
Furthermore, since the above-described prior art uses a precision actuator for driving the probe, there is a limit to the scanning speed and scanning range, and there is a problem that it is difficult to record and reproduce data at a high speed.
[0015]
In addition, when recording and reproducing data on an optical disk using a nonlinear optical material as a mask, a general recording / reproducing apparatus can be used. In this case, the conventional land / groove is provided on the optical disc, and data is recorded / reproduced by using near-field light generated in a minute opening. For this reason, although the recording density in the radial direction of the disk can be increased, it is difficult to increase the recording density in the track direction. In the above-described experiment, the track pitch is 1.2 μm and the recording density in the radial direction is the same as when no near-field light is used.
[0016]
Further, when a tracking error is detected with respect to the wobble tracking mark shown in FIG. 27 by a recording / reproducing apparatus that can irradiate near-field light, the following problems occur. That is, as shown in FIG. 30, when the tracking mark m1 and the tracking mark m2 are scanned through the course Tc ′ shifted from the track center Tc, the entire area of the spot S ′ is the tracking mark m1 and tracking. It will hit mark m2. Therefore, as shown in FIG. 31, the detection light obtained from the tracking mark m1 and the tracking mark m2 has substantially the same detection light intensity h even though the laser beam scans on the course shifted from the track center Tc. Indicates.
[0017]
Further, when the track control is performed so that the detection signals have the same peak value, the intensity difference between the detection signals is not clear, so that an accurate tracking signal cannot be obtained. In addition, since the spot diameter is small, the amount of light of the entire detection light is small, and there is a disadvantage that the intensity difference between the portion where the wobble tracking mark is formed and the portion where the wobble tracking mark is not formed becomes unclear. Furthermore, since the difference in the intensity of the detection signals is small, there is a problem that the influence of noise is large and the error becomes large.
[0018]
  The present invention has been made in order to solve the above-mentioned problems. Accurate tracking is performed when data is recorded / reproduced with respect to an optical recording medium using the optical near-field effect or the pseudo near-field effect. An optical recording medium capable of recording data at a high density on an optical recording medium and reproducing the recorded data by acquiring a signalBodyThe purpose is to provide.
[0027]
[Means for Solving the Problems]
  In order to solve the above-described problems and achieve the object, an optical recording medium according to the first aspect of the present invention includes a recording layer, a plurality of tracks provided in the recording layer, and laser light on the tracks. With near-field lightscanningA first tracking mark having a size including a spot when the laser beam is formed, and a laser beam formed from the first tracking mark at a certain distance in the circumferential direction of the optical recording medium.scanningA tracking mark pair having a circular second tracking mark having a size including a spot when the first tracking mark and the second tracking mark have a diameter of the optical recording medium from the track. The track so that the distance in direction is equalLocated on the track center of the optical disc and shifted in opposite directions in the radial direction of the optical recording medium with respect to the track center.The fixed distance is equal to a distance in the circumferential direction of the optical recording medium between the first tracking mark and a first tracking mark on a track adjacent to the track on which the first tracking mark is formed.And the distance between the second tracking mark and the second tracking mark on the adjacent track in the circumferential direction of the optical recording mediumIt is characterized by that.
[0028]
  According to the invention described in claim 1,The storage capacity of the optical disk can be increased.
[0029]
  The optical recording medium according to a second aspect of the present invention further includes a nonlinear optical material layer, and the nonlinear optical layer transmits only the light by transmitting only the irradiated portion so that the irradiated portion is transparent.lightIs a near-field light.
[0030]
  This claim2According to the invention described in (1), the irradiated laser light can be converted into near-field light by the optical recording medium.
[0033]
  Claim3The optical recording medium according to the described invention is characterized in that the recording layer is made of a phase change material.
[0034]
  This claim3According to the invention described in the above, a conventional recording / reproducing apparatus can be used for recording / reproducing data on / from the optical recording medium of the present invention. Further, the recording layer can be erased and can have high sensitivity.
[0035]
  Claim4In the optical recording medium according to the invention, the recording layer is made of Ge.₂Sb₂Te_FiveIt is a thin film.
[0036]
  This claim4According to the invention described in the above, a conventional recording / reproducing apparatus can be used for recording / reproducing data on / from the optical recording medium of the present invention.
[0037]
  Claim5The optical recording medium according to the invention is characterized in that the recording layer is an AgInSbTe thin film.
[0038]
  This claim5According to the described invention, a conventional recording / reproducing apparatus can be used for recording / reproducing data with respect to the optical recording medium of the present invention. Further, the recording layer can be erased and can have high sensitivity.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of an optical recording / reproducing apparatus, a recording / reproducing method, a computer-readable recording medium storing a program for causing a computer to execute the method, and an optical recording medium according to the present invention will be described below with reference to the accompanying drawings. This will be described in detail.
[0040]
(Embodiment 1)
Embodiment 1 is a diagram for explaining an optical disk recording / reproducing apparatus (recording / reproducing apparatus) according to the present invention. In the first embodiment, prior to the description of the recording / reproducing apparatus, an optical disk recorded and reproduced by the recording / reproducing apparatus will be described.
[0041]
FIG. 1 is a cross-sectional view for explaining an optical disc and for explaining a layer structure of the optical disc. The illustrated optical disc includes a polycarbonate substrate 104, a SiN protective layer 101, a SiN protective layer 103, and a data recording layer 102. Each of the SiN protective layers 101 and 103 has a thickness of 20 nm, and the data recording layer 102 has a thickness of 15 nm. Both the SiN protective layer and the data recording layer are formed or laminated by vapor deposition.
[0042]
A recording / reproducing apparatus according to the present embodiment, which will be described later, includes a near-field probe using a fiber with a sharpened tip. Then, the laser light L is incident on the optical disk from the data recording layer 102 side shown in FIG. 1 as near-field light L ″. The data recording layer 102 is made of a phase change material, and the reflectance of the light irradiated portion changes. The portion where the reflectance has changed becomes a recording mark (data bit) 105, and the data is reproduced by detecting the recording mark 105 based on the difference in intensity of the reflected light of the irradiated light.
[0043]
At this time, the near-field light L ″ emitted from the probe enters the SiN protective layer of the optical disk and reaches the data recording layer 102. Then, a recording mark 105 is formed on the data recording layer 102, and the light transmitted through the data recording layer 102 exits from the polycarbonate substrate 104 to the outside of the optical disk as propagating light L ′ ″. According to the near-field light L ″, a recording mark 105 having the following size limited by the light diffraction limit can be formed on the data recording layer 102.
[0044]
Note that information (address information) necessary for forming the recording mark 105 is discretely recorded in an area for recording data. The mark formed for recording address information is formed in a size larger than that limited by the diffraction limit. The address information includes an absolute address, a relative address, and sample servo information for sampling a track servo signal when a track is formed on the optical disc.
[0045]
FIG. 2 is a diagram showing a servo area of the optical disk used in the first embodiment. The illustrated servo area includes a wobble tracking mark having a pair of tracking marks m1 and m2 and a wobble tracking mark having a pair of tracking marks m3 and m4. In the figure, the track center is denoted by Tc, the center of the tracking mark m1 is denoted by the mark center Mc1, and the center of the tracking mark m2 is denoted by the mark center Mc2. Further, Tp shown in the figure indicates a track pitch. A data bit db is formed at the track center Tc.
[0046]
The tracking marks that make a pair with respect to the track center are arranged in opposite directions with respect to the track center Tc and shifted by the same length. In the wobble tracking mark shown in FIG. 2, the distance d between the tracking mark m1 and the mark center Mc1 and the distance d between the tracking mark m2 and the mark center Mc2 are both ¼ track pitch.
[0047]
FIG. 3 is a diagram for explaining the recording / reproducing apparatus according to Embodiment 1 for recording data on the optical disc described above. The recording / reproducing apparatus according to the first embodiment detects a laser light source 301 such as a laser semiconductor that irradiates a laser beam L to an optical disc, and a reflected light L ′ that is generated when the irradiated laser beam L is reflected by the optical disc 304. And a servo signal detection device 303 that acquires an error signal based on a detection time during which the laser beam L is detected. The error signal indicates a tracking error, and tracking is performed so that the tracking signal becomes zero. When the value of this error signal is not 0, the error signal becomes a tracking error signal.
[0048]
FIG. 4 is a diagram for explaining the configuration of the servo signal detection device 303 in more detail. The servo signal detection device 303 includes a delay circuit 401 and a pulse width comparator 402.
[0049]
Next, the operation of the recording / reproducing apparatus described above will be described. FIG. 5 shows a state in which a laser beam is scanned with near-field light on a wobble tracking mark in which the tracking mark m1 and the tracking mark m2 are paired. The laser light becomes spot light on the optical disk. A spot of spot light is shown in the figure as a spot 501. FIG. 6 is a diagram for explaining detection light obtained by tracking performed in the state shown in FIG. The vertical axis in FIG. 6 indicates the intensity of the detection light, and the horizontal axis indicates time.
[0050]
When the laser beam spot 501 scans the track center Tc shown in FIG. 5, the detection light P1 is first detected from the tracking mark m1, and then the detection light P2 is detected from the tracking mark m2. When the laser beam scans on the track center Tc, the detection light intensity h and P1 of the detection light P1 are equal to the detection light intensity h of the detection light P2, and the detection time width T1 of the detection light P1 and the detection time of the detection light P2 The width T2 becomes equal. In this case, the difference between the two becomes 0 and the error signal becomes 0.
[0051]
On the other hand, for example, as shown in FIG. 30, when the laser beam scans on the course Tc ′ shifted from the track center Tc, the detection time width T1 of the detection light P1 and the detection time of the detection light P2 as shown in FIG. The width T2 is different. The recording / reproducing apparatus of Embodiment 1 obtains a tracking signal from the difference in the peak width of the detection light shown in FIG.
[0052]
In order to obtain the tracking signal, the recording / reproducing apparatus shown in FIG. 3 inputs a signal a generated based on the detection lights P 1 and P 2 obtained by the photodetector 302 to the servo signal detection apparatus 303. As shown in FIG. 4, the signal a is branched in the servo signal detection device 303. One of the branched signals a is input as a signal d to the pulse width comparator 402 without passing through the delay circuit 401, and the other is delayed by the delay circuit 401 and input as a signal b to the pulse width comparator 402.
[0053]
8A and 8B are diagrams for explaining processing performed in the pulse width comparator 402, where FIG. 8A shows the waveform of the signal b, and FIG. 8B shows the waveform of the signal d. ing. In each of (a) and (b), the vertical axis represents the intensity of the detection light, and the horizontal axis represents time. First, the signal d is input to the pulse width comparator 402. Next, the signal b is input. The pulse width comparator 402 calculates the difference in the detection time width between the detection light P1 of the signal b and the detection light P2 of the signal d from the equation T1-T2.
[0054]
FIG. 9 is a diagram for explaining a configuration for calculating the difference between the detection time widths described above in the pulse width comparator 402. FIGS. 10A to 10D are diagrams for explaining the signal processed in FIG. 9. The vertical axis represents the intensity of the signal obtained by shaping the waveform of the detection light. Shows the time. The configuration shown in FIG. 9 includes a waveform shaper 901, a waveform shaper 902, a subtracter 903, and an integrator 904.
[0055]
The signal b is delayed by the delay circuit 401 and input to the waveform shaper 901. The waveform is shaped and input to the subtractor 903 as the signal e shown in FIG. The signal e indicates the detection time width T1 of the detection light P1. On the other hand, the signal d is waveform-shaped by the waveform shaper 902 to become a signal n shown in FIG. The signal n is input to the subtractor 903 as a signal indicating the detection time width T2 of the detection light P2. The subtracter 903 subtracts the signal n from the signal e to generate a signal f shown in FIG. The signal f represents T1−T2 which is a difference in detection time width.
[0056]
The signal f is input to the integrator 904 and is time-integrated to become a signal g shown in FIG. The signal g is a signal having an intensity proportional to the detection time width difference T1-T2. This intensity becomes an error signal, that is, a tracking signal. The integrator 904 is adjusted (reset) so that the integration constant becomes 0 before time integration of the signal f.
[0057]
The recording / reproducing apparatus of the first embodiment operates as described above and detects a tracking error signal based on T1−T2 which is a difference in detection time width. Then, a recording mark 105 is recorded on the data recording layer 102 on the optical disc while controlling a probe driving unit such as a pickup actuator so that the detected tracking error signal becomes zero.
[0058]
The configuration described above can detect a tracking error regardless of the intensity of the detection light when the laser light detects the tracking mark. For this reason, for example, even when the spot 501 having a small diameter is scanned with respect to the wobble tracking mark shown in FIG. 5, the time (detection time) when the spot 501 scans the tracking mark m1 and the tracking mark m2 are scanned. The tracking error can be accurately detected by changing the time to perform.
[0059]
FIG. 11 is a diagram illustrating a servo signal detection device 1101 that is another configuration example of the servo signal detection device 303. FIGS. 12A to 12D are diagrams for explaining signals processed in the servo signal detection device 1101. The signal shown in FIG. 12 is obtained when the wobble tracking mark formed by the tracking mark m1 and the tracking mark m2 shown in FIG. 5 is scanned with the spot 501, and the course at the time of scanning is shifted from the track center Tc. . The vertical axis of FIG. 12 shows the intensity of the detection light in (a), and shows the intensity of the signal obtained by shaping the waveform of the detection light in (b) to (d). Moreover, the horizontal axis of FIG. 12 has shown time in any of (a)-(d).
[0060]
A servo signal detection device 1101 in FIG. 11 includes a waveform shaper 1102, a polarity switch 1103, an integrator 1104, and a switch 1105. The laser light L emitted from the laser light source 301 is applied to the optical disk 304 to generate reflected light L ′. The reflected light L ′ is detected by the photodetector 302 and input to the servo signal detection device 1101 as a signal a.
[0061]
The signal a shown in FIG. 12A is input to the waveform shaper 1102 and shaped as shown in FIG. The signal i is branched immediately before the polarity switch 1103, one is input to the polarity switch 1103, and the other is directed to the switch 1105. The switch 1105 is connected to the terminal 1105a until the detection light P1 in the signal i is input to the integrator 1104. Then, the detection light P2 is switched to the terminal 1105b at the timing when it is input to the integrator 1104. By this switching, the signal j input to the integrator 1104 is in a state where the polarity of only the signal corresponding to the detection light P2 is inverted as shown in FIG.
[0062]
The signal j is time-integrated by the integrator 1104 to become a signal k shown in FIG. A signal corresponding to a difference between a time width T1 of the signal corresponding to the detection light P1 and a time width T2 of the signal corresponding to the detection light P2 in the signal k is output to the outside as a tracking signal or a tracking error signal.
[0063]
The servo signal detection device 1101 described above can detect the tracking error regardless of the intensity of the detection light when the tracking mark is detected, similarly to the servo signal detection device 303. For this reason, for example, even when the spot 501 having a small diameter is scanned with respect to the wobble tracking mark shown in FIG. 5, the time (detection time) when the spot 501 scans the tracking mark m1 and the tracking mark m2 are scanned. The tracking error can be accurately detected by changing the time to perform. Note that the integrator 1104 shown in FIG. 11 also needs to be reset before time integration of the signal.
[0064]
Next, the recording / reproducing method of Embodiment 1 will be described. FIG. 13 is a flowchart for explaining the tracking process in the recording / reproducing method of the present embodiment. In the illustrated flowchart, first, the photodetector detects the detection light P1 (step S1301). Subsequently, the detection light P2 is detected (step S1302). Next, the servo signal detection device obtains T1-T2 by subtracting the detection time width T2 of the detection light P2 from the detection time width T1 of the detection light P1 (step S1303). Then, the obtained T1-T2 is time integrated (step S1304), and a tracking signal based on the integrated value of T1-T2 is detected (step S1305).
[0065]
According to the recording / reproducing method of Embodiment 1, it is determined from the detected tracking signal whether there is a tracking error (step S1306). As a result of the determination, if a tracking signal other than 0 is generated, that is, it is determined that there is a tracking error (S1306: Yes), the tracking error is corrected by adjusting the pickup that drives the probe (step S1307). If it is determined in step S1306 that there is no tracking error (S1306: No), the process returns to step S1301 to detect the detection light P1.
[0066]
The recording / reproducing method for the optical disc described above is realized by executing a program prepared in advance on a computer such as a personal computer or a workstation. This program is recorded on a computer-readable recording medium such as a hard disk, floppy disk, CD-ROM, MO, or DVD, and is executed by being read from the recording medium by the computer. The program can be distributed via the recording medium and as a transmission medium via a network such as the Internet.
[0067]
Further, the first embodiment described above is not limited to the configuration described above. That is, in the first embodiment, data is recorded on the optical disc provided with the wobble tracking mark shown in FIG. However, the recording / reproducing apparatus of the present invention is not limited to recording data on the optical disk of FIG. Hereinafter, another example of an optical disk that can record data with the recording / reproducing apparatus of the first embodiment will be described.
[0068]
FIG. 14 is a diagram for explaining another example of the optical disc applicable to the recording / reproducing apparatus of the first embodiment, and is a diagram for explaining a wobble tracking mark of the optical disc. The wobble tracking mark shown in FIG. 14 has a tracking mark pair in which m1 'and m2' are paired and a tracking mark pair in which m3 'and m4' are paired. Each tracking mark pair is formed by shifting the tracking mark for each track (track of the track center Tc1, track of the track center Tc2). For this reason, the track pitch Tp 'is set to be larger than the track pitch Tp shown in FIG. Can be narrowed. For example, when the diameter of the wobble tracking mark is 0.8 μm, the minimum track pitch has been 1.6 μm in the past, whereas according to the example shown in FIG. In this case, a track pitch of 1.8 μm corresponding to the tracking mark diameter can be realized.
[0069]
FIG. 15 is a diagram for explaining another example of the optical disc applicable to the recording / reproducing apparatus of the first embodiment. FIGS. 16A and 16B are diagrams for explaining detection light obtained from the optical disc shown in FIG. The optical disk shown in FIG. 15 has a clock tracking mark area separately from a servo area in which wobble tracking marks made up of tracking marks m8 and m9 are formed. In the clock tracking mark region, tracking marks m5 to m7 are formed with the track center Tc as the center. Both the servo area and the clock tracking mark area are provided between the data areas.
[0070]
FIGS. 16A and 16B are diagrams illustrating detection light obtained from the tracking marks m5 to m9 shown in FIG. The vertical axis in FIG. 16 indicates the intensity of the detection light, and the horizontal axis indicates time. FIG. 16A shows detection light detected when the spot 1501 moves out of the track center Tc. FIG. 16B shows detection light when the spot 1501 moves on the track center Tc. The detected light is shown.
[0071]
The detection light P5 in FIG. 16 is detection light obtained from the tracking mark m5. The detection light P6 is obtained from the tracking mark m6, the detection light P7 is obtained from the tracking mark m7, the detection light P8 is obtained from the tracking mark m8, and the detection light P9 is obtained from the tracking mark m9. From the clock tracking mark area shown in FIG. 15, a clock signal necessary for writing data can be obtained. Therefore, both the tracking signal and the clock signal can be obtained from the tracking mark shown in FIG.
[0072]
  In addition,FIG.The wobble tracking mark shown in (2) can be formed at a position where the distance between the paired tracking marks in the optical disc track direction and the distance between the adjacent tracking marks on the adjacent tracks in the optical disc track direction are equal.FIG.Place the tracking mark asLightThe disk will be described in detail in the second embodiment.
[0073]
Furthermore, the recording / reproducing apparatus of the first embodiment uses a probe with a sharpened tip of the fiber to generate near-field light. However, as a configuration for generating near-field light, a head or slider may be provided with a minute opening, and the near-field light may be generated by passing light through the minute opening. In the first embodiment, the laser light is incident on the optical disk from the substrate side. However, the laser light may be incident on the back surface (optical disk surface) with respect to the substrate. The first embodiment is not limited to the configuration in which laser light is used as near-field light, but can also be applied to a configuration in which recording and reproduction of an optical disk is performed using general beam-shaped laser light.
[0074]
Further, the first embodiment uses a phase change material for the data recording layer of the applied optical disc. However, the optical disc applied to the recording / reproducing apparatus of the first embodiment uses a phase change material for the data recording layer. It is not limited to what was used, What is necessary is just to produce a contrast in transmitted light or reflected light by irradiation of laser light. In addition, the contrast here includes a contrast caused by a change in optical constant such as a rotation of a polarization plane or a change in birefringence in addition to a difference in light intensity due to a change in absorbance or reflectance. As materials other than the phase change material used for the data recording layer, there are a magneto-optical material and a material exhibiting an electro-optic effect.
[0075]
(Embodiment 2)
Next, a second embodiment of the present invention will be described. Embodiment 2 is an embodiment of the optical disc of the present invention. The optical disk shown in the figure has almost the same layer structure as the optical disk of the first embodiment described above.
[0076]
FIG. 17 is a cross-sectional view of an optical disc for explaining the layer structure of the optical disc of the second embodiment. The optical disc according to the second embodiment includes a SiN protective layer 1701, a SiN protective layer 1703, a data recording layer 1702, and a polycarbonate substrate 1704. In each of the above layers, the SiN protective layers 1701 and 1703 are laminated to 20 nm, and the data recording layer 1702 is laminated to 15 nm. Lamination is performed by vapor deposition. In the figure, L represents laser light, and L ″ represents near-field light. The data recording layer 1702 of Embodiment 2 is a phase change layer made of a phase change material.
[0077]
FIG. 18 is a diagram for explaining the tracking marks of the optical disc according to the second embodiment. In the optical disc according to the second embodiment, a plurality of tracks are formed in the servo area of the data recording layer 1702. Since the track is formed along the circumferential direction of the optical disk, the direction of the track is shown in the drawing along with the radial direction of the optical disk as the circumferential direction of the optical disk.
[0078]
In the drawing, the track center of the track is Tc1, and the track center Tc2 of the track adjacent to the track centered on the track center Tc1 is shown. The first tracking mark m1 and the second tracking mark m2 are formed on the track of the track center Tc1, and the first tracking mark m3 and the second tracking mark m4 are formed on the track center Tc2. Has been.
[0079]
  The tracking mark m1 and the tracking mark m2 are formed at a certain distance d1 in the circumferential direction of the optical disc, and form a tracking mark pair. Similarly, in adjacent tracks, the tracking mark m3 and the tracking mark m4 form a tracking mark pair. Tracking mark pairTheOptical disc between racking mark m1 and tracking mark m3ZhouDirection distance d3, optical disc between tracking mark m2 and tracking mark m4ZhouThe direction distance d2 is equal to the distance d1. In the second embodiment, as shown in the figure, the distance between the tracking marks is the distance between the centers of the tracking marks.
[0080]
  By forming a wobble tracking mark as shown in FIG.The figureThe servo area can be made narrower than the servo area shown in FIG. 14, and the data recording area can be made wider. Therefore, the second embodiment has an effect that the storage capacity of the optical disk can be increased.
[0081]
When a phase change material is used for the data recording layer of the optical disc according to the second embodiment, the phase change material is, for example, Ge.₂Sb₂Te_FiveIt is conceivable to use AgInSbTe. Ge for data recording layer₂Sb₂Te_FiveFIG. 19 shows the optical disk of the second embodiment using a thin film, and FIG. 20 shows the optical disk of the second embodiment using an AgInSbTe thin film as a data recording layer. The optical disk of Embodiment 2 shown in FIG.₂Sb₂Te_FiveA recording mark 2005 is formed on the thin film 1902, and the recording mark 2005 is formed on the AgInSbTe thin film 2002 in the optical disc of the second embodiment shown in FIG.
[0082]
Incidentally, the wobble tracking mark shown in FIG. 18 needs to have a wide servo area for recording the entire tracking mark because the tracking mark of each track is shifted in the track direction (indicated by r in the figure) as shown in FIG. May occur. In order to eliminate the need for a wide servo area with the configuration shown in FIG. 18, the second embodiment can also be configured as shown in FIG.
[0083]
In the servo area shown in FIG. 22, a series of wobble tracking mark groups is formed for every appropriate number of tracks (6 in FIG. 22), the head tracking mark m1 of the adjacent track group M1, and the head of the track group M2. The tracking mark m2 is formed so as to match. By forming in this way, it is possible to prevent the tracking mark from being shifted in the radial direction of the optical disc and the servo area from being widened.
[0084]
In the case where the wobble tracking mark is formed as shown in FIG. 22, when the position of the track is roughly detected, only a specific tracking mark (for example, the first tracking mark) included in each track group may be sequentially detected. For this reason, the wobble tracking mark in FIG. 22 can easily and rapidly detect position information when the head or slider is moved in the radial direction of the optical disk.
[0085]
An appropriate number of tracks included in one track group is geometrically determined by the track pitch and the diameter of the wobble tracking mark. When twice the track pitch is the diameter of the wobble tracking mark, 6 to 8 is the appropriate number of tracks included in one track group. In particular, when the number of tracks is set to 8, binaries can be easily handled by a computer, and the number of tracks and their addresses can be set without excess or deficiency.
[0086]
(Embodiment 3)
Next, the optical disk of Embodiment 3 will be described. The optical disc of the third embodiment has the same layer structure as the optical disc of the second embodiment. For this reason, in the third embodiment, illustration and description of the same configuration as the optical disk of the second embodiment are omitted.
[0087]
FIG. 23 is a diagram for explaining the optical disc of the third embodiment. The illustrated optical disc includes a groove G for each predetermined number of tracks, and includes an area where a wobble tracking mark is formed on a land R of the groove G, that is, a servo area. In the optical disk according to the third embodiment, the diffracted light generated in the groove G can be detected by the two-divided photodiode provided in the recording / reproducing apparatus, and the tracking error can be detected by the output difference of the photodiode. According to the third embodiment, a push-pull signal can be obtained from a groove in addition to a signal obtained by sample-serving a tracking mark. Therefore, for example, the tracking error can be detected more reliably than when the tracking error is detected using only the wobble tracking mark as in the optical disc of the second embodiment.
[0088]
(Embodiment 4)
Next, the optical disk of Embodiment 4 will be described. The optical disk according to the fourth embodiment may be applied to any of the tracking marks of the optical disk described in the first embodiment, the optical disk according to the second embodiment, and the optical disk according to the third embodiment. For this reason, in the fourth embodiment, only the layer structure of the optical disk of the fourth embodiment will be described, and the description of the tracking marks will be omitted.
[0089]
FIG. 24 is a diagram for explaining the optical disc of the fourth embodiment. The illustrated optical disc further includes a nonlinear optical material layer in addition to the optical discs of the second and third embodiments described above, and the nonlinear optical layer is a laser in which only the irradiated portion that is irradiated with light is transparent. The light L is transmitted and the transmission term is changed to near-field light.
[0090]
That is, the optical disc shown in FIG. 24 includes a polycarbonate substrate 2401, a SiN protective layer 2402, a SiN protective layer 2404, a SiN protective layer 2406, a data recording layer 2405, and an Sb mask layer 2403 that is a nonlinear optical material layer. Yes. The data recording layer 2405 of Embodiment 4 is a phase change layer made of a phase change material. The Sb mask layer 2403 transmits only the laser light L collected by the condensing lens 2407 and makes the transmission term near-field light L ″ by making only the irradiated portion transparent to light transparent. . In each of the above layers, the SiN protective layers 2404 and 2406 are stacked to 20 nm, the data recording layer 2405 is 15 nm, the Sb mask layer 2403 is 15 nm, and the SiN protective layer 2402 is stacked to 17 nm. In addition, all lamination | stacking is made | formed by vapor deposition.
[0091]
In the optical disk of Embodiment 4, the laser beam L collected by the condenser lens 2407 is incident from the polycarbonate substrate 2401 side during recording. The laser light L is focused on the Sb mask layer 2403, and the region corresponding to the power of the laser light L is made transparent. The transparent portion becomes a minute opening and transmits the laser light L. The transmitted laser light L becomes near-field light L ″ and oozes out to the data recording layer 2405 to form a recording mark 2408 smaller than the diffraction limit of the light.
[0092]
In the fourth embodiment described above, the laser light emitted from the recording / reproducing apparatus can be converted into near-field light on the optical disc side. For this reason, the optical disc of Embodiment 4 can form a recording mark having a size smaller than the diffraction limit of the laser beam by using a recording / reproducing apparatus that is not configured to generate near-field light.
[0093]
In addition, as a data recording layer of the optical disk of Embodiment 4, for example, Ge₂Sb₂Te_FiveA thin film or an AgInSbTe thin film can be used. FIG. 25 shows that the data recording layer is formed of Ge.₂Sb₂Te_FiveIt is a diagram showing an example in which a recording mark 2508 is formed as a thin film 2505. FIG. 26 is a diagram showing an example in which the data recording layer is an AgInSbTe thin film 2605 and a recording mark 2608 is formed.
[0098]
【The invention's effect】
  As described above, according to the first aspect of the present invention, the servo area can be narrowed and the data recording area can be widened. For this reason, the recording density of the optical recording medium can be further increased. Also, the first tracking mark of the tracking mark pairAnd secondTwo tracking marks are used so that the distance from the track in the radial direction of the optical recording medium is equal.Located on the track center of the optical disc and shifted in opposite directions in the radial direction of the optical recording medium with respect to the track center.PlacedIn addition, the fixed distance between the first tracking mark and the second tracking mark constituting the tracking mark pair is the first tracking mark and the first tracking mark on the track adjacent to the track on which the first tracking mark is formed. Equal to the distance in the circumferential direction of the optical recording medium and equal to the distance in the circumferential direction of the second tracking mark and the second tracking mark on the adjacent track.Thus, by obtaining a tracking signal according to the time width during which reflected light from the tracking mark pair is detected, data is recorded on the optical recording medium using the near-field effect of light or the pseudo near-field effect. Accurate tracking signal can be obtained during playbackAt the same time, it is possible to prevent crosstalk while shortening the distance between tracking mark pairs for tracking.Therefore, data can be recorded on the optical recording medium at a high density, and the recorded data can be reproduced. In addition, the recording density of the optical recording medium can be increased to speed up access to the optical recording medium, and an optical recording medium capable of high recording density and high speed access can be provided.
[0099]
  Claim2In the invention described in (1), the irradiated laser light can be converted into near-field light by an optical recording medium. For this reason, even if a recording / reproducing apparatus that cannot generate near-field light is used, a mark having a size smaller than the diffraction limit of light can be formed by the near-field light to increase the data recording density on the optical recording medium. The recording medium can be provided.
[0101]
  Claim3The present invention provides an optical recording medium capable of positioning a track with higher accuracy and recording and erasing data at a high density while using a recording / reproducing apparatus equipped with an existing optical system. There is an effect that can be done.
[0102]
  Claim4The invention described in 1) provides an effect that it is possible to provide an optical recording medium capable of positioning a track with higher accuracy and recording data at a high density while using a recording / reproducing apparatus having an existing optical system. .
[0103]
  Claim5The invention described in (1) can position a track with higher accuracy while using a recording / reproducing apparatus having an existing optical system, and can record, append, or redraw data at a high density. In addition, the sensitivity of the data recording layer can be increased, and marks can be recorded and erased reliably. Furthermore, there is an effect that it is possible to provide an optical recording medium capable of obtaining a sharp signal at the boundary between a recording mark and an unrecorded portion.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining a layer structure of an optical disc applied to a recording / reproducing apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a diagram showing a servo area of the optical disc shown in FIG.
FIG. 3 is a diagram for explaining a recording / reproducing apparatus according to Embodiment 1 of the present invention;
4 is a diagram for explaining in more detail the configuration of the servo signal detection device shown in FIG. 3; FIG.
FIG. 5 is a diagram showing a state where a laser beam is scanned with near-field light on a wobble tracking mark.
6 is a diagram for explaining detection light obtained by tracking performed in the state shown in FIG. 5; FIG.
FIG. 7 is a diagram for explaining a difference in peak width from which a tracking signal can be acquired.
FIG. 8 is a diagram for explaining processing performed in a pulse width comparator;
FIG. 9 is a diagram for explaining a configuration for calculating a difference in detection time width in a pulse comparator.
FIG. 10 is a diagram for explaining signals processed in FIG. 9;
11 is a diagram for explaining another configuration example of the servo signal detection circuit in FIG. 3; FIG.
12 is a diagram for explaining signals processed in a servo signal detection circuit in FIG. 11; FIG.
FIG. 13 is a flowchart for explaining tracking processing in the recording / reproducing method according to Embodiment 1 of the present invention;
FIG. 14 is a diagram for explaining another example of an optical disc that can be applied to the recording / reproducing apparatus in the first embodiment of the invention.
FIG. 15 is a diagram for explaining another example of an optical disc that can be applied to the recording / reproducing apparatus in the first embodiment of the invention;
16 is a diagram for explaining detection light obtained from the optical disk shown in FIG. 15;
FIG. 17 is a diagram for explaining a layer structure of an optical disc according to a second embodiment of the present invention.
FIG. 18 is a diagram for explaining tracking marks of the optical disc according to the second embodiment of the present invention.
FIG. 19 is a diagram for explaining another configuration example of the optical disc according to the second embodiment of the present invention.
FIG. 20 is a diagram for explaining another configuration example of the optical disc according to the second embodiment of the present invention.
FIG. 21 is a diagram for explaining points to be improved in the wobble tracking mark shown in FIG. 18;
FIG. 22 is a diagram for explaining a configuration example of a servo area of the optical disc according to the second embodiment.
FIG. 23 is a diagram for explaining an optical disc according to a third embodiment of the present invention.
FIG. 24 is a diagram for explaining an optical disc according to a fourth embodiment of the present invention.
FIG. 25 is a diagram for explaining another configuration of the optical disc according to the fourth embodiment of the present invention.
FIG. 26 is a diagram for explaining another configuration of the optical disc according to the fourth embodiment of the present invention.
FIG. 27 is a diagram for explaining a conventional method for detecting a tracking error.
FIG. 28 is a view for explaining detection light obtained by irradiating the wobble tracking mark shown in FIG. 27 with laser light.
FIG. 29 is a diagram for explaining a conventional wobble tracking mark.
FIG. 30 is a diagram for explaining a problem when a tracking error is detected from the wobble tracking mark shown in FIG. 29;
FIG. 31 is another diagram for explaining a problem when a tracking error is detected from the wobble tracking mark shown in FIG. 29;
[Explanation of symbols]
101, 103, 1701, 1703, 2402, 2404 2406, SiN protective layer
102, 1702, 2405 Data recording layer
104, 1704, 2401 Polycarbonate board
1902, 2505 Ge₂Sb₂Te_FiveThin film
2002, 2605 AgInSbTe thin film
2403 Sb mask layer
2407 Condensing lens
301 Laser light source
302 Photodetector
303, 1101 Servo signal detection device
304 optical disc
401 delay circuit
402 Pulse width comparator
901, 902, 1102 Waveform shaper
903 subtractor
904, 1104 integrator
1101 Servo signal detection device
1103 Polarity switch
1105 switch

Claims (5)

A recording layer;
A plurality of tracks provided in the recording layer;
On the track, a circular first tracking mark having a size including a spot when the laser beam is scanned with near-field light, and a predetermined distance from the first tracking mark in the circumferential direction of the optical recording medium. And a tracking mark pair having a circular second tracking mark having a size including a spot when the laser beam is scanned with near-field light,
The first tracking mark and the second tracking mark are positioned on the track center of the track so that the distances in the radial direction of the optical recording medium from the track are equal to each other, and the optical recording medium with respect to the track center. An optical recording medium that is arranged to be shifted in the opposite direction in the radial direction and that has the constant distance between the first tracking mark and the first tracking mark on the track adjacent to the track on which the first tracking mark is formed. rather equal to the circumferential direction of the distance, and the second tracking marks, characterized in that equal to the distance of the optical recording medium circumferential direction of the second tracking marks on the adjacent tracks optical recording medium. Furthermore, a nonlinear optical material layer is provided,
2. The optical recording medium according to claim 1, wherein the nonlinear optical layer is transparent only at a portion to be irradiated that is irradiated with light , transmits the light, and converts the transmitted light into near-field light.   The optical recording medium according to claim 1, wherein the recording layer is made of a phase change material. The optical recording medium according to claim 1, wherein the recording layer is a Ge ₂ Sb ₂ Te ₅ thin film.   The optical recording medium according to claim 1, wherein the recording layer is an AgInSbTe thin film.

Images