JP2002352443A - Optical data storage medium and optical recording-and- reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical data storage medium and an optical recording- and-reproducing device which can obtain a tracking signal accurately and quantitatively, record data with high density and reproduce the recorded data. SOLUTION: In the optical data storage medium, clock tracking marks for obtaining clock signals are provided at a prescribed interval in a track center, and a pair of wobble tracking marks for obtaining tracking error signals are arranged with a prescribed deviation in distance from the track center and with a prescribed deviation in distance in the direction of the track.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical recording medium.

[0002]

2. Description of the Related Art As one of recording media for recording data, there is an optical recording medium (optical disk) for recording data using light and reproducing the recorded data. As a typical example of an optical disk, an optical disk using a thin film of an amorphous alloy composed of a rare earth metal and a transition metal for a recording layer is given. When data is recorded on this optical disk, the optical disk is irradiated with light 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 its magnetization direction changes to become a recording mark.

The above-mentioned light is a laser light emitted from a semiconductor laser or the like. The laser light is condensed by the lens optical system and becomes a spot light, which is applied to the recording layer. The laser beam can form a smaller recording mark as the spot diameter is smaller. Therefore, in recording data on the optical disk, the spot diameter of the laser beam is an important parameter that determines the recording density of the optical disk.

[0004] The spot diameter of the laser beam cannot be made smaller than the wavelength of the laser beam due to the diffraction limit of the light. In recent years, near-field light has been used for recording and reproduction of optical discs in order to increase the recording density of optical discs by reducing the spot diameter of laser light. As an example in which near-field light is used for recording and reproduction of an optical disk, an optical fiber with a processed tip is mounted on a precision actuator driven by a piezoelectric element, and while controlling the position, a recording mark having a diameter of 60 nm is formed in platinum / optical disk.
An experiment has been reported in which recording was performed on a cobalt multilayer film and this recorded mark was reproduced. The probe used in the experiment was processed into a cone-shaped tip, and was coated with metal except for a region of several tens of nm of the processed tip (Appl.
ied Physics Letters, Vol.62, No.2, pp.142-144, 199
2).

Some conventional optical disks have a non-linear optical material layer made of a non-linear optical material on the substrate side of the recording layer. An optical disk having a non-linear optical material layer records data on the recording layer by irradiating the recording layer with light from the substrate side (non-linear optical material layer side). At this time, the non-linear optical material layer becomes a small opening through which light is transmitted only at the portion irradiated with the light. Therefore, the light that has passed through the opening becomes near-field light and can form a smaller spot diameter on the spot light recording layer (Applied
Physics Letters, Vol. 73, No. 15, pp. 2078-2080, 199
8). In this specification, such a configuration is also expressed as using a non-linear optical material as a mask.

[0006] The experiments described in the above-mentioned documents are as follows.
A SiN protective layer on a polycarbonate optical disc substrate,
The recording was performed using an optical disk laminated by depositing a recording layer of Ge ₂ Sb ₂ Te ₅ thin film and a protective layer of Sb. This experiment reports that a recording mark having a diameter of 90 nm was formed by irradiating a laser beam from the substrate side.

A recording / reproducing apparatus (recording / reproducing apparatus) for recording data on an optical disc or reproducing data recorded on the optical disc requires a laser beam spot diameter for accurately scanning a laser beam on a track of the optical disc. Is detected to be off the center of the track. The detection is performed by irradiating the laser beam onto the tracking mark on the optical disk and detecting a signal based on the reflected light. The deviation of the laser beam from the center of the track is called a tracking error, and the tracking error is detected by a tracking signal. In this specification, a signal indicating occurrence of a tracking error among tracking signals is particularly referred to as a tracking error signal.

A typical method for checking a tracking error is a sample servo method. The sample servo method is a method applied to an optical disk in which a sample servo area (hereinafter, simply referred to as a servo area) is discretely provided on a track and a pair of tracking marks is provided in the servo area. The pair of tracks is formed so as to be shifted from the track center by the same distance in the radial direction of the optical disc. Such a tracking mark is called a wobble tracking mark.

A tracking error for a wobble tracking mark is checked by a so-called operation push-pull method (far-field method). Specifically, light is applied to each of the two tracking marks forming the wobble tracking mark, the difference in the light intensity of the light reflected by each tracking mark is obtained, and the obtained value is used as a tracking signal. Further, in the operation push-pull method, the laser light is servoed in the radial direction of the optical disk so that a tracking signal obtained in a region where there is no wobble tracking mark becomes 0 in the sample and hold circuit (optical disk technology, Radio Technology, 1990). ).

FIG. 32 is a diagram for explaining a method of detecting the tracking error described above, and shows a servo area where a wobble tracking mark is formed. In FIG. 32, the tracking mark m1 and the tracking mark m2 of the wobble tracking marks are 1/1 from the track center Tc in the radial direction of the optical disk.
There is a 4 track pitch shift.

FIG. 33 is a diagram showing reflected light (referred to as detected light) detected by irradiating the wobble tracking mark shown in FIG. 32 with laser light. The vertical axis represents the intensity of the detected light, and the horizontal axis represents the intensity. Shows the detection time of the detection light. Further, P1 in the drawing indicates the detection light obtained from the tracking mark m1, and P2 indicates the detection light obtained from the tracking mark m2. When the laser beam scans the tracking mark through a course Tc ′ deviated from the track center Tc, a difference in detected light intensity occurs between P1 and P2 as shown in FIG. At this time, the tracking signal is
It 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.

Conventionally, as shown in FIG. 34, when a plurality of recording mark rows are written in one groove, a wobble tracking mark larger than the recording mark for actually writing data is written in the track pitch of the mark row. The sample servo is applied.

[0013]

However, when not only data recording on an optical disc but also near field light is applied to various fields, a probe manufactured by sharpening the tip of an optical fiber is used. When data is recorded 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 periodically fluctuates due to the eccentricity of the optical disk, making control difficult. May occur.

Further, in the above-mentioned prior art, since a precision actuator is used for driving the probe, the scanning speed and the scanning range are limited, and it is difficult to record and reproduce data at high speed. is there.

When recording and reproducing data on an optical disk using a non-linear optical material as a mask, a general recording and reproducing apparatus can be used. In this case, the optical disc is provided with the same land and groove as the conventional one, and the data is recorded and reproduced using the near-field light generated at the 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 experiment described above, the track pitch was 1.2 μm.
m, the recording density in the radial direction is the same as when no near-field light is used. Further, when a tracking error is detected with respect to the wobble tracking mark shown in FIG. 32 by a recording / reproducing apparatus capable of irradiating near-field light, the following problem occurs.

FIG. 35 is a diagram for explaining a problem that occurs when the wobble tracking mark shown in FIG. 32 is scanned using near-field light. FIG. 36 is similar to FIG.
FIG. 7 is a diagram for explaining detection light obtained by tracking performed in the state illustrated in FIG. 5. That is, even when the near-field light scans the tracking mark m1 and the tracking mark m2 through the course Tc 'shifted from the track center Tc as shown in FIG. Mark m2
Will be hit. Therefore, as shown in FIG.
The detection light obtained from the tracking mark m1 and the tracking mark m2 shows almost the same detection light intensity h even though the laser light scans on a course shifted from the track center Tc.

When track control is performed so that the detection signals have the same peak value, an accurate tracking signal cannot be obtained because the difference in the intensity of the detection signals is not clear. In addition, since the spot diameter is small, the amount of the entire detection light is small, and there is a disadvantage that the difference in intensity between the portion where the wobble tracking mark is formed and the portion where the wobble tracking mark is not formed is not clear. Further, there is also a problem that the influence of noise is large because the difference in the intensity of the detection signal is small, and the error increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended for use in recording / reproducing data on / from an optical recording medium using a near-field effect of light or a pseudo near-field effect. It is an object of the present invention to provide an optical recording medium and a recording / reproducing apparatus capable of acquiring a tracking signal accurately and quantitatively, recording data at a high density, and reproducing the recorded data.

Another object of the present invention is to provide an optical recording medium and a recording / reproducing apparatus capable of detecting a tracking shift amount of a light beam based on a tracking signal and obtaining more detailed information on tracking.

[0020]

[MEANS FOR SOLVING THE PROBLEMS] To solve the above-mentioned problems,
In order to achieve the object, according to the first aspect of the present invention, in an optical recording medium for recording information, a plurality of clock tracking marks for obtaining a clock signal are provided at a track center at a predetermined distance, and a tracking error signal is obtained. For this purpose, a pair of wobble tracking marks are provided so as to be shifted from the track center by a predetermined length and shifted by a predetermined distance in the track direction.

According to a second aspect of the present invention, the wobble tracking mark has a wedge-shaped shape, and a tip of the wedge-shaped shape is perpendicular to the track center and crosses the track center by a predetermined length. . In the invention according to claim 3, the wobble tracking mark is provided subsequent to the clock tracking mark.

According to a fourth aspect of the present invention, the wobble tracking mark provided at a predetermined length is
A wobble tracking mark provided on an adjacent track is shifted in the track direction by a distance equal to the predetermined length. In the invention according to claim 5, the predetermined distance at which the clock tracking mark is arranged is equal to the predetermined length at which the wobble tracking mark is arranged.

In the invention according to claim 6, the clock tracking mark has a rectangular shape. In a seventh aspect of the present invention, the clock tracking mark has a rectangular shape crossing a plurality of adjacent tracks vertically.

According to the present invention, a groove is provided for each of a fixed number of tracks, and the wobble tracking mark is provided on a land portion of the groove area. In the invention according to claim 9, the recording layer of the optical recording medium is a phase change type recording layer.

In the tenth aspect, the recording layer of the phase change type is a Ge ₂ Sb ₂ Te ₅ thin film. In the eleventh aspect, the phase change type recording layer is made of Ag
An InSb thin film is used. According to a twelfth aspect of the present invention, a nonlinear optical material layer is provided on the optical recording medium, and near-field light is generated using the nonlinear optical material layer as a mask.

According to a thirteenth aspect of the present invention, there is provided a recording / reproducing apparatus for recording / reproducing information on / from the optical recording medium according to any one of the first to twelfth aspects, wherein Clock generation means for generating a signal; tracking error generation means for generating a tracking error from a detection time difference of reflected light from the pair of wobble tracking marks;
Is provided.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an optical recording medium and a recording / reproducing apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

(Embodiment 1) In Embodiment 1 of the present invention, an optical recording medium (optical disc) of the present invention will be described first. FIG. 1 is a view for explaining the optical disc of the first embodiment, and is a cross-sectional view for explaining a layer structure of the optical disc. The illustrated optical disk is an optical disk on which data is optically recorded and reproduced. Further, a polycarbonate substrate 104, a SiN protective layer 101, a SiN protective layer 103, and a data recording layer 102 are provided. The thickness of each of the SiN protective layers 101 and 103 is 20 n.
m, the thickness of the data recording layer 102 is 15 nm. Si
Both the N protective layer and the data recording layer are formed or deposited by vapor deposition.

A recording and reproducing apparatus according to the first embodiment described below
A near-field probe using a fiber whose tip is sharpened is provided. Then, the data recording layer 102 shown in FIG.
The laser light L is incident on the optical disk from the side as near-field light L ''. A portion of the data recording layer 102 irradiated with light becomes a recording mark 105. Data recording layer 102
May be used as long as contrast is generated in transmitted light or reflected light by irradiation with laser light. The contrast here includes not only a difference in light intensity due to a change in absorbance or reflectance, but also a contrast caused by a change in an optical constant such as rotation of a polarization plane or a change in birefringence.
Materials used for the data recording layer include a magneto-optical material and a material exhibiting an electro-optical effect.

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 the optical disk as propagation light L ′ ″ from the polycarbonate substrate 104. Near-field light L ''
Can form a recording mark 105 of the following size limited by the diffraction limit of light on the data recording layer 102.

Data (address information) necessary for forming the recording mark 105 is discretely recorded in an area for recording data to be recorded on the optical disk.
The size of a mark formed for recording address information is larger than the size 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.

FIG. 2 is a diagram showing a servo area of the optical disk according to 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 a mark center Mc1, and the center of the tracking mark m2 is denoted by a mark center Mc2. Further, Tp shown in the drawing indicates a track pitch. In the track center Tc, data bits db formed for recording data are formed.

The tracking marks forming a pair are arranged in opposite directions 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 １ ／ track pitch.

The second tracking mark m2 paired with the first tracking mark m1 is formed without overlapping at least a part of the first tracking mark m1 on the same track. Then, the first tracking mark m1
Has a wedge-like shape in which the length along the track direction of the optical disc changes at a constant rate with respect to the length along the radial direction of the optical recording medium, and the second tracking mark m2
Has a wedge-like shape obtained by inverting the first tracking mark m1 in the track direction.

Next, a recording / reproducing apparatus for recording or reproducing data on / from the optical disk shown in FIG. 2 will be described.
FIG. 3 is a diagram for explaining the recording and reproducing device according to the first embodiment. The illustrated recording / reproducing apparatus includes a laser light source 301 such as a laser semiconductor for irradiating a laser beam L to an optical disk, and a light detection device for detecting a reflected light L ′ generated by reflecting the irradiated laser beam L on the optical disk 304. Vessel 30
2 and a servo signal detection device 303 that obtains an error signal based on the detection time during which the laser light L is detected. The error signal indicates a tracking error, and the tracking is performed so that the tracking signal becomes zero. When the value of the error signal is not 0, the error signal becomes a tracking error signal.

FIG. 4 is a diagram for explaining the configuration of the servo signal detecting device 303 in more detail. The servo signal detecting device 303 includes a delay circuit 401 and a pulse width comparator 40.
And 2.

Next, the operation of the recording / reproducing apparatus described above will be described. FIG. 5 shows a state in which a wobble tracking mark having a pair of a tracking mark m1 and a tracking mark m2 is scanned by laser light with near-field light. The laser light is shaped into a beam of light (beam light) by an optical mechanism (not shown), and becomes a spot light on the optical disk. The spot of the spot light is shown as a spot 501 in the figure. 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.

As shown in FIG. 5, when the laser beam spot 501 scans over the track center Tc, the detection light P1 is first detected from the tracking mark m1.
Next, the detection light P2 is detected from the tracking mark m2. When the laser beam scans over the track center Tc,
The detection light intensity h of the detection light P1 is equal to the detection light intensity h of the detection light P2, and the detection time width T1 of the detection light P1 is equal to the detection time width T2 of the detection light P2. In this case, the difference between the two becomes zero, and the error signal becomes zero.

FIG. 7 is a diagram showing a case where the spot 501 of the laser beam scans on a course Tc 'shifted from the track center Tc. As shown in FIG. 7, when the laser beam scans a course Tc ′ shifted by Te shifted from the track center Tc, as shown in FIG.
1 is different from the detection time width T2 of the detection light P2. The recording / reproducing apparatus of the first embodiment obtains a tracking signal from the difference in the peak width of the detection light shown in FIG.

In order to obtain the tracking signal, the recording / reproducing apparatus shown in FIG.
1, the signal a generated based on P2 is input to the servo signal detection device 303. The signal a is, as shown in FIG.
The servo signal detection device 303 branches. One of the branched signals a is a signal d and a delay circuit 401
Are input to the pulse width comparator 402 without passing through the other, and one is delayed by the delay circuit 401 and input to the pulse width comparator 402 as a signal b.

FIGS. 9A and 9B show the pulse width comparator 4
10A and 10B are diagrams for explaining the processing performed in step S02, wherein FIG. 10A shows the waveform of the signal b, and FIG. 10B shows the waveform of the signal d. 10A and 10B, the vertical axis indicates the intensity of the detection light, and the horizontal axis indicates the time. Pulse width comparator 4
02, first, a signal d is input. Next, the signal b is input. The pulse width comparator 402 detects the detection light P1 of the signal b.
The difference between the detection time widths of the signal d and the detection light P2 of the signal d is represented by T1-T
It is calculated from the equation (2).

FIG. 10 is a diagram for explaining a configuration in which the pulse width comparator 402 calculates the difference between the detection time widths described above. 11 (a) to 11 (d) are diagrams for explaining the signals processed in FIG. 10, in which the vertical axis represents the intensity of the signal obtained by shaping the waveform of the detection light, and the horizontal axis represents the intensity. Shows the time. The configuration shown in FIG. 10 includes a waveform shaper 1001, a waveform shaper 1002, and a subtractor 1003.
And an integrator 1004.

The signal b is delayed by the delay circuit 401 and input to the waveform shaper 1001, where the waveform is shaped and the signal b is
The signal e shown in FIG. The signal e indicates a detection time width T1 of the detection light P1. On the other hand, the signal d is waveform-shaped by the waveform shaper 1002 to become a signal n shown in FIG. The signal n is a signal indicating the detection time width T2 of the detection light P2,
Enter 3 The subtractor 1003 subtracts the signal n from the signal e to generate a signal f shown in FIG. The signal f represents T1-T2, which is the difference between the detection time widths.

The signal f is input to the integrator 1004 and time-integrated to obtain a signal g shown in FIG. Signal g
Is a signal having an intensity proportional to the difference T1-T2 in the detection time width. This intensity becomes an error signal, that is, a tracking signal. The integrator 1004 is adjusted (reset) so that the integration constant becomes 0 before time-integrating the signal f.

As described above, in the tracking mark of the first embodiment, one tracking mark m1 is formed in a wedge shape, and the second tracking mark m2 is formed on the same track as at least a part of the first tracking mark m1. The first tracking marks are formed in a wedge-like shape without being overlapped and inverted in the radial direction of the optical disc.
For this reason, the signal f shown in FIG. 11C changes in proportion to the degree of the tracking error.

FIG. 12 is a diagram showing the relationship between the signal f and the amount of tracking error (the distance between the position of the spot 501 and the position of the track center Tc). A in FIG.
The straight line indicated by indicates the tracking signal of the optical disc according to the first embodiment, and the curve indicated by B indicates the tracking signal obtained from the conventional tracking mark shown in FIG.

As shown, the straight line A corresponds to the first embodiment.
Indicates that the signal f obtained from the optical disk is proportional to the amount of tracking error. Curve B
According to the graph, it can be seen that the signal f obtained from the conventional optical disk changes rapidly when the amount of tracking error increases. Such a change in the signal B occurs because the spot light deviating from the tracking mark approaches one of the outer peripheral portions of the pair of circular tracking marks.

From the results shown in FIG. 12, the wedge-shaped tracking mark formed on the optical disk of the first embodiment is more stable against track deviation than the conventional circular tracking mark, and has a highly reliable tracking error. It can be said that a signal can be generated. Further, the optical disc of the first embodiment, which can generate a tracking error signal according to the amount of tracking error, can quantitatively detect the tracking error. By performing tracking based on this detection result, it is possible to accurately and stably control the spot to move on the track center Tc using only a linear circuit having a relatively simple configuration.

Further, the above-described configuration can detect a tracking error irrespective 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 scanning time of the spot 501 over the tracking mark m1 (detection time) and the scanning over the tracking mark m2 are detected. The tracking error can be accurately detected by different time periods.

FIG. 13 is a diagram showing a servo signal detecting device 1301 which is another example of the configuration of the servo signal detecting device 303. FIGS. 14A to 14D are diagrams for explaining signals processed in the servo signal detection device 1301. FIG. It should be noted that the signal shown in FIG.
The wobble tracking mark composed of the tracking mark m1 and the tracking mark m2 shown in FIG.
1, and the course at the time of scanning is shifted from the track center Tc. The vertical axis in FIG. 14 shows the intensity of the detection light in (a), and the intensity of the signal obtained by shaping the waveform of the detection light in (b) to (d).
Further, the horizontal axis in FIG. 14 indicates time in any of (a) to (d).

The servo signal detecting device 1301 shown in FIG.
It includes a waveform shaper 1302, a polarity switcher 1303, an integrator 1304, and a switch 1305. The laser light L emitted from the laser light source 301 is
04 to generate reflected light L ′. Reflected light L '
Is detected by the photodetector 302 and the servo signal detection device 1
The signal 301 is input to 301.

The signal a shown in FIG. 14A is input to the waveform shaper 1302, and is shaped as shown in FIG. The signal i is branched just before the polarity switch 1303, one of which is input to the polarity switch 1303 and the other is directed to the switch 1305. The switch 1305 is connected to the terminal 1305a until the detection light P1 of the signal i is input to the integrator 1304. Then, at the timing when the detection light P2 is input to the integrator 1304, the terminal 1305b
Is switched to Due to this switching, the polarity of the signal j input to the integrator 1304 is inverted, as shown in FIG. 14C, only the signal corresponding to the detection light P2.

The signal j is time-integrated by the integrator 1304 to become a signal k shown in FIG. Of the signal k, the signal corresponding to the difference between the time width T1 of the signal corresponding to the detection light P1 and the time width T2 of the signal corresponding to the detection light P2 is output to the outside as a tracking signal or a tracking error signal.

The above-described servo signal detecting device 1301
Can detect a tracking error irrespective of the intensity of detection light when a tracking mark is detected, similarly to the servo signal detection device 303. Thus, for example,
When the spot 501 having a small diameter is scanned with respect to the wobble tracking mark shown in FIG.
Since the scanning time of 01 on the tracking mark m1 (detection time) differs from the scanning time of the tracking mark m2, a tracking error can be accurately detected. Note that the integrator 1304 shown in FIG.
Also needs to be reset before performing the time integration of the signal.

The first embodiment described above is not limited to the above-described configuration. Hereinafter, another example of the optical disc according to the first embodiment will be described. FIG.
FIG. 8 is a diagram for explaining another example of the optical disc of the first embodiment, and is a diagram for explaining wobble tracking marks on the optical disc. The wobble tracking mark shown in FIG. 15 has a tracking mark pair having a pair of m1 ′ and m2 ′ and a tracking mark pair having a pair of m3 ′ and m4 ′. Each tracking mark pair is a track (track of track center Tc1;
The tracking marks are formed so as to be shifted for each track (track of the track center Tc2), so that the track pitch Tp 'can be narrower than the track pitch Tp shown in FIG.

For example, if the diameter of a wobble tracking mark is 0.8 μm, the conventional minimum track pitch is 1.6 μm, whereas according to the example shown in FIG. In the case of 0.9 μm, 1.8 μm corresponding to the tracking mark diameter
Track pitch can be realized.

FIG. 16 is a diagram for explaining another example of the optical disk of the first embodiment. FIG. 17 (a),
FIG. 17B is a diagram for explaining detection light obtained from the optical disc shown in FIG. The optical disk shown in FIG. 16 has a clock tracking mark area separately from a servo area where a wobble tracking mark composed of tracking marks m8 and m9 is formed. The clock tracking mark area includes tracking marks m5 to m
7 is formed around the track center Tc.
The clock tracking mark area is provided before the servo area, and both are provided between the data areas.

FIGS. 17A and 17B are diagrams for explaining detection light obtained from the tracking marks m5 to m9 shown in FIG. The vertical axis of FIG. 16 indicates the intensity of the detection light,
The horizontal axis indicates time. FIG. 17A shows spot 1
Numeral 601 indicates the detection light detected when the spot 1501 is shifted from the track center Tc. FIG. 2B shows the detection light detected when the spot 1501 moves on the track center Tc.

The detection light P5 in FIG. 17 is the detection light obtained from the tracking mark m5. The detection light P6 is from the tracking mark m6, the detection light P7 is from the tracking mark m7, and the detection light P8 is from the tracking mark m6.
8, the detection light P9 is obtained from the tracking mark m9. A clock signal necessary for writing data can be obtained from the clock tracking mark area shown in FIG. Therefore, both the tracking signal and the clock signal can be obtained from the tracking mark shown in FIG.

The wobble tracking mark shown in FIG. 16 is located at a position where the distance between a pair of tracking marks in the optical disk track direction and the distance between adjacent tracking marks on an adjacent track in the optical disk track direction are equal. Can be formed. FIG.
By arranging tracking marks as shown in 6,
The distance between the tracking marks is appropriate to prevent crosstalk of tracking signals between adjacent tracks.

The detection lights P5 to P7 obtained from the clock tracking marks m5 to m7 shown in FIG. 17 are input to the clock generation circuit 600 shown in FIG. 18 to generate a stable clock signal.

The detection lights P5 to P7 are input to the phase comparator 601. Periodic pulses are output from the detection lights P5 to P7, and the frequencies f ₀ and f ₁ (= Mf
Voltage-controlled oscillator 604 generated with ₀ ) as the center frequency
The frequency output from the frequency divider 605 is compared with the frequency (f ₁ / MＭf ₀ ) obtained by dividing the frequency by M, and the comparison result is output to the low-pass filter 602.

The output of the low-pass filter 602 is input to the sample and hold circuit 603. Sample hold circuit 60
In 3, the output of the low-pass filter 602 is output to the voltage controlled oscillator 604 during a period in which the detection lights P5 to P7 are input, and a low level with respect to the detection light P7 during a period until the detection light P5 is input from the detection light P7. The output value of the bandpass filter 602 is held and output to the voltage controlled oscillator 604.

The voltage controlled oscillator 6 thus obtained
Clock signal f output from the ₁Is write and read
Other tracking used for clock signals that serve as time references
As a reference clock signal for detecting
Used for accurate tracking with few errors
Can be made. To obtain a highly accurate clock signal
The number of clock tracking marks is shown in FIG.
Thus, eight or more are desirable.

Although the clock tracking mark shown in FIG. 19 is circular, it may be rectangular as shown in FIG. By making it rectangular, detection light can be obtained at a correct position even if scanning is performed off the track center. In addition, the clock tracking mark may extend over an adjacent track as shown in FIG.

The phase change of the optical disk according to the first embodiment
Ge as the data recording layer_TwoSb _TwoTe_FiveThere is a thin film
Alternatively, an AgInSb thin film can be used. FIG.
Sets the data recording layer 102 of the optical disc shown in FIG.
e_TwoSb_TwoTe_FiveCross section of optical disk with thin film 1802
FIG. According to the optical disc shown in FIG.
High S / N ratio and accurate tracking error signal
Can be obtained. It also increases the sensitivity of the data recording layer.
Therefore, recording and erasing of marks can be performed reliably. In addition,
To obtain a sharp signal at the boundary between the peak and the unrecorded part.
Can be.

FIG. 23 is a diagram showing a cross section of an optical disk in which the data recording layer 102 of the optical disk shown in FIG. 1 has an AgInSb thin film 1902. According to the optical disk shown in FIG. 23, an S / N ratio is high and an accurate tracking error signal can be obtained. As a result, a recording mark having a size equal to or smaller than the size limited by the diffraction limit of light can be accurately formed.

FIG. 24 is a diagram showing a cross section of an optical disk in which the data recording layer 102 of the optical disk shown in FIG. A phase change material is a material that undergoes a phase change (a crystalline phase, an amorphous phase, or the like) by irradiating strong writing light. When a plurality of stable phases can be changed reversibly, it can be used as a RAM, and when it changes irreversibly, it can be used as a write-once recording medium. Further, any material may be used as long as contrast is generated in a plurality of phases in the transmitted light or the reflected light when a weak light for reading is irradiated. The contrast includes not only a difference in light intensity due to a change in absorbance or reflectance but also a contrast caused by a change in an optical constant such as rotation of a polarization plane or a change in birefringence.

Further, the recording / reproducing apparatus of the first embodiment uses a probe having a sharpened fiber tip for generating near-field light. However, as a configuration for generating near-field light, a small opening may be provided in a head or a slider, and near-field light may be generated by passing light through the small opening. In the first embodiment, the laser beam is incident on the optical disk from the substrate side. However, the configuration may be such that the laser beam is incident on the rear surface (the optical disk surface) of the substrate. Further, 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 are performed using general beam-shaped laser light.

(Embodiment 2) Next, an optical disc according to Embodiment 2 of the present invention will be described. The optical disk according to the second embodiment has the same layer structure as the optical disk according to the first embodiment described with reference to FIG. Therefore, in the second embodiment, the description of the layer structure of the optical disc will be omitted.

FIG. 25 is a diagram for explaining tracking marks on the optical disc of 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. In the figure, 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 track of the track center Tc1 is formed with the first tracking mark m1 and the second tracking mark m2, and the track of the track center Tc2 is formed with the first tracking mark m3 and the second tracking mark m4. Have been.

The tracking marks m1 and m2 are formed at a fixed distance d1 in the radial direction of the optical disk and form a tracking mark pair. Similarly, in an adjacent track, the tracking mark m3 and the tracking mark m4 form a tracking mark pair. The tracking mark pairs are discretely arranged on the optical disk, and the radial distance d3 between the tracking mark m1 and the tracking mark m3 in the optical disk direction and the radial distance d2 between the tracking mark m2 and the tracking mark m4 are any of: Is also equal to the distance d1. In the second embodiment, the length of the pitch of the tracking marks is referred to as the distance between the tracking marks as illustrated.

By forming a wobble tracking mark as shown in FIG. 25, the optical disc of the second embodiment can prevent crosstalk of tracking signals between adjacent tracks. Further, the servo area can be made narrower than the servo area shown in FIG. 15, and the data recording area can be made wider. Therefore, the second embodiment can increase the storage capacity of the optical disc.

In the wobble tracking mark shown in FIG. 25, as shown in FIG. 26, the tracking mark of each track is shifted in the track direction (indicated by r in the figure), and the servo area for recording the entire tracking mark is widened. May need to be taken. Embodiment 2 can be configured as shown in FIG. 27 in order to eliminate the need to increase the servo area by the configuration shown in FIG.

In the servo area shown in FIG. 27, a series of wobble tracking marks is formed for each appropriate number of tracks (six in FIG. 27), and the head tracking mark m1 of the adjacent track group M1 and the track group M2
Is formed so as to coincide with the tracking mark m2 which is the head of. By forming in this way, it is possible to prevent the tracking area from being shifted in the radial direction of the optical disk and the servo area from being spread.

When wobble tracking marks are formed as shown in FIG. 27, when a track position is roughly detected, only a specific tracking mark (for example, a leading tracking mark) included in each track group must be sequentially detected. I just need. Therefore, the wobble tracking mark in FIG. 27 can easily and quickly detect position information when the head or the slider is moved in the radial direction of the optical disk.

The 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 or more and 8 or less are appropriate numbers of tracks included in one track group. In particular, when the number of tracks is set to 8, the binary can be easily handled by the computer, and the number of tracks and the address thereof can be set without excess and deficiency.

(Embodiment 3) Next, an optical disc according to Embodiment 3 will be described. The optical disc of the third embodiment has the same tracking marks as those of the first or second embodiment. Therefore, in the third embodiment, the description of the tracking marks on the optical disc is omitted.

FIG. 28 is a diagram for explaining the optical disc according to the third embodiment. The optical disc of the third embodiment is
The nonlinear optical layer includes a non-linear optical material layer, and the non-linear optical layer is such that only an irradiated portion to be irradiated with light is transparent and transmits light, and the transmitted light is converted into near-field light.

That is, the optical disc of the third embodiment
As shown in FIG. 28, the polycarbonate substrate 2101
, SiN protective layer 2102, SiN protective layer 2104, S
iN protective layer 2106, data recording layer 2105, and
An Sb mask layer 2103 which is a non-linear optical material layer is provided. The Sb mask layer 2103 is such that only the irradiated portion to be irradiated with light becomes transparent, transmits the laser light L condensed by the condenser lens 2107, and turns the transmitted light into near-field light L ''. . Each of the above-mentioned layers has a thickness of 20 nm for the SiN protective layers 2104 and 2106, and
5 is 15 nm, Sb mask layer 2103 is 15 nm, Si
A 17 nm N protective layer 2102 is stacked. The lamination is performed by vapor deposition.

At the time of recording, the optical disk according to the third embodiment is provided with a condenser lens 2107 from the polycarbonate substrate 2101 side.
The laser beam L condensed by the light is incident. Laser light L
Focuses on the Sb mask layer 2103 and makes the region corresponding to the power of the laser beam L transparent. The transparent portion becomes a minute opening and transmits the laser beam L. The transmitted laser light L becomes near-field light L '' and exudes to the data recording layer 2105 to form a recording mark 2108 smaller than the light diffraction limit.

The phase change of the optical disk according to the third embodiment
Ge as the data recording layer_TwoSb _TwoTe_FiveThere is a thin film
Alternatively, an AgInSb thin film can be used. FIG.
Is the data recording layer 2105 of the optical disk shown in FIG.
Ge_TwoSb_TwoTe_FiveOf an optical disc with a thin film 2405
It is a figure showing a section. In the figure, Ge_TwoSb_TwoTe_FiveThin film 2
The recording mark formed at 405 is shown as 2408.
According to the optical disc shown in FIG. 29, the S / N ratio is high,
Also, accurate tracking error signal can be obtained
You. It also increases the sensitivity of the data recording layer,
Erasing can be performed reliably. Also, record marks and unrecorded parts
And a sharp signal can be obtained at the boundary between.

FIG. 30 shows the data recording layer 2105 of the optical disk shown in FIG.
FIG. 2 is a diagram showing a cross section of an optical disc having the above configuration. In the figure, AgI
The recording marks formed on the nSb thin film 2505 are
As shown. According to the optical disc shown in FIG.
An N ratio is high and an accurate tracking error signal can be obtained. Thus, a recording mark having a size equal to or smaller than the size limited by the diffraction limit of light can be accurately formed.

(Embodiment 4) Next, an optical disc according to Embodiment 4 will be described. The optical disc according to the fourth embodiment has the same layer structure as the optical disc according to the twelfth or third embodiment. Therefore, in the fourth embodiment, illustration and description of the layer structure of the optical disc are omitted.

FIG. 31 is a schematic diagram for explaining the optical disc of the fourth embodiment. The illustrated optical disk has a groove G for every fixed number of tracks, and has a region where a wobble tracking mark is formed on a land R of the groove G, that is, a servo region. In the optical disc according to the third embodiment, the diffraction light generated in the groove G is detected by the two-division photodiode provided in the recording / reproducing apparatus, and the tracking error can be detected by the output difference of the photodiode.

According to the fourth embodiment, a push-pull signal can be obtained from a groove in addition to a signal obtained by sample-serving a tracking mark. Therefore, the tracking error can be detected more reliably than when the tracking error is detected using only the wobble tracking marks as in the optical disks according to the first and second embodiments.

In the third embodiment described above, the laser beam irradiated by the recording / reproducing apparatus can be converted into near-field light on the optical disk side. For this reason, the optical disc of the third embodiment
A recording mark having a size equal to or smaller than the diffraction limit of laser light can be formed using a recording / reproducing apparatus having no configuration for generating near-field light.

[0088]

According to the present invention, even when the near-field effect of light or the pseudo near-field effect is used, a more accurate clock signal can be obtained than the clock tracking mark, and the detection time of the wobble tracking mark can be reduced. An accurate and quantitative tracking signal can be obtained. For this reason, it is possible to provide an optical recording medium capable of recording data at a high density and reproducing the recorded data.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a layer structure of an optical disc according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a servo area of the optical disc of the first embodiment shown in FIG.

FIG. 3 is a diagram for explaining the recording / reproducing device according to the first embodiment of the present invention.

FIG. 4 is a diagram for explaining the configuration of the servo signal detection device shown in FIG. 3 in more detail;

FIG. 5 is a diagram showing a state in which the wobble tracking mark according to the first embodiment of the present invention is scanned by laser light with near-field light.

FIG. 6 is a diagram for explaining detection light obtained by tracking performed in the state shown in FIG. 5;

FIG. 7 is a diagram showing a case where a spot of a laser beam scans on a course shifted from a track center.

FIG. 8 is a diagram for explaining detection light obtained by tracking performed in the state shown in FIG. 7;

FIG. 9 is a diagram for explaining processing performed in the pulse width comparator.

FIG. 10 is a diagram illustrating a configuration for calculating a difference between detection time widths illustrated in FIG. 9;

FIG. 11 is a diagram for explaining signals processed in FIG. 10;

12 is a diagram illustrating a relationship between a signal f illustrated in FIG. 11 and an amount of a tracking error.

FIG. 13 is a diagram showing another configuration example of the servo signal detection device.

14 is a diagram for explaining signals processed in the servo signal detection device shown in FIG.

FIG. 15 is a diagram for explaining another example of the optical disc of the first embodiment.

FIG. 16 is a diagram for explaining still another example of the optical disc of the first embodiment.

FIG. 17 shows tracking marks m5 to m shown in FIG.
9 is a diagram for explaining detection light obtained from No. 9. FIG.

FIG. 18 is a diagram illustrating a configuration example of a clock generation circuit.

FIG. 19 is a diagram showing another example of the tracking mark.

FIG. 20 is a diagram showing another example of the tracking mark.

FIG. 21 is a diagram illustrating another example of a tracking mark.

FIG. 22 is a diagram for explaining a configuration in which a data recording layer is a Ge ₂ Sb ₂ Te ₅ thin film in the optical disc of the first embodiment.

FIG. 23 is a diagram for explaining a configuration in which a data recording layer is an AgInSb thin film in the optical disc of the first embodiment.

FIG. 24 is a diagram illustrating a configuration in which a data recording layer is made of a phase change material in the optical disc of the first embodiment.

FIG. 25 is a diagram illustrating a tracking mark of the optical disc according to the second embodiment of the present invention.

FIG. 26 is a diagram for explaining points to be improved in the tracking mark shown in FIG. 25;

FIG. 27 is a diagram for describing a configuration example of a servo area of the optical disc according to the second embodiment.

FIG. 28 is a diagram for explaining the optical disc of the third embodiment.

FIG. 29 is a diagram for describing a configuration in which the data layer is a Ge ₂ Sb ₂ Te ₅ thin film in the optical disc of the third embodiment.

FIG. 30 is a diagram for explaining a configuration in which a data recording layer is made of an AgInSb thin film in the optical disc of the third embodiment.

FIG. 31 is a schematic diagram for explaining the optical disc of the fourth embodiment.

FIG. 32 is a diagram illustrating a method for detecting a tracking error.

FIG. 33 is a diagram showing detection light detected by irradiating the wobble tracking mark shown in FIG. 32 with laser light.

FIG. 34 is a diagram for explaining a conventional wobble tracking mark.

FIG. 35 is a diagram for describing a problem that occurs when the wobble tracking mark illustrated in FIG. 32 is scanned using near-field light.

FIG. 36 is a diagram for explaining detection light obtained by tracking performed in the state shown in FIG. 35;

[Explanation of symbols]

101, 103, 2102, 2104, 2106 Si
N protective layer 102, 1702, 2105 Data recording layer 104, 2101 Polycarbonate substrate 105, 2108 Recording mark 301 Laser light source 302 Photodetector 303 Servo signal detecting device 304 Optical disk 401 Delay circuit 402 Pulse width comparator 501, 1501, 1601 Spot 600 Clock generation circuit 601 Phase comparator 602 Low pass filter 603 Sample hold circuit 604 Voltage controlled oscillator 605 Divider 1001, 1002, 1302 Waveform shaper 1003 Subtractor 1004, 1304 Integrator 1303 Polarity switch 1305 Switch 1802, 2405 Ge
₂ Sb ₂ Te ₅ thin film 1902,2505 Ag
InSbTe thin film 2002 Phase change material 2103 Sb
Mask layer 2107 Condensing lens

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/24 565 G11B 7/24 565J

Claims (13)

[Claims] In an optical recording medium for recording information, a plurality of clock tracking marks for obtaining a clock signal are provided at a track center at a predetermined distance, and a pair of wobble tracking marks for obtaining a tracking error signal are provided. An optical recording medium which is provided to be shifted from the track center by a predetermined length and by a predetermined distance in the track direction. 2. The wobble tracking mark has a wedge-shaped shape, and a tip of the wedge-shaped shape is perpendicular to the track center and intersects the track center by a predetermined length. The optical recording medium according to claim 1, wherein 3. The optical recording medium according to claim 1, wherein the wobble tracking mark is provided subsequent to the clock tracking mark. 4. The wobble tracking mark provided at a predetermined length shifted from the wobble tracking mark provided at an adjacent track in the track direction by a distance equal to the predetermined length. The optical recording medium according to claim 1, 2 or 3. 5. The optical recording medium according to claim 1, wherein said predetermined distance at which said clock tracking mark is disposed is equal to said predetermined length at which said wobble tracking mark is disposed. 6. The optical recording medium according to claim 1, wherein said clock tracking mark has a rectangular shape. 7. The optical recording medium according to claim 1, wherein the clock tracking mark has a rectangular shape crossing a plurality of adjacent tracks vertically. 8. A wobble tracking mark is provided for each of a fixed number of tracks, and the wobble tracking mark is provided at a land portion of the groove area.
The optical recording medium according to any one of the above. 9. The optical recording medium according to claim 1, wherein the recording layer of the optical recording medium is a phase change type recording layer. 10. The recording layer of the phase change type according to claim ₂ , wherein said recording layer is Ge ₂ Sb.
The optical recording medium according to claim 9, wherein the a ₂ Te ₅ thin film. 11. The phase change type recording layer is made of AgInS.
The optical recording medium according to claim 9, wherein the optical recording medium is a b thin film. 12. The optical recording medium according to claim 1, wherein a non-linear optical material layer is provided on the optical recording medium, and near-field light is emitted using the non-linear optical material layer as a mask. 13. A recording / reproducing apparatus for recording / reproducing information on / from an optical recording medium according to claim 1, wherein a clock signal is generated from reflected light from the clock tracking mark. And a tracking error generating means for generating a tracking error from a detection time difference of reflected light from the pair of wobble tracking marks.