JPH04141833A - Tracking control method - Google Patents

Abstract

PURPOSE:To detect tracking deviation without previously providing a highly precise pit for an optical recording medium by detecting the polarized state of a beam on a track adjacent to a target track and detecting a tracking error. CONSTITUTION:The recording tracks in an optical anisotropy direction different by 45 degrees at every adjacent track in accordance with the polarized direction of the optical beam in linear polarized light. Out of random polarized light outputted from a light source 1, a polarized component corresponding to the optical anisotropy direction of a recording layer 23 is selectively absorbed. When the spot of the light of random polarized light is deviated from the target track, the polarized component whose part corresponds to the adjacent track whose optical anisotropy direction differs by 45 degrees in random polarized light is selectively absorbed and light quantities received by sensors 6a and 6b differ, the difference of the light quantities is detected and tracking is executed. Thus, the highly precise pit or a guide groove is not necessary to be previously provided in the recording medium where a photochromic material is included in the recording layer, and tracking can highly precisely be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a tracking control method for performing tracking control on an optical recording medium.

(b) Prior Art Recently, research on the use of photochromic materials in the recording layer of media has been actively conducted. Such photochromic materials have properties such that when irradiated with light of a predetermined wavelength, the structure of the molecules changes due to a photochemical reaction, and the optical characteristics for light with a specific wavelength change in accordance with the change in the structure of the molecules. have. Furthermore, when irradiated with light of another predetermined wavelength, the changed molecular structure returns to its original structure.

Therefore, when the 7 otochromic material having the properties described above is used in the recording layer of a medium, the following information recording or reproducing method is performed. For example, information is recorded by changing the absorption rate of the recording layer for a specific wavelength by irradiating light with a predetermined wavelength, and the light having the specific wavelength is applied to the recording layer for recording or non-recording. A recording and reproducing method is known that takes advantage of the fact that the two have different absorption rates. In addition, information is recorded by causing birefringence in the recording layer using linearly polarized light having a predetermined wavelength, and by irradiating light with little absorption by the recording layer, the transmitted or reflected light is used to record information on the recording layer. A recording/reproducing method is known that performs reproduction by detecting the presence or absence of birefringence.

Further, information is erased by irradiating light having another predetermined wavelength to return the structure of the molecules to their original state.

By the way, in order to detect the track deviation of the light beam spot, in conventional optical recording such as compact discs, pits and guide grooves are provided in advance on the optical recording medium, and the amount of reflected light diffracted by these is measured at the far field. The push-pull method detects the distribution using a 2-split photodetector, the heterodyne method uses a 4-split photodetector to detect the distribution of the amount of diffracted light, and the spot is slightly vibrated left and right with respect to the track to cause amplitude modulation in the reflected light. , a two-ring method that detects by phase detection, and a three-beam method that uses two sub-beams in addition to the main beam are known.

(c) Problems to be solved by the invention However, in the conventional tracking deviation detection method, it is necessary to provide highly accurate pits or guide grooves on the optical recording medium in advance, and it is difficult to apply it to flexible optical tapes. there were. Furthermore, when providing highly accurate pits or guide grooves on an optical disk, highly accurate manufacturing is required.

The present invention aims to solve this problem and proposes a method for detecting tracking deviation without previously providing highly accurate pits or guide grooves in an optical recording medium made of a photochromic material.

(d) Means for Solving the Problems The present invention has been made in view of the above-mentioned problems, and provides a tracking control method for performing tracking control on a medium in which adjacent tracks have different optical anisotropy. The present invention provides a tracking control method characterized in that a tracking error is detected by detecting the polarization state of a beam applied to a track adjacent to a target track.

(E) Effect According to the present invention, when a light beam hits a track next to the target track (track to be reproduced), the polarization state of the light beam in the hit portion depends on the optical anisotropy of this adjacent track. It becomes something. The polarization state of the light beam at the target track portion and the polarization state of the light beam at adjacent track portions are different depending on the difference in optical anisotropy of each track. Tracking errors are detected by monitoring this difference.

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

(First example) The first embodiment will be described below.

As the photochromic material contained in the recording layer in the first embodiment, photochromic materials such as flukyto-based, diallylethene-based, spiropyran-based, etc. can be used. −
The structure of a spiropyran-based photochromic material used as an example is shown in FIG. 1 and will be explained. The molecular structure of such a material changes from a spiropyran type to a merocyanine type by irradiation with ultraviolet light, and returns from a merocyanine type to a spiropyran type by irradiation with visible light or heating.

The recording layer contains a photochromic material in a non-oriented state without oriented molecules. When such a medium is irradiated with linearly polarized light of a wavelength that is absorbed by the photochromic material, the probability that molecules in the photochromic material that have a specific orientation will cause a photochemical reaction depending on the polarization plane of this linearly polarized light is is high. Therefore, when the recording layer is scanned with the linearly polarized light, optical anisotropy occurs depending on the polarization plane of the linearly polarized light (here, this refers to the fact that the absorbance of the linearly polarized light has a polarization direction dependence). A directional recording portion is formed.

Furthermore, the following principle is used to reproduce information and detect tracking deviation. That is, as shown in FIG. 2, the absorbance of the recording layer irradiated with linearly polarized light for recording is different from that of the recording layer that is not irradiated, and the absorbance of the recording layer irradiated with linearly polarized light for recording is different. On the other hand, the absorbance of the linearly polarized light for reproducing which has an angle θ with the polarization plane of the linearly polarized light for recording differs depending on the angle θ. That is, the absorbance of linearly polarized light in a specific direction (optical anisotropy direction) changes significantly (in the case of FIG. 2, θ=0°). Therefore, when randomly polarized light is irradiated onto a recording layer that has undergone optical anisotropy due to linearly polarized light, the absorbance of the polarized light component of the randomly polarized light that corresponds to the optical anisotropy direction is Significant changes (
In the case shown in Figure 2, the absorbance of the polarized light component at θ = 0° decreases significantly), so information can be reproduced by utilizing the difference in absorbance with the recording layer that does not have optical anisotropy. be exposed.

Although the relationship shown in FIG. 2 may differ depending on the photochromic material and the wavelength of recording or reproducing light, the following description will be made assuming that the relationship shown in FIG. 2 exists.

If the optical anisotropy direction introduced into the recording layer differs by 45 degrees between adjacent tracks, when reproducing information by irradiating randomly polarized light, the target track (the track to be reproduced) and the adjacent track The light generated by irradiating the above randomly polarized light has anisotropy in the polarization state (anisotropic distribution of light intensity) between the light related to the target track and the light related to the adjacent track.
Therefore, information can be reproduced while tracking is performed by detecting the difference in the polarization state.

FIG. 3 is a diagram showing a reproducing optical system of the recording/reproducing apparatus according to the first embodiment.

The recording medium (20) is made by spinning a solution of the photochromic material dissolved in a solvent of MEK (methyl ethyl ketone) with PVB (polyvinyl butyral) added as a binder onto a transparent substrate (21) made of glass, quartz, or resin. A recording layer (23) with a thickness of 1 μm is formed using a coding method, a coating method, a vapor deposition method, etc. so that the photochromic material is dispersed in a non-oriented manner, and then a layer such as A1 inside is formed on the recording layer (23). It is produced by forming a reflective layer (22).

A linearly polarized light beam such as an Ar ion laser (for example, λ
-360 nm) onto the optical recording medium (20) so that the polarization direction differs by 45° for each adjacent track. As a result, as shown in the conceptual diagram of the tracks in FIG. In the figure, the direction of the angular dependence of absorbance is shown.
A recording track (indicated by the arrow direction) is formed. below,
Reproducing information from the optical recording medium (2o) on which information is recorded in this manner will be described in detail below.

A first light source (1) such as a He-Ne laser shown in FIG.
Reproduction is performed by manipulating each recording track with an incident light beam output from a wavelength of λ-633 nm (for example, λ-633 nm). The intensity of the incident light beam output from the first light source (1) is set to be sufficiently small so that each recording layer (23) does not react with the incident light beam, and the new incident light beam is randomly distributed in the same direction. It's polarized. The outputted incident light beam passes through the half mirror (3). It is preferable that the half mirror (3) has the same reflection and transmission intensity for S waves and P waves.

The randomly polarized light transmitted through the half mirror (3) is focused on the recording layer (23) via the objective lens (4), reflected by the reflective layer (22), and emitted from the optical recording medium. . At this time, among the randomly polarized light, the recording layer (2
3) Polarized light components according to the optical anisotropy direction are selectively absorbed. Thereafter, the emitted light passes through an objective lens (4), is reflected by a half mirror (3), and enters a polarizing beam splitter (5).

Of the incident light, the S wave component is sent to the sensor (6a),
The P wave component is received by the sensor (6b). sensor(
The outputs received by 6a and 6b are added in a circuit (7) to form an RF output signal.

Note that when the spot of randomly polarized light is scanned only on the target track, the sensors (6a) (6b)
The optical system, particularly the half mirror (3) and the polarizing beam splitter (5), are adjusted so that the amounts of light reaching the two sides are equal.

Therefore, if the spot of the randomly polarized light deviates from the target track (for example, in FIG.
If the optical anisotropy direction of the randomly polarized light is shifted in the direction of the adjacent track 1), a portion of the randomly polarized light has a polarization component corresponding to the adjacent track 1 whose optical anisotropy direction differs by 45 degrees from the track 2. Selectively absorbed. As a result, the sensor (6a
) (6b) differs (for example, the amount of light received by the sensor (6a) increases), and tracking can be performed by detecting this difference in light amount. Also, when tracking deviation occurs in the opposite direction to the above (in the direction of track 3), a difference occurs in the amount of light received by the sensors (6a) and (6b). At this time, since the optical anisotropy directions of the adjacent tracks (track 1 and track 3) are perpendicular to each other, the amount of light from the opposite sensor (for example, sensor (6b)) increases. Therefore, by detecting the output difference between the sensors (6a) and (6b) using the circuit (8), tracking servo can be performed by driving an actuator (not shown) included in the objective lens (4) system. can.

Note that the above-mentioned recording medium may be any optical recording medium such as an optical tape or an optical disk.

As described above, according to the first embodiment, the tracking detection method described above does not require the provision of highly accurate pits or guide grooves in advance, and can be applied to flexible optical tapes and the like. However, there is a drawback that tracking cannot be performed if optical anisotropy does not occur in a track adjacent to the track to be reproduced.

(Second example) A second embodiment of the present invention will be described below.

Incidentally, the same parts as in the first embodiment are given the same reference numerals, and the explanation thereof will be omitted.

In the initial state of the recording medium (sen), the recording layer (23) is irradiated with a linearly polarized light beam (for example, λ = 360 nm) at a constant power (DC state) so that the angle differs by 45 degrees for each adjacent track. , an optical anisotropy (here, the absorbance of linearly polarized light is dependent on the polarization direction) is generated in advance at an angle of 45 degrees between all tracks and adjacent tracks. Information is recorded by applying a linearly polarized light beam (for example, λ=633
(A conceptual diagram is shown in FIG. 5. The diagonal lines indicate the unrecorded portion and indicate the direction of optical anisotropy, and the voids indicate the recorded portion.)

Information is reproduced using the same principle as in the first embodiment, for example, using the optical system shown in FIG. 3 of the first embodiment. That is,
Information is reproduced by irradiating randomly polarized light in the same direction and utilizing the difference in absorbance between recorded and unrecorded areas.

However, in the case of the same photochromic material as in the first embodiment, the output relationship between the recorded portion and the unrecorded portion is reversed from that in the first embodiment. Also, tracking is performed by detecting the difference in light amount between the sensors (6a) and (6b) based on the anisotropy of the polarization state between adjacent tracks, as in the first embodiment.

As described above, according to the second embodiment, the drawbacks of the first embodiment are overcome, and furthermore, there is no need to provide highly accurate pits or guide grooves in advance, and tracking can be performed even during recording. It can also be applied to flexible optical tapes.

(Third Example) A third example will be described in detail below with reference to the drawings. Incidentally, the same parts as in the first embodiment are given the same reference numerals, and the explanation thereof will be omitted.

The optical recording medium (20) is recorded in the same manner as in the first embodiment. As a result, the recording layer (23) is irradiated with linearly polarized light, causing birefringence, whose neutral axis direction becomes the polarization direction of the linearly polarized light. Therefore, as shown in FIG. 4, recording tracks having optical anisotropy (in this case, the neutral axis direction of birefringence) in directions different by 45 degrees are formed for each adjacent track.

Hereinafter, the recording medium (20
) The following principle is used for information reproduction and detection of tracking deviation.

In the case where a recording layer in which birefringence has occurred is irradiated with linearly polarized light in its neutral axis direction, and in the case in which the recording layer in which birefringence has not occurred is irradiated with linearly polarized light, the first example As described above (the direction of the difference in absorbance and the direction of birefringence are generally the same direction), information can be reproduced by detecting the difference in absorbance. In addition, when the recording layer is irradiated with linearly polarized light in the same direction as the neutral axis direction of birefringence, the polarization state of the transmitted light and reflected light from the recording layer is linearly polarized light, but the above-mentioned neutral If the axial direction and the polarization direction of the linearly polarized light do not match, the polarization state of the transmitted light from the recording layer and its reflected light will be elliptically polarized light or circularly polarized light.

Therefore, if the direction of optical anisotropy (neutral axis direction of birefringence) is different for different tracks, if a tracking deviation occurs, a difference will occur in the polarization state, and the tracking deviation can be detected. .

FIG. 6 is a perspective view showing a reproducing optical system of a recording/reproducing apparatus according to a third embodiment.

Reproduction is performed by operating each recording track with an incident beam output from a first light source (11) such as a He-Ne laser (for example, λ=633 nm).

The intensity of the incident light beam output from the first light source (11) is set to be sufficiently small so that each recording layer (23) does not react with the incident light beam, and the new incident light beam is linearly polarized. There is. The emitted incident light beam is reflected by a half mirror (3). It is preferable that the half mirror (3) has the same reflection and transmission intensity for S waves and P waves. The linearly polarized light reflected by the half mirror (3) is transmitted through the two-wavelength plate (2). At this time,
The neutral axis of the K wavelength plate (2) is set to match the polarization direction of the linearly polarized light, and as a result, the transmitted light is in a linearly polarized state. The transmitted linearly polarized light is focused on the recording layer (23) via the objective lens (4), reflected by the reflective layer (22), and emitted from the optical recording medium (20). At this time, the polarization direction of the linearly polarized light is the recording layer (23
) is adjusted to match the neutral axis direction of the birefringence that occurs. Therefore, the reflected light emitted from the recording medium (20) is in a linearly polarized state.

The reflected light passes through the wavelength plate (2) and the half mirror (3) in a linearly polarized state, and then passes through the polarizing beam splitter (5).
). The polarizing beam splitter (5) is arranged so that the intensity ratio of the P wave and the S wave with respect to the linearly polarized reflected light is equal. Therefore, the sensor (6
The amounts of light received by a) and the sensor (6b) are equal.

The reproduced RF output is the sum of the outputs of the sensors (6a) and (6b). In addition, in the unrecorded part (part without birefringence),
The linearly polarized light that is irradiated onto the recording layer (23) is also incident on the polarizing beam splitter (5) in a linearly polarized state, so the same amount of light is received by the sensors (6a) and (6b). The sum of the outputs of the sensors (6a) and (6b) is outputted as an RF high output. Here, since there is a difference in absorbance between the recorded portion and the unrecorded portion, information can be reproduced based on the RF high output difference.

Next, if the spot of the linearly polarized light irradiated onto the recording medium (20) deviates from the target track (for example, if it deviates from the target track 2 in the direction of track 1 in FIG. 4), the linearly polarized light Since the polarization direction differs by 45 degrees from the neutral axis direction of the birefringence of track 1, the reflected light emitted from the recording medium (20) includes an elliptically polarized component (or circularly polarized component) in addition to the linearly polarized component. included. Hereinafter, in order to simplify the explanation, it is assumed that the effect of birefringence of the optical recording medium (20) is equivalent to a wavelength plate. Therefore, the description will be made assuming that the reflected light includes a circularly polarized component in addition to the linearly polarized component. Of this reflected light, the circularly polarized component is placed on the wavelength plate (2).
By passing through the circularly polarized light component, the circularly polarized light component is converted into a linearly polarized light component whose polarization plane direction differs by 45 degrees from the above-mentioned linearly polarized light component. The converted linearly polarized light component passes through the half mirror (3). After that, the polarizing beam splitter (5)
It becomes a wave (or S wave) component, and the sensor (6a) and the sensor (
6b). Further, among the reflected light, the linearly polarized light component generated by track 2 (target track) is received by the sensors (6a) and (6b) in the same amount of light as described above. As a result, a difference in output between the sensor (6a) and the sensor (6b) occurs based on the tracking deviation, and by detecting this output difference, a tracking error signal can be generated.
) tracking servo can be executed by driving the system.

As described above, according to the third embodiment, the tracking detection method described above does not require the provision of highly accurate pits or guide grooves in advance, and can be applied to flexible optical tapes and the like. However, if there is no optical anisotropy in a track adjacent to the track to be reproduced, tracking cannot be performed.

(Fourth example) A fourth embodiment of the present invention will be described below.

Incidentally, the same parts as in the third embodiment are given the same reference numerals, and the explanation thereof will be omitted.

In the initial state of the recording medium (20), a linearly polarized light beam (for example, λ = 360 nm) is applied to the recording layer (23) at a constant power (DC) at an angle of 45 degrees for each adjacent track.
irradiation (state)) to cause birefringence in advance in which all tracks and adjacent tracks have neutral axes in directions that differ by 45 degrees. Information is recorded by applying a linearly polarized light beam (for example,
λ = 633 nm) (5th
The figure is a conceptual diagram; the diagonal lines indicate the unrecorded portion, indicating the neutral axis direction of birefringence, and the voids indicate the recorded portion).

Information is reproduced using the same principle as in the third embodiment, for example, using the optical system shown in FIG. 6 of the third embodiment. That is,
Information is reproduced by irradiating linearly polarized light and utilizing the difference in absorbance between recorded and unrecorded areas. However, in the case of the same photochromic material as in the third embodiment, the output relationship between the recorded portion and the unrecorded portion is reversed from that in the third embodiment.

Also, in tracking, as in the third embodiment, the linear polarization state changes to the elliptical polarization state (or circular polarization state) by adjacent tracks, so that the sensor (6a) (6b)
This is done based on the difference in the amount of light received.

As described above, according to the fourth embodiment, the drawbacks of the third embodiment are solved, and there is no need to provide highly accurate pits or guide grooves in advance, and tracking can be performed even during recording.

It can also be applied to flexible optical tapes.

However, in the first to fourth embodiments, the size is set to be sufficiently small so that the photochromic material of the recording layer does not cause a reaction during information reproduction, but there is a tendency for information to be destroyed.

(Fifth example) A fifth embodiment of the present invention will be described below.

The optical recording medium (20) is recorded in the same manner as in the first embodiment, and as shown in FIG. An optical recording medium in which a recording track is formed, that is, when linearly polarized light for recording is irradiated, birefringence occurs in the recording layer (23), and the polarization direction of the linearly polarized light becomes its neutral axis direction. (money)
The following principle is used to reproduce information and detect tracking deviation.

When a recording layer with birefringence is irradiated with circularly polarized light,
The resulting reflected or transmitted light has an elliptical polarization state. On the other hand, when a recording layer with no birefringence is irradiated with circularly polarized light, the resulting reflected or transmitted light remains circularly polarized light without changing its polarization state. Therefore, information is reproduced by detecting the difference in intensity between the elliptically polarized light and the circularly polarized light transmitted through the polarizer.

Also, since the neutral axis direction of birefringence differs by 45° between adjacent tracks, tracking deviation occurs from the target track and the track next to it when circularly polarized light is irradiated onto a recording layer where birefringence has occurred. The neutral axes of the reflected or transmitted elliptically polarized light differ by 45°. Also, to determine which side of the target track the track deviation is occurring on, the neutral axes of the reflected or transmitted light of the elliptically polarized light generated from the two adjacent tracks are perpendicular to each other, so use a polarizing beam splitter or the like to sort it out. Can be detected.

Therefore, tracking can be performed by detecting the difference in the polarization direction of the linearly polarized light.

FIG. 7 is a perspective view showing a reproducing optical system of a recording/reproducing apparatus according to a fifth embodiment.

Photochromic materials usually have low absorption of near-infrared wavelengths, so a semiconductor laser (for example, λ=780 nm) is usually used for reproducing information.

Reproduction is performed by operating each recording track with an incident light beam output from a first light source (12) such as a semiconductor laser. The newly incident light beam is linearly polarized. The output linearly polarized light is converted into circularly polarized light by a wavelength plate (10), then reflected by a No. 1-7 mirror (3) and irradiated onto an optical recording medium (20). In order to simplify the explanation, the effect of birefringence of the optical recording medium (20) in which birefringence has occurred is equivalent to a wavelength plate, and circularly polarized light irradiated onto the recording layer (23) in which birefringence has occurred. The following description will be made assuming that the light is reflected as linearly polarized light.

Circularly polarized light passes through the objective lens (4) to the optical recording layer (23).
), the circularly polarized light is emitted from the optical recording medium (20) as linearly polarized light having an inclination of 45° with respect to the direction of the neutral axis of birefringence. The emitted linearly polarized light passes through the objective lens (4) and then passes through the half mirror (3).
). Then, a part of it is reflected by the half mirror (31) and passed through the polarizer (30) to the sensor (61).
) is received. Note that it is desirable that the half mirror (31) has the same reflection intensity for S waves and P waves. or,
When the recording layer (23) in which no birefringence occurs is irradiated, the light is emitted from the optical recording medium (20) as circularly polarized light. The emitted circularly polarized light passes through an objective lens (4) and then passes through a half mirror (3). Thereafter, a portion of the light is reflected by the half mirror (31), transmitted through the polarizer (30), and received by the sensor (61). At this time, the neutral axis direction of the polarizer (30) is adjusted in advance so as to cause a difference in the intensity of the linearly polarized light and the circularly polarized light transmitted through the polarizer (30), and the sensor (61) Information is reproduced based on the output difference.

Further, the remaining linearly polarized or circularly polarized light, which is partially reflected by the half mirror (31), is separated by the polarizing beam splitter (5) and received by the sensors (6a) and (6b). Note that if the reproduction light spot is illuminated only on the target track, the sensors (6a) (6b)
) A polarizing beam splitter (5) is arranged in advance so that the same amount of light is received by the two.

Next, when the spot of the circularly polarized light irradiated onto the optical recording medium (20) deviates from the target track (for example, when it deviates from the target track 2 in the direction of track 1 in FIG. 4), the above-mentioned compound Because the neutral axis direction of refraction differs by 45 degrees,
The reflected light emitted from the recording medium (coin) includes, in addition to the linearly polarized component generated from track 2, a linearly polarized component whose polarization direction differs by 45 degrees from the linearly polarized component generated from track 1. The polarizing beam splitter (5) sends linearly polarized light generated from track 2 to sensors (6a) and (6b).
Track 1 is set to receive the same amount of light.
There is a difference in the amount of linearly polarized light generated by the sensors (6a) and (6b). Furthermore, when the spot of the circularly polarized light irradiated on the optical recording medium (20) shifts from the target track 2 to the track 3, the polarization direction of the linearly polarized light generated from the track 3 shifts to the track 1. Since the polarization direction differs by 90@ from the polarization direction of the linearly polarized light generated from track 1, the magnitude relationship of the outputs of the sensors (6a) and (6b) is opposite to that when shifted to track 1.

Therefore, by detecting the output difference between the sensors (6a) and (6b), a tracking error signal is obtained, and tracking servo is performed using this signal.

As described above, according to the fifth embodiment, the tracking detection method described above does not require the provision of highly accurate pits or guide grooves in advance, and can be applied to flexible optical tapes and the like. Furthermore, information can be reproduced and tracking deviation detected without destroying the information. However, there is a drawback that tracking cannot be performed if optical anisotropy does not occur in a track adjacent to the track to be reproduced.

(6th example) A sixth embodiment of the present invention will be described below.

Incidentally, the same parts as in the fifth embodiment are given the same reference numerals, and the explanation thereof will be omitted.

In the initial state of the recording medium (20), a linearly polarized light beam (for example, λ = 360 nm) is applied to the recording layer (23) at a constant power (DC) at an angle of 45 degrees for each adjacent track.
irradiation (state)) to cause birefringence in advance in which all tracks and adjacent tracks have neutral axes in directions that differ by 45 degrees. Information is recorded by applying a linearly polarized light beam (for example,
λ = 633 nm) (5th
A conceptual diagram is shown in the figure. Note that the diagonal lines indicate unrecorded areas and indicate the neutral axis direction of birefringence, and the gaps indicate recorded areas).

Information is reproduced using the same principle as in the fifth embodiment, for example, using the optical system shown in FIG. 7 of the fifth embodiment. That is,
Information is reproduced based on the output difference of the sensor (61) based on the difference in the polarization state of the reflected light of the recorded portion and the unrecorded portion generated by irradiation with elliptically polarized light. However, in the case of the same 7 otochromic material as in the fifth embodiment, the outputs of the recorded portion and the unrecorded portion are reversed from those of the fifth embodiment.

Also, tracking is performed using elliptically polarized light generated by adjacent tracks, as in the fifth embodiment.
) (6b) based on the difference in the amount of light received.

As described above, according to the sixth embodiment, the drawbacks of the fifth embodiment are solved, and there is no need to provide highly accurate pits or guide grooves in advance, and it can also be applied to flexible optical tapes.

(Seventh Example) A recording method for an optical recording medium will be described in detail with reference to the drawings. Incidentally, the same parts as in the first embodiment are given the same reference numerals, and the explanation thereof will be omitted.

FIG. 8 is a top view of an optical recording medium for explaining the recording method.

In the figure, (101) is a recording light beam spot of linearly polarized light. (102) is a monitoring light beam spot of linearly polarized light for performing tracking control during recording of information, and has the same wavelength and approximately the same intensity as the reproduction light beam. (104) (1,05) are tracks on which information has been recorded, and (103) is a track where information is currently being recorded. As shown in FIG. 8, optical anisotropy such as birefringence is induced such that the direction of optical anisotropy differs by 45° for each adjacent track. Therefore, by fixing the relative positions of the recording light beam spot (101) and the monitoring light beam spot (102) and performing tracking servo of the monitoring light beam spot (102) with respect to the track (104), Truck (10
3) is formed correctly.

Therefore, by recording information as described above, correct tracking servo can be performed at the time of recording.

In addition, in the first to seventh embodiments, linearly polarized light and circularly polarized light can also be obtained by using elliptically polarized light, and the numerical values that define angles do not represent exact numerical values, but may vary slightly. It is also clear that it can be used with Furthermore, the wavelength of the light beam used for recording and reproduction is the same as that in the first to seventh embodiments.
The wavelengths are not limited to those used in the examples, and any suitable wavelength may be used.

(G) Effects of the Invention According to the present invention, there is no need to provide highly accurate pits or guide grooves in advance in a recording medium containing a photochromic material in the recording layer, and there is a method for performing highly accurate tracking. can be provided.

[Brief explanation of the drawing]

1 to 4 relate to the first embodiment of the present invention, in which FIG. 1 shows the chemical structure of the photochromic material contained in the recording layer, FIG. 2 shows the absorbance, and FIG. A diagram showing the optical system for reproduction, Figure 4 is a conceptual diagram of the recording track,
5 relates to a second embodiment of the present invention, FIG. 5 is a conceptual diagram of a recording track, FIG. 6 relates to a third embodiment of the present invention and is a diagram showing an optical system for reproduction, and FIG. The figure relates to a fifth embodiment of the present invention and shows an optical system for reproduction, and FIG. 8 relates to a seventh embodiment of the present invention and shows a conceptual diagram of a recording track.

Claims (1)

[Claims] (1) A tracking control method that performs tracking control on a medium in which adjacent tracks have different optical anisotropy, and the tracking control method detects the polarization state of the beam applied to the track next to the target track, thereby causing tracking errors. A tracking control method characterized by detecting.