JPH05225582A - Method and device for focusing or tracking optical recording medium - Google Patents

Abstract

PURPOSE:To stabilize a servo function by using the optical mechanical system servo beam of a wavelength different from a recording beam and a reproducing beam and focusing or tracking the information recording part on a medium. CONSTITUTION:A radiant light beam from an Ar laser light source 5 is synthesized with the beam of a He-Ne laser light source 6 by a dichroic mirror 12 at a recording time and converged on a medium 1. Only the beam from the light source 5 is converged on the medium 1 at a reproducing time. On the other hand, a light source 7 performing focus servo and tracking servo uses the semiconductor laser whose wavelength is not absorbed by the medium 1 and is converged on the medium 1 through a polarizing beam splitter 14, a lambda/4 plate 10 and an objective lens 4. The reflected beam is detected by a photodetector 16 for focus servo and tracking servo through the splitter 14 and a servo circuit 18 is operated. Thus, stable servo is performed without destroying information recorded previously at an accessing time and a stand-by time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of recording or reproducing in a photon mode, and to a focusing or tracking method and apparatus for recording or reproducing light.

[0002]

2. Description of the Related Art In recent years, research for applying a photochromic material as an optical recording medium has been actively pursued.

When a photochromic material is irradiated with light of a predetermined wavelength, the structure of the molecule changes due to a photochemical reaction, the optical characteristics for light of a specific wavelength change according to the change in the molecular structure, and light of other wavelengths. It is known that the structure of the molecule changed by applying heat or heat returns to its original state.

In view of this feature, recording on the photochromic optical recording medium is performed by a change in molecular structure caused by irradiation with light of a specific wavelength, and reproduction is performed by detecting a change in optical characteristics accompanying this.

Since such a recording process occurs due to a photochemical reaction and has wavelength selectivity, for example, photochromic materials having different light absorption regions are laminated or mixed, and recording / reproduction is performed by laser light corresponding to absorption of each material. Thus, wavelength multiplexing recording is possible.

In this case, naturally, it is necessary to use beam light sources having different wavelengths corresponding to the absorption of each material, and such a recording / reproducing apparatus is disclosed in, for example, Japanese Unexamined Patent Publication No. 2-210624 (G11B 7).
/ 13).

By the way, when recording / reproducing using a photochromic medium, the precision of recording / reproducing is improved by performing focus servo or tracking servo of the optical mechanism system used in the conventional optical disk apparatus.

Regarding this technique, although nothing is mentioned in the above-mentioned publication, a conventionally known compact disc,
It is considered that the methods known for MO discs and write-once discs can be used as they are.

The above-mentioned conventional servo technique is carried out by separating a part of reflected light of a laser beam for recording information on a disk or a laser beam for reproducing information and detecting it by an appropriate optical system. There is. Such a technique is described in, for example, "Optical Memory Symposium '88 Papers",
It is disclosed on page 3, published by the Japan Optical Industry Technology Promotion Association, September 1988.

FIG. 5 is a block diagram of an optical system using such a conventionally known servo technique. In this figure, 101 is an optical recording medium, 102 is a He—Ne laser light source for reproducing information, 103 is an AO modulator, 104 is a deflecting beam splitter, and 105 is λ /
4 plates, 106 and 107 are dichroic mirrors, 108 is an Ar laser light source for recording information, 109 is a λ / 4 plate, 110 is a photodetector that detects light emitted from the light source 102 and reflected by the medium 101, and 111 is Similarly, a focus servo circuit and a tracking servo circuit for detecting a focus or tracking shift using the reflected light, 112 adjusts a gain based on the shift amount detected by the circuit 111 to realize a highly accurate focus and tracking. This is an automatic gain adjustment circuit for.

[0011]

However, when the focus servo or the tracking servo is performed by using the reproducing beam (the same applies to the recording beam) as described above, the following problems occur. It was

1. PIN-P commonly used for light detection
The D (photodetector) 110 has a high sensitivity near a wavelength of 800 nm as shown in FIG.
Since the wavelength of light used for recording / reproducing of a photochromic medium has been a short wavelength (400 to 700), the detector output during reproduction is particularly low and the servo gain becomes small, resulting in an unstable servo function.

2. If the power of the reproducing light is increased to solve the above-mentioned problem 1, there is a possibility that the information recorded on the medium may be destroyed even if the detector output can be earned.

3. Since the photochromic medium is a recording system that uses a photochemical reaction, the reaction will progress to some extent no matter how small the power of light is irradiated, so it is not when recording or reproducing information (for example, when accessing the medium or a track). It is desirable not to irradiate the medium with light during recording / playback standby above), but in order to activate the servo function, it is necessary to irradiate light during access or during standby to determine the servo amount. However, the recorded information was deteriorated.

In view of the problems of the prior art, the problem to be solved by the present invention is to suppress the deterioration of recorded information due to the light for focus or tracking servo and to perform focus or tracking with high servo amount detection accuracy. A method and apparatus are provided.

[0016]

According to the method of the present invention, information is recorded by irradiating an optical recording medium with light having a recording wavelength, and irradiating the medium with light having a reproducing wavelength to reflect light on the medium. At the time of recording / reproducing of the optical recording medium for reading out the recorded information by detecting the information recorded on the medium by using the servo light of the optical mechanism system having a wavelength different from that of the recording light and the reproducing light. The optical recording medium is formed by laminating a photochromic material on a substrate, and a groove having a depth Δ for servo of an optical mechanism is formed on the substrate, and the depth of the groove is With respect to the wavelength λ _R of the reproduction light and the substrate refractive index n _{R at the} wavelength λ _R ,

[0017]

[Equation 2]

It is determined so as to satisfy the above condition.

Further, the apparatus of the present invention records / records on an optical recording medium.
A lens system that collects light for reproduction / erasure or servo, a light source that emits light of a wavelength for recording or reproducing information on the medium, and a wavelength for performing servo of a focus or tracking optical mechanism system. Light source that emits light, a means that guides the light emitted from each of these light sources to the same optical path toward the medium, and a detection means that detects the reflected light from the medium of the light emitted from the reproduction light source and the servo light source. And consists.

[0020]

By using the servo light of the optical mechanism system separately from the recording / reproducing light, the crosstalk due to each light of the detection light caught by the detector for detecting the deviation of focus or tracking can be removed. It is possible to perform accurate servo control of the.

In particular, if the wavelength of the reproduction light is determined so as to satisfy the equation 2, the tracking error signal due to the reproduction light becomes zero, and the influence of the reproduction light on the detection light entering the detector can be removed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A focus or tracking method and apparatus for an optical recording medium according to the present invention will be described below in detail with reference to the drawings based on each embodiment.

[First Embodiment] FIG. 1 is a block diagram showing the outline of a recording / reproducing and focusing or tracking device for an optical recording medium according to the first embodiment.

In the figure, 1 is a photochromic optical recording medium in which a recording layer 3 of a photochromic material is laminated on a substrate 2, and 4 is the medium 1 by a servo circuit described later.
An objective lens that can move the position (tracking) and change the focal length (focusing),
5 is a wavelength of 458n used for erasing information on the medium 1
m is an Ar laser light source, 6 is a He-Ne laser light source having a wavelength of 633 nm used for recording / reproducing information on the recording medium 1, and 7 is a semiconductor laser light source having a wavelength of 780 nm used for detecting focus shift or tracking shift. is there.

Reference numerals 8, 9 and 10 are first to third λ / 4 plates corresponding to the light sources 5 to 7, 11 and 12 are first and second dichroic mirrors, and 13 and 14 are first and second deflectors. Beam splitter, 15 and 16 are first and second photo detectors, 17 is AO
Modulator (Acoustic Optic modulation), 18 is the second
A servo circuit for focusing or tracking that adjusts the objective lens 4 based on the detection data of the photodetector 16.

In such a structure, the light emitted from the erasing light source 5 passes through the first λ / 4 plate, is reflected by the first dichroic mirror 11 and enters the objective lens 4, and the objective lens 4 acts. The information is erased at a desired point on the medium 1 by being focused and tracked.

At the time of recording information, the recording / reproducing light source 6 outputs recording light of high power, and the AO modulator 17 shapes the light into pulses. This light is reflected by the second dichroic mirror 12 via the first deflecting beam splitter 13 and the second λ / 4 plate 9, passes through the first dichroic mirror and enters the objective lens 4, and the objective lens 4 performs focusing. Also, information is recorded at desired points on the medium 1 by being tracked.

At the time of reproducing information, the recording / reproducing light source 6 outputs reproducing light of weak power. This reproducing light passes through the AO modulator 17, the first deflecting beam splitter 13, the first λ / 4 plate 9, the second and first dichroic mirrors 12 and 11 and is focused and tracked by the objective lens 4 like the recording light. To the desired point on the medium 1, where it is reflected and follows the reverse path, the objective lens 4, the first,
The light enters the second dichroic mirrors 11 and 12, the first λ / 4 plate 9 and the first deflection beam splitter 13.

Then, it is reflected by the first deflecting beam splitter 13 and enters the first photodetector 15, where a change in reflectance is detected and a reproduction output signal is taken out.

By the way, when accessing the above information recording / reproducing,
In addition, the servo control is activated during standby, and the objective lens 4 can be instantaneously moved to the next operation. During this servo control, light is output from the servo light source 7.
This light passes through the second deflection beam splitter 14
The light enters the objective lens 4 through the λ / 4 plate 10, the second dichroic mirror, and the first dichroic mirror.

The light emitted from the objective lens 4 is condensed on the medium 1, reflected by the medium 1 and returned to the objective lens 4 again.
Then, the first and second dichroic mirrors 11, 12 and the second λ
After passing through the / 4 plate, it enters the second deflecting beam splitter 14, where it is reflected and the reflected light is detected by the second photodetector.

The second photodetector 16 employs, for example, a four-division PIN type photodetector used in the conventionally known astigmatism method, and the detector 16 is deformed by the deformation of the reflected light of the servo light due to the focus shift. The focus shift is determined by detecting the change in the incident power entering the.

In this way, the second photo detector 16
When the focus shift is detected by, the detection signal is input to the servo circuit 18 for focusing or tracking, and the necessary calculation is performed here to output the control output for changing the position and the focal length of the objective lens 4 by the necessary amount. The circuit 18
Is output from.

One of the features of this structure is that the output of the first photodetector 15 which detects the reflected light of the reproducing light source 6 during reproduction is used only for reproducing recorded information, and the photochromic material 3 has no absorption. In the wavelength range, the reflected light from the newly provided servo light source is used by the second photo detector 16
The focus error signal and the tracking error signal are obtained by this.

With the above structure, since the photochromic material 3 does not have absorption at 780 nm, the recorded information is not destroyed during access or during reproduction standby, and the detection efficiency of the second photodetector 16 near 780 nm is high.
Stable focus servo or tracking servo is performed.

Further, at the time of recording information, the recording / reproducing light source 6 is caused to emit light with a high power, the light is modulated by the AO modulator 17 according to the recording signal, and the medium 1 is irradiated. Conventionally, in the configuration shown in FIG. 5, when the reflected light from the recording / reproducing light source 102 is detected and servo control is performed, high power light reaches the photodetector 110 for servo detection. Therefore, the photodetector 110 enters the photodetector 110. The automatic gain adjustment circuit 112 that adjusts the gain in accordance with the incident power was required. However, in the present embodiment, the light of 780 nm irradiates the medium 1 with the same power during reproduction and recording. The adjusting circuit 112 is unnecessary, and the servo circuit system has a simple structure.

Another feature of this structure is a groove (not shown) formed on the surface of the substrate 1 which is usually formed for performing tracking servo even in the conventional optical disk system.
Is the point of depth Δ.

Regarding the depth Δ of the groove, for example, “Optical Memory Technology” published by Trikeps Co., Ltd., 1988, page 38, the depth Δ of the groove where the tracking error signal becomes maximum is the wavelength of light used for detection. λ, where n is the refractive index of the substrate for this wavelength,

[0039]

[Equation 3]

Is known to be

On the other hand, in the conventional structure in which the reproduction of information and the servo control are performed by the same beam, crosstalk occurs from the tracking error signal in the low frequency region of the reproduction signal.

Therefore, in order to prevent the influence of this kind of crosstalk, the signal recorded / reproduced on / from the medium is actually a signal modulated by various methods so as not to contain a low frequency component. This means that the crosstalk from the tracking error signal to the reproduction signal limits the recording signal used.

Therefore, in this embodiment, the wavelength of light used for reproducing information and the wavelength of light used for servo control are made different from each other.
The depth Δ of the tracking groove used was set so as to maximize the tracking error signal corresponding to the servo light.

Therefore, the maximum condition of the expression 3 is not satisfied for the reproduction light, and the crosstalk from the tracking error signal to the reproduction signal is greatly reduced.

Especially for the wavelength λ _S of the light for servo

[0046]

[Equation 4]

For the reproduction light wavelength λ _R

[0048]

[Equation 5]

[0049] n _S both (although relative each lambda _S and the refractive index n of the substrate 2 is generally dependent on the wavelength of, n with respect to lambda _{R R}
The groove depth Δ was set so that

As a result, the gain of the servo detection output was large, and the crosstalk from the tracking error signal did not occur in the reproduced signal at all.

If crosstalk from the tracking error signal to the reproduced signal can be prevented in this way, the frequency used for the reproduced signal can be used from a low frequency, and the degree of freedom of the used signal can be greatly expanded. As a result, the recording capacity is increased.

[Second Embodiment] Next, an embodiment of an optical mechanism system in which the focusing or tracking method of the optical recording medium of the present invention is applied to a wavelength multiplex recording system will be described in detail with reference to FIGS. Although the present embodiment discloses the two-wavelength multiplex recording method, it goes without saying that the wavelength multiplex recording method with high multiplicity can be extended.

First, FIG. 2 is a block diagram showing an optical mechanism system, and the same components as those in FIG. 1 are designated by the same reference numerals and detailed description thereof will be omitted.

The photochromic material contained in the photochromic medium 1 is, for example, 2- (1,2-dimethyl-3
-Indolyl) -3- (2,3,5-trimethyl-3-thienyl) maleic anhydride (hereinafter abbreviated as asymmetric indole-thiophene type) and 2,3-bis (2-methylbenzo [b] thiophene-3 -Yl) Maleic anhydride (hereinafter abbreviated as symmetrical benzothiophene type) laminated or mixed to form the recording layer 3
Was used.

The asymmetric indole-thiophene type has a molecular structure and an absorption spectrum as shown in the structural formula and absorbance characteristic diagram of FIG. That is, when the recording layer 3 is irradiated with blue light having a wavelength of 400 to 480 nm, the state shown by the solid line in FIG.
On the contrary, when the light of m is irradiated, it has the property of changing from the state shown by the broken line to the state shown by the solid line.

Therefore, the medium 1 containing the photochromic material is irradiated with blue light on the entire surface of the medium 1 in advance to be in the state (erased state) shown by the broken line in FIG.
Recording can be performed by using a He-Ne laser light source 6 that emits light of 3 nm with a relatively high power and by modulating and irradiating according to an information signal to be recorded, and similarly, light with a wavelength of 633 nm with a constant low power. The reproduced signal can be obtained by irradiating the medium and detecting the intensity change of the reflected light on the medium 1.

On the other hand, the symmetrical benzothiophene type has a molecular structure and an absorption spectrum as shown in the structural formula and absorbance characteristic diagram of FIG. That is, when blue light having a wavelength of 400 to 460 nm is irradiated, the state shown by a solid line changes to a state shown by a broken line, and when light having a wavelength of 500 to 600 nm is emitted, the state shown in FIG.
On the contrary, it has the property of changing from the state shown by the broken line to the state shown by the solid line.

Therefore, the medium 1 containing the photochromic material is irradiated with blue light on the entire surface of the medium 1 in advance to be in the state (erased state) shown by the broken line in FIG.
Recording can be performed by using an Ar laser light source 5 that emits 4.5 nm light with relatively high power and by modulating and irradiating according to the information signal to be recorded. The reproduced signal can be obtained by irradiating the medium and detecting the intensity change of the reflected light on the medium 1.

Therefore, as the light source for wavelength multiplexing recording / reproducing using these photochromic materials, the Ar laser 5 and the He-Ne laser 6 can be used, but this embodiment is limited to the use of such a gas laser. Not S
It is also possible to use a light source using an HG element, a short wavelength semiconductor laser, or the like.

First, the optical system of the Ar laser light source 5 system will be described. 19 is an ND filter for changing the light intensity for recording or reproduction, and 20 is a pulse intensity modulation of the light coming from the ND filter 19. AO modulator,
Reference numeral 21 is a beam expander for expanding and shaping the pulsed beam, 31 is a deflecting beam splitter, and 22 is a photodetector.

In the Ar laser light source 5 system, at the time of recording, the light emitted from the light source 5 is adjusted to a relatively high power level by the ND filter 19 and intensity modulated according to the recording signal by the AO modulator 20, and the beam expander is used.
After being appropriately enlarged and shaped by 21, the P-wave is transmitted through the deflecting beam splitter 31, and is converted into circularly polarized light by the λ / 4 plate 8.

Next, the light having a wavelength of 514.5 nm is totally transmitted and the wavelength is 633n.
He by the dichroic mirror 12 that totally reflects m light
-Combined with the light from the Ne laser light source 6, and a wavelength of 780n
Recording is performed by reflecting all light having a wavelength of m or more and totally reflecting light having a wavelength of 750 nm or less by the dichroic mirror 12 and condensing the light on the medium 1 by the objective lens 4.

On the other hand, during reproduction, the light emitted from the light source 5 is adjusted to a low power by the ND filter 19 and is kept constant power (CW) by the AO modulator 20. The same operation is performed.

The reflected light from the medium 1 is reflected by the objective lens 4,
After passing through the dichroic mirrors 11 and 12 and the λ / 4 plate 8, the S-wave enters the deflecting beam splitter 21, is reflected, and is detected by the photodetector 22.

Further, in the case of the He-Ne laser light source 6 system, the light is the same as in the Ar laser light source 5 system except that the light is reflected by the dichroic mirror 12, the ND filter 23, the AO modulator 17, the beam expander 24, the deflecting beam splitter. Recording / reproduction is performed by transmitting or reflecting light through the 13, λ / 4 plate 9, dichroic mirrors 11, 12, and photodetector 15.

By the way, the light source 7 for performing the focus servo and the tracking servo has, for example, a wavelength of 7 since the material of the medium 1 used in this embodiment has no absorption at 700 nm or more.
An 80 nm semiconductor laser is used.

The semiconductor laser light source 7 is a driving circuit 25.
The laser light is emitted at a constant power during recording and reproduction by the deflecting beam splitter 14 and the λ / 4 plate 10,
The objective lens 4 collects the light on the medium 1, and the reflected light passes through the objective lens 4, the λ / 4 plate 10 and the deflection beam splitter 14 again, and then the optical system for focus servo and tracking servo (optical system including a photodetector). ). As a method of detecting the focus error signal and the tracking error signal for executing these servos, various methods such as a conventionally known astigmatism method and push-pull method can be used. Then, the focus or tracking servo circuit 18 is operated by this detection signal, and a necessary optical system such as an objective lens is adjusted to perform servo.

[0068]

As described above, the present invention eliminates the disadvantages that the servo of the optical system such as the objective lens can be performed more stably and the information already recorded is destroyed at the time of access or reproduction standby. Moreover, it is possible to prevent the crosstalk from the tracking error signal of the reproduction output, and as a result, the degree of freedom of the tracking error signal that can be used is increased, and the recording capacity of the medium can be increased.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a recording / reproducing apparatus for an optical recording medium adopting the present invention.

FIG. 2 is a configuration diagram showing a second embodiment in which the present invention is applied to a recording / reproducing apparatus for optical multiplex recording.

FIG. 3 is a diagram showing a structural formula and an absorbance characteristic of an asymmetric indole / thiophene type photochromic material.

FIG. 4 is a diagram showing a structural formula and an absorbance characteristic of a symmetrical benzothiophene type photochromic material.

FIG. 5 is a block diagram showing a recording / reproducing apparatus for a conventional optical recording medium.

FIG. 6 is a diagram showing a spectral sensitivity characteristic of a PIN type photodetector.

[Explanation of symbols]

1 medium 5, 6 recording / reproducing light source 7 servo light source 15, 22 reproducing light detection photodetector 16 focus or tracking servo photodetector

Claims (3)

[Claims] 1. Information is recorded by irradiating an optical recording medium with light having a recording wavelength, and irradiating the medium with light having a reproducing wavelength and detecting reflected light from the medium. During the recording / reproducing of the optical recording medium for reading out, the information recording portion on the medium is focused or tracked using the optical mechanism servo light having a wavelength different from that of the recording light and the reproducing light. A method for focusing or tracking an optical recording medium. 2. The optical recording medium is formed by laminating a photochromic material on a substrate, a groove having a depth Δ for tracking is formed on the substrate, and the depth Δ of the groove is defined as the depth of the reproducing light. substrate refractive index n at a wavelength lambda _R and wavelength lambda _{R
For R} , The tracking method for an optical recording medium according to claim 1, wherein the tracking method is defined so as to satisfy the above condition. 3. A lens system for condensing light for recording / reproducing / erasing or optical mechanism servo on an optical recording medium, and a light source for emitting light of a wavelength for recording or reproducing information on the medium. A light source that emits light of a wavelength for performing servo of an optical system for focusing or tracking, a means that guides the light emitted from each of these light sources to the same optical path toward the medium, the reproduction light source and the servo light source. A focus or tracking device for an optical recording medium, which comprises a detecting means for detecting the light emitted from the medium and reflected by the medium.