JPH0750028A - Optical disk device - Google Patents

Abstract

PURPOSE:To realize a superresolution phenomenon stably and to obtain an excellent reproduced signal against the fluctuation of a laser light source for reproduction and the fluctuation of the optical characteristics of a disk in the reproduction of the optical disk having a nonlinear optical material layer. CONSTITUTION:After the starting, at first the optimum laser light intensity for reproduction is determined, and the reproduction is performed by using the laser light having the above described determined light intensity in this optical disk device 10. Information is formed on the information track of an optical, disk 40 by the information pits at the shortest pitch. The intensity of the laser light is changed, and the information is reproduced. A laser-light- source control device 2 controls a laser light source 3 so as to obtain the laser light intensity when the changing rate of the amplitude of the reproduced signal becomes the maximum value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for reproducing an optical disk having a non-linear optical material layer.

[0002]

2. Description of the Related Art In recent years, an optical disc in which fine information pits are formed in a concavo-convex shape in a circular shape has been considered to have a large capacity. Therefore, by changing the sensitivity of the recording medium or controlling the laser light output of the optical head, a recording mark having a diameter smaller than the light spot diameter of the laser light focused by the lens is formed on the optical disc medium. It is possible to However, at the time of reproduction, the spot diameter of the reproduction laser light condensed by the lens is the light spot diameter limited by the wavelength of the laser light in the reproduction optical head and the numerical aperture of the objective lens for condensing the laser light. It cannot be smaller than the minimum limit.

That is, in the reproduction of information recorded on an optical disc with concave and convex recording marks (hereinafter, the recording marks are also referred to as pits or information pits), the wavelength of the reproducing laser light is λ, and the laser light is focused. When the numerical aperture of the objective lens used is NA, the pitch of the recording marks at the reproduction limit (hereinafter, also referred to as the shortest pitch) is λ / 2NA. From this, in order to identify and reproduce the recording mark with a shorter pitch, it is possible to use a laser beam with a short wavelength λ,
It is conceivable to use a lens having a large numerical aperture NA, but it is technically difficult to shorten the wavelength of a semiconductor laser used for reproduction, and it is small to incorporate a lens having a large numerical aperture into a reproducing apparatus for an optical disc. It is difficult from the viewpoints of optimization and controllability.

On the other hand, as a method of improving the recording density of an optical disk, a method of effectively reducing the light spot at the time of reproduction is provided in addition to the method of focusing on the wavelength of the laser beam and the numerical aperture of the objective lens described above. 2-96926. This is because, when the information track of the recording medium is scanned with the laser beam during reproduction, the identification state occurs in the scanning spot due to the irradiation of the scanning beam that scans the recording medium, and as a result, the effective scanning spot is larger than the original scanning spot. This is a method in which a layer of a non-linear optical material that produces an optical effect that is considerably small is provided on the optical disc, and the information surface of the optical disc is optically scanned.

FIG. 3 is a sectional view of a general optical disc using a non-linear optical material. Optical disc 4 shown in FIG.
In 0A, the third-order nonlinear optical material layer 42, the reflective layer 43, and the protective film 44 are laminated on the transparent substrate 41,
The optical disc 40A is configured. The optical disc 40A has an information track for recording information.
The information track is formed in a concentric or spiral shape, and a pit portion is formed in an uneven shape on the information track, and a land portion is formed between the pits of the pit portion. The thickness of the third-order nonlinear optical material layer is approximately 1/2 of the optical wavelength of the reproducing laser beam optically.

The optical disc 40A shown in FIG. 3 uses a third-order nonlinear optical material as the nonlinear optical material.
An optical characteristic called a third-order nonlinear optical phenomenon is used for reproduction. That is, an optical phenomenon is used in which the refractive index and the transmittance of a substance change non-linearly with respect to the change of the light intensity when the light intensity of the irradiated laser light exceeds a certain level. The diameter of the laser beam condensed above is effectively made smaller than the theoretical minimum diameter determined by the wavelength of the laser beam and the numerical aperture of the objective lens to obtain high resolution. According to this method, it is said that a super-resolution phenomenon capable of improving the resolution beyond the limit resolution determined by the wavelength of laser light and the numerical aperture of the objective lens can be obtained.

The above-mentioned third-order nonlinear optical material will be described below. For third-order nonlinear optical materials, see "Laser spectroscopy" (Mark D. Levenson, Sat.
oru S. Kano Ohmsha, 1988)
, "Phase conjugate spectroscopy" (Junichi Sakai, Asakura Shoten 19
Published in 1990). The third-order nonlinear optical material has a property that almost all substances have, but as a material used in the optical disc 40A shown in FIG. 3, X (3) representing the degree of the third-order nonlinear optical material is relatively large. Large ones are needed and the materials used are naturally limited.

The third-order nonlinear optical phenomenon is a phenomenon in which the absorption coefficient and the refractive index of the optical material change nonlinearly according to the intensity of light incident on the third-order nonlinear optical material. For example, in an organic dye-based material or the like, when a dye is irradiated with a laser beam having a wavelength in the vicinity of the absorption wavelength of the dye, it has a property that the absorption coefficient of the dye sharply decreases with light having a certain light intensity or more, This is known as the saturation absorption phenomenon. This phenomenon is a pure physical phenomenon and is reversible, and it can be used for optical discs that utilize the super-resolution phenomenon because it quickly recovers the original absorption coefficient when the light intensity incident on the dye is weakened. .

Further, in the case of a direct transition type semiconductor or the like, when light having a frequency near the band gap of the semiconductor enters, the carrier density in the excited state extremely increases, saturation absorption occurs, and at the same time, the refractive index lowers. In addition, it can be used for optical discs that utilize the super-resolution phenomenon.
In addition to this, there is a photochromic phenomenon as a pure chemical phenomenon. This is because when a substance is irradiated with light, it receives light energy and isomerizes or dissociates, changing its molecular structure and, as a result, changing the absorption coefficient of the substance at a specific wavelength. Since the transmittance changes with light, it can be called a third-order nonlinear optical material in a broad sense.

Although an example of the third-order nonlinear optical material has been shown above, any material in which the light transmittance of a substance irradiated with light changes according to the light intensity is generally called a third-order nonlinear optical material. FIG. 4 is a diagram showing an example of the optical characteristics of the third-order nonlinear optical material. In FIG. 4, the horizontal axis represents the light intensity, and the curve C1 represents the transmittance of the third-order nonlinear optical material. As shown by the curve C1, when the light intensity with which the third-order nonlinear optical material is irradiated is gradually increased, the transmittance of the material sharply increases near a certain light intensity. Further, as indicated by the curve C2, the light intensity of the laser light becomes maximum at the beam center, and the light intensity decreases as the distance from the center increases. Then, the center portion CC of the light beam is used for manifesting the super-resolution phenomenon.

As described above, it is well known that the laser light has a higher light intensity toward the center thereof and has a so-called Gaussian distribution. Therefore, if the intensity of the laser beam with which the third-order nonlinear optical material layer 42 of the optical disc 40A is irradiated is appropriately adjusted, the transmittance of the third-order nonlinear optical material layer 42 is improved only at the central portion of the laser beam. Therefore, the reflective layer 4
The spot diameter of the laser light that reaches 3 is smaller than the minimum spot diameter shown in the optical theory. However, in an actual optical disc reproducing apparatus, fluctuations in laser output, dirt on the objective lens, asymmetry of birefringence in the disc substrate, variations in transmittance, and variations in film thickness and absorption coefficient of the third-order nonlinear optical material. Due to variations in
It was found that the light intensity of the laser light with which the next non-linear optical material layer 42 is irradiated may change by 50% or more, and it is difficult to obtain the above-mentioned super-resolution phenomenon as expected.

FIG. 5 is a diagram for explaining the fluctuation of the substantial light spot diameter. In FIG. 5, a large number of pits P formed on the information track are shown. (A) in the figure
FIG. 6 is a diagram when a laser beam having an optimal light intensity for reproducing the optical disc is irradiated, and the diameter of the laser beam converged by the objective lens is as shown by C3 on the incident side of the third-order nonlinear optical material layer 42. The beam diameter is large and becomes small on the emission side, and the beam diameter becomes optimum for reproduction as indicated by C4. The effective light spot diameter refers to the diameter of the light spot after passing through the third-order nonlinear optical material layer.

On the other hand, FIG. 3B is a diagram in the case where a laser beam having a light intensity lower than that in the case of FIG.
Since the light intensity of the laser light incident on the second-order nonlinear optical material layer 42 is smaller than the optimum light intensity, the beam diameter C5 on the output side of the third-order nonlinear optical material layer 42 is the optimum size indicated by C4. It is smaller than. In this case, an undesired super-resolution phenomenon occurs, the information signal read from the information pit is deformed, the output of the information signal becomes small, or the reading becomes impossible. On the contrary, if the light intensity of the laser light is too large, the beam diameter on the output side of the third-order nonlinear optical material layer 42 becomes larger than the optimum diameter, and the necessary super-resolution phenomenon does not occur. The information signal read from the pit may be deformed, the output of the information signal may be reduced, or the information may not be read.

[0014]

In a method of reproducing a high-density optical disc by providing a third-order nonlinear optical material layer on an optical disc to cause a super-resolution phenomenon, a method of reproducing laser light for irradiating the third-order nonlinear optical material layer is described. There has been a problem that the state of the reproduced signal changes greatly due to changes in the light intensity and variations in the optical characteristics of each disc. The optical disk device of the present invention has been invented in view of the above problems, and its purpose is to:
In reproducing an optical disc having a non-linear optical material layer,
It is an object of the present invention to provide an optical disc device that stably exhibits a super-resolution phenomenon and can obtain a good reproduction signal with respect to a variation of a reproduction light source and a variation of optical characteristics for each disc.

[0015]

In the optical disk device of the present invention, a non-linear optical material layer made of an optical material whose optical transmittance changes non-linearly in response to a change in light intensity and a reflective layer are laminated on a transparent substrate. It is a device that reproduces an optical disk in which uneven information pits are formed on a track provided in a circular shape by using a laser beam from a laser light source, and uses a reproduction signal from the optical disk after starting. An optical disk device is provided with a laser light source control device that determines an optimum light intensity for reproduction of the laser light source, and then controls the laser light source so as to have the determined light intensity. Further, the optical disk device of the present invention is, in the laser light source control device, a scanning signal generating means for generating a scanning signal for changing the light intensity of the laser light source with time, and a predetermined reproduction signal from the optical disk. Corresponding to the signal amount detecting means for detecting the amount of the frequency component, the change rate detecting means for detecting the change rate of the output of the signal amount detecting means, and the laser light intensity when the output of the change rate detecting means becomes maximum. A storage unit for storing a signal for storing the signal, and outputting a signal according to the output of the scanning signal generating unit to change the laser light intensity, and then outputting a signal according to the output of the storage unit. It is a configured optical disk device.

[0016]

In the third-order nonlinear optical material layer provided on the optical disc, when laser light having an appropriate light intensity is irradiated,
Since the transmittance becomes high only in the central portion of the laser spot, a light spot whose diameter is effectively smaller than the light spot diameter of the irradiated laser light is irradiated to the reflective layer of the optical disc, and An image phenomenon is obtained. In order to stably obtain the super-resolution phenomenon, it is necessary to set the light intensity of the laser light with which the third-order nonlinear optical material layer is irradiated to near the optimum value. Therefore, after the optical disk device is started, the information from the shortest pit formed on the track is detected while changing the output of the laser light source, and the laser light output that maximizes the change rate of the amplitude of this signal is detected. Then, the optical disk is reproduced with the detected laser light output.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical disk device according to the present invention has a third-order nonlinear optical material layer made of an optical material whose optical transmittance changes non-linearly with respect to a change in light intensity and a reflective layer, which are laminated on a transparent substrate to form a circular shape. An optical disc device for reproducing an optical disc having information pits formed on a track provided therein by using laser light from a laser light source, the laser light source using a reproduction signal obtained from the optical disc. Is an optical disc device including a laser light source control device that determines the light intensity during reproduction and controls the laser light source so that the light intensity becomes the same.

An embodiment of the optical disk device of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing a main part of an embodiment of an optical disk device of the present invention. As shown in FIG. 1, the optical disc device 10 is a device that reproduces a signal from information pits formed in an uneven shape on a circular information track provided on the optical disc 40. Figure 3
FIG. 6 is a cross-sectional view of a general optical disc using a nonlinear optical material. As shown in FIG. 3, the optical disc 40 has a structure in which a substrate 41, a third-order nonlinear optical material layer 42, a reflection layer 43, and a protective film 44 are laminated, and is substantially the same as the optical disc 40A described in the conventional example. Is.

However, in the optical disc 40, the information tracks provided in a circular shape are provided with a light intensity setting track for setting the light intensity of the laser beam used at the time of reproduction for one revolution of the disc. A large number of pits are continuously formed on the light intensity setting track at substantially the same pitch, and this pitch is the shortest pitch corresponding to the highest repetition frequency recorded on the optical disc.
It is noted that this is an information signal obtained from an optical disc using the super-resolution phenomenon, and that the signal component from the shortest information pit is the one that changes the most with a change in laser light intensity.

The third-order nonlinear optical material layer 42 of the optical disc 40 is a substrate 4 made of polycarbonate resin.
1. Using a sputtering device, GaAs, In
It is formed by using one of P, CdS, etc., and has a film thickness of 780 nm at a laser light wavelength of λ /
It is set to be 2. A reflective layer 43 made of aluminum is formed on the third-order nonlinear optical material layer 42, and a protective film 44 made of an ultraviolet curable resin is formed thereon.
Is provided.

In the optical disk device 10 shown in FIG.
The laser light emitted from the laser light source 3 is collimated by the collimator lens 4 and passes through the beam splitter 5. The laser light passing through the beam splitter 5 is condensed by the objective lens 6 and forms a light spot on the optical disc 40. Focus control is performed so that the laser light forms a light spot on the optical disc 40, and tracking control is performed so that the light spot scans the center of the information track. The focus control and tracking control are performed by the objective lens 6
Is moved by the actuator 7.

The laser light reflected by the reflection layer 43 of the optical disk 40 passes through the objective lens 6, is reflected by the beam splitter 5, and enters the condenser lens 8. The laser light condensed by the condenser lens 8 enters a two-divided photodetector 9. The two-divided photodetector 9 is arranged such that its dividing line substantially corresponds to the center line of the information track. The output Sd of the two-divided photodetector 9 consists of two signals output from the two divided photodetectors. From these two signals, a focus error signal for performing focus control and tracking control are applied. Although a tracking error signal for generating the signal is generated, these devices are not shown.

The output Sd of the two-divided photodetector 9 is
It is supplied to the laser light source control device 2, and the light intensity of the laser light source 3 is controlled according to the output signal Sc of the laser light source control device 2. In the optical disk device 10,
After the optical disc 40 is loaded and activated, the signal Sc
By gradually changing the light intensity of the laser light source 3, the information of the light intensity setting track provided on the optical disc 40 is reproduced, and the amplitude of the reproduced signal is detected. Then, when the rate of change in the amplitude of the signal becomes maximum, the value Scp of the signal Sc applied to the laser light source 3 is stored.

After that, the output Sc of the laser light source control device 2 is fixed to the Scp, this signal is input to the laser light source 3, and the light intensity of the laser light is maintained at the optimum light intensity for reproducing the optical disc. It FIG. 2 is a block diagram showing an embodiment of the laser light source control device according to the present invention. The laser light source control device 2 will be described below with reference to FIG. Immediately after the optical disc 40 is mounted in the optical disc device 10 and started up, the optical disc 40 is output to the laser light source 3 via the output terminal 31 of the switch 29 shown in FIG. The switch 29 is a semiconductor switch that is switched by a signal from its control terminal 32. Further, the scanning signal generating means 28 is controlled to start or stop generation of a signal by a signal applied from the mechanical controller of the optical disk device 10 to the control terminal 33.

FIG. 6 is a diagram showing the state of the laser beam intensity and its control device when the laser beam intensity is set. When the optical disk device 10 is started, the light intensity of the laser light source 3 is controlled as shown in FIG. That is, the laser light intensity immediately after startup is a predetermined value P1 which is set to P2 which is smaller than P1 at the time t1 when the pull-in operation of the focus control and tracking control is completed. It increases at a constant rate from the time t1 to a time t2 after a lapse of a predetermined time Tc, and at time t2, it is set to P3 larger than the P1. The time Tc is smaller than the time required for the optical disc 40 to rotate once.

Between the times t1 and t2, the amplitude of the signal read from the light intensity setting track is detected, and the time tp at which the rate of change thereof is maximum is detected, and the light at this time tp is detected. Assuming that the intensity is P4, after the time t2, the light intensity of the laser light source 3 is P
It is set to 4. In FIG. 6B, from the time t1 to t2.
The amplitude Va of the reproduced signal and the change rate Vd of the amplitude are shown at the time point, and the change rate Vd is maximized at the time tp.

In FIG. 2, the signal Sd consisting of two signals from the photodetector 9 is applied to the RF signal detection circuit 22 and the two signals are added to generate the RF signal Sr. This RF signal Sr is applied to the signal amount detection means 15. The RF signal Sr is supplied as a reproduction signal to a decoding device (not shown) or the like, but the description thereof is omitted. In the signal amount detecting means 15, the RF signal S
Only a predetermined frequency component of r is detected by the bandpass filter 23 and the amplitude detection circuit 24, and its amplitude Va is detected and output to the change rate detection means 25.

The center frequency of the bandpass filter is
It is set near the frequency corresponding to the shortest pit of the optical disc 40. Further, the amplitude detection circuit 24 detects the peak value or peak-peak value of the signal. The change rate detection means 25 detects the change rate by sampling the amplitude Va at predetermined time intervals, but may be configured by a simple differentiating circuit, for example.

The output Vd of the change rate detecting means 25 is applied to the storage means 16 which detects the point where the output Vd becomes maximum and stores the output level of the scanning signal generating means 28 at that time. The storage means 16 is composed of a peak detection circuit 26 for detecting a point where the signal Vd is maximum and a sample hold circuit 27 for storing the output level of the scanning signal generation means 28 at that time. The output of the scanning signal generating means 28 is applied to the hold circuit 27. After the time t2, the output terminal 31 of the switch 29 is connected to the output side of the storage means 16, and the output of the storage means 16 is output to the laser light source 3.

In the optical disk device of the present invention, when the reproduction evaluation is performed using the optical disk 40 provided with the third-order nonlinear optical material layer 42 and, for example, a semiconductor laser light source having a wavelength of 780 nm, the light intensity of the reproduction light is optimized. Since the laser light source control device 2 for setting the value is provided, at the time of reproduction, first, the laser light intensity is automatically set to the optimum value according to the characteristics of the optical disk to be used and the reproduction device, and the required super resolution is set. The image phenomenon was satisfactorily exhibited, and a high density optical disc having an information signal pit width and a pit length of ⅔ as compared with the conventional optical disc could be reproduced very favorably with a C1 error ratio of 0.5%.

When the optical disc 40 is reproduced by a reproducing device which does not have the laser light source control device, although the super-resolution phenomenon appears and an information signal is obtained, the C1 error ratio is as large as 5%, which is normal. It couldn't be reproduced.
In the laser light source control device 2, when the optimum laser light intensity for reproduction is determined, in the embodiment, the light intensity of the laser light source is continuously changed by the scanning signal generating means 28. Is changed discontinuously for each revolution of the disc, the average value of the amplitude of the component corresponding to the shortest pit in the reproduction signal is determined for each revolution of the disc, and the condition that the rate of change is maximized is detected. good. in this case,
The track in which the pits with the shortest pitch are continuously formed as described in the embodiment is not always necessary.

[0032]

According to the optical disk device of the present invention, the light intensity of the laser beam irradiating the nonlinear material layer of the optical disk can be set to an appropriate value for reproduction, and the super-resolution phenomenon can be well expressed. Therefore, it is possible to stably reproduce a high-density optical disc having a nonlinear optical material layer.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of an embodiment of an optical disk device of the present invention.

FIG. 2 is a block diagram showing an embodiment of a laser light source control device according to the present invention.

FIG. 3 is a cross-sectional view of a general optical disc using a nonlinear optical material.

FIG. 4 is a diagram showing an example of optical characteristics of a third-order nonlinear optical material.

FIG. 5 is a diagram illustrating a variation of a substantial light spot diameter.

FIG. 6 is a diagram showing a laser light intensity and a state of a controller thereof when setting the laser light intensity.

FIG. 7 is a diagram showing a positional relationship between information pits and a super-resolution portion.

[Explanation of symbols]

 2 Laser Light Source Controller 3 Laser Light Source 4 Collimator Lens 5 Beam Splitter 6 Objective Lens 7 Actuator 8 Condensing Lens 9 2 Split Photo Detector 10 Optical Disk Device 15 Signal Amount Detecting Means 16 Storage Means 25 Change Rate Detecting Means 28 Scanning Signal Generating Means 40 optical disc

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[Procedure amendment]

[Submission date] March 9, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of an embodiment of an optical disk device of the present invention.

FIG. 2 is a block diagram showing an embodiment of a laser light source control device according to the present invention.

FIG. 3 is a cross-sectional view of a general optical disc using a nonlinear optical material.

FIG. 4 is a diagram showing an example of optical characteristics of a third-order nonlinear optical material.

FIG. 5 is a diagram illustrating a variation of a substantial light spot diameter.

FIG. 6 is a diagram showing a laser light intensity and a state of a control device thereof when setting the laser light intensity.

[Explanation of reference numerals] 2 laser light source control device 3 laser light source 4 collimator lens 5 beam splitter 6 objective lens 7 actuator 8 condenser lens 9 2 split light detector 10 optical disk device 15 signal amount detection means 16 storage means 25 change rate detection means 28 scanning signal generating means 40 optical disk

Claims (2)

[Claims] 1. An optical disk device for reproducing the information pits of an optical disk in which a non-linear optical material layer and a reflective layer are laminated on a transparent substrate to form information pits by using laser light from a laser light source. And a laser light source control device for controlling the laser light source to have the determined light intensity after determining the light intensity at the time of reproduction of the laser light source using the reproduction signal from the optical disc. Optical disk device. 2. In the laser light source control device, a scanning signal generating means for generating a scanning signal for changing the laser light intensity, and a signal amount detecting means for detecting an amount of a predetermined frequency component of the reproduction signal. And a change rate detecting means for detecting a change rate of the output of the signal amount detecting means, and a storage means for storing a signal corresponding to the laser light intensity when the output of the change rate detecting means is maximum, 2. The optical disk device according to claim 1, wherein after outputting a signal according to the output of the scanning signal generating means, a signal according to the output of the storage means is output.