JPH04324133A - Optical recording medium and recording and/or reproducing device thereof - Google Patents

Abstract

PURPOSE:To provide the optical recording medium of a transmission type which allows servo, such as focus servo, at the time of recording or reproducing and the recording and/or reproducing device thereof. CONSTITUTION:The optical recording medium 1 is constituted by laminating and forming a semi-reflection layer 3 and a recording layer 4 on a substrate 2. This optical recording medium 1 is irradiated with light for recording or reproducing and the focus servo, tracking servo, etc., are executed by using the light reflected by the semi-reflection layer 3.

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 and a recording and/or reproducing apparatus thereof.

0002

BACKGROUND OF THE INVENTION In recent years, research on the use of photochromic materials in the recording layer of optical recording media has been actively conducted.

Photochromic materials have the property that when irradiated with light of a predetermined wavelength, the structure of the molecules changes due to a photochemical reaction, and the optical properties of the molecules change. Furthermore, when a molecule with the above structure is irradiated with light of another predetermined wavelength, the molecule returns to its original structure.

Therefore, when a photochromic material is used in the recording layer of an optical recording medium, information is recorded by changing the absorbance by irradiation with light of a predetermined wavelength, and the change in absorbance with respect to light of a specific wavelength is detected. A recording and reproducing method for reproducing information is known.

However, the above-mentioned reproduction method has a problem in that even when the light for reproducing information is weak, a photochemical reaction occurs in the molecules and the recorded information is destroyed.

[0006] Furthermore, as a recording/reproducing method other than the above, for example, Japanese Patent Application Laid-Open No. 63-259850 (G11B 7/2
4) The publication discloses a recording method on an optical recording medium using a photochromic material having optical rotation.

[0007] In this method, molecules of a photochromic material have optical rotation in one state before and after a reversible chemical reaction because they have asymmetric carbon atoms, and in the other state they do not have asymmetric carbon atoms. Therefore, by utilizing the fact that it does not have optical rotation, it is possible to distinguish, for example, whether information is recorded or not based on the presence or absence of optical rotation.

However, when the method using optical rotation described above is applied to a reflective optical recording medium, the incident linearly polarized light for reproduction is transmitted through a recording layer having optical rotation, and the plane of polarization is rotated by an angle δ. is reflected by the reflective layer and transmitted through the recording layer again, the plane of polarization rotates by an angle δ in the opposite direction,
As a result, no rotation of the plane of polarization occurs between the reflected light and the incident light, making it impossible to reproduce information.

[0009] Therefore, the method using optical rotation described above is used for transmissive optical recording media, but for transmissive optical recording media, the focus servo used in ordinary reflective optical recording media is used. There was a problem that the system could not be used.

This is because, in the case of the reflective optical recording medium 101 shown in FIG. Focus servo is performed by taking advantage of the fact that the light does not return to parallel light after transmission, but in the case of a transmission type optical recording medium 101', a focus shift (indicated by a broken line in the figure) occurs as shown in FIG. Also objective lens 102
Even after passing through ', the light becomes parallel, so focus servo cannot be performed.

[0011]

SUMMARY OF THE INVENTION In consideration of the above points, the present invention aims to realize a transmissive optical recording medium capable of servo control such as focus servo, and a recording and/or reproducing apparatus thereof.

0012

[Means for Solving the Problems] The optical recording medium of the present invention includes:
An optical recording medium in which at least a recording layer is formed on a substrate, further comprising a semi-reflective layer.

Further, the recording and/or reproducing apparatus for an optical recording medium of the present invention irradiates light onto an optical recording medium in which at least a recording layer and a semi-reflective layer are formed on a substrate, and a part of the light is It is characterized in that servo is performed based on the reflected light generated by being reflected by the semi-reflective layer.

[0014]

[Function] Since the optical recording medium has a semi-reflective layer, part of the recording light or reproduction light is reflected, and servo can be performed based on this reflected light. Recording or reproduction can be performed using the other part of the optical beam.

[0015]

Embodiment A first embodiment will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of an example of an optical recording medium 1 used in a first embodiment of the present invention. This optical recording medium 1
is glass, PMMA (polymethyl methacrylate),
Part of the reproducing light and/or recording light is transmitted onto a base (substrate) 2 made of a material such as PC (polycarbonate),
In addition, a semi-reflective layer 3 having a property of partially reflecting is formed by vapor deposition or the like.

A recording layer 4 containing a material whose optical rotation is changed by light irradiation or heating is formed on the semi-reflective layer 3 by a spin coating method, a vapor deposition method, an LB method, or the like.

Further, on the recording layer 4, a protective layer 5 made of an ultraviolet curing resin or the like is formed which transmits the reproducing light and/or the recording light.

The semi-reflective layer 3 may be, for example, an Al thin film with a thickness of approximately 300 angstroms, or various metal thin films such as Au, Ag, and Cu, alloy thin films, or a film corresponding to the wavelength of light for recording and/or reproduction. A dielectric multilayer film can be used. In particular, the dielectric multilayer film is desirable because it absorbs almost no light and can be designed to efficiently reflect and transmit light. The reflectance of the semi-reflective layer 3 can be set as appropriate by changing its layer thickness, etc., but if the reflectance is about 20%, the servo described below can be performed.

[0020] The recording layer 4 also has a material whose optical rotation is changed by the above-mentioned light irradiation or heating, such as the one disclosed in Japanese Patent Laid-Open No. 63-259850 (G11B7/24). Various photochromic materials such as spiropyran-based photochromic materials, azobenzene-based and diarylethene-based photochromic materials can be used as appropriate.

Furthermore, the optical recording medium 1 used in the first embodiment may have a structure as shown in FIGS. 2 and 3. Note that the same parts are given the same reference numerals and their explanations will be omitted. In particular, the protective layer 5 made of the ultraviolet curable resin described above can protect the recording layer 4, etc., but since the protective layer 5 itself is easily scratched and deposited, as shown in FIG. It is desirable that the optical recording medium 1 has a structure in which the optical recording medium 4 is sandwiched between the substrates 2.

Further, in the optical recording medium shown in FIGS. 1 to 3, the incident light (reproducing light and/or recording light) may be made to enter from either the upper or lower surface of the optical recording medium 1.

The optical recording medium 1 described above can record information by a change in the optical rotation occurring in the recording layer 4, and can reproduce information by detecting the change in the optical rotation using, for example, a polarizer.

Next, FIG. 4 shows a schematic diagram of an example of a reproducing apparatus for reproducing the above-mentioned optical recording medium 1 based on this principle. Note that a medium drive device and the like are not shown.

Reference numeral 6 denotes a reproduction light source such as a semiconductor laser that outputs a linearly polarized laser beam with a wavelength of 0.78 μm, for example. Further, 7 is a drive circuit for driving this light source 6 for reproduction. The laser beam outputted from the reproduction light source 6 is collimated by a lens 8 and then transmitted through a beam splitter 9 to be incident on an objective lens 10 .

The laser beam incident on the objective lens 10 is
A part of the light passes through the semi-reflective layer 3 of the optical recording medium 1 (see FIG. 1) and is focused on the recording layer 4, and a part of the light is reflected by the semi-reflective layer 3.

The laser beam focused on the recording layer 4 rotates its plane of polarization in accordance with the optical rotation based on the information recorded on the recording layer 4, so that after being converted into parallel light by the objective lens 20, A difference occurs in the amount of light passing through the polarizer 25 and the lens 26, and a reproduced signal based on a change in the output of the photodetector 27 is obtained.

Further, the laser beam reflected by the semi-reflective layer 3 passes through the objective lens 10 again, and then a part of it is reflected by the beam splitter 9 and passes through the focus error detection optical system 3.
0 and reaches the photosensor 31.

The error signal obtained from the photo sensor 31 is sent to the actuator 33 via the focus servo circuit 32.
, 33', and the above-mentioned optical recording medium 1
The objective lenses 10 and 20 are driven so as to reduce focus errors caused by warpage and other causes.

For focus error detection by the focus error detection optical system 30 and photosensor 31, various methods such as the conventional astigmatism method and knife edge method are used. At this time, the objective lenses 10 and 20 are adjusted and driven so that the distance between them is always constant.

By providing the semi-reflective layer 3 on the transmissive optical recording medium 1 that utilizes optical rotation as described above, some of the light incident on the optical recording medium 1 is reflected by the semi-reflective layer 3. Focus servo can be performed using light.

Next, FIG. 5 shows the reproduction device of the second embodiment.
This will be explained in detail with reference to. 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 1 used in this embodiment is the same as that used in the first embodiment.

In the first embodiment, the same focus servo circuit or the like was used to drive the objective lenses 10 and 20, but in this embodiment, the focus servo circuit or the like for driving the objective lens 10 is independently used. A focus servo circuit and the like are provided to drive the objective lens 20.

The objective lens 10 is driven by a focus servo circuit 32, etc., as in the first embodiment. Therefore, when this objective lens 10 is driven, the objective lens 20
The transmitted light is no longer parallel.

On the other hand, the laser beam that has passed through the semi-reflective layer 3 of the optical recording medium 1 is partially reflected by the beam splitter 9' and then passes through the focus error detection optical system 30' to the photosensor 31'. reach.

The error signal obtained by the photosensor 31' is fed back to the actuator 33' via the auxiliary focus servo circuit 32', and the objective lens 20 parallelizes the laser beam after passing through the objective lens 20. so that it becomes light (so that focus error is reduced)
Driven.

[0038] The focus error detection optical system 30'
Various methods such as the conventional astigmatism method and the knife edge method are similarly used to detect focus errors by the photosensor 31'.

Furthermore, information is reproduced using a laser beam transmitted through the beam splitter 9' in the same manner as in the first embodiment.

In the case of this reproducing device, the objective lens 1
Since objective lenses 10 and 20 can be driven separately, objective lenses 10 and 2 can be driven separately.
There is no need to keep the distance between 0 constant in advance.

[0041] As described above, the optical recording medium used in the present invention is
Since optical rotation occurs even in wavelength regions where the photochromic material has low absorbance and wavelength regions where it has no absorbance, non-destructive readout is possible by reproducing information using light in these wavelength regions. Further, the polarization state of the light used in the recording and/or reproducing apparatus of the present invention is not limited to linear polarization, but other polarization states such as elliptically polarized light can also be used.

In addition, the detection system for reflected light requires a focus servo system that has the function of focusing the light to the diffraction-limited light spot on the optical recording medium 1, but the detection system for transmitted light cannot obtain a good reproduction signal. An auxiliary focus servo may be sufficient. Therefore, although the first and second embodiments both have a focus servo system for driving the objective lens 20, this servo system may be omitted and the objective lens 20 may be fixed.

In addition, in the first and second embodiments, the focus servo is used in the reproducing device, but it can also be used in a recording device, and furthermore, in a recording/reproducing device. Various servos can be similarly performed based on the light reflected by the semi-reflective layer.

The optical recording medium of the present invention may be a disk or a tape. Further, the optical recording medium of the present invention is not limited to the embodiments, but only needs to have at least a semi-reflective layer and a recording layer, and for example, the semi-reflective layer and the recording layer do not need to be in contact with each other. Furthermore, the optical recording material used in the recording layer of the optical recording medium of the present invention may utilize optical properties other than optical rotation such as absorbance and birefringence; Can do servo. In this case, it is necessary to change the optical system of the recording and/or reproducing apparatus for the optical recording medium, the wavelength (light source, etc.) of the light used, and the polarization state as appropriate.

[0045]

Effect of the invention: Since the optical recording medium has a semi-reflective layer, part of the recording light or reproduction light is reflected, and servo can be performed based on this reflected light. Of the reproduction light, recording or reproduction can be performed using the light that has passed through the optical recording medium.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an example of an optical recording medium used in a first embodiment of the present invention.

FIG. 2 is a sectional view of another optical recording medium used in the above embodiment.

FIG. 3 is a sectional view of still another optical recording medium used in the above embodiment.

FIG. 4 is a schematic diagram showing a playback device according to a first embodiment of the present invention.

FIG. 5 is a schematic diagram showing a reproducing device according to a second embodiment of the present invention.

FIG. 6 is a diagram for explaining focus servo of a conventional reflective optical recording medium.

FIG. 7 is a diagram for explaining focus servo of a conventional transmissive optical recording medium.

[Explanation of symbols]

1 Optical recording medium 2 Base 3 Semi-reflective layer 4 Recording layer

Claims (2)

[Claims] 1. An optical recording medium comprising at least a recording layer and a semi-reflective layer stacked on a substrate. 2. An optical recording medium in which at least a recording layer and a semi-reflective layer are laminated on a substrate is irradiated with light, and a part of the light is reflected by the semi-reflective layer to generate reflected light. An optical recording medium recording and/or reproducing device characterized by performing servo.