JPH07129996A - Optical wavelength multiplex recording and reproducing device - Google Patents

Abstract

PURPOSE:To make recording and reproducing possible with simple constitution and to reduce the size and cost of the device by constituting an optical member of a specific combination. CONSTITUTION:The recording light from a light source section 1 is reflected by a deflection beam splitter 2, is passed through a quarter-wave plate 24 and is cast to an optical wavelength multiplex recording medium 4 and recording is conducted by a two photon recording method at the time of recording. The reflected light is again passed through the quarter-wave plate 24, is rotated 90 deg. in the plane of polarization and is transmitted through the deflection beam splitter 2 to avert the return beam to the light source 1 section. At this time, the return beam is partly reflected by a polarization beam splitter 23 and is supplied to a detecting section 28, by which a servo signal is obtd. The linearly polarized light from the light source section 1 is cast to the recording medium and the return beam is again passed through the quarter-wave plate 24 to rotate the plane of polarization by 90 deg. and is made incident on the photodetecting part 3 through the deflection beam splitter 2, by which recording information is obtd. at the time of reproducing. The device is simply constituted and the size, weight and cost of the device are reduced by combining the light source lens, the beam splitters and the quarter-wave plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength multiplex recording / reproducing apparatus, and more particularly to a reproducing mode for a recording medium on which optical wavelength multiplex recording is carried out, by reading information on the recording medium by observing an absorption spectrum of the reproducing light. The present invention relates to an optical wavelength multiplex recording / reproducing apparatus applied when the mode is adopted.

[0002]

2. Description of the Related Art Information recording media capable of multiple recording in the wavelength region of light include those utilizing phenomena such as photochemical hole burning (PHB) and photochromism.
The principle of wavelength multiplexing recording using PHB is, for example, as described in JP-A-53-99735, one broad absorption band (nonuniformity) exhibited by a light absorbing dye dispersed in a transparent medium at extremely low temperatures. In the absorption band), a narrow band laser beam is irradiated to form a sharp depression (hole).

It is said that a large number of holes can be formed in the nonuniform absorption band by changing the wavelength of the laser light to be irradiated little by little, and theoretically 10 to 1000 holes can be formed. It is being appreciated.

However, since a large-scale cooling device is required to perform recording / reproduction at such an extremely low temperature, there is a practical problem. On the other hand, PHB at room temperature is a problem.
As a recording material capable of recording information by Sm is BaC
A BaClF: Sm-based recording material doped into an 1F-based crystal matrix has been investigated.

FIG. 7 shows the Sm²⁺Energy level model
Fig.⁷F₀Is the ground state, ^FiveD₀Is the first excitation
Metastable state of 4f^FiveWide absorption band of 5d
ing. Recording on recording media with this recording material
Shows the recording process with a solid arrow in FIG.
Selected wavelengths, for example at wavelengths 689-691 nm
Recording light λs (λ₁~ Λ_n) Irradiation of the ground state
Electron F₀To metastable level D₀Sm on a particular site²⁺
At the same time as resonantly exciting only the desired wavelength λg (<
Irradiate with gate light of 500 nm) to photoionize 2
Perform stepwise photoexcitation. The electrons emitted by this
It couples to nearby traps via the conducting band. Because of this
Sm on the specific site mentioned above²⁺Is Sm³⁺Next to that
Sm in Ito²⁺The distribution of
There will be a hole in the vector which will not record any information.
To be done. By changing the wavelength of recording light,
Sm in G²⁺Control the distribution of the
This enables multiple recording.

The above-mentioned recording method is a recording method by two-stage photoexcitation, but the conduction band is close to the metastable level depending on the composition of the recording material, the manufacturing method, etc., and the gate described above is used in the recording. There is a so-called two-photon recording method in which the above-described photoionization is performed by two photons of recording light having a selected wavelength λs (λ _{1 to} λ _n ) without using light to perform the same recording.

[0007] Then, the reproduction of the recorded information, ⁷ by irradiation of reproducing light by selecting wavelength ^{_{λ 1 ~λ n F 0 - 5}} D
The hole is detected by observing the absorption spectrum of ₀ , or as shown by the dotted arrow in FIG. 7, as shown in the reproduction process, for example, by excitation by irradiation with one-wavelength light λ _{exc with} a reproduction wavelength of 420 nm different from the recording wavelength. The recorded information is reproduced by detecting the holes by observing the emission spectrum of the emitted fluorescence.

To erase information from this recording medium, as shown by the broken line arrow in FIG. 7, λ _er of the wavelength of energy corresponding to the depth of the trap is irradiated. In this way, electrons from the trap are released, Sm ³⁺ returns to Sm ²⁺ , and the holes are erased.

[0009]

DISCLOSURE OF THE INVENTION The present invention is directed to the above-mentioned wavelength multiplexing recording and reproduction, and particularly to the reproduction of a hole by observing its absorption spectrum by irradiating an optical wavelength multiplexing recording medium with reproduction light of a wavelength whose reproduction mode is selected. Provided is an optical wavelength multiplex recording / reproducing apparatus capable of performing recording and reproduction with a simple structure in the case of adopting a reproduction mode of detecting, that is, reproducing recorded information.

[0010]

The first aspect of the present invention is to provide at least a light source section 1 as shown in FIG.
A polarization beam splitter 2, a quarter wavelength plate 24,
The optical wavelength multiplexing recording medium 4 is provided with a plurality of wavelength lights from the light source unit 1 through the polarization beam splitter 2 and the quarter wavelength plate 24. The return light from is detected by the photodetector 3 through the quarter-wave plate 24 and the polarization beam splitter 2.

In a second aspect of the present invention, the light source section 1 is a light source for generating a plurality of wavelengths of light and a gate light of a predetermined wavelength in the configuration of the above-described first invention.

According to a third aspect of the present invention, in the structure of the above-mentioned first aspect, the light source section 1 is provided with a hologram light synthesizing element, and light of a plurality of wavelengths is synthesized on the same axis through the light synthesizing element. And take it out.

[0013]

According to the present invention, it is possible to perform recording on an optical wavelength multiplex recording medium by the so-called two-step photoexcitation recording method or two-photon recording method having an extremely simple structure, and particularly, when reproducing the reproduction light, By observing the absorption spectrum of the return light of irradiation to the optical wavelength multiplexing recording medium, it is possible to reproduce the holes of each wavelength, that is, each recorded information by the optical wavelength multiplexing recording.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic structure of an example of the device of the present invention. The optical wavelength multiplex recording medium 4 has, for example, a disk shape as described above, and the recording material layer 4C, eg, S, which causes the PHB phenomenon at room temperature on the substrate 4A via the reflective film 4B such as Al.
r _X Ca _1-X FCl: Sm (0 <x <1), Sr _X Ba
_1-X FCl: Sm (0 <x <1) is adhered and formed, and a transparent protective film or a protective substrate 4D is arranged thereon. This recording medium 1, that is, a disk, is rotationally driven around its central axis O.

In the example shown in FIG. 1, the optical wavelength multiplex recording on the optical wavelength multiplex recording medium 4 is recorded by the two-photon recording method, that is, by recording light having different wavelengths λ _{1 to} λ _n , and reproduced, that is, optical wavelength multiplex recording. The recording information is read from the medium 4 when the reproduction spectrum of the wavelengths λ _{1 to} λ _n is applied to the optical wavelength division multiplexing recording medium 4 to detect the return light by the reflection of the absorption spectrum.

This recording / reproducing apparatus includes a light source section 1, a polarization beam splitter 2, a quarter wavelength plate 24, and a photodetecting section 3.
In this example, the collimator lens 2 is provided in the optical path between the light source unit 1 and the polarization beam splitter 2.
1, a first beam splitter 22, and a second beam splitter 23 are arranged, and a quarter wavelength plate 24 and an objective lens 25 are provided between the polarization beam splitter 2 and the optical wavelength multiplexing recording medium 4. Is arranged, and the condenser lens 27 is arranged between the polarization beam splitter 2 and the light detection unit 3.

The light source unit 1 has a wavelength λ selected at the time of recording.
s (λ₁~ Λ_n) Recording light according to the recording information
For example, on / off modulation is performed before emission, and a predetermined wave is output during playback.
Long λ _excOf the reproduction light of the_erOut
It is made to shoot.

In this structure, at the time of recording, the wavelength λs selected from the light source unit 1, that is, the respective wavelengths λ _{1 to} λ _n.
The recording light modulated according to the respective recording information is directed to the collimator lens 21 → beam splitter 22 → polarization beam splitter 23 → polarization beam splitter 2, where the recording light is reflected and the quarter wavelength plate 24 → objective lens Two
5 through which the light wavelength multiplex recording medium 4 is condensed and irradiated by the lens 25 to perform the optical wavelength multiplex recording by the two-photon recording method.

At this time, the light reflected by the optical wavelength multiplexing recording medium 4 passes through the quarter wavelength plate 24 again,
When the recording light is linearly polarized light such as laser light, the plane of polarization of the recording light is 90 ° by passing back and forth through the quarter-wave plate 24.
Since it rotates, most of the light returning to the light source unit 1 can be avoided by passing through the polarization beam splitter 2, but the polarization plane can be changed by selecting the transmittance and reflectance of each polarization in the polarization beam splitter 23. When a part of the polarized light rotated by 90 ° can be also reflected, this return light is returned to the polarization beam splitter 23, and this polarized light is reflected and detected by the detection unit 28, for example, a tracking servo signal. Can also be obtained. Thus, even when a part of the return light is reflected by the polarization beam splitter 2, the return light can be efficiently directed to the detection unit 28 by the polarization beam splitter 23, and the detection can be performed efficiently. In addition, the return light from the light source unit 1 to the laser can be effectively blocked, and the generation of noise can be avoided.

At the time of reproduction, the selected wavelength λ ₁
The linearly polarized light of ˜λ _n is generated from the light source unit 1 and directed toward the collimator lens 21 → beam splitter 22 → polarization beam splitter 23 → polarization beam splitter 2.
Here, the reproduction light is reflected and passes through the quarter-wave plate 24 → the objective lens 25, and this lens 25 condenses and irradiates the optical wavelength multiplex recording medium 4. Λ ₁ irradiated in this way
Light to [lambda] _n, the optical wavelength multiplexing recording medium 4 passes through the recording layer 4C mainly reflecting film 4B in reflection to the objective lens 25 → 1
The quarter wave plate 24 is returned to the polarization beam splitter 2. Since the return light travels back and forth through the quarter-wave plate 24, its polarization plane is rotated by 90 °, so that most of it passes through the polarization beam splitter 2 and the condenser lens 2
The light is incident on the light detection unit 3 by the light source 7.

In this case, the photodetection section 3 is composed of photodetection means such as a photomultiplier tube, and the reproduction light from the light source section 1 to the optical wavelength multiplex recording medium 4 has its respective wavelengths λ _{1 to} λ.
_n light is sequentially generated in a time-division manner so that the light detecting section 3 sequentially outputs λ ₁ to λ from the optical wavelength multiplexing recording medium 4.
A return light having a wavelength of _n is detected to read holes, that is, recorded information.

On the other hand, even during this reproduction, a part of the reproduced light is reflected from the WDM recording medium 4 toward the polarization beam splitter 23. In this case as well, a part of the light returned by the reflection is polarized. The beam can be directed to the beam splitter 23, and reflected by the beam splitter 23 to be incident on the detector 28, and a tracking servo signal can be obtained.

A part of the reproduction light emitted from the light source unit 1 is directed to the detection unit 29 by the beam splitter 22, the light source intensity is detected, and the light intensity of the reproduction light with respect to the reproduction signal is detected by this detection signal. Cancel the effects of fluctuations.

In the above-mentioned example, recording is performed on the optical wavelength multiplex recording medium 4 by the two-photon recording method, but a schematic configuration of an example of the two-step photoexcitation recording method is shown in FIG. In FIG. 2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals and duplicate description is omitted, but in this case, the light source unit 1 selects the selected wavelength λs (λ
_{1 to} λ _n ) recording light and excitation light λ _exc are taken out first
Light source 31 and a second light source 32 for extracting gate light having a predetermined wavelength λg. In this case, reproduction light can be switched and emitted from either the first or second light source 31 or 32.

The gate light from the second light source 32 is made to coincide with the selected recording light from the first light source 31 via the collimator lens 41 and the beam splitter 42.

A filter 26 which transmits only the selected wavelength range is arranged between the polarization beam splitter 2 and the condenser lens 27.

In this configuration, in the recording, in this example, the recording light according to the recording information of the wavelengths λ _{1 to} λ _{n is} wavelength-multiplexed from the first light source 31 in the same manner as described in FIG. In addition to being directed to the recording medium 4, in this example, the second light source 32 simultaneously generates gate light of a predetermined wavelength λg, and the recording light of the above wavelength λs is emitted through the collimator lens 41 and the beam splitter 42. The wavelength multiplexing recording medium 4 is irradiated.

In this way, optical wavelength multiplex recording is performed on the optical wavelength multiplex recording medium 4.

When reproducing, the second light source 3
2, the light of wavelength λs (λ _{1 to} λ _n ) is sequentially extracted as described above, directed to the optical wavelength multiplex recording medium 4 in the same manner as described with reference to FIG. 1, and reproduced by the same method. .

In both of FIG. 1 and FIG. 2, at the time of erasing, the recording is erased by generating the wavelength λ _er from the light source unit 1 and irradiating it to the optical wavelength multiplexing recording medium 4.

In the above-described structure, when the light source section 1 or the first and second light sources 31 and 32 thereof extract light of a plurality of wavelengths, a laser or the like that emits light of each wavelength is used. However, as shown in FIG. 3, for example, the light from each light source that generates light of each wavelength, for example, λ _{1 to} λ _n , is emitted from each of FIGS.
As shown in, the collimator lens 21 can be made to coincide with the optical path axis.
As shown in FIG. 4, it is desirable that the light is combined in advance on the same axis by the photosynthesis element 51 before being made incident on the collimator lens 21. The means for matching the plurality of lights, that is, the light combining element 51, can be configured by, for example, matching the lights from the respective light sources S on the same axis by using optical fibers, or by using a beam combiner using a hologram.

A photosynthesis element using this hologram, that is,
The beam combiner is manufactured, for example, as shown in FIG.
Examples of wavelengths applied to the transparent substrate 61 to perform synthesis
Then λ ₁~ Λ_nTo the photosensitive layer showing the photosensitivity in the range of
Without a predetermined wavelength λ₁Object light L_{su b}Example for substrate 21
For example, make the light incident at a right angle and have the same wavelength λ.₁Reference light L
_refObject light L_subAngle θ with respect to the optical axis of₁(0
<Θ₁Interference exposure is performed by making the light incident at <90 °. Next same
Other wavelengths by the same method₂ Similar object light with respect to
L_subAnd angle θ₂ (Θ₂ ≠ θ₁, 0 <θ₁<90 °)
Reference light L_refInterference exposure using
Predetermined wavelength λ₃~ Λ_nAbout each wave
Long object light L_subIrradiation and a predetermined different angle θ₃
~ Θ_nReference light L depending on the incident angle of_refOrder by irradiation with
Next interference exposure is performed. After that, develop and fix the photosensitive layer.
The photosynthetic element by hologram
A beam combiner is manufactured.

On the other hand, as shown in FIG. 6, the holographic photosynthesis element 51, ie, beam combiner, produced by the above-mentioned method, converts the light having the above wavelengths λ _{1 to} λ _n into the above incident angles θ _{1 to} θ, respectively. If they are incident with _n , they can be coincidentally combined on the same axis and emitted, and thus the light thus combined on the same axis is incident on the lens 21 of FIG.

According to the above-mentioned configuration of the present invention, an optical lens, a beam splitter, and a 1/4 are provided as the recording / reproducing means.
It is simply composed of a combination of wave plates. Since the configuration of the combination of the optical lens, the beam splitter, the quarter-wave plate, etc. is an extension of the technology in the recording / reproducing pickup generally used for optical discs, magneto-optical discs, etc. However, if a medium exhibiting the PHB phenomenon at room temperature is used as the optical wavelength multiplex recording medium 4, it is possible to avoid providing a cooling device, and the overall size is smaller, lighter and more compact. It can be constructed at low cost.

[0035]

According to the present invention, as described above, the recording / reproducing means can be simply constituted by a combination of an optical lens, a beam splitter, a quarter-wave plate, etc., and is small, lightweight and compact as a whole. In addition, it can be constructed at a low cost, and brings an extremely great advantage in the practical application of the optical wavelength multiplex recording / reproducing apparatus.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of a device of the present invention.

FIG. 2 is a schematic configuration diagram of an example of a device of the present invention.

FIG. 3 is a configuration diagram of an example of a light source unit of the device of the present invention.

FIG. 4 is a configuration diagram of an example of a light source unit of the device of the present invention.

FIG. 5 is an explanatory diagram of the production of a photosynthetic element by hologram.

FIG. 6 is an operation diagram of a photosynthesis element.

FIG. 7 is a model diagram of energy levels of Sm ²⁺ .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source part 31 1st light source 32 2nd light source 2 Polarization beam splitter 3 Optical detection part 4 Optical wavelength multiplexing recording medium

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[Procedure amendment]

[Submission date] March 3, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

However, since a large-scale cooling device is required to perform recording / reproduction at such an extremely low temperature, there is a practical problem. On the other hand, PHB at room temperature is a problem.
As a recording material capable of recording information according to, a material obtained by doping a halide crystal matrix of an alkaline earth metal with Sm,
For example, SrFCl _x Br _1-x : Sm ²⁺ is being studied.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic structure of an example of the device of the present invention. The optical wavelength multiplex recording medium 4 has, for example, a disk shape as described above, and the recording material layer 4C, eg, S, which causes the PHB phenomenon at room temperature on the substrate 4A via the reflective film 4B such as Al.
_{r x Ca 1-x FCl y} Br 1-y: Sm (0 <x <1,0
_{<Y <1), Sr x} Ba 1-x FCl y Br 1-y: Sm
(0 <x <1, 0 <y <1) is adhered and formed, and a transparent protective film or protective substrate 4D is arranged thereon. This recording medium 1, that is, a disc, has a central axis 0
It is driven to rotate around.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

In this configuration, in the recording, in this example, the recording light according to the recording information of the wavelengths λ _{1 to} λ _{n is} wavelength-multiplexed from the first light source 31 in the same manner as described in FIG. In addition to being directed to the recording medium 4, in this example, at the same time, the second light source 32 generates gate light of a predetermined wavelength λg, and the gate light of the above wavelength λs is passed through the collimator lens 41 and the beam splitter 42 together with the recording light. The multiplex recording medium 4 is irradiated.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

When reproducing, the first light source 3
1, the lights of wavelength λs (λ _{1 to} λ _n ) are sequentially extracted as described above, directed to the optical wavelength multiplex recording medium 4 in the same manner as described with reference to FIG. 1, and reproduced by the same method. .

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

A photosynthesis element using this hologram, that is,
The beam combiner is manufactured, for example, as shown in FIG.
Examples of wavelengths applied to the transparent substrate 61 to perform synthesis
Then λ ₁~ Λ_nTo the photosensitive layer showing the photosensitivity in the range of
Without a predetermined wavelength λ₁Object light L_{su b}Example for substrate 21
For example, make the light incident at a right angle and have the same wavelength λ.₁Reference light L
_refObject light L_subAngle θ with respect to the optical axis of₁(0
<Θ₁Interference exposure is performed by making the light incident at <90 °. Next same
Other wavelengths by the same method₂ Similar object light with respect to
L_subAnd angle θ₂ (Θ₂ ≠ θ₁, 0 <θ₂<90 °)
Reference light L_refInterference exposure using
Predetermined wavelength λ₃~ Λ_nAbout each wave
Long object light L_subIrradiation and a predetermined different angle θ₃
~ Θ_nReference light L depending on the incident angle of_refOrder by irradiation with
Next interference exposure is performed. After that, develop and fix the photosensitive layer.
The photosynthetic element by hologram
A beam combiner is manufactured.

Claims (3)

[Claims] 1. A light source unit, a polarization beam splitter, a quarter-wave plate, and a photodetector unit, and a plurality of wavelength light beams from the light source unit, the light source unit, and the polarization beam splitter. The optical wavelength multiplex recording medium is irradiated with the quarter wavelength plate and the return light from the optical wavelength multiplex recording medium is detected by the photodetector through the quarter wavelength plate and the polarization beam splitter. Optical wavelength multiplex recording / reproducing device. 2. The optical wavelength multiplexing recording / reproducing apparatus according to claim 1, wherein the light source unit is a light source that generates a plurality of wavelengths of light and a gate light of a predetermined wavelength. 3. A light wavelength multiplex recording, wherein the light source section is provided with a photosynthesis element using a hologram, and light of a plurality of wavelengths is synthesized on the same axis through the photosynthesis element to be extracted. Playback device.