JP2505790B2 - Optical recording / reproducing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical recording / reproducing method for recording / reproducing information by light, and in particular, for wavelength control of a light source when performing optical recording / reproducing of a wavelength multiplexing system. The present invention relates to an optical recording / reproducing method suitable for simplification.

[Conventional technology]

As a method of dramatically improving the information recording density by a light beam, wavelength-multiplexed optical recording as described in JP-A-53-99735 has been proposed. in this way,
By irradiating a storage medium having a non-uniform absorption spectrum spread with a laser beam having a narrow spectrum width, a narrow spectrum hole (a non-absorption point where the absorption characteristic disappears in the absorption band) is opened on the absorption spectrum. By sweeping the wavelength of the laser light, modulating the light intensity according to the information to be recorded, and irradiating the storage medium with the laser light, a row of holes is formed on the absorption spectrum corresponding to the recorded information. Information is recorded. At the time of reproduction, in order to read the recorded information, laser light of which intensity is weakened is irradiated onto the recording medium while sweeping the wavelength, and reflected or transmitted light is detected.

In addition, the photochemical hole burning (photochemica
l hole burning)
382, (1983), pp. 202-205 (SPIE 382 (198
3), pp202-205).

[Problems to be solved by the invention]

When performing wavelength-division multiplexing optical recording / reproducing, it is necessary to match the wavelength of light used during recording with the wavelength of light used during reproduction. For that purpose, the dispersive element and the Fabry-
Generally, a wavelength measuring device such as a Perot-resonator is used. However, if the optical recording / reproducing device is provided with such a wavelength measuring function, there is a problem that the structure and adjustment become complicated.

An object of the present invention is to provide an optical recording / reproducing method capable of matching the wavelength of light at the time of recording and the wavelength of light at the time of reproducing without providing a wavelength measuring device in the main body of the optical recording / reproducing apparatus. .

[Means for solving problems]

The above-mentioned purpose is previously set in a partial area of the recording medium.
The wavelength information corresponding to each wavelength to be used is recorded by light of each wavelength, the wavelength information is read from the area at the time of recording and reproduction, and the wavelength of the light source is used by the wavelength information signal. It is achieved by tuning to each wavelength.

[Action]

One method of carrying out the above means is to provide a wavelength reference region in a part of the recording medium by the number of multiplicities, and use a well-controlled light source in advance, and for each wavelength, its unique Area, pattern (or hole)
Make a record of. For example, an area i on the recording medium
First, a specific pattern is recorded in advance with light having a wavelength λ _i . When the wavelength multiplicity is N, N reference areas are prepared. When information is recorded or reproduced using such a recording medium, a recording light source or a reproduction light source is used to change a reference area corresponding to a desired wavelength, for example, an area i when a wavelength λ _i is desired to be used. to access. Therefore, if the wavelength of the light source is swept, a signal is detected only when the wavelength of the light source coincides with λ _i. Therefore, if the signal is fed back to the light source, the wavelength of the light source is tuned at the wavelength λ _i . be able to. Therefore, if recording and reproduction are performed using the tuned light having the wavelength λ _i , it is possible to use the light having the same wavelength during recording and reproduction. As a result, the recording / reproducing apparatus main body does not need a function for wavelength measurement, and the apparatus can be simplified.

Another method of implementing the above means is to provide one or more reference tracks in a recording medium, and previously use a well-controlled wavelength light source on the reference tracks for each wavelength to be used. A different pattern (for example, a bit pattern) is recorded. For example, on the reference track, a pattern having a reference wavelength and different for each wavelength is recorded in advance. When recording and reproducing information, a part of the light from the light source is used to access the reference track, and if the wavelength of the light source is swept at this time, each time the wavelength of the light source matches the reference wavelength, Since the pattern corresponding to the wavelength can be read, the wavelength can be recognized by the signal of the pattern. Therefore, by electrically feeding back the light source by this signal, the wavelength can be tuned so that the light of the required wavelength becomes strong. Therefore, even if a light source having low wavelength stability is used, the wavelengths at the time of recording and reproducing can be matched and the wavelengths can be fixed without measuring the absolute value of the wavelength. In addition, the reference track, by recording the pattern multiplex here,
Since the number of tracks can be suppressed to one or a small number, the information recording capacity can be increased.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In the figure, the recording medium 20 is put in a dewar 22 with a window,
Liquid helium temperature maintained. The recording medium 20 has a reference area 18. Now, one of the reference regions 18 is saturated with absorption at a wavelength of 830 nm by a single mode oscillation dye laser. When recording information, use GaAs
The output of a semiconductor laser (hereinafter referred to as a semiconductor laser) 1 is
After collimating with the lens 2, the beam splitter 3
Partly divided for wavelength reference, but the remaining output goes to the mirror 4. This divided part of the light is guided to the reference area 18 via the movable mirror 5 and the movable lens 7. At this time, the laser drive circuit 12 is used to sweep the wavelength of the laser light of the semiconductor laser 1. When the wavelength of the laser light matches the pre-recorded wavelength of 830 nm, the laser light passes through the reference area 18. Therefore, the transmitted laser light is guided to the light receiver 9 by the lens 8 to generate an electrical signal. Convert to. This signal is amplified by the amplifier 10, and is fed back to the laser drive circuit 12 using the feedback circuit 11 so that the intensity of the light transmitted through the reference area 18 is maximized. As described above, the wavelength of the laser light of the semiconductor laser 1 is tuned to 830 nm, so that the laser light is transmitted through the mirror 4, the optical modulator 21, the movable mirror 13, and the movable lens 14 to the area 19 where information is to be recorded.
Then, the optical intensity is modulated by the optical modulator 21 and recording is performed. This record is recorded by the lens 15, the light receiver 16 and the analyzer 17.
I'm monitoring. During this recording, a part of the laser light of the semiconductor laser 1 is always guided to the reference area 18 and the wavelength is tuned by the above method, so the wavelength of the laser light is fixed at 830 nm. Has been done. The intensity of the light guided to the reference area 18 is weakened so as not to change the state of the reference area 18.

Similarly, in the case of reproduction, the information recorded in the area 19 is read while tuning the wavelength of the laser light of the semiconductor laser 1. In this case, the optical modulator 21 is used to read the probe light. The strength is reduced so that the area 19 remains unchanged. The signal from the area 19 is the lens 15 and the receiver.
Light is received using 16, and analysis is performed by the analyzer 17.

For other different wavelengths, another reference region 18 is used and the same as above.

In the above embodiment, if the wavelengths to be used are numbered and the areas of the storage medium are also numbered, if the wavelength multiplicity is N and the number of areas is M, then information can be managed in an N × M matrix. In this method, when accessing this wavelength number, the position of the reference area is accessed.

According to the present embodiment, even if the wavelength recorded in advance in the storage medium differs depending on the medium, since the wavelength can be managed by the number as described above, it can be used without any problem. This is because even if the multiplicity increases in the future,
Correspondence of the device can be facilitated.

Next, another embodiment of the present invention will be described with reference to FIG.
In the figure, 31 is Dewar for liquid helium, 32 is LiF: Mg
A recording medium using the, 35 is a GaAlAs semiconductor laser (hereinafter referred to as a semiconductor laser), 36 is a movable beam splitter, 37
Is a mirror, 38, 39, 44 and 45 are lenses, and 48 is an optical modulator which works with the lens 44 together with the beam splitter 36. Further, 40 and 46 are photodetectors, 41 is an amplifier, 42 is a detector, 43 is a laser drive circuit, and 47 is a controller.

Recording medium 32 kept at liquid helium temperature in Dewar 31
For example, by using a single mode dye laser whose wavelength is controlled in advance, by hole burning, for example, the wavelength λ
₁ = 833 nm light, a bit pattern with a repetition frequency f, and light with a wavelength λ ₂ shifted from λ ₁ to 40 GHz to the long wavelength side, a bit pattern with a repetition frequency f ₂ ,
It is stored in the reference track 33 provided on the recording medium 32.

Information is recorded using the photoconductor laser 35. The laser beam from the semiconductor laser 35 is a movable beam splitter.
A part of the weak light, which is guided to the information track 34 by the 36 and the lens 44, is swept on the reference track 33 by using the mirror 37 and the lens 38. Now, considering the case of recording at the wavelength λ ₁ , after the light transmitted through the reference track 33 is focused on the photodetector 40 by using the lens 39 and the output of the photodetector 40 is amplified by the amplifier 41, , Is detected by the detector 42. If the detection frequency is set to f and the output light of the semiconductor laser 35 is wavelength-swept using the laser drive circuit 43, the detection output becomes maximum when the wavelength of the laser light matches λ ₁ , so keep this state. Laser drive circuit
Return to 43. As a result, the wavelength of the output light of the semiconductor laser 35 can be tuned to λ ₁ . When recording at the wavelength λ ₂ , the detection frequency is set to f ₂ and the same operation is performed to tune the output wavelength of the semiconductor laser 35 to λ ₂ . In the above state, the light intensity is modulated using the optical modulator 48 to record information.

At the time of reproduction, with the light intensity weakened by the optical modulator 48, the information track 34 is accessed, and the transmitted light is focused on the photodetector 46 using the lens 45, and the output of the photodetector 46 is controlled. Department
Signal processing at 47.

In the above embodiment, the beam was swept one-dimensionally in space, but the same effect can be obtained even if the optical system is fixed and the recording medium is rotated.

According to this embodiment, since the wavelength information is multiplexed and recorded on the reference track, the number of reference tracks can be minimized. Therefore, the recording capacity of the recording medium can be used much for information recording. it can. Further, the wavelength to be used does not need to know its absolute value and can be managed by numbers such as λ ₁ and λ ₂ , so that even if the standard of the multiplicity or the standard of the wavelength used changes, It is only necessary to make changes, and it is not necessary to make changes or improvements to the recording / reproducing apparatus itself.

〔The invention's effect〕

According to the present invention, when performing optical recording / reproducing, it is not necessary for the main body of the optical recording / reproducing apparatus to have a function of measuring the wavelength of the light source, and the characteristics of the light source are less susceptible to variations, fluctuations, aging, etc. It is possible to use a light source such as a laser having poor wavelength stability, which simplifies the configuration and adjustment of the device and improves the economical efficiency.

[Brief description of drawings]

1 and 2 are configuration diagrams showing an embodiment of the present invention. Explanation of symbols 1 ... Semiconductor laser, 3 ... Beam splitter 9 ... Receiver, 11 ... Feedback circuit 12 ... Laser drive circuit, 16 ... Receiver 17 ... Analyzer, 18 ... Reference area 19 Area where information is to be recorded 20 Recording medium, 21 Optical modulator 32 Recording medium 33 Reference track 34 Information track 35 Semiconductor laser 36 Beam splitter 37 ...... Mirror 40,46 …… Photo detector, 42 …… Detector 43 …… Laser drive circuit, 47 …… Control unit 48 …… Optical modulator

Claims (3)

(57) [Claims] 1. A wavelength-multiplexing optical recording / reproducing method for recording and reproducing information with different wavelengths of light on a recording medium, wherein a wavelength corresponding to each wavelength to be used is previously set in a partial area of the recording medium. Information is recorded with light of each wavelength, the wavelength information is read from the area at the time of recording and reproduction, and the wavelength of the light source is tuned to each wavelength to be used by the wavelength information signal. Optical recording / reproducing method. 2. The optical recording / reproducing method according to claim 1, wherein a reference area for each wavelength to be used is provided in a part of the recording medium, and the reference area corresponds to the wavelength. The optical recording / reproducing method is characterized in that wavelength information to be recorded is recorded respectively. 3. The optical recording / reproducing method according to claim 1, wherein one or a plurality of reference tracks are provided in the recording medium, and wavelength information is provided on the reference tracks, and the pattern is different for each wavelength. An optical recording / reproducing method characterized by multiple recording.