JPH06162546A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain recording (or erasing) and reproducing with a super-low power reproducing system with the use of a more simplified optical system device configuration by using the semiconductor laser of minute resonance structure as a light source. CONSTITUTION:Radiated light from a light source 1 composed of the semiconductor laser of minute resonance structure is reflected by a beam splitter 3 and condensed on an optical recording medium 5 by an objective lens 4. At the time of recording, light with the laser intensity of several tens of mW orders is radiated from the light source 1 by a light source driving system 2. When performing the super-low power reproducing of a photochromic medium, a current to be injected to the light source 1 by the circuit 2 is controlled by a muA order, and radiated power is set to be nW-muW order on the medium 5. At such a time, reflected light from the medium 5 is detected by a photodetector 6 provided with the self-function of an optical current, and a reproduced output can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing apparatus for a photon mode optical recording medium capable of high density recording.

[0002]

2. Description of the Related Art Recently, research has been actively conducted to apply a photochromic material which reacts in a photon mode as an optical recording medium capable of rewriting information at a high density in the next generation. When a photochromic material is irradiated with light of a predetermined wavelength, the structure of the molecule changes due to a photochemical reaction, and the optical characteristics such as the absorbance and the refractive index with respect to light of a specific wavelength change accordingly, and the light and heat of other wavelengths are changed. It has the property that the changed molecular structure returns to its original state when added.

Therefore, recording on the photochromic optical recording medium is performed by changing the molecular structure by irradiation with light of a specific wavelength.
Regeneration is carried out by detecting the change in the optical characteristics associated with this change, particularly the change in the absorbance.

By the way, as a problem peculiar to such a photon mode type optical recording medium, it is well known that if the reproduction of the recorded information is repeated by detecting the change in the absorbance, the recorded information is destroyed. . This is because the reaction of molecules occurs in the photon mode, and there is no threshold for the reaction.

Therefore, the present inventors have not previously lowered the recording sensitivity by a photodetection method having an ultra-low reproduction laser power and a photocurrent self-amplification function such that the SN ratio is limited by the shot noise limit. As a Japanese Patent Application No. 4-199990, we proposed an ultra-low power reproduction system that can reproduce 100,000 times while ensuring the required SN ratio.

[0006]

In the ultra low power reproducing system used in the above proposal, the reproducing laser power is on the order of several nW to several μW. However, as is well known, a light source (semiconductor laser) currently used in a general optical disk device or the like needs to be operated with a certain level of radiation power (at least 1 mW or more) in order to operate stably.

Therefore, in order to apply such a semiconductor laser to the ultra-low power reproducing system, the semiconductor laser is operated with a radiation power of 1 mW or more, and then the radiation laser power is adjusted by a power adjusting element using an ND filter or liquid crystal or electro-optical crystal. Has to be adjusted to about several mW to several μW. Thus, considering the compatibility with the conventional optical disk device, an extra power adjusting element is required in addition to the light source, which causes inconvenience in terms of downsizing and cost reduction of the pickup itself.

Further, when used as a recording device (or erasing device), it is necessary to switch between ultra-low laser power and high laser power in the reproducing mode and the recording (or erasing) mode. As shown in FIG. 3, in addition to the light source 101, its drive system 102, and the laser power adjusting element 201, a control circuit 202 for controlling the laser power by a recording-reproducing mode signal is required. This leads to an increase in the cost of the entire apparatus, which is not desirable. In FIG. 3, 103 is a beam splitter, 1
Reference numeral 04 is an objective lens, 105 is an optical recording medium, and 106 is a photodetector.

The present invention has been made in view of the above problems of the prior art, and provides an optical recording / reproducing apparatus capable of realizing recording (or erasing) / reproduction by an ultra-low power reproducing system with a simpler optical system device configuration. It is intended to be provided.

[0010]

The present invention is directed to a semiconductor laser light source having a microresonator structure capable of controlling emitted light intensity by an injected current and suppressing spontaneous emission, and emitting from the light source. Lens system for condensing the reflected light on the recording medium, a photodetector for detecting the light reflected by the medium, and a control circuit for controlling the injection current to the light source according to the recording or reproducing mode. , Consists of.

[0011]

It has been difficult to operate the conventional semiconductor laser with an ultra-low power of several μW or less as described in the section of the prior art. This is due to the input current −
Looking at the relationship of the optical output, it was necessary to flow a current above the threshold for stable laser oscillation, and spontaneous emission was observed below that, and the threshold was usually on the order of tens of mA. . That is, it has been impossible to set the current to a level slightly higher than the threshold value by such an input-output non-linear characteristic and the spontaneous emission component and to stably generate an ultra-low laser power of μW order or less.

On the other hand, a semiconductor laser having a microcavity structure is, for example, the 38th Japan Society of Applied Physics Joint Lecture Meeting (1
Spring 991) 30P-F-7-9, 39th Joint Lecture of Applied Physics (Spring 1992) 29P-C-14, 53rd Annual Conference of Japan Society of Applied Physics (Autumn 1992) 16
a-V-3, Applied Physics Vol. 61 No. 9 (1992) P8
90-901 "Microcavity laser: Current status and prospects" It is possible to set a very low threshold value as reported by Hiroyuki Yokoyama, and stable laser power control by injection current is possible even at a very low power output. Is. It is said that this is because when the resonator structure is reduced to the order of the wavelength of light, fluctuations in the vacuum field are affected and spontaneous emission of light is suppressed.

FIG. 2 is a diagram showing the input-output characteristics of a microcavity laser. By adjusting the reflectance R of the cavity surface, it is possible to control the μW-order laser output with a linearity by a μA-order current. Recognize.

[0014]

EXAMPLE A semiconductor laser in which spontaneous emission is suppressed by the microresonator structure as described in the above section can be used as a light source of an ultra-low power reproducing system. Further, in the recording mode, as can be seen from FIG. 2, a sufficient laser power for recording of several tens of mW can be obtained by increasing the injection current to the order of several tens of mA.

By using a semiconductor laser in which spontaneous emission is suppressed by such a microcavity structure for reproduction, an additional effect is produced. This is because the conventional semiconductor laser had noise due to spontaneous emission,
In the present invention, since the noise of the laser is reduced, the SN is high.
It becomes possible to obtain a ratio reproduction signal output.

One embodiment of the optical recording / reproducing apparatus of the present invention will be described in detail below. FIG. 1 shows the configuration of an optical recording / reproducing apparatus having a semiconductor laser, which has the input-output characteristics as shown in FIG. 2 and whose spontaneous emission is suppressed by a microresonator structure, as a light source 1. The emitted light from the light source 1 is reflected by the beam splitter 3 and is condensed by the objective lens 4 onto the optical recording medium 5. At the time of recording, the light source driving circuit 2 causes the light source 1 to emit laser intensity of the order of several tens of mW. Further, when performing ultra-low power reproduction of the photochromic medium, the current injected into the light source 1 by the circuit 2 is μ
The radiation power is controlled in the A order and the radiation power is nW on the medium 5.
It is set to be in the μW order. At this time, medium 5
The reflected light from the photodetector 6 has a photocurrent self-function.
A reproduction output is obtained by being detected by (for example, an avalanche photodiode).

Here, the reproduction light power P _REP is a typical value, and more strictly, it is determined as follows.

[0018]

[Equation 1]

However, the SNR is the SN required for the system.
The power ratio, e is the electric charge of 1.6 × 10 ⁻¹⁹ [C], B is the system bandwidth [Hz], η is the sensitivity to the photodetector gain [A / W], and γ is the pickup efficiency ( The ratio of the reflected light from the medium coupled to the photodetector), R _ave is the average reflectance of the medium, ΔR is the change in reflectance between the recorded mark portion and the unrecorded portion of the medium, and κ is the Boltzmann constant 1.38. × 10
^-23 [J / K], T is absolute temperature [K], I _amp is average noise current [A] of playback preamplifier, Z is average noise current [A] of playback preamplifier, and Z is impedance of playback preamplifier [A]. Ω].

When the reproduction of the photochromic optical recording medium is performed with the ultra-low reproduction power determined by the above equation 1,
It is possible to satisfy both the sufficient SN ratio and the number of times of reproduction of about 100,000 times.

As is clear from the comparison between the conventional apparatus shown in FIG. 3 and the apparatus according to the present invention shown in FIG. 1, the adjusting element 2 of the conventional apparatus is shown.
01 and the control circuit 202 are unnecessary in the device of the present invention, and the structure of the device is greatly simplified.

[0022]

As described above, according to the present invention, there is provided an optical recording / reproducing apparatus which has a simpler structure, lower cost, ultra-low power reproduction with a sufficient SN ratio, and can be used for recording. The effect that can be provided can be expected.

[Brief description of drawings]

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

FIG. 2 is an input current-optical output characteristic diagram of a semiconductor laser having a microcavity structure.

FIG. 3 is an input current-optical output characteristic diagram of a conventional semiconductor laser.

FIG. 4 is a diagram showing a configuration of a conventional optical recording / reproducing apparatus.

[Explanation of symbols]

 1 light source 2 light source drive circuit 3 beam splitter 4 objective lens 5 medium 6 photodetector

Claims (1)

[Claims] 1. A semiconductor laser light source having a microresonator structure capable of controlling emitted light intensity by an injected current and suppressing spontaneous emission, and collecting light emitted from the light source on a recording medium. A lens system to illuminate,
An optical recording / reproducing apparatus comprising: a photodetector that detects light reflected by the medium; and a control circuit that controls an injection current to the light source according to a recording or reproducing mode.