JPS5920168B2 - optical recording/playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rewritable optical recording/reproducing device using a disk-shaped recording medium.

Conventionally, various attempts have been made to record information signals such as video signals and audio signals on disk-shaped recording media at high density.

Specifically, a spiral or concentric track is formed on the disk surface, and minute irregularities of several μm or less are arranged along the track. High-density information recording can be achieved by making the changes in the shape of the unevenness correspond to recorded information. To read information, a light source such as a laser beam that can be focused on a minute spot with high energy density is used, and a beam with a constant spot diameter is irradiated onto the minute recording element while following the track on the disk. A recording element whose degree of diffraction differs depending on the recorded signal gives a change in the intensity of reflected light or transmitted light, and when this is detected by a photoelectric conversion element, the recorded signal is reproduced. In this case, the information is recorded using another device, such as a laser beam that is much more powerful than the reproduction beam, onto a record disc made of a material such as photoresist.This becomes the master disc, which can be duplicated in the same way as an audio record. Created. Therefore, these well-known examples were non-rewritable recording media. In recent years, remarkable optical properties have been discovered in amorphous materials, that is, materials that do not have long-range regularity in their structure like crystals, and among them, the transition from an amorphous state to a crystalline state by light irradiation has been discovered. Must be reversible.

Also, when irradiating light near the absorption edge of an amorphous material,
A wavelength shift of the absorption edge may occur. Using the former property, when irradiated with light with energy above the threshold level, the optical properties (density) change,
Since the change is reversible, it can be used as a rewritable high-density optical recording material. More specifically, an amorphous material is formed into a thin film of several hundred λ and deposited on the disk base material. Chalcogenide glass, which is the most common amorphous material, often takes on a light brown color due to absorption of energy above the writing threshold, but turns black due to crystallization. Information can be read by irradiating a beam with energy below the writing threshold, and can be reproduced by the same method as in the past. On the other hand, the above-mentioned recording state, that is, the crystalline state, is heated to become a high-temperature amorphous phase, and by quenching, the original amorphous state can be restored. Specifically, this can be achieved by irradiating a pulsed laser beam with high energy exceeding the writing threshold. On the other hand, when configuring an apparatus for recording and reproducing information signals using such a recording material, the most practical laser to be used as a light source is a He--Ne gas laser.

However, when functionally performing any or all of the functions of recording, playback, and erasing at the same time, it is difficult to irradiate beams corresponding to different modes with a single laser light source and perform various controls associated with each mode. The configuration of the device becomes extremely complicated and is difficult in practice. Furthermore, the method of using two or more gas laser tubes is also disadvantageous in that the apparatus becomes larger. ``In view of the above-mentioned conventional technology, the present invention uses a semiconductor laser as an erasing light source, miniaturizes the device, obtains erasing conditions suitable for the recording material, and has the features of easily monitoring erasing information. Regarding semiconductor lasers, research on semiconductor lasers has become active in recent years due to the advantages of miniaturization, high efficiency, and ease of modulation. However, products that are capable of continuous oscillation at room temperature are emerging.

In this case, a semiconductor laser having a heterojunction structure of GaAs and (GaAl)As, in which Al is added to a -V group compound semiconductor such as GaAs and a different compound, is typical. The example shown in Figure 1 is a semiconductor laser with a double heterojunction structure.
The A-plane and the N-plane constitute a resonator, and the P-GaAs portion is a light emitting region. In general, the characteristics of light obtained from GaAs semiconductor lasers are that the oscillation wavelength is 8000λ to 9000λ, and the luminous flux spreads only about 100 nm in a plane parallel to the bonding surface, but in a plane perpendicular to the bonding layer thickness (0. 5μm～2μm
It spreads out over several hundred to a thousand angles, depending on the degree. Therefore, it is difficult for the lens optical system to converge such rapidly diffusing light onto a spot of several micrometers or less. Therefore, a minute spot is obtained using a semiconductor laser in which a fiber ribbon is bonded to a light emitting layer. The present invention will be explained below according to the drawings.

FIG. 1 is a schematic diagram showing the structure of a semiconductor laser with a fiber, in which 1 is a semiconductor laser and 2 is a fiber ribbon bonded to a light emitting region, preferably a focusing fiber. Figure 2 is a structural diagram of the read/erase head 3 consisting of a semiconductor laser and an objective lens, and A is a cross-sectional view.
B is a top view of the head 3, 4 is a protective cover for the fiber 12, 5 is a package for the semiconductor laser 1 with good heat dissipation, 6 is a magnet attached to the end of the package 5, and 7 is an electromagnet. , by applying a current to the input terminal 8. 9 is an objective lens, 10 is a holder that supports the objective lens 9 and the semiconductor laser 1, 11 is a magnet, 12
1 is a leaf spring, and 13 is a coil.

FIG. 3 is a configuration diagram of an apparatus according to an embodiment of the present invention, with 14
15 is a laser light source, 15 is a relay lens, 16 is a movable reflecting mirror with a rotation axis, 17 is a half mirror, 18 is a turntable, 19 is a motor for driving the turntable, 20
21 is a disc recorder, and 21 is a divided photodetector divided into four areas.

22 is an addition and subtraction amplifier which outputs a reproduction signal, a tracking signal and a focusing signal; 23 is a reproduction signal output terminal; and 24 is a housing movable toward the center of the disk as the turntable 18 rotates. be.

Figure 4 shows the disk recorder 20 and the playback and erasing head 3.
In the enlarged view of the vicinity, 25 is a track formed on the disk recorder 20, 26 is the main recording part recorded on the track 25, 27 is a read beam spot, and 28 is an erase beam spot.

FIG. 5 is a block diagram of the addition/subtraction amplifier 28, in which 29 is a signal input terminal of the split photodetector 21, 30 is an addition circuit, 31 is a subtraction circuit, 32 is a reproduced signal output terminal, 33 is a tracking signal output terminal, 34 is a focusing signal output terminal. Next, the operation will be explained.

As shown in FIG. 1, the semiconductor laser used as the erasing light source of the present invention has a light-emitting layer bonded with a large number of focusing fiber ribbons 2, with a width of several μm at one end of the fiber.
A rectangular spot with a length of several tens of μm can be obtained.
The read and erase head 3 shown in FIG.
0, the objective lens 9 used for reproduction and control and the erasing semiconductor laser 1 are held close to each other. The head 3 itself has the same structure and function as a voice coil, and moves the holder 10 in the vertical direction in the figure while being braked by a leaf spring 12 due to the current applied to the coil 13 and the action of the magnet 11. can be done. That is, the objective lens 9 is moved to the disk recorder 2 by a focusing signal.
It can be maintained at a constant distance from 0. On the other hand, the semiconductor laser 1 is housed in a package 5, and the fiber 12, which is extremely thin and easily broken, is also covered by a protective cover 4.
This semiconductor laser 1 is movable in the vertical direction in FIG. That is, by switching the direction of the current applied to the terminal 8, an attractive force or a repulsive force is generated between the electromagnet 7 and the permanent magnet 6. When operating in a mode other than erasing, a current is applied to the terminal 8 so that an attractive force is generated, and the tip of the fiber 2 is kept at a sufficiently far distance from the disk recorder 20 so that they do not come into contact and damage each other. Do it like this.
In the erase mode, a current in the opposite direction is applied and the repulsive force advances the package 5 to a position where it is restricted by the holder 10. That is, the fiber 12 advances to a position where it can maintain a distance sufficient to form a sufficiently small beam spot on the disk recorder 20. Next, the specific operation of the apparatus will be explained with reference to FIG. 3 and subsequent figures.

A substantially parallel beam emitted from the laser light source 14 is transmitted through the relay lens 1
5 to converge and expand. Movable mirror 16 with a rotation axis
As shown in FIG. 4, the beam, which has once changed its traveling direction and is incident on the objective lens 9 of the reproduction/erasing head 3 through the half mirror 17, is aligned with the optical axis of the objective lens 9 in the direction of the disk recording type. 20 in the track tangent direction. Therefore, if the reproduction beam spot 27 is focused on the smallest spot on the track 25}, the reflected light is reflected on the back surface of the half mirror 17 and then projected onto the left and right centers of the split type detector 21. However, when the distance between the objective lens 7 and the track 25 changes, that is, when the focus shifts, the reflected beam moves to the left (A, D side) or right (B, C side) of the detector 21. In addition, if the reproduction beam spot 27 deviates from the track 25 and no longer correctly illuminates the microscopic amorous element 26, the detector 2
The reflected light projected onto 1 is directed upward and downward (A, B side and C, D
side) becomes unbalanced. Therefore, in the adder/subtractor amplifier 20 shown in FIG. 5, for the output signal of the split type detector 21, if (A+B)(D+C) is the tracking signal, if (A+D)-(B+C) is the tracking signal, it is the focusing signal A+B+C+D. A reproduced signal can be obtained by summing all the sums. The tracking error signal obtained at the terminal 33 is
The movable reflector 16 is rotated to reduce the error signal, and the focusing error signal obtained at the terminal 34 causes a current to flow through the coil 13 of the read/erase head 3'', which also reduces the error. In this way, a part of the reflected light of the reproduction beam is used to perform tracking control and focusing control, and the reproduction beam 2
7 can be accurately irradiated onto the minute recording element side along the track 25. On the other hand, as mentioned above, since the semiconductor laser 1 used as the erasing light source is provided close to the objective lens 9, there is no problem even if the focusing control and tracking control are also used as control using the reproduction beam during the erasing operation. do not have.

Further, in the erasing mode, even if the reproduction beam spot 27 is irradiated, the erasing conditions are not affected in any way, and there is the advantage that erasing information can be monitored functionally.
That is, while reproducing the recorded information, it becomes possible for the operator to erase only the portion that needs to be erased. At this time, the operation of the device is as follows in the reproducing/erasing head 3:
Due to the action of the electromagnet 7, the tip of the fiber 1 2 moves close to the disk recording disk 20, and at the same time, an erasing pulse signal is applied to the semiconductor laser 1, and the erasing beam spot 28 is irradiated. In this case, as mentioned above, due to the properties of amorphous semiconductors, in the erase mode, the crystals are melted into an amorphous state by high-temperature heating, and then returned to the original amorphous state while maintaining that state by quenching. It is necessary to irradiate pulsed light with a small duty force. There is a close relationship between the pulse period T1 and pulse width τ of this applied pulse and the longitudinal size l of the rectangular beam spot. That is, turntable 1
8 is rotated by the motor 19 at a constant angular velocity: ω, and if the diameter of the outermost recordable track of the disk recorder 20 is R, then for the size l of the erasing beam spot 28, l>Rω(T+τ ) holds true. As playback progresses further from the outer circumference to the inner circumference, that is, as the housing 24 moves toward the inner circumference in conjunction with the rotation of the turntable 18, the disc recording disk 20 is constantly exposed to a beam of equal energy density and a cooling beam. In order to meet these conditions, the pulse period must be made long and the pulse width τ must be made small. (
However, the spot length 2 is constant. ) It is possible to reproduce and erase information on a disc-shaped recording disk made of amorphous semiconductor material using the above-mentioned device, and although it is not shown in the drawing, information can also be easily recorded using the above-mentioned device. be able to.

That is, when a He--Ne gas laser similar to that used for reproduction is used as a light source during recording, a high-output laser light source is used and an optical modulator is provided in front of the relay lens 15. This modulator is A
・0. (acousto-optic effect) modulator or E.0 (electro-optic effect) modulator is used. Furthermore, during recording, tracking control is not required, but can be performed in the same manner as during playback.
Furthermore, if it is inconvenient to use a large laser light source and optical modulator, it is also effective to use a semiconductor laser for writing as well as for erasing. At this time, a substantially circular beam is irradiated onto the recording track using a continuous wave type semiconductor laser. The rest can be omitted as they can be done in the same way as in the previous example. As described above, in the present invention, by using a small semiconductor laser that can be directly modulated and integrating it with a reproducing head, an erasing method that can easily control focusing and tracking can be realized. Information can always be monitored and partially erased.

Furthermore, it was difficult to converge the light from a semiconductor laser into a minute spot using a lens optical system, but this problem was solved by using a focusing fiber.

[Brief explanation of the drawing]

The drawings relate to the present invention; FIG. 1 is a configuration diagram of a semiconductor laser, FIG. 2 is a configuration diagram of a read/erase head, and FIG. 3 is a configuration diagram of a read/erase head.
Figure 4 is a block diagram of an optical recording device according to an embodiment of the present invention.
This figure is a diagram explaining the function of FIG. 3, and FIG. 5 is a detailed diagram illustrating an addition/subtraction amplifier that is a component of the present invention. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Fiber 1, 3... Reproduction/erase head, 9...
Objective lens, 14... Laser light source, 16...
...Movable reflective mirror, 17...Half mirror, 20...Disc recorder, 21...
・Divided photodetector, 22... Addition/subtraction amplifier.

Claims (1)

[Claims] 1. An objective lens that focuses a light beam from a first light source as a recording/reproduction beam onto a recording medium that can be recorded and erased depending on the irradiation conditions of the light beam, and a distance between the objective lens and the recording medium is always constant. a control means for controlling the
It has a semiconductor laser and a plurality of optical fibers each having one end disposed along the bonding surface of the semiconductor laser, and the other end of the plurality of optical fibers is arranged so that the light emitted from the optical fibers is connected to the recording medium. an optical recording/reproducing device fixed integrally with the objective lens so that the information track irradiated with the reproducing beam is irradiated as a rectangular beam extending in the direction of the information track in close proximity to the recording/reproducing beam; .