JPS61292234A - Optical head for erasure - Google Patents

Abstract

PURPOSE:To obtain the form of an optimum erasure light spot by giving a specific phase difference to the specific part of a light beam wave front. CONSTITUTION:Electrooptic elements 35, 36, 37 of a phase converting means 21 have the same thickness (the thickness is in the depth direction in figure), and they are insulated respectively by an insulation plate 39 and connected. The polarized direction of the incident light beam is directed to the arrow, that is, the same as the direction of double refraction and when applying a voltage to the electrooptic element 36, a phase difference is given to only the light beam passing through the said part. Various light spots are formed by the value and position of the phase difference given to the light beam and formed suitable for erasure while being scattered in the track direction. Thus, the recording/reproducing light spot and the erasure light spot are formed from one semiconductor laser and no positional-shift is caused.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical head capable of erasing signals by annealing recorded bits of an optical disk.

2. Description of the Related Art In recent years, optical disk devices have been actively developed and commercialized as large-capacity information storage devices, such as still image disk file devices and correspondence file devices. An optical disk device is a device that records information bits on a thin memory film by irradiating a laser beam onto a disk that rotates at high speed, and then lowers the power of the same laser to read changes in the reflectance of the recorded bits. Now, when using a thin film made of tellurium oxide with germanium and soot added as a memory thin film, for example, when recording information bits, a light spot with high power density narrowed down to the diffraction limit (8 legs with a diameter of 0.8 μm) is used. As a result, the thin film is rapidly heated and cooled, transitioning to a state with low reflectance, and recording is completed.Also, when erasing recorded bits, a light beam with low power density and shaped into an ellipse is used to erase the recorded bits. A spot (ellipse diameter of about 10 μm) is irradiated onto the recorded bit, and this external thin film is annealed (slowly cooled) and transferred to its original pre-recording state with high reflectance, completing erasure.

9. Optical technology that emits a light spot that can be annealed in erasing recorded bits. has been proposed as an optical head for optical disk devices having erasing and rewriting functions.

A conventional example of such an optical head will be described below with reference to the drawings. FIG. 6 is a diagram showing a schematic configuration of a conventional optical head, in which reference numeral 1 denotes a recording/reproducing semiconductor laser, and wavelengths λ1. Laser light with a power of approximately 8 mW is irradiated during recording and approximately 1 mW during reproduction. 2 is a semiconductor laser for erasing, which emits wavelengths λ2. Laser light with a power of approximately 10 mW is irradiated. 3 and 4 are condenser lenses, and semiconductor lasers 1,
This is to condense the light beam from 2. 5 and 6 are a pair of cylindrical lenses, and 07 is also a cylindrical lens that shapes the light beam of the semiconductor laser 1 into a substantially circular shape. Gives astigmatism. A polarizing beam splitter 8 reflects the S-polarized laser beam and transmits the P-polarized light beam. 9 and 1o are wave plates, respectively.

Reference numeral 11 denotes an optical filter, which transmits a light beam of wavelength λ1 and reflects a light beam of wavelength λ2. 12 and 13 are aperture lenses, 14 is a disk having a memory thin film for recording and reproducing, and 15 is a cylindrical lens for detecting a focus control signal by an astigmatism method. Reference numeral 16 denotes a signal detector, which includes a plurality of light-receiving elements for detecting reproduction signals, focus control signals, and tracking control signals. Based on the focus control signal and tracking control signal obtained from the signal detector 16, the aperture lens 12 performs focus control and tracking control. Reference numeral 17 indicates a recording/reproduction light spot focused on the disk 14, 18 indicates an elliptical erase light spot, and 19 indicates a recording bit string.

Next, the operation of the conventional optical head configured as described above will be explained. First, during recording or reproduction, a light beam of a predetermined power is emitted from the recording/reproduction semiconductor laser 1. This S-polarized light beam is reflected by the polarization beam splitter 8, passes through the % wavelength plate 9, and then An optical spot for recording and reproduction is formed on the disk 14 by the aperture lens 12.
Irradiate at the end of the first stage. During recording, this light spot 17 increases its power, rapidly heats and cools the memory thin film of the disk 14, changes its state, and changes its reflectance.

This creates recording bits. During playback, the power of the light beam is lowered to irradiate the optical spot (...) 17 without causing any change in the state of the memory thin film on the disk 14, and the reflected light is focused by the aperture lens 12 and polarized. Return to beam splitter 8.

At this time, the returned light beam is changed from S-polarized light to P-polarized light by reflection on the disk 14 and the two-wavelength plate 9. Therefore, polarized beam splitter 1. It passes through the wavelength 8, and the H wavelength plate 10. After passing through the optical filter 11, the aperture lens 13
The search can be narrowed down to the signal detector 16. The cylindrical lens 15 imparts astigmatism to this aperture light to enable focus detection. In addition, even in the light beam during recording,
It goes without saying that reflected light can be detected as described above.

Next, in erasing, the erasing semiconductor laser 2 emits a light beam with a predetermined power. This S-polarized light beam is reflected by the polarization beam splinter 8, passes through the % wave plate 10, is reflected by the optical filter 11 with wavelength λ2, returns to the AW plate 10, and passes there. The light becomes P-polarized light and then passes through the polarization beam splitter 8. The light then passes through the wavelength plate 9 and is focused onto the disk 14 by the aperture lens 12 as an erasing light spot 18 .

This light spot 18 is given astigmatism by the cylindrical lens 7, has an elliptical shape, and has a light intensity distribution as shown in FIG. That is, since the power density is low and the recording bit is irradiated for a long time, the recording bit is heated by the thermal energy and then slowly cooled to receive the effect of annealing. Therefore, the state of the memory thin film in that area changes, and erasing is performed by returning to the reflectance before recording. Note that the erasing light spot 18
The reflected light from the disk 14 is condensed by the aperture lens 12, passes through the Z wave plate again, and enters the polarizing beam splitter 8. At this time, since the light beam has changed from P-polarized light to S-polarized light, it is reflected by the polarized beam splitter and vine 8 and escapes in the direction of the recording/reproducing semiconductor laser 1. The optical axes of the erasing light beam and the recording/reproducing light beam are slightly shifted to prevent the escaped erasing light beam from being concentratedly incident on the recording/reproducing semiconductor laser 1.

Problems to be Solved by the Invention The problems of the above configuration will be explained below. In the conventional configuration, semiconductor lasers are required for recording and reproducing and for erasing. Therefore, the light source position for recording and reproduction is different from the light source position for erasing, and therefore the optical paths thereof are also different. In such a configuration, if there is a change in the temperature environment, for example, the recording/reproducing semiconductor laser 1 and the erasing semiconductor laser 2 will shift from their original positions, but generally the direction and amount of shift between the two will be Since they are different, a relative shift occurs between the recording/reproducing light spot 17 and the erasing light spot 18. When this deviation occurs in the direction perpendicular to the track, the recording/reproducing optical spot 17 and the erasing optical spot 18
This causes the trace line to shift, resulting in unerased areas.

Furthermore, when a shift occurs in the optical axis direction, the focal point positions of the recording/reproducing light spot 17 and the erasing light spot 18 shift in the optical axis direction, resulting in erasing in a defocused state, and sufficient erasing may not occur. It will not be done.

In addition, in the conventional method of forming an erasing beam using the cylindrical lens 7, the shape of the erasing spot 18 is limited to a symmetrical shape, and this shape is not necessarily the most suitable spot shape for erasing. The shape of 18 cannot be changed. Recording power, 14221
40 Since the shape of the optimum erasing light spot 18 changes depending on the rotational speed, it is also desirable to be able to change this shape instantaneously.

As mentioned above, the problems with the conventional method are, firstly, that the shape of the erasing light spot 18 cannot be changed relatively freely and instantaneously, and secondly, the shape of the recording/reproducing light spot 18 cannot be changed relatively freely and instantaneously. This is because the spot 17 and the erasing light spot 18 are misaligned. The present invention aims to solve the above two problems, and provides an erasing beam forming method that does not cause these problems.

Means for Solving the Problems The present invention provides a specific phase difference to a specific portion of the light beam wavefront, thereby making the width of the irradiation spot on the optical disk recording surface in the track direction wider than the width in the direction perpendicular to the track, and Erasing is performed by irradiating a spot.

By imparting a phase difference to a portion of the wavefront of the working light beam, the shape of the spot focused by the aperture lens can be changed. In this method of erasing by slow cooling, the shape of the erasing light spot only needs to be made long in the track direction, and this shape can be achieved by giving a specific phase difference to a specific part of the light beam wavefront. Example 1. Shown in Figure 2. FIG. 1 is a view taken from a direction perpendicular to the disk surface, and FIG. 2 is a view taken from a direction within the disk surface. First, the optical path will be explained.

The light emitted from the semiconductor laser 20 is converted into a parallel light beam by the collimator lens 21, and the phase converter 22 converts the light into a parallel light beam.
pass through. The erasing optical spoiler 34b (FIG. 3) is formed by the phase converting means 22, and the method thereof will be described later. Thereafter, the light beam passes through the polarization beam splitter 23, which has P-polarization transmission and S-polarization reflection characteristics, to be incident as P-polarization, and after being reflected on the reflection surface 24, it passes through the X-wave plate 26 and becomes circularly polarized light, and the aperture The light is focused onto the recording medium 28 in the disk 27 by the lens 26 to form a light spot 34.

The optical path after reflection from the recording medium 28 is as follows.

After passing through the aperture lens 26 and the X wavelength plate 25, the circularly polarized light is converted into linearly polarized light.
Since the light beam 3 becomes S-polarized light, it is reflected here and goes toward the beam splitter 29. Beam splitter 29 splits the light beam into two, one of which is connected to tracking detector 30 . The other one passes through the detection lens 32 and reaches the focus detector 31 . 33 is a knife that blocks part of the light beam. As methods for tracking and focus detection, the well-known push-pull method and Naifetsu method are shown here.

Next, a method of forming the erasing light spot 34b will be explained. The configuration of the phase conversion means 21 is shown in FIG. This figure is a view seen from the optical axis direction. 35°3'6 and 37 are electro-optical elements made of the same material and have the same thickness,
(Thickness is in the depth direction in the figure) Each is insulated and connected by an insulating plate 39. Electro-optical element 35.36.
The material of 37 is, for example, PLZT.

Reference numeral 38 denotes an electrode for applying a voltage to the electro-optical element 36. The direction of birefringence of the electro-optical element 35°36.37 is the direction of the arrow in the figure, which coincides with the direction of voltage application. The polarization direction of the light beam incident on the phase conversion means 21 is the same as the direction of the arrow in the figure, that is, the direction of birefringence. In such a configuration, when a voltage is applied to the electrodes, the refractive index in the direction of the arrow of the electro-optical element 36 to which the voltage is applied changes. This causes a difference in the optical path length required. Therefore, when a voltage is applied to the electro-optical element 36, a phase difference can be imparted only to the light beam that has passed through this portion. When no voltage is applied to the electro-optical element 36, the thickness and refractive index of the electro-optical elements 35, 36, and 37 are the same, so no phase difference occurs, and it is the same as when there is nothing, and this state is the recording/reproducing state. becomes.

Next, the shape of the erasing light spot 34b created when a phase difference is given to a portion of the light beam as described above will be explained using a specific example. It is assumed that the light beam enters the phase converting means 21 in a circular shape shown by the dotted line in FIG. When a phase difference is provided by the central strip-shaped electro-optical element 36 as in the configuration shown in FIG. 4, the shape of the erasing optical spoiler 34b becomes as shown in FIG. 6. In this figure, the electro-optical elements 35, 3θ, and 37 are arranged in the Y direction, and this direction is defined as the track direction.

The figure (-) shows the beam width W1 in FIG. W2. W3 ratio is 1
:2:1 and the electro-optical element 36 has a phase difference of 2π/3. It can be seen that the three light spots are dispersed in the track direction. Figure (b) shows Wl:W2
:W3=1:4:1, and this is the result when the phase of the electro-optical element 36 is given as 2πi. Figure (c) shows the result of laminating two electro-optical elements, setting the laminating line so that it is in the center of the light beam, and giving a phase difference i to one semicircle. In this way, various light spots can be created depending on the magnitude and position of the phase difference given to the light beam, and can be dispersed in the track direction to form a shape suitable for erasing. It is also possible to form a long light spot continuous in the track direction on the semiconductor ray. However, in Figure (d), the track direction is the X direction. Figure (e) shows the shape of a spot for recording and reproducing, which is made without applying a voltage to the electro-optical element, and has a shape that is almost a perfect circle. At this time, the phase converting means 21 does not have any function, so it is the same as when there are parallel glass plates.

Effects of the Invention In the method of forming an erasing light spot using the phase conversion means 21, the shape of the erasing light spot can be changed by controlling the voltage applied to the electro-optical element. It is possible to form erasing beam shapes suitable for each of the circumference and the outer circumference.

In addition, in the present invention, since a recording/reproducing optical spot and an erasing optical spot can be formed using one semiconductor laser, the optical system can be simplified, and the cost can be reduced and the size can be reduced. It also has the advantage that there is no misalignment between the recording/reproducing light spot and the erasing light spot, which was a problem when using the optical disc.

[Brief explanation of the drawing]

1st. Fig. 2 is a principle diagram of an optical head for erasing in an embodiment of the present invention, Fig. 3 is a diagram showing the shapes of a recording/reproducing light spot and an erasing light spot for explaining the optical head, and Fig. 4 is a diagram showing the shapes of a recording/reproducing light spot and an erasing light spot for explaining the same optical head. 5 is a diagram showing an example of the shape of the erasing light spot formed by the present invention. FIG. 6 is a diagram showing the principle of the conventional erasing optical head. FIG. 7 is a diagram showing the shape of the erasing light spot for explaining the optical head. 20... Semiconductor laser, 21... Collimator lens, 22... Phase conversion means, 23...
...Polarizing beam splitter, 25...K
Wave plate, 26...Aperture lens, 27...
・Disk, 34... Light spot. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
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Claims (1)

[Claims] A phase difference is given to a part of the light beam, and this light beam is imaged as a dispersed or long light spot in the track direction on the disk recording medium using an aperture lens, and the recording medium is slowly cooled by this irradiated light spot. An optical head for erasing, which is characterized by erasing using