JPS6242342A - Erasure optical head - Google Patents

Abstract

PURPOSE:To decrease remarkably areas remained unerased by giving a phase difference to a part of a light beam before the incidence in an aperture lens to decrease the peak intensity of an erasure spot and widening the width in the track orthogonal direction. CONSTITUTION:An erasure bean forming means 20 consists of a cylindrical lens 23 and a phase providing section 22. The cylindrical lens 23 gives an astigmatism to a light beam 24 to prolong an erasure light spot 18 in the track direction and the phase provision section 24 gives a phase difference to a part of the light beam 24. The shape of the erasure light spot 18 is changed depending on the shape of the phase provision section 22 and the phase difference to be given, and as the shape of the section 22, for example, a center band shape or a center circular shape is preferred and the phase difference to be given is pi preferably. Since the central light intensity of the erasure light spot 22 is nearly constant obtained in this way, a part having a constant erasure characteristic is widened and the erasure width in the track orthogonal direction is widened.

Description

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

Conventional technology In recent years, optical disk devices have been actively developed and commercialized as large-capacity information storage devices, such as stationary disk file devices and two-character file devices.0 Optical disk devices irradiate a laser beam onto a disk that rotates at high speed. This device records information bits on the memory thin film, lowers the power of the same laser, and reads 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 (pictures), a light spot with a high power density narrowed down by the diffraction limit of 1 (diameter 0.8 μm 8 degrees) is used. irradiate. In this way, the thin film is rapidly heated and cooled, transitioning to a state with low reflectance, and recording is completed. In addition, when erasing a recorded bit, a light spot with a low power density and shaped in the shape of an ellipse (about 10 μm in diameter) is irradiated onto the recorded bit, and the thin film in this area is annealed (slowly cooled). Erasing is completed by transitioning to the original pre-recording state with high reflectance.

As described above, an optical head that emits a light spot that can be annealed in erasing recorded bits has been proposed as an optical head for an optical disk device 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 about 8 mW during recording and about 1 mW during reproduction is irradiated. 2 is a semiconductor laser for erasing, which emits wavelengths λ2. A laser beam with a power of about 1 omWaff is irradiated. 3 and 4 are condenser lenses, and semiconductor lasers 1 and 2
It focuses the light beam from the A pair of cylindrical lenses 5 and 6 shape the light beam of the semiconductor laser 1 into a substantially circular shape. Similarly, T is a cylindrical lens, which imparts astigmatism to the light beam of the semiconductor laser 2 in order to make the shape of the aperture light elliptical. A polarizing beam splitter 8 reflects the S-polarized laser beam and transmits the P-polarized light beam. 9 and 10 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. Reference numerals 12 and 13 are aperture lenses, ↑4 is a disk having a memory thin film for recording and reproduction, and 1S is a cylindrical lens for detecting a focus control signal using an astigmatism method. Reference numeral 16 denotes a signal detector, which includes a plurality of light receiving elements for detecting a reproduction signal, a focus control signal, and a tracking control signal. . 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, in recording or reproducing, a recording/reproducing semiconductor laser 1 emits a light beam of a predetermined power. This S-polarized light beam is reflected by the polarization beam splitter 8 and passes through the false wavelength plate 9, and then is irradiated onto the disk 14 by the aperture lens 12 as a recording/reproducing light spot 17. During recording, this light spot 17 increases its power and rapidly heats up the memory thin film of the disk 14.
Rapidly cool and change the state to change the reflectance.

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

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 false wave plate 9. Therefore, it passes through the polarizing beam splitter 8, and the % wave plate 1
0. After passing through the optical filter 11, the light can be narrowed down to a signal detector 16 by an aperture lens 13. The cylindrical lens 16 imparts astigmatism to this aperture light to enable focus detection. It goes without saying that reflected light can also be detected in the light beam during recording 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 polarizing beam splitter 8, passes through the false wave plate 10, and since it has a wavelength of λ2, it is reflected by the optical filter 11, returns to the % wave 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 false wave 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 annealing effect. 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 false 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 polarizing beam splitter 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. As shown in FIG. 2, in the conventional method, a long erasing light spot 18 is formed in the direction of the track 21 using a cylindrical lens. Therefore, since nothing has been done with respect to the shape of the erasing light spot 18 in the direction perpendicular to the track 21, which is a direction perpendicular to this direction, basically the track 21 of the recording/reproducing light spot 17 and the erasing light spot 18 is The extent in the orthogonal direction is the same. In such a configuration, if the recording/reproducing optical spot 1γ and the erasing optical spot 18 are relatively shifted in the direction perpendicular to the track 21 due to a change in the temperature environment, for example, the difference between the two will occur (as shown by the dotted line in FIG. 2). The trace line is misaligned, resulting in unerased areas. In order to prevent unerased parts, the focal length of the condensing lens 4 should be shortened so that the track 21 of the erasing light spot 17
It would be possible to increase the width in the orthogonal direction, but in this method, the erasing light spot 18 spreads out in a similar manner, which causes the problem that the base area also becomes wider and the recorded portion on the adjacent track is erased. One way to widen the erasing width is to increase the erasing power, but this method increases the light intensity in the center too much and damages the recording material. Damage to the recording material due to unerased data and overpower,
There is a problem of adjacent cancellation, and a method to solve this problem is desired. The present invention aims to solve these problems, and provides a method for solving them at the same time.

Means for Solving the Problem The shape of the light intensity distribution of the erasing light spot focused and formed on the disk recording medium by the aperture lens is changed by giving a phase difference to a part of the light beam before it enters the aperture lens. Erasing is performed by lowering the peak intensity of the erasing light spot 7) and widening the width in the direction perpendicular to the track, and irradiating this erasing light spot.

By imparting a phase difference to a portion of the working light beam, the shape of the erasing light spot formed using the aperture lens can be manipulated. By widening the width of the erasing light spot in the direction perpendicular to the track, it is possible to eliminate unerased spots even if the erasing light spot is slightly shifted, and since the peak intensity is also reduced, damage to the recording material due to overpower can be prevented. be able to.

EXAMPLE An example of the present invention is shown in FIG. Numbers 1 to 19 correspond to those with the same numbers in the conventional example and perform the same functions.

2o is an erasing beam forming means. Therefore, the only difference from the conventional example of the present invention is the erasing beam forming means 2Q, and the method for forming the erasing spot 18 will be described below. An example of the configuration of the erasing beam forming means 2° is shown in FIG. The erasing beam forming means 2o is composed of a cylindrical lens 23 and a phase imparting section 22. The function of the cylindrical lens 23 is the same as the conventional one, and the light beam 24
The erasing light spot 18 is lengthened in the track direction by giving astigmatism to the lens. The phase imparting section 22 is a part related to the present invention, and thereby imparts a phase difference to a portion of the light beam 24. The shape of the erasing light spot 18 can be changed depending on the shape of the phase imparting section 22 and the phase difference provided, but the shape of the phase difference imparting section that meets the purpose of the present invention may be, for example, a central band shape (Fig. 3?L). ), central circular shape (Figure b)
If the phase difference that gives a good value is π, then π is good. A preferred method for providing a phase difference is to deposit a transparent material such as 5i02 in the above-mentioned strip or circular shape to a thickness of about 0.9 μm.

Next, FIG. 4 shows the shape of the erasing light spot 18 formed in this manner. When the shape of the phase imparting portion 22 is made into a band shape, it becomes as shown in FIGS. 4a and 4b, and since the band width is different between FIG. Figures c and d show cases where the phase imparting portion 22 has a circular shape, and the diameters are different in figures C and d. A substantially trapezoidal shape can be obtained from these. Note that FIG. e shows the shape of the erasing spot in the conventional case where there is no phase imparting section 22. The erasing light spot 22 obtained in this way has a substantially constant light intensity at the center, so the area where the erasing characteristics are constant is wider than that of the conventional spot 4, FIG. can do. Therefore, it is possible to reduce the number of unerased areas caused by the misalignment between the recording spot 22 and the erasing spot compared to the conventional technique. Furthermore, compared to the conventional erasing light spot shown in FIG. 4e, the erasing light spot of the present invention has a lower light intensity at the center, so that damage to the recording material due to overpower can be prevented.

Effects of the Invention The effect of the present invention in forming a trapezoidal light spot is that the erasing width in the direction perpendicular to the track can be widened without causing damage to the recording material due to overpower, and therefore, the erasure width can be minimized. This can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of an erasing optical head in an embodiment of the present invention, Fig. 2 is a diagram showing the positional relationship between a general recording/reproducing spot and an erasing spot, and Fig. 3 is an erasing optical head which is the main part of the present invention. FIG. 4 is a characteristic diagram showing the shape of the erasing spot formed according to the present invention. FIG. 5 is a principle diagram showing the structure of a conventional erasing optical head. FIG. 6 is a diagram showing the shape of the erase spot in the track direction by the same method. 3, 2... Semiconductor laser for erasure, 4... Condensing lens, 12...・Aperture lens, 2o...
Erasing beam forming means, 22 ... phase imparting section, 23
...Cylindrical lens. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Fig. 17--Erase beam type liquid means 22a, l)-11 phase Application part 23-Cylindrical lens 24-Improvement Fig. 4 (a Y (μm) <b) -3-2-lO/ 2 3 Fig. 4 (C Y (μm) (d) 4th Figure (e) Y (μm) Figure 5 Figure 6 - Track direction Position 1

Claims (1)

[Claims] The light intensity distribution shape of the erasing light spot focused and formed on the disk recording medium by the aperture lens is adjusted to the peak intensity of the erasing light spot by giving a phase difference to a part of the light beam before entering the aperture lens. An erasing optical head characterized in that the erasing optical head performs erasing by lowering the head and widening the width in the direction perpendicular to the track, and irradiating the erasing light spot.