JPH0612683A - Optical reading and reproducing device - Google Patents

Abstract

PURPOSE:To improve focus control and to miniaturize and make thin the device with the use of a half-mirror by arranging optical parts on a plane and arranging the quadripartite lines of a photodetector at 45 degrees to a valid tracking direction. CONSTITUTION:A laser beam in the (x) axis direction from a semiconductor laser diode 1 is bent by 90 degrees in the (y) axis direction through the half- mirror, bent for 90 degrees in the (y) axis direction through a collimator lens 3 and a reflection mirror, passes through an objective lens 5 and is made incident on a disk 6. The light reading recording information is reflected, made incident through a mirror 2 on the photodetector 7 and converted into signal. In this case, the direction of a focal line by the astigmatic effect of the mirror 2 is '0' degree to the valid tracking direction and the direction of the quadripartite lines of the photodetector 7 is arranged at approximately 45 degrees to the valid tracking direction. Thus, the diode 1, the mirror 2, the lens 3, the mirror 4 and the photodetector 7 can be arranged on the same plane.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to focus control of an optical reading / reproducing apparatus such as a compact disc (CD) player, and more particularly to astigmatism using a half mirror. Concerning the law. 2. Description of the Related Art Japanese Laid-Open Patent Publication No. 56-57013 and Japanese Laid-Open Publication No. 59-1678 have been proposed as a focus detection method for an optical reading / reproducing apparatus.
Astigmatic method using a half mirror (parallel plane plate) as described in No. 63 is known. However, conventionally, in the case of the astigmatism method, in many cases, the direction of the focal line of the light spot is tilted by 45 degrees with respect to the effective track direction on the photodetector, and it is common. By the way, in the case of the half mirror system, when the inclination is set to 45 degrees, the position of the laser diode has a structure having an angle of 45 degrees with respect to the pickup moving direction. In addition, in order to make the pickup thin, if the axis of the detection optical system is placed horizontally with respect to the disc by a reflection mirror, etc., the configuration becomes more complicated.
There is a drawback that it becomes very difficult to fix the optical component and shape the case that is the base thereof. SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical reading / reproducing apparatus which does not have the above-mentioned drawbacks and which performs good focus control using a half mirror. As can be seen from FIG. 1 and FIG. 2 showing the present embodiment, the present invention determines the direction of the focal line of the light spot on the photodetector as an effective track. The photodetector is divided into four division lines at 45 degrees with respect to the effective track direction. Thereby, the optical components can be arranged on the same plane, and the pickup shape can be simplified. However, when such a photodetector arrangement is adopted, the following new problems occur, but the present invention solves these new problems by the method described below. In the present invention, in the optical reading / reproducing apparatus using the laser light emitting element, the optical element having the astigmatism effect, the objective lens and the photodetector, the focal line of the optical element having the astigmatism effect is The direction is arranged at about 0 degree with respect to the direction of the information track of the information recording medium projected on the photodetector surface, and the photodetector has a square light receiving pattern divided into four areas by diagonal lines, and The dividing line is characterized in that it is arranged at approximately 45 degrees with respect to the direction of the information track projected on the photodetector surface. Further, according to the present invention, when the information surface of the information recording medium is located at the focal point of the laser beam focused by the objective lens, the light spot on the photodetector is unequal to the four divided areas of the photodetector. The focus servo, which is configured to be distributed in a quantity, is configured to electrically inject an offset and focus the laser light focused by the objective lens on the information surface of the information recording medium. It has a feature. FIG. 3 shows the arrangement of the conventional photodetector 10 and the focus signal detection circuit in the astigmatism focus detection system. This is such that the direction of the focal line of the light spot on the photodetector is inclined by 45 degrees with respect to the effective track direction, and the 4-division line of the photodetector is arranged at 0 degree with respect to the effective track. In contrast to the conventional example shown in FIG. 3, the drawbacks of the photodetector arrangement shown in FIG. 2 according to the present invention are as follows.
The following can be considered. (1) A focus error occurs in the information track section and the mirror section between the tracks. (2) In the case of a two-dimensional objective lens driving method,
A tracking error occurs due to the tracking of the objective lens in the tracking direction. (3) In a disk having a defect in the disk protection mold (for example, a thing that scatters light such as bubbles, fingerprints, scratches, etc.), the information track followability deteriorates due to the defect. However, regarding the above point (1), the modulation factor is 6
Even if the disc is 0% or more, the focus error is set to 0.3 by setting the focus error detection sensitivity appropriately.
It is possible to make it less than or equal to μm. Regarding the point (2), the steady feed deviation of the optical reader is reduced,
By setting the tracking amount of the objective lens in the track direction to be small, it is possible to make the focus error negligible. Next, with regard to the above point (3), it was found that the offset can be greatly improved by electrically injecting an offset into the focus servo loop according to the present invention. Therefore, a detailed illustration of the improvement of the followability to the defective disk will be given below. It will be explained. First, as a typical example, consider the case where dust is attached to the disk surface. FIG. 4 shows the positional relationship between the light spot 12 and the dust 11 on the disk protection mold surface. That is, the dust on the protective mold surface first passes through the portion (A) of the light spot on the mold surface in the order of yellow as the disc is reproduced. If the reproduction is further continued, it similarly passes through the portions (B) and (C), and finally passes through the outside of the light spot. Next, FIGS. 5 to 7 show focus error signals when the dust passes through the light spot as shown in FIG. The thick line is a waveform simulating the case where the objective lens is always focused on the disk, and the dotted line is the response of the actual servo loop. FIG. 5 shows a conventional photodetector arrangement, and FIG. 6 shows a photodetector arrangement according to the present invention. Here, in the conventional example of FIG. 5, the disturbance of the focus error signal due to the dust occurs in an S shape at the maximum when passing through (A) and (C). For this reason, the objective lens is defocused in a certain direction at the part a, but becomes a signal to be defocused in the opposite direction when it comes past the part b and comes to the part c, and the defocus of the objective lens is corrected. Whereas the sixth
In the case of the figure, the disturbance of the focus error signal due to the dust is small when passing through (A) and (C), but is maximum at the time of passing through (B) and occurs in a W shape. For this reason, the objective lens is defocused in the direction of the a portion, but when it passes through the D portion and reaches the C portion, it becomes a signal that is further accelerated in the same direction as the a portion, and a large defocus is reached after the dust passes. It Therefore, depending on the size of dust, defocusing is performed until the degree of modulation disappears, and as a result, the missing time of the tracking signal becomes long, and eventually an information track following error occurs. This is a drawback of the arrangement of the photodetectors shown in FIG. 2, but in the present invention, the focus detection circuit of the optical disk device using the optical system of the arrangement of the photodetectors is electrically shown in FIG. The above drawbacks are improved by injecting an offset into. That is, when an offset is electrically injected into the offset terminal of FIG. 2, the waveform of FIG. 6 becomes the focus error waveform shown in FIG. Especially (B)
Explaining the case of passing a part, as a result of injecting an offset, the steady-state focus offset deviation during normal reproduction is r. However, when the dust comes to the center of the light spot, the reproduced disc information signal 13 has a light amount of α at the time of normal reproduction but decreases to a light amount of β as shown in the part B of FIG. . Along with this, the gain of the focus servo loop also decreases in proportion, so that the focus error signal increases due to the injected offset, as in the part (b) when passing through FIG. 7 (B). Therefore, when passing through the portion (B), it is possible to correct the disturbance of the focus error signals of (a) and (c) due to the dust by the injection offset voltage of the portion (b), and follow the disc defect portion. The characteristics can be greatly improved, and further, the characteristics can be improved as compared with the conventional photodetector arrangement shown in FIG. EXAMPLE This example will be described below with reference to FIGS. 1 and 2. FIG. 1 shows the optical system of the optical reading / reproducing apparatus of this embodiment. The divergent laser light in the x-axis direction emitted from the semiconductor laser diode 1 has a half amount of light by the half mirror 2, is bent 90 degrees in the z-axis direction, enters the collimator lens 3, and is collimated. The collimated laser light is bent 90 degrees in the y-axis direction by the reflection mirror 4, passes through the objective lens 5, enters the disk 6 as the information recording medium, reads the recorded information, is reflected, and returns to the original optical path again. Return and reach the half mirror 2. Of this, about half the amount of light passes through the half mirror 2 this time, enters the photodetector 7, and converts the read information into an electric signal. Here, in this embodiment, the direction of the focal line due to the astigmatism effect of the half mirror 2 is 0 with respect to the effective track direction of the disk.
In addition, the direction of the four-division line of the photodetector 7 is arranged at about 45 degrees with respect to the effective track direction of the disk. Therefore, the semiconductor laser diode 1, the half mirror 2, the collimator lens 3, the reflection mirror 4, and the photodetector 7 can be arranged on the same plane, which simplifies the method of fixing the optical component and the optical component which is the base of the optical component. There is an effect that the case shape and processing of the optical reading device can be simplified, and the optical reading device can be downsized and thinned. Next, FIG. 2 shows a focus error detection circuit of this embodiment. Photodetector 7 divided into four in FIG.
The sum of the detectors facing each other is subtracted by the operational amplifier 8 to obtain the focus error detection signal. In the photodetector arrangement of this embodiment, the direction of the 4-division line is effective for the disk. Regarding the drawback in the case of 45 degrees with respect to the track direction, the above-mentioned solution is characterized by injecting the offset voltage into the offset terminal 9 in FIG. Further, regarding the optical system of the present embodiment,
As a result of injecting the offset voltage into the focus error detection circuit, the laser light is adjusted so as to be in focus on the disc information surface. That is, when the laser focal point is formed on the disc information surface, the light spot on the photodetector is not evenly distributed to each of the four divided detectors, but converted to the displacement amount of the objective lens. Then, it is defocused by about 1.4 μm. As described above, according to the present embodiment, it is possible to obtain an optical disk reproducing apparatus that can perform good disk signal reproduction and that has sufficient follow-up characteristics even for defects in the protective mold portion of the disk. According to the present invention, since the optical components can be arranged on one plane, the mounting method of the optical components and the structure and processing of the case which is the mounting base of the optical components can be simplified. As a result, it is possible to provide an inexpensive optical disc device which can make the optical reading / reproducing device compact and thin, and which can follow the defective disk well, for example, can follow ψ1 mm or more for dust on the disk surface. The present invention can also be applied to an optical reading / reproducing apparatus vertically arranged with respect to the disk without the reflection mirror, and can provide a cheaper optical reading / reproducing apparatus. Further, the photodetector arrangement according to the present invention can be applied to astigmatism systems other than the half mirror astigmatism system, and can improve the performance of following a defective disk.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an arrangement of optical components according to an embodiment of the present invention. FIG. 2 is a focus signal detection circuit diagram according to an embodiment of the present invention. FIG. 3 is a focus signal detection circuit diagram of a conventional example. FIG. 4 is a front view of the disc mold surface. FIG. 5 is a focus error signal waveform diagram. FIG. 6 is a waveform diagram of a focus error signal. FIG. 7 is a waveform diagram of a focus error signal. FIG. 8 is a disk information signal waveform diagram. [Explanation of Codes] 1 ... Semiconductor laser diode 2 ... Half mirror 3 ... Collimating lens 4 ... Reflecting mirror 5 ... Objective lens 6 ... Disk 7 ... Photodetector 8 ... ...... Operational amplifier 9 ............ Offset terminal 10 ...... Photo detector 11 ...... Dust on the disk protection mold surface 12 ...... Light spot on the disk protection mold surface 13 ...... Disk information signal waveform

Claims (1)

[Claims] 1. In an optical reading / reproducing apparatus using a laser light emitting element, an optical element having an astigmatism effect, an objective lens, and a photodetector, the direction of the focal line of the optical element having the astigmatism effect is on the photodetector surface. The photodetector has a square light receiving pattern divided into four areas by a diagonal line, and the dividing line is the photodetector surface. An optical reading / reproducing apparatus, wherein the optical reading / reproducing apparatus is arranged at an angle of about 45 degrees with respect to the direction of the information track projected above. 2. When the information surface of the information recording medium is located at the focal point of the laser beam focused by the objective lens, the light spots on the photodetector are distributed in unequal amounts in the four divided areas of the photodetector. The focus servo is configured to electrically inject an offset to focus the laser light focused by the objective lens on the information surface of the information recording medium. 1. The optical reading / reproducing apparatus according to item 1.