JPH0476830A - light head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical disk device, and more particularly to an optical head structure that is easy to assemble and has high productivity. [Conventional technology]

Conventionally, a photodetector in an optical head for an optical disk has a plurality of light-receiving elements having a fixed shape, as described in, for example, Japanese Patent Laid-Open No. 63-222339. The process of assembling the optical head requires a step of positioning the light beam guided to the photodetector at a predetermined position with respect to the above-mentioned light receiving element. [Problems to be Solved by the Invention] However, it takes time to align the photodetector, which can be said to be one of the reasons why the price of the optical head is high. Moreover, parts shift may occur due to changes over time, and the positional relationship between the light beam incident on the photodetector and each light-receiving element may become out of order. Since these act as an offset on the focus shift or track shift control system, a problem arises in that stable recording, reproduction, or erasing cannot be performed. In view of the above, an object of the present invention is to provide an optical head having a signal reproducing system that is easy to assemble and is not affected by changes over time.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention uses a multi-division light-receiving element divided into a matrix as a photodetector for signal reproduction. Furthermore, unlike conventional optical heads, the light-receiving surface is not physically determined, but a light-receiving area consisting of a plurality of matrix elements is virtually set. The amount of light received is calculated between a plurality of light receiving areas to obtain a light spot control signal and an information reproduction signal. [Operation] By comparing the optical signals received by each matrix element, the center position of the light intensity of the light beam incident on the photodetector can be determined. Based on this, a light receiving area of a predetermined size is virtually determined on the matrix. By calculating the sum of the optical signals of the matrix elements existing within a predetermined light-receiving area, that area can be regarded as one physically determined light-receiving surface. By calculating light reception signals between a plurality of light reception areas, various light spot control signals and information reproduction signals can be obtained. According to the present invention, there is no need to align the photodetector when assembling the optical head. Therefore, the ease of assembling the optical head is improved. Furthermore, according to the present invention, the center position of the light intensity of the light beam incident on the photodetector can always be known. Therefore, even if optical axis misalignment occurs due to changes over time or other reasons,
By moving the light-receiving area within the matrix accordingly, stable signal reproduction is always possible. [Embodiment] An embodiment of the present invention will be described below with reference to FIG. This embodiment relates to a magneto-optical disk device. The semiconductor laser light source 1 has two light emitting points 1a and lb (not shown). The emitted light from the semiconductor laser light source 1 is turned into a parallel beam by the collimating lens 2, and the light intensity distribution is shaped into a circular shape by the beam shaping prism 3. The light then passes through a polarizing beam splitter 4 and a mirror 5 and is focused onto a disk 7 by a focusing lens 6 as a focusing spot 8 . Various roles can be considered for the narrowing spots 8a and 8b as shown in Table 1. The light reflected by the disk 7 passes through the aperture lens 6, the mirror S, the polarizing beam splitter 4, and the lens 9, and is separated by the Wollaston prism 10 into both p and S polarized components. The Wollaston prism 10 is rotated so that the polarization direction of the incident light is approximately 45 degrees with respect to the bonding surface of the prism, and the light quantities of the eight emitted light beams are approximately equal. In this embodiment, a λ/2 plate is intentionally not used. This is extremely effective when two or more types of lasers are used and the two focusing spots have different wavelengths. When rotating the polarization direction using a λ/2 plate without rotating the Wollaston prism, the λ/2 plate must be designed with an intermediate wavelength of one or both. Then, one or both of the lights will no longer be completely linearly polarized, but will become elliptically polarized to some extent. This is undesirable because it leads to C/N deterioration of the magneto-optical signal. Therefore, in a magneto-optical disk device that uses two or more wavelengths, it is preferable not to use a λ/2 plate in the magneto-optical signal reproducing system, but to use a rotating Wollaston prism or a polarizing beam splitter. As shown in FIG.
a to 12d, and virtual photodetection areas A to G (details will be described later) are formed on each light receiving surface. The focus shift signal AP, track shift signal TR2, magneto-optical reproduction signal MO, address information reproduction signal ID, etc. are obtained by the following calculation formulas. However, the symbol AG in the following formula is A-
Let it represent the total amount of light received by each photodetection area of G. AF = (A+C)-B TR=E-F M○ = (A+B+C)-(E+F): D-
G ID = (A+B+C)+(E+F)=D+G FIG. 2 shows an example of the light receiving surface 12 and the light detection area. These shapes are not limited to those shown in FIG. 2, and any shape will not affect the essence of the present invention. The light receiving surface 12 is composed of light receiving elements XIJ arranged in a matrix as shown in FIG. The number of elements is mXn. Each light receiving element is composed of, for example, a PIN photodiode or a CCD sensor, and outputs a current or voltage corresponding to the amount of light received. Outputs in the "row" direction and "column" direction of the matrix are led to gate circuits 101a and 101b, respectively, and the signals of the light receiving elements to be detected are selected according to instructions from the controller 103. The selected signal is calculated and processed by the signal processing circuit 102 and sent to a higher-level controller (not shown) as a focus shift signal, track shift signal, magneto-optical reproduction signal, address information reproduction signal, etc. The signal detection method using each light receiving element will be explained in detail with reference to FIG. To simplify the explanation, the number of matrix elements is assumed to be 4×4, and each light receiving element is a photodiode. For example, when selecting the light receiving element D23, H2 and v3 may be selected as the output terminals. Also, if H1 to H4 and ■2 are selected, the light receiving elements D: 2, D22, D32, D42
A sum signal of . Even when there are many matrix elements, the output signal can be obtained using the same concept. Selection of the output terminal is performed by the aforementioned gate circuit. By the method described above, it is possible to know the intensity distribution of light incident on the light receiving element. Since the light receiving element has a spatial extent, the obtained light intensity distribution is discontinuous. Therefore, the signal processing circuit 102 performs smoothing processing (so-called smoothing processing). As a result, the center position of the light intensity distribution on the matrix can be specified. Based on the identified center of light intensity distribution, photodetection areas (A, B, and C in the figure) having a predetermined size are virtually set. By summing the signals of the light receiving elements within this photodetection area, it is regarded as one conventional photodetection area and various signals are reproduced. The shape of the light-receiving area and the like may be set in advance in the memory inside the controller 103. Furthermore, if the light flux on the light receiving surface moves due to changes over time, the center of intensity is redetected and the light detection area is reset, so that stable signal inspection can always be performed. Conventionally, when assembling an optical head, it was necessary to position the light beam of the detection system at a predetermined position on a predetermined photodetector. Furthermore, the positional shift of the photodetector caused by changes over time has been a factor that adversely affects the servo as an offset in the focus shift detection system, track shift detection system, and the like. According to the present invention, since the photodetection area is set after the optical head is assembled, there is no need to precisely align the photodetector during assembly. Therefore, the optical head assembly process can be simplified. In this embodiment, the center of the light intensity distribution is used as the reference, but it is also possible to use a plurality of light receiving elements to detect the outer periphery of the received light beam and use that as the reference. In addition, in Fig. 2, multiple light receiving areas are set on the photodetector.
Forming one large light-receiving area with a matrix light-receiving element,
A plurality of virtual light detection areas may be formed. Furthermore, it goes without saying that the present invention is applicable not only to magneto-optical disks but also to, for example, read-only type, write-once type, or phase change type optical disk devices.

【Effect of the invention】

As described above, according to the present invention, there is no need to precisely align the photodetector when assembling the optical head. Therefore, the ease of assembling the optical head is improved. Furthermore, according to the present invention, the center position of the light intensity of the light beam incident on the photodetector can always be known. Therefore, even if optical axis misalignment occurs due to changes over time or other reasons, stable signal reproduction is always possible by moving the light receiving area within the matrix accordingly.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the overall configuration of an embodiment of the present invention,
FIG. 2 is a diagram showing the configuration of the photodetector, FIG. 3 is a diagram explaining details of the light receiving portion of the photodetector, and FIG. 4 is a diagram explaining the operation of the light receiving element. Explanation of symbols 1... Semiconductor laser light source, 2... Collimating lens, 3... Beam shaping prism, 4... Polarizing beam splinter, 5... Mirror, 6... Stopping lens, 7...
...Disc, 8...Filtering spot, 9. Paruns, 10...Wollaston prism, 11...Photodetector, 12...Light receiving area, 101...Gate circuit, 1
02...Signal processing circuit, 103...Controller agent Patent attorney Ogawa ysyA mouth ■ Diagram, Hi-tcon Y Rourke ■ Diagram

Claims (1)

[Claims] 1. In an optical head mounted on an optical disk device, at least one of a focus shift detection signal, a track shift detection signal, and a recording information signal is detected by a multi-segment photodetector divided into a matrix. An optical head characterized by: 2. The optical head according to claim 1, wherein the light intensity center position of the light beam incident on the multi-divided photodetector is detected from the amount of light received by each matrix element in the multi-division photodetector. 3. Claims 1 and 2, characterized in that a virtual light-receiving area consisting of a plurality of matrix elements is set on the multi-segment photodetector based on the light intensity center. Light head as described. 4. A patent characterized in that a plurality of light-receiving areas are set and the optical signal of each light-receiving area is calculated to generate at least one of a defocus detection signal, a track deviation detection signal, and a recording information signal. An optical head according to claims 1, 2, and 3. 5. Claims 1, 2, 3 and 5, characterized in that the light receiving area is set by moving on the multi-segment photodetector as the center of the light intensity shifts. The optical head according to item 4.