JPS60187941A - Optical information detector - Google Patents

Abstract

PURPOSE:To decrease member of components and optical length and also to attain the small size and light weight of the detector by fixing a light source, a beam splitter, a cylindrical lens adhered to one end face, a four-split photodiode and a converging lens at a prescribed distance. CONSTITUTION:The light from a light source 2 of a semiconductor laser 1 is focused on an information recording face of an optical disc 5 via a beam splitter (BS) 3 and a condenser lens 4. The reflected ligh is reflected on the BS3 via the converging lens 4 and made incident on a photodiode 7 via a cylindrical lens (CL) 6. The light source 2 and the BS3 are adhered so tha the distance (a) of the both is 3-4mm. and the generating line of the CL6 is in parllel with the direction of the diagonal line of the end face of the BS3, and focus of the CL6 is taken as 10-30mm., and the relative position of all optical components is fixed. Thus, the optical length is decreased, the number of components is reduced and the small size and light weight of the device are attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] An optical information detection device used in an optical digital device such as a digital audio player includes: (1) detecting information recorded on an optical disk; ■ Misalignment in the optical axis direction between the focus of the convergent light and the information recording surface of the optical disc (focus error)
f Detection, ■ Position the focal point of the convergent light in the direction perpendicular to the track of the optical disc information example (trace and ri).
Queller) 1-Detect. The function of '+3filJ' is required.

Among the above methods, a simple method is used for the trunk error detection method, but the Puncible method, which does not require a special optical system for the P river, requires fewer optical parts and requires a detection circuit. Because it is simple, it is the method that can be made the most compact, and it does not require a lot of work. However,
This method has the disadvantage that if the converging lens is shifted from the optical axis in order to correct the tracking error, the position of the light beam on the photodiode will be -C, which will cause an error in tracking error detection. In order to compensate for this drawback, it is necessary to move the entire optical system in order to correct the traverse error so that the optical axis of the converging lens and other optical systems does not shift even if the traverse error is corrected. , in this case, the focus error is corrected using the convergence lens y: chisel? You can move the entire optical system or move the entire optical system, but the method of driving the entire optical system in the tracking direction and driving only the converging lens in the focusing direction will inevitably make the mechanism complicated. Moreover, when the entire optical system is driven, the weight of the moving parts becomes very heavy, so in the end, the P-F-Ship method reduces the diffraction efficiency of the information phase (B+7) on the disk. σ is not very expensive and is not often used in optical information detection devices for digital audio discs where low cost is important. In particular, when the most stable astigmatism method is used as the focus error detection method, a cylindrical lens with a focal length of 90,011 mm to 120.0 mm, which is commonly used in conventional methods, is used ( Since the optical path length of the optical system becomes longer and the entire optical system becomes larger, it is extremely difficult to drive the entire optical system. In order to make it possible to adopt the push-pull method and provide products with low cost and good stability, we have made improvements to the optical system to shorten the optical path length and reduce the number of parts.
The objective is to make the optical system smaller and lighter.

[Structure of the invention]

The configuration of an embodiment of the present invention will be described below based on the drawings. FIG. 1 shows an embodiment of the present invention, in which light emitted from a light source 2 within a semiconductor laser 1 passes through a beam splitter 3 and enters a converging lens 4. In FIG. Then, 4+ points f are connected to the information recording surface of the optical disk 5, and it is reflected from that surface, passes through the converging lens 4, is reflected by the beam splitter 3 in a direction 90 degrees from the optical axis, and is reflected by the cylindrical lens. The light enters the photodiode 7 which is divided into 4 parts according to 6f.

At this time, as the distance between the beam splitter 3 and the light source 2 increases, the distance from the 4-split photodiode to the beam splitter 3 also increases.
It is important to make the length α as short as possible. However, when shortening the length cLf, in order to obtain a constant detection range of the focus error signal, the focal length of the cylindrical lens must be shortened.1. ′! e Take the cylindrical lens away from the 4-split photodiode 7+i
Since both of the above two conditions have limits, there is a lower limit to the value of length α.

Therefore, in the present invention, the value of α when there is no glass attached to the semiconductor laser is set to 4 sn% beam sub1), the length of one side of the ivy 3'k4''s cylinder 91), the thickness of the cal lens 6, ft1. 1. The focal length of the cylindrical lens is ?16.511 m. 1. The cylindrical lens 6 has a diameter of 16.511 m. The nocal lens 6 has one end surface of the beam splitter with the direction of the diagonal line of the end surface and the direction of the generatrix of the curved surface of the cylindrical lens. This is to make the focal length of the cylindrical lens 6 as long as possible.This is to make the focal length of the cylindrical lens 6 as long as possible. Under the distance M50 imlJ, the shorter the focal length, the higher the production cost, so by attaching the cylindrical lens to the beam splitter as described above, the cost due to the shortening of the focal length of the cylindrical lens can be reduced. increase can be minimized.

Furthermore, if the cylindrical lens 6f is attached to the beam shank 3, there is no need to add another cylindrical lens holding mechanism, and the weight and cost can be reduced accordingly.

- Due to the arrangement of the optical system described in F, the detection range of the focus error signal is calculated to be about 20 μm, and the distance b is about 6
．． Q mR. The b value of an optical system that uses the same focus error signal detection method is approximately 20 to 301, which means that the optical system is quite /J\ type, and due to stiffness, the optical system itself In addition to this, the holding mechanism for the optical system can also be made lighter and lighter.

Furthermore, by fixing the relative position of the entire optical system, there is no need to provide a collimator lens that converts divergent light into parallel light as in the past, and convergent lenses can be used to correct aberrations such as optical axis misalignment. Since this is no longer necessary, a lens with a simpler configuration can be used, and the optical system can be made significantly smaller and lighter in these aspects as well.

[Effects of the Invention] As described above, the optical information detection device of the present invention allows the optical system and its holding mechanism to be made smaller and lighter. This makes it possible to drive the entire optical system as one unit, with a small number of parts and
In addition, a simple push-pull method of the detection circuit is adopted for track error detection.

This makes it possible to provide inexpensive and stable products.

[Brief explanation of the drawing]

(The zo plane is a configuration diagram showing one embodiment of the present invention. 1... Semiconductor laser 2... Light source 3... Beam splitter 4... Converging lens 5... Optical disk 6... Cylindrical lens 7... Quadrant photodiode Continued ■ Inventor Nakajima Floating 0 Inventor Seiji Hoshi 6-31-1 Kameido, Koto-ku, Tokyo Seiko Electronics Co., Ltd. 6-31-1 Kameido, Koto-ku, Tokyo Seiko Electronics Co., Ltd.

Claims (1)

[Claims] (1) A light source, a cubic beam splitter, a converging lens that converges the diverging light emitted from the light source, and a method for detecting whether the focus of the convergent light that has passed through the lens is accurately located on the information surface of the optical disk. In an optical information detection device consisting of a cylindrical lens and a 49F photodiode that converts optical signals into electrical signals, the distance between the light source and the end face of the beam splitter on the light source side is set from 30 mm to 4 mm.
Q m0, and the focal length of the cylindrical lens is 1
0.0" and 30.0 nm, and the generating line of the curved surface of the cylindrical lens is parallel to the direction of the diagonal line of the end surface of the beam splitter on one end surface of the cylindrical lens. An optical information detection device characterized in that the relative positions of all the optical components mentioned above are fixed.