KR930000841Y1 - Focus error checking device of optical pick-up - Google Patents

Abstract

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Description

Focus error detection device for optical pickup

Fig. 1A is a schematic diagram showing the main parts of a conventional focus error detection apparatus for optical pickup.

FIG. 1B is a front view showing an image formation state on a two-segment photodetector used in FIG.

Figure 2 (a) is a schematic diagram of the main portion of the focus error detection apparatus of the optical pickup of the present invention.

Figure 2 (b) is a rear view of the focusing lens showing the main part of the present invention.

Figure 2 (c) is a front view showing the imaging state on the two-segment photodetector used in the present invention.

* Explanation of symbols for main parts of the drawings

a, b, c: light beam 2: split photodetector

3: shading film 10: focusing lens

11: optical axis 31: distal end

The present invention relates to a focus error detection device of an optical pickup device that reads a bit signal on an optical disc.

BACKGROUND ART Optical pick-up focus error detection apparatuses used in compact disc players and the like have already been known using astigmatism, knife edge, and edge prism. Among them, the knife edge method has a large amount of light loss and a dynamic range. Although it is a disadvantage that the polarity is reversed when it is increased, the photodetector is easy to adjust, so it is currently used a lot.

In general, the light emitted from the light source passes through a beam splitter (not shown) and is focused on the signal surface of the optical disk by one objective by a objective lens (not shown), and the light beam is reflected again to be parallel by the objective lens. It becomes light, and when it passes through the beam splitter, it splits out and exits to one side.

The light beam emitted from this beam splitter (not shown) is shown as a, b, and c in FIG. 1, and the light beam is again incident on the focusing lens 1 and placed in the rear of the two split photodetector 2 Detects the output difference signal, thereby correcting the focus error.

In FIG. 1, when the light beam a is closer than the focal length between the above-described objective lens and the signal surface of the optical disk, the reflected light becomes divergent light, is incident and separated by the beam splitter, and becomes the light beam a. As shown in FIG. 2A on the upper side of the two-segment photodetector 2 passing through the focusing lens 1 in the figure, the output difference signal + (or-) is detected by contrast and thereby correcting the focus error. do.

Similarly, the light beam b is farther than the focal length between the objective lens and the signal surface of the optical disk described above. At this time, the light beam b becomes condensed light and is emitted from the beam splitter to the light beam c. This causes the focusing lens 1 of FIG. After passing through, it is imaged on the lower side of the two-segment photodetector 2 to form (C) of FIG. 2, and at this time, the output difference signal becomes-(or +).

Next, when the distance between the objective lens and the signal surface of the optical disk coincides with the focal length, the reflected beam reflected through the objective lens becomes parallel light so that the light beam emitted from the beam splitter is emitted from the beam splitter in FIG. ) And the dichroic beam b passes through the focusing lens 1 and focuses on the center portion of the two-segment photodetector 2, and is formed as a dot. At this time, the output difference signal from the photodetector 2 is It becomes spirit.

Here, the knife-edge method is one side (lower end in Fig. 1) based on the optical axis 11 in Fig. 1 to detect an output difference signal in the division of light and dark in the two-segment photodetector (2). Will be blocked. That is, the sharp upper end of the knife edge plate 4 must be exactly matched to the optical axis 11 to block the lower end (in FIG. 1) of the light beam 11, and thus the adjustment of the knife edge plate 4 described above. This very difficult drawback causes a problem in the generation of the output difference signal in the above-described two-segment photodetector 2.

Accordingly, an object of the present invention is to provide a focus error detection device of an optical pickup that is easy to adjust the blocking plate and easy to assemble, in order to solve the above-mentioned conventional problems.

That is, the present invention, in order to achieve the above object, in the arrangement of a two-segment photodetector at the focal position of the focusing lens, the converging lens coincides with its optical axis on the surface facing the two-segment photodetector side. It is comprised by forming the light shielding film which has a front-end | tip to one side.

Hereinafter, an embodiment of the present invention will be described in detail with emphasis on FIG.

First, a general optical system uses the same optical system as the conventional optical system described above, and a characteristic element of the present invention is a focusing lens 10 that focuses light beams a, b, c, etc. on the surface of a two-segment photodetector 2. Formed by forming a light shielding plate 3 having a tip portion 31 coinciding with the optical axis 11 at a semicircular portion on one side of the focusing lens 10 on the rear surface of the lens, that is, on the surface facing the two-segment photodetector 2 side. will be.

As described above, when the distance between the signal surface of the optical disc and the objective lens coincides with the focal length as described above, the reflected light is reflected by the luminous flux of the focusing lens 10 of FIG. (11) is incident on the light beam b in equilibrium with the light beam b, and it forms an image in the center of the two-segment photodetector 2, whereby the output difference signal of the photodetector 2 is zero and is detected to be in a steady state. Likewise, when the distance between the objective lens and the information surface of the optical disk is closer than the focal length of the objective lens, the light beam is incident on the focusing lens 10 with the light beam a. At this time, the light blocking film 3 formed on the rear surface of the focusing lens 10 is The tip portion 31 coincides with the optical axis 11 so that the light beam incident on one side of the optical axis 11 (lower in FIG. 2 (a)) is completely blocked and darkened in the above-described two-segment photodetector 2. It is divided into a part and a stepped part, as shown in (A) of FIG. 2 (c). The output difference signal becomes + (or-) to the two-segment photodetector 2, thereby correcting the focus error.

In addition, in the case of the light beam c, the signal surface of the optical disc is farther than the focal length of the objective lens. In this case, the light beam of one side is blocked by the light shielding film 3 of the focusing lens 10 so that the light beam of one side is blocked. As shown in (C) of (c), the two-segment photodetector 2 is imaged in light and dark, whereby the output difference signal is detected. As a result, a bipolar error signal can be obtained. Therefore, the conventional method using a knife edge plate has a problem that the adjustment is difficult because the knife edge plate must be precisely aligned to the light side, but the present invention is formed by integrally forming a light shielding film on the focusing lens itself, so no such difficult adjustments It is unnecessary, and at the same time, there is an advantage that the assembly is also reduced.

Claims (1)

In the arrangement of the two-segment photodetector 2 at the focal position of the focusing lens 10, the luminous flux 11 and its light beam 11 are placed on the surface of the converging lens 3 facing the two-segment photodetector 2 side. An optical pickup focus error detection device, characterized in that a light shielding film (3) having a matching tip portion (31) is formed on one side.