JPS634435A - Optical information processor - Google Patents

Abstract

PURPOSE:To contrive to design an optical system without taking spot interval into account and to extend the degree of freedom in design by forming the surface shape of an element protection member of a photodetector in a way that a face corresponding to a central element is formed in parallel with the face of the said element and a face corresponding to elements at both sides is tilted more toward the direction parted from the central element. CONSTITUTION:Three light beams reflected in an optical disk 5 return to the optical path, pass through an objective lens 4, are reflected in a beam splitter 3 and projected onto a photodetector 8. The surface of the element protection member 9 corresponding to a main element 10 is formed in parallel with the surface of the main element 10 and the surface corresponding to a side element 11 is tilted more toward the direction parted from the main element 10 like a prism. As a result, since the optical axis 13 of the side spot is refracted in the surface of the element protection member 9, the axis is bent in a direction being parted from the main element 10 and the interval of the three spots on the photodetector 8 is spread more than that as the case with the element protection member 9 using a single board.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement in an optical information processing device used for recording and/or reproducing information on so-called optical discs such as video discs and digital audio discs.

(Prior Art) Generally, optical information processing devices using optical disks as information recording media have been put into practical use as high-density, large-capacity recording and reproducing devices.

This type of optical information processing device has conventionally been configured as shown in FIG. 6, and includes a light source 1 such as a semiconductor laser, a beam splitter 3, an objective lens 4, and a photodetector 8. The beam passes through a beam splitter 3 and is focused onto an optical disk 5 by an objective lens 4. When recording information on the optical disk 5, the optical 1i! ! 1 to form holes called bits on the optical disk 5. Further, when reproducing information, the amount of reflected light of the light focused by the objective lens 4 increases or decreases depending on the presence or absence of pits. The reflected light returns along the original optical path, is split by the beam splitter 3, and reaches the photodetector 8. This photodetector 8 can read the optical information as an electrical signal.

Now, in order to record information at high density on the optical disk 5,
Bits are formed concentrically or spirally on the optical disk 5. The width of the bits, the interval between bits, etc. are set to values close to the diffraction limit determined by the objective lens 4 and the wavelength of light in order to improve recording density. During recording, the optical disc 5 is rotated in order to continuously form bits on the optical disc 5. However, since the optical disk 5 is not an ideal plane and has surface wobbling, eccentricity, etc., it is always not at the focal position of the objective lens 4, that is, a focal shift occurs. So, in some way,
The focal position of the objective lens 4 and the position of the bit on the optical disk 5 must always match. or,
In order to be able to read the bit string continuously even if the optical disk 5 is eccentric, track deviation must be detected and the bit string must be constantly scanned by the light spot obtained by the objective lens 4. It won't happen.

Therefore, various optical systems for detecting this focal shift and track shift have been proposed.

A three-beam method is a typical example of a method for detecting track deviation, and its mechanism is shown in FIG. That is, a diffraction grating 2 is provided between the beam splitter 3 and the light source 1, and the diffraction grating 2 divides the light beam into three beams. By appropriately adjusting the angle of the diffraction grating 2, as shown in FIG.
If the sub-beam spot (half of the sight tube 6-b) is placed on the bit string (track) 7 as shown in the figure, if the light beam deviates from the track 7 as shown in (a) and (b) of the figure, Since the amount of reflected light from the beam that deviates from the track increases, two secondary beam spots (side spots) are created.
If the amount of reflected light 6-b is detected by the three-split photodetector 8, the characteristics shown in FIG. 9 can be obtained.

(Problem to be Solved by the Invention) When using the three-beam method to detect track deviation, the spot interval on the optical disk 5 focused by the objective lens 4 and the optical disk 5 on the photodetector 8 An important issue is the spot spacing of the reflected light. The smaller the spot interval on the optical disk 5, the better to avoid problems such as eccentricity, misalignment between the PtJH feed axis and the spot position, and adjustment errors in the rotation angle of the diffraction grating.

However, the spot interval on the photodetector 8 is between the sub beam spot (side spot) 6-b and the main beam spot (
Main spot) It is better to separate it to prevent it from overlapping with 6-a. Spot spacing on optical disk 5 and photodetector 8
The spot interval above is roughly determined by the focal length of the objective lens 4 toward the optical disk 5 side and the photodetector all! ! ! It is determined by the ratio between the focal length and the focal length.

Normally, when designing an optical system, the side spot and main spot on the photodetector 8 do not overlap 1, and the photodetector 8
The distance between the elements is as far as possible. Although the spacing between the three spots puts a limit on the design of the optical system, one possible measure for downsizing the apparatus is to shorten the focal length of the objective lens 4. When using the 3-beam method, the spacing between these three spots becomes close, severely limiting the design. If an optical system can be designed without considering this spot interval, the degree of freedom in design increases.

An object of the present invention is to provide an optical information processing device with a wider degree of freedom in design.

[Structure of the Invention] (Means for Solving the Problems) In this invention, the surface shape of the element protection member of the photodetector is
The surface corresponding to the central element is parallel to the element, and the surfaces corresponding to the elements on both sides are inclined to be higher in the direction away from the central element, and are directly molded together with the element.

According to this invention, the distance between the three spots on the photodetector can be widened without widening the distance between the three spots on the optical disk focused by the objective lens, and as a result, the light detection By preventing the main spot and side spot on the instrument from overlapping, it is possible to increase the degree of freedom in design even when the focal length of the objective lens toward the photodetector side is shortened when downsizing.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

The optical information processing device of the present invention is constructed as shown in FIGS. 1 to 4. FIG. 1 is a configuration diagram showing the optical system, and FIG. 2 is a diagram showing the positions of three spots on an optical disk. FIG. 3 is a cross-sectional view showing the shape of the photodetector and the state of the optical axis, and FIG. 4 is a plan view showing the state of the spot on the photodetector.

That is, if the same parts as in the conventional example (Fig. 7) are given the same reference numerals, as shown in Fig. 1, the light sources 1 and 1 are placed on the same line.
A diffraction grating 2, a beam splitter 3, an objective lens 4, and an optical disk 5 are arranged at predetermined intervals. Furthermore,
A photodetector 8 is disposed at a predetermined distance from the beam splitter 3 in a direction substantially orthogonal to the same line. This photodetector 8 is divided into three elements, and as is clear from FIG. 2, it has three elements, that is, a main element 10 and side elements 11 on both sides thereof. and side element 1
An element protection member 9 is provided to cover 1. In this case, the shape of the element protection member 9 is such that the surface corresponding to the central element, that is, the main element 10, is formed parallel to the main element 10, and the surfaces corresponding to the elements on both sides, that is, the side elements 11, are formed as they move away from the main element 10. It is sloping upward.

Now, during operation, the light emitted from the light source 1 is passed through a diffraction grating 2 and a beam splitter 3 to split the beam into three directions.
, and focus the spot onto the optical disk 5 using the objective lens 4. On this optical disk 5, as shown in FIG. It's narrowed down. The three lights reflected from the optical disk 5 return to the original optical path, pass through the objective lens 4,
The light is reflected by the beam splitter 3 and irradiated onto the photodetector 8.

Information recorded on the optical disc 5 can be read by photoelectric conversion by this photodetector B8.

As mentioned above, the element protection member 9 protects the main element 1
The surface corresponding to 0 is formed parallel to the main element 10, and the surface corresponding to the side element 11 has a prismatic shape that increases in height as the distance from the main element 10 increases. As a result, the optical axis 1 of the main spot 6-a
3 is refracted on the surface of the element protection member 9, so it bends in a direction away from the main element 10, and the spacing between the three spots on the photodetector 8 is wider than when the element protection member 9 is a simple plate. As shown in FIG. 4, compared to the conventional side spot 1.4 in which the optical axis is not bent, the side spot 15 when the optical axis is bent is located at a position further away from the main spot 16.

(Modification) FIG. 5 shows a modification of the present invention, which provides the same effects as the above embodiment.

That is, in this modification, in order to reduce the cost of the photodetector 8, plastic is used as the material for the element image 11m1i19, and the lead frame 17, element substrate 18, main element 10. The side element 11 is integrally molded and covered with a plastic mold.

The feature of this invention is the surface shape of one element protection member, so when plastic molding, the main element 1
The surface corresponding to 0 may be formed parallel to the main element 10, and the surface corresponding to the side element 11 may be formed to be higher or thicker as the distance from the main element 10 increases.

[Effects of the Invention] According to the present invention, the distance between the three spots on the photodetector 8 can be widened without widening the distance between the three spots on the optical disk 5 focused by the objective lens 4. As a result, the main spot 6-a and the side spot 6-a on the photodetector 8 are prevented from overlapping, and when downsizing, the degree of freedom in design can be increased even if the focal length of the objective lens 4 is shortened. .

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an optical system of an optical information processing device according to an embodiment of the present invention, FIG. 2 is a plan view showing the positions of three spots on an optical disk, and FIG. Similarly, FIG. 4 is a cross-sectional view showing the shape of the photodetector and the state of the optical axis, FIG. 4 is a plan view similarly showing the state of the spot on the photodetector, and FIG. Figures 6 and 7 are configuration diagrams showing optical systems (two examples) of conventional optical information processing devices, and Figures 8 (a), (b), and (C).
9 is a plan view showing the positions of three spots on the optical disk, and FIG. 9 is a characteristic curve diagram showing the relationship between the side element difference signal and the amount of deviation from the track. DESCRIPTION OF SYMBOLS 1... Light source, 2...-Diffraction grating, 3... Beam splitter, 4... Objective lens, 5... Optical disk, 8
... Photodetector, 9.19 ... Element protection member, 10 ... Main element (center element), 11 ... Side element (both sides elements). Applicant's agent Patent attorney Takehiko Suzue Go to Figure 1, Figure 2, Figure 3 81 - 〇 Figure 7 Figure 9

Claims (2)

[Claims] (1) In order to record information on an information recording medium and/or reproduce information that has already been recorded, at least a light source, a beam splitter, an objective lens, and a spot focused by the objective lens should be made into three beams. an optical information processing device comprising a diffraction grating and a photodetector divided into three elements for detecting light reflected by the information recording medium and covered with an element protection member; An optical device characterized in that the surface shape of the member is such that the surface corresponding to the central element is parallel to the element, and the surfaces corresponding to the elements on both sides are inclined so as to become higher in the direction away from the central element. information processing device. (2) The optical information processing device according to claim 1, wherein the element protection member is formed of a plastic mold.