JPS62293525A - Focus error detector - Google Patents

Abstract

PURPOSE:To facilitate the manufacture of an optical splitter and to make the error detection exact by providing a prism part and a non-prism part dividing a signal into two by the optical splitter whose reflected axis is made coincident with the boundary between both the parts and outputting a signal through the photodetection by a photodetector. CONSTITUTION:The optical splitter 9 has the prism part 9a and the non-prism part 9b and the boundary 9c of both the parts is arranged vertically on an optical axis. When an information recording medium 6 and an objective lens 5 are in the focused position, a light spot appears at each split band of light receiving faces 8a, 8b and 8c, 8d of the split type photodetector 8 and no focus error signal is detected. When the medium 6 and the lens 5 are not focused, the light spot appears in a semi-circular form at the inner or the outer side of the split band. Thus, the focus error is detected by operating a photodetection signal in response to the light receiving quantity of the detector 8. Thus, the splitter is formed easily and the focus error signal with high reliability is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus error detection device in an optical information recording/reproducing device for optically recording information on an information recording medium or reproducing information from the information recording medium.

[Prior art]

Conventionally, various types of devices have been proposed as focus error detection devices in optical information recording and reproducing devices that record and reproduce information by condensing a light beam onto a recording medium. For example, a simple one is known that has a Foucault prism and a photodetector in which four photodetecting elements are arranged in one direction (Japanese Patent Laid-Open No. 57-18
No. 032, JP-A-58-208946).

FIG. 4 is a schematic diagram showing the main parts of the optical system of a conventional optical information recording/reproducing apparatus. A recording/reproducing light beam emitted from a light source 1 such as a semiconductor laser passes through a beam splitter 2, and this diverging light passes through a silimeter lens 3 and becomes parallel light. This parallel light is converted into a rotating wave by the A wavelength plate 4, and is condensed and irradiated onto an information recording medium 6 such as an optical disk by an objective lens 5. The irradiated light is reflected by the information recording medium 6, and the reflected light is sent to the objective lens 5, the wavelength handler 4,
The light is received by a light receiving device (not shown) through a collimating lens 3 and a beam stabilizer 2. On the other hand, a portion of the reflected light is reflected by the beam subrifter 2 and is used for detecting a focus error.

This reflected light beam is split into two by a light splitter 7 made of a Foucault prism having two refracting surfaces, and the split reflected light enters each of the four light receiving surfaces of a split photodetector 80 to generate a focus error signal. Sent. By calculating this focus error signal, the polarity and magnitude of the signal are determined, and the direction and amount of the error are detected, which is a so-called Foucault method.

Furthermore, if we explain the focus error detection device in detail,
As shown in FIG. 5, the light splitter 7 is made of a pentagonal prism-shaped glass body, and its cross-sectional shape is inclined at the same angle with respect to the long side where the light should enter, and the two sides where the light should be output are inclined. It forms a pentagon with The ridge line 7c between the two inclined refraction surfaces 7a and 7b, which are the output surfaces of the light splitter 7, is the beam splitter 2.
It is arranged so that it intersects perpendicularly to the optical axis of the reflected light. Further, as shown in FIG. 6, the split type photodetector 8 has four
It has three light receiving surfaces 8a, 8b, 8c, and 8d. Separation zones are provided at the boundaries of these light receiving surfaces 8a, 8b, 8c and 8d.

The light detection surfaces are arranged in a line in a plane perpendicular to the optical axis at a position corresponding to the distance between the light receiving device (not shown) and the beam splitter 2 and in a direction perpendicular to the ridgeline 7c of the light splitter 7. be done. Furthermore, the center of the separation zone between the light receiving surfaces 8b and 80 is aligned with the optical axis. and outer light receiving surfaces 8a and 8d
Let Sa and Sd be the photodetection signals corresponding to the amount of received light, respectively,
If the photodetection signals corresponding to the amount of light received by the inner light-receiving surfaces 8b and 8c are respectively sb and Sc, then the formula (Sa+Sd)
The calculated value of (Sb+Sc) is detected as the value of the focus error signal.

That is, as shown in FIG. 6(B), when the information recording medium 6 and the objective lens 5 are in the focused position, the light beam split into two by the light splitter 7 is split into two by the light receiving surfaces 8a, 8b and 8c・
At the center of the 8d separation zone, there is a light spot (y) S H+32
appears as. In this case, the value of the focus error signal is (Sa+Sd) (Sb+Sc) =0.

If a focus error occurs, please refer to Figure 6 (a) or (
(c) Either of the following conditions will occur. FIG. 6(a) shows a case where the distance between the information recording medium 6 and the objective lens 5 is too short, and the optical slots S3 and S on the split type photodetector 8 are
A semicircular shape appears on the inner light receiving surfaces 8b and 8c, respectively. Therefore, the value of the focus error signal is negative. Also, the 6th
Figure (c) shows a case where the information recording medium 6 and the objective lens 5 are too far apart, and is it a split type optical detection? Light spot S on 58
5 and Sc appear semicircularly on the outer light receiving surfaces 8a and 8d, respectively. Therefore, the value of the focus error signal is positive. Note that the magnitude q of the calculated value of the focus error signal corresponds to the amount of focus error.

[Problem that the invention seeks to solve]

In the conventional focus error detection device as described above, if the accuracy of the apex angle of the light splitter 7 is low, the ridge line 7C will not be a straight line, resulting in loss of ti of light or refracted light at the light receiving surface. The reliability of the focus error signal value decreases due to scattering, etc.

In order to reduce the tn loss and scattering of light, high-level techniques are required to improve the finishing accuracy of the apex angle of the light splitter 7. That is, the two refraction surfaces 7a forming the light splitter 7
Both sides of the refracting surface and 7c are sloped, and the angle of inclination of the two surfaces needs to be finished to be equal, so there is a problem in that a technique is required to improve the finishing accuracy of the refractive surface.

The present invention has been made to solve these problems, and improves the finishing accuracy of a light splitter that splits the light beam incident on a split-type photodetector into two in order to detect focus errors. It is an object of the present invention to provide a focus error detection device that makes it easy to do this and makes it possible to obtain a highly reliable focus error signal.

[Means for solving problems]

The present invention splits the reflected light beam from an object to which light is condensed and irradiated into two by a light splitter arranged in the optical path, and receives the divided light beam by a photodetector having a plurality of light receiving surfaces. In a focus error detection device that detects a focus error based on an output signal of a photodetector, the light splitter has a prism part and a non-prism part whose light incident surface and light exit surface are parallel, and the prism part and It is characterized in that the boundary with the non-prism portion is arranged to coincide with the optical axis of the reflected light beam.

[Effect]

In the present invention, the light beam reflected from the recording medium is divided into two by a light splitter in which only one of the two parts is a prism,
These two divided light beams are divided into two by an optical beam having multiple light receiving surfaces.
The output device receives the light and outputs a signal, and the focus error is detected from this output signal.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a schematic diagram showing a configuration in which the present invention is applied to an optical information recording and reciprocating device. Reference numerals 1 to 6 in the figure are the same as those of the conventional device, and the same parts are indicated by the same reference numerals. A recording/reproducing light beam generated from light #1 of a semiconductor laser or the like passes through a beam splinter 2, and this diverging light passes through a collimator lens 3 and becomes parallel light. This parallel light is converted into a rotating wave by the A wavelength plate 4, and is condensed and irradiated onto an information recording medium 6 such as an optical disk by an objective lens 5. The irradiated light is reflected by the information recording medium 6, and the reflected light passes through the objective lens 5, the A wavelength plate 4, the collimating lens 3, and the beam splitter 2, and is received by a light receiving device (not shown). Ru. On the other hand, a portion of the reflected light is reflected by the beam splinter 2 and used for detecting focus errors.

FIG. 2 shows a light splitter 9 according to the present invention, which is made of a pentagonal prism-shaped glass body, and its cross-sectional shape is such that the four sides of the pentagon form two sets of straight lines parallel to each other, and the other side forms two sets of adjacent lines. It forms an obtuse angle with the side. That is, a so-called single-roof prism is formed, which has a shape similar to that of a square prism with a rectangular cross section, with one edge in the height direction removed by tapering.

The light splitter 9 is composed of a prism portion 9a that largely refracts incident light, that is, the tapered portion, and a non-prism portion 9b whose light incident surface and light exit surface are parallel. The incident light is divided into two parts. In this light splitter 9, the long side surface without an inclined surface is directed toward the light incident side, and the opposite sloped side surface is directed toward the light output direction, and the ridge line 90, that is, the prism part and the non-prism part The boundary is on the optical axis and is perpendicular to the optical axis. The split type photodetector 8 has light receiving surfaces 8a and 8b that receive light transmitted through the non-prism portion 9b, and light receiving surfaces 8c and 8 that receive light transmitted through the prism portion 9a.
Consists of d.

Separation zones are provided at the boundaries between the light receiving surfaces 8a and 8b and between the tombs 8C and 8d, respectively. The four light receiving surfaces are arranged at positions corresponding to the distance between the light receiving device (not shown) and the beam splitter 2. Furthermore, the light-receiving surfaces 8a and 8b are arranged on a plane perpendicular to the optical axis of the incident light, and the center of the separation zone is aligned with the optical axis. Moreover, the light receiving surfaces 8c and 8d are 8a
- It is arranged on the same plane as 8b, at a position where the light beam emitted from the prism part of the light splitter converges almost at the center of the separation zone of these light receiving surfaces. And the outer light receiving surface 8a, 8
The photodetection signals corresponding to the amount of light received at d are respectively 5a to 3d,
If the light detection signals corresponding to the light receiving ports of the inner light receiving surfaces 8b and 8c are respectively 5b and 3c, then the formula (Sa + Sd) (S
b+Sc) is detected as the value of the focus error signal.

Next, the operation of the present invention will be described. As shown in FIG. 3(b), when the information recording medium 6 and the objective lens 5 are in the focused position, the light spots S1 and 32 on the split type photodetector 8 are separated from the light receiving surface 8a. It appears at the center of each separation zone 8b, 8c, and 8d. Therefore, the value of the focus error signal in this case is (Sa+5d)-(Sb+Sc) =
It becomes 0. FIGS. 3A and 3C show cases where a focus error occurs. FIG. 3(a) shows a case where the distance between the information recording medium 6 and the objective lens 5 is too short, and the spots S3 and S on the split type photodetector 8 are different from the inner light receiving surfaces 8b and 80. Each appears in a semicircular shape. In this case, the value of the focus error signal is negative. In addition, FIG. 3(c) shows a case where the distance between the information recording medium 6 and the objective lens 5 is too far, and the sub-position 1-55 on the split type photodetector 8 and the S
5 appears in a semicircular shape on the outer light-receiving surfaces 8a and 8d, respectively. Therefore, in this case, the value of the focus error signal is positive. Note that the magnitude of the value of the focus error signal obtained as described above corresponds to the magnitude of the focus error. Therefore, from this value, the information recording medium 6 and the objective lens 5
It becomes possible to detect the distance and polarity between the

In this embodiment, a focus error detection device in an optical information recording/reproducing device is described in detail, but it can also be used as a focus error detection device in other devices, for example, a focus error detection device in an autofocus camera. Of course, it can also be used as a temporary aid.

〔effect〕

In the present invention, by configuring the light splitter with a single-roof type prism, there is no need to finish the angle of inclination to be the same as in the case where both sides are inclined, and only one side is finished at a predetermined inclination. , it becomes easy to finish the ridgeline on the light emitting side into a straight line, and variations in the split light emitted from the light splitter are averaged, resulting in an excellent effect that a highly accurate focus error signal can be obtained.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIG. 1 is a schematic diagram showing the configuration of an optical information recording and reproducing device equipped with a focus error detection device according to the present invention, and FIG. A perspective view of the divider, FIG. 3 is a schematic diagram showing its detection state, FIG. 4 is a schematic diagram showing the configuration of an optical information recording/reproducing device equipped with a conventional focus error detection device, and FIG. FIG. 6, a perspective view of the light splitter used, is a schematic diagram showing its detection state. l...Light source 5...Objective lens 6...Information recording medium 8...Divided photodetector 9...Light splitter
In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A light beam reflected from an object to which light is condensed and irradiated is divided into two by a light splitter disposed within the optical path, and the divided light beam is sent to a photodetector having a plurality of light receiving surfaces. In the focus error detection device, the light splitter includes a prism portion and a non-prism portion in which a light incident surface and an exit surface are parallel to each other. . A focus error detection device, characterized in that a boundary between a prism portion and a non-prism portion is arranged to coincide with an optical axis of the reflected light beam.