JPS5984352A - Device for detecting focal error - Google Patents

Abstract

PURPOSE:To miniaturize a focal error detecting device and make the operation of the device easier, by forming three light spots on a recording medium through a diffraction grating and detecting a luminous flux with two optical detectors by + or - primary diffraction light cut of three kinds of convergent luminous fluxes of the reflected lights. CONSTITUTION:A light emitted from a light source 7 becomes a parallel luminous flux by means of a lens 8 and diffracted by a diffraction grating 9, and then, forms three light spots of zero degree and + or - primary diffraction light on a recording medium by means of a lens 2. Their reflected lights retrogress and are reflected by a beam splitter 3 and condensed by a lens and the + or - primary convergent luminous fluxes are made to incident to optical detectors 12b and 12c. Each of the optical detectors 12b and 12c is composed of a central part 12d and 12f, whose area is smaller than that of the primary convergent luminous flux, and peripheral part 12e and 12g. When the output of the central parts 12d and 12f is differential-amplified, a focal error signal is obtained and, when the outputs of the central part 12d or 12f and peripheral part 12e or 12g are respectively added to each other and the difference between them is obtained, a tracking signal is obtained. Therefore, the device can be miniaturized and the operation of the device becomes easier.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an apparatus having at least one of the functions of optically reading information recorded on tracks on a recording medium and optically recording information on a recording medium. The present invention relates to a focus error detection device used.

2. Description of the Related Art Conventionally, a device shown in FIG. 1 has been proposed as a focus error detection device for an optical information reproducing device that reads information recorded on a disk-shaped recording medium. FIG. 1 shows only the reflected light from the recording medium (1) of this type of device. The focus error detection mechanism of the conventional device will be described below with reference to the figures.

Record 8! Light reflected from the medium (1) is focused by a lens (2) and split into two directions by a beam splitter (3). One optical path is below the beam splitter (3) in Figure 1, and the other optical path is to the right of the beam splitter (3).

In the divided lower optical path in the figure, a pinhole (4a) is placed at a position a certain distance away from the convergence point - where nine reflected lights are condensed, and in a direction away from the beam splitter +31. In the other figure, in the right optical path, a pinhole (4b) is placed at a position that is the same distance away from the focal point fa as described above, and in a direction approaching the Heems fritter (3). .

Holes of the same size and constant warp resistance are formed in the central portions of the pinholes (4a) and (4b). The light fluxes passing through the pinhole are detected by photodetectors (5a) and (5), respectively.
b) is a mechanism in which the light is incident on the

FIG. 1 shows a case where the focal length of the lens (2) and the distance between the lens (21 and the recording medium f1) are the same, that is, the focal point is split and focused. In other words, in Figure 1.

The reflected light from the recording medium i11 passes through the pinholes (4a) and (4b) placed around 1 apart from the condensed light Jfa with equal light intensity to the 9-element detector (
5a) and (5b). A differential amplifier (6) is imaged on the photodetectors (5a) and (5b),
The difference between the two photodetectors (5a) and (5b) is increased by lυ1.
After lj, the output becomes zero.

Next, when the recording medium 0) is close to the lens (21).

The reflected light from the recording medium (1) is focused at the focal point f in Figure 1.
8, i.e. beam splitter (3)
The light is focused in the direction away from. [7] Therefore, it is clear that the light intensity that passes through the pinhole (4b) is smaller than the light intensity that passes through the pinhole (4b).

At this time, the differential amplifier (6) which is the output of the photodetector (5a)
The output of the 9 photodetector (5b) is differentially increased 1 to the negative input n1 of the
] to the positive input terminal of the device (6), a clearly negative differential output signal is obtained.

Conversely, in FIG. 1, the recording medium (1) is
When moving away from 21, the 9 reflection source is focused at a point near the focal point fa in Fig. 1, so the pinhole (
It is clear that the light intensity transmitted through 4a) is lower than the light intensity transmitted through the pinhole (4b). Therefore, a positive output signal is obtained in the differential amplifier lJ (6).

In this way, a negative or positive focus error detection signal is obtained depending on whether the recording medium [1] approaches or moves away from the lens (2).

According to the conventional device configured as described above.

Since the reflected light is split in two directions, two separate pinholes and photodetectors are required to detect each light. Moreover, these two separate pinholes must be placed at positions equidistant in front and behind the focal point of the reflected light when there is no error between the focal length of the lens and the distance between the lens and the recording medium. However, the disadvantage is that the adjustment of the beam splitter and pinhole is complicated. Another drawback is that it is difficult to miniaturize the device because the light beam is split into two directions.

Therefore, the main object of the present invention is to provide a focus error detection device that eliminates the above-mentioned disadvantageous forces.

This invention can be summarized as an optical information 44+ generation device.

This is a focus error detection device d used in an optical information recording device, an optical information recording device, etc.

A diffraction grating is inserted into the optical path for irradiating light onto the recording medium, creating at least three light spots on the recording medium, and three types of light beams are emitted while making the optical path of the reflected light beam from the recording medium turn once. This is a focus error detection device that can detect a focus error by determining the light intensity of a convergent light beam using a single photodetector.

The above-mentioned objects and other objects and features of the present invention will become more apparent from the following detailed description made with reference to the nine drawings.

FIG. 2 shows the position of the diffraction grating (9) in the irradiation optical path system of a focus error detection device according to an embodiment of the present invention. A diffraction grating (9) is placed in the irradiation optical path.

The original spot on the recording medium fII is divided into at least three spots as shown in FIG. (+1a) is the 0th order diffracted light.

(11b) and (NC) are due to ±1st-order diffracted light.

Therefore, the reflected light from the recording medium (1) is also at least 3
It is thought that there are different types of luminous flux.

FIG. 4 shows a recording medium (1) in an embodiment of the present invention.
The figure shows a reflection optical path system showing the positional relationship between the 34 types of light beams reflected by the light beam and the photodetector. In Figure 4, (+
oa), (+ob), (+0 are each photodetectors. The photodetector (1oa) is placed near the focal point of the 0th-order diffracted light, and the photodetector (10b) is located near the focal point. A photodetector (4oc) is placed f behind the focal point by a certain distance h'lJf It.

Further, the photodetector (Job) and (10C) are photodetectors that have the same light-receiving area and are smaller than the cross-sectional area of the light beam.

FIG. 4(a) shows the case where the recording medium (1) is at the focal point position [2]. In this case, the photodetector (1ob) and (10
The intensity of the light incident on both sides is equal. Photodetector (+oa
) is for detecting information signals.

Fig. 4 (1) 1 shows the case where the recording medium (11 is also recently published as the in-focus position IW). In this case, the one-source detector (+O
The intensity of light incident on C) becomes greater than the intensity of light C when incident on the photodetector (+ob).

FIG. 4(C) shows a case where the recording medium [1] is further away than the focal position 1i':f. In this case, the light intensity incident on the one-source detector (+ob) is the photodetector (+Oc)
K becomes larger than the incident light intensity.

The photodetector (+ob) and (10 outputs are differentially j”?l
msu) 1ba.

Depending on whether the recording medium (1) approaches or moves away from the lens (21), a negative or positive focus error detection signal is obtained.

In the above embodiment, independent photodetectors are used, but three photodetectors formed on one substrate may also be used as shown in FIG. In the case of Figure 5,
Angle the board with respect to the optical axis, and attach the photodetector (+2b)
The positions of (12C) and (12C) must be placed in front of and behind the focal point.

Next, Figure 0-6 shows the photodetector and electrical connections.

Photodetectors (12b) and (+2c) are ±1 from the diffraction grating.
They are used to detect one light next time, and the central part (
+2d), (+2f) and peripheral part (12e), (12
g) This medium heat part (+2d) is composed of many parts,
(+2f) is an area smaller than the cross-sectional area of the light beam. As described above, the focus error can be detected by differentially amplifying the central outputs of the photodetector (+2b) and the photodetector (+20). Also, a photodetector (
12kl) and (+2(!)), respectively, in the medium heat part and peripheral part. Find the light intensity incident on the entire photodetector (+2b) and (12C).

It is clear that by taking the difference between them, the sensor can be used for two-spot track tracking.

As described above, according to this emitted J, the diffraction grating divides the emitted light to the recording medium into at least three or more beams.

A condenser that converts reflected light from the recording medium into a convergent beam, and a first photodetector in front of the converging point of the convergent beam.

Afterwards, a second photodetector is placed in front of the focal point at a predetermined equal distance, and when the focal point position relative to the recording medium is the focal point position, the first and second photodetectors
The effective light-receiving area of the photodetector is smaller than the cross-sectional area of the luminous flux at that position. Receive the light, and
The photodetector is configured to receive the first-order diffracted light of another force, and the focus error can be detected using the light beam divided by the nine diffraction gratings, so the device can be made smaller.

Unfortunately, since the optical path can be the same as the optical path for track tracking in the two-spot method, the adjustment becomes much simpler.

4 F゛HA JI-1'L DESCRIPTION OF THE DRAWINGS Fig. 1 is a principle diagram showing conventional focus error detection, and Fig. 2 is a diagram showing the principle of conventional focus error detection, and Fig. 2 is a diagram illustrating a recording medium according to an embodiment of the present invention placed in the irradiation optical path. 1 diagram showing the principle of operation of diffracted photons.

FIG. 3 is a principle diagram showing a light spot on a recording medium.

FIG. 4 is an operation explanatory diagram showing an example of the operation of the present invention. 41,6
The figure is a wiring diagram of a photodetector and cold air in another embodiment of the present invention in which it is combined with a sensor for two-point track tracking.

In the figure, (1) is a recording medium, and (2) is a condenser lens.

(9) is a diffraction grating, (10a) + (TO'b) and (+oc) are photodetectors, (12a), (+z
b), (+2c) is a photodetector.

In Figure 9, the same reference numerals indicate the same, J, or equivalent parts.

Agent Nobu Kuzuno - Figure 1 Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) Used in a device that has at least one of the functions of optically reading information recorded on tracks on a recording medium and optically recording information on a recording medium, and records light emitted from a light source. In the focus error detection device fF't that detects the error between the focal length of the lens condensing light onto the medium and the distance between the lens and the recording medium, diffraction is performed to divide the emitted light toward the recording medium into at least three beams and separate them into three parts. a grating, a condensing device that converts the reflected light from the recording medium into a convergent beam, a first photodetector in front of the converging point of the convergent beam, a second photodetector behind the converging point; When the condenser lens is placed at a predetermined equal distance from the recording medium and the position of the condensing lens with respect to the recording medium is the focused position, the effective light receiving area of the first and second photodetectors is equal to the amount of light flux at that position. First and second photodetectors each having a smaller cross-sectional area are provided, the first photodetector receives the first-order diffracted light from the diffraction grating, and the second photodetector receives the other first-order diffracted light. a focus error detection device configured to receive light; (2) The first and second photodetectors are formed on the same substrate, and the substrate is arranged at a predetermined angle with respect to the optical axis of the 0th-order diffracted light by the 9-diffraction grating. A focus error detection device according to claim 1. (3) The first and second photodetectors are divided into a central part and a peripheral part. 1. A focus error detection device according to claim 1 of the patent application, characterized in that the cross-sectional area of the light beam at a certain position is smaller than the cross-sectional area of the light beam at a certain position.