JPH02216629A - Optical head device - Google Patents

Abstract

PURPOSE:To improve the reliability of an optical head and to reduce the cost by constituting second photodetectors, which detect the change of diffracted light, on a semiconductor substrate constituting a first photodetector as one body. CONSTITUTION:A first photodetector 1b and second photodetectors 11 and 12 are unified and are produced on one semiconductor substrate. A hologram element 2 diffracts and separates reflected light so that a focus error signal or a tracking error signal can be detected in the vicinity of the light reception plane of the first photodetector 1b. The focus error signal is taken out by operating the difference signal between respective difference signals 11a-11b and 12a-12b of second photodetectors 11 and 12 unified with the first photodetector 1b. Thus, the reliability of the optical head is improved and the cost is reduced.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an optical disc that records information on the information recording surface of an optical disc, or erases and reproduces recorded information using a fine spot focused on the light of a semiconductor laser. The present invention relates to an optical head device used in the device.

2. Description of the Related Art Conventionally, an optical head device used in an optical disk device is disclosed in, for example, Japanese Patent Laid-Open No. 62-97141.

A conventional optical head device will be described below with reference to FIG. In FIG. 2, 1 is a semiconductor laser that generates light, and la is a light emitting element 1 of the semiconductor laser inside it.
a and a first photodetector 1b. This first photodetector 1b monitors the right halo emitted from the light emitting element in the direction opposite to the optical disk side. A hologram element 2 separates the reflected light from the optical disk 4 by diffraction. 3 is a condensing lens that condenses the light from the semiconductor laser 1 into a minute spot on the optical disk 4. Reference numeral 4 denotes an optical disk, and 5 an information recording surface of the optical disk 4, on which information is recorded or reproduced using a minute spot of light from the semiconductor laser 1. 6 is a focal point, which indicates the focal point of a minute spot of light from the semiconductor laser 1 on the information recording surface 5. Reference numeral 7 denotes incident light that enters the optical disk 4 from the semiconductor laser 1. Reference numeral 8 denotes a halo, which faces in the opposite direction from the semiconductor laser 1 to the optical disk 4, is monitored by the first photodetector 1b, and is used to control the optical output of the semiconductor laser 1. 9 and 10 are reflected lights from the optical disk 4, which are separated by diffraction O by the hologram element 2. Reference numeral 11 denotes a second photodetector divided into two parts, which is composed of two photodetectors 11a (!:llb) and detects the reflected light 9. Reference numeral 12 denotes a second photodetector divided into two parts, It is composed of two photodetectors 12a and 12b to detect reflected light 10.

FIG. 3 is a diagram showing how a focus error signal is generated from the outputs of the second photodetectors 11 and 12. The outputs of the photodetectors 11a and flb are differentiated by a differential amplifier 13, resulting in 14 differential outputs V1 (V1=11a
- output of 11b). Similarly, the outputs of the two photodetectors L2a and 12b of the second photodetector 12 are
5, a differential output v2 of 16 is obtained (V
2=output of 12a-output of 12b). Differential output V1 and V
2 is further differentiated by a differential amplifier 17 to become a one-day focus error signal FE.

The operation of the optical head configured as described above will be described below. Here, the focus error signal will be explained, and the tracking error signal will be omitted.

First, it is necessary to control the position of the condenser lens 3 so that the incident light 7 from the semiconductor laser 1 is focused on the information recording surface of the optical disk 4. This is called focus control, and the hologram element 2 diffracts and separates the reflected light from the optical disk 4 into two reflected lights 9 and 10, and generates 18 focus error signals FE from the difference signal between them. Specifically, when the focus is just right, the reflected light 9 enters the center of the two-part dividing line of the second photodetector 11, and the difference signal output V1=1
1a-11b becomes zero. In addition, the reflected light 9 enters the middle of the two-part dividing line of the second photodetector 11, and the difference signal output V2
=12a-12b is zero. Two difference signals ■1 and v
The focus error signal FE, which is the difference signal between the two, becomes zero.

Next, if the focus is shifted, the reflected light from the optical disc 4 will not enter the center of the two dividing lines of the photodetectors 11 and 12,
lean towards one side. For example, due to the bias of the reflected light, light enters the photodetectors fla and 12b, but no light enters the photodetectors 11b and 12a. Therefore, the focus error signal FE, which is a difference signal between them, has a certain value. On the circuit side, focus control is performed so that this focus error signal FE becomes zero.

Further, the outputs of the second photodetectors 11 and 12 are summed and used to read information on the optical disc 4.

On the other hand, the optical output of the semiconductor laser 1 may vary greatly depending on temperature and changes over time, which affects the reliability of recording and reproduction of the optical disk device. Therefore, in order to keep the optical output constant, the backlight 8 of the semiconductor laser 1 is transferred to the first photodetector 1.
It is monitored and controlled using b.

Problems to be Solved by the Invention However, in the above configuration, the first photodetector 1
b and the second photodetectors 11 and 12 are configured separately, the assembly and adjustment of the optical head becomes complicated, and the mechanical fixation may shift due to temperature or changes over time, resulting in This method has problems such as a decrease in reliability due to movement of the relative positions of the detectors, and difficulty in reducing costs because a number of photodetectors are used.

In view of this, the present invention makes the assembly and adjustment of each optical head a military standard, eliminates the effects of temperature and aging changes, improves reliability, and reduces costs. In between, there is a hologram element that creates diffracted light from the reflected light from the information recording surface and changes the diffracted light corresponding to the focusing error or tracking error of the semiconductor laser light with respect to the information recording surface, and the semiconductor laser information recording device. a first photodetector that monitors light emitted in the opposite direction to the light emitted onto the surface; and a second photodetector that detects changes in diffracted light on the same semiconductor substrate as that constituting the first photodetector. This is an optical head with an integrated detector.

According to the above-described configuration, the present invention includes a second photodetector that detects a change in diffracted light corresponding to a focus error or a tracking error on the same semiconductor substrate that constitutes the first photodetector that monitors the afterlight of a semiconductor laser. By configuring the photodetector, the first and second photodetectors are integrated, improving the reliability of the optical head and reducing costs.

Embodiment FIG. 1 is a conceptual diagram showing an optical head device in an embodiment of the present invention. The parts changed in FIG. 2 of the conventional example described above will be explained.

1 is a semiconductor laser, and in addition to a light emitting element 1a and a first photodetector 1b that monitors the halo 8, it also includes a second photodetector 11.12 that detects reflected light 9.10 from the optical disk 4. Built-in. First photodetector 1b and second photodetector 1
1.12 are integrated and fabricated on the same semiconductor substrate.

The operation of the optical head configured as described above will be described below. In the following explanation, the generating circuit for the focus error signal FE is completely the same as that in the conventional example shown in FIG. 3.

The hologram element 2 diffracts and separates the reflected light so that a focus error signal or a tracking error signal can be detected near the light receiving plane of the first photodetector 1b. For this purpose, the respective difference signals 11a-11b of the second photodetector 11.12 integrated with the first photodetector 1b,
The focus error signal FE can be extracted by taking the difference signal between 12a and 12b. Specifically, when the focus is just right, the reflected light 9 is placed in the middle of the bisecting line of the second photodetector 11.
is input, and the difference signal output V1=11a-11b becomes zero. Further, the reflected light 9 enters the middle of the two-part dividing line of the second photodetector 11, and the difference signal output V2=12a-12b becomes zero. The focus error signal FE, which is the difference signal between the two difference signals v1 and v2, becomes zero.

Next, if the focus is shifted, the reflected light from the optical disc 4 will not enter the center of the two dividing lines of the photodetectors 11 and 12,
lean towards one side. Therefore, the focus error signal FE, which is a difference signal between them, has a certain value. On the circuit side, focus control is performed so that this focus error signal FE becomes zero.

As described above, according to this embodiment, the hologram element is used to diffract and separate the reflected light from the optical disk, and on the same semiconductor substrate that constitutes the first photodetector that monitors the afterlight of the semiconductor laser. By configuring a second photodetector that detects changes in diffracted light corresponding to focus errors or tracking errors, the first and second photodetectors can be integrated, improving the reliability of the optical head and reducing costs. can be reduced.

In this embodiment, the focus error signal was detected using the Knifezi method, but the diffraction pattern of the hologram element may be changed to detect a spot size, or an astigmatism method may be used.

As described in detail, according to the present invention, the same semiconductor that constitutes the first photodetector that uses a hologram element to diffract and separate reflected light from an optical disk and monitors the backlight of a semiconductor laser. By integrally configuring a second photodetector that detects changes in diffracted light corresponding to focus errors or tracking errors on the substrate, it is possible to improve the reliability of the optical head and reduce costs. It can be done, and its practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of an optical head device according to an embodiment of the present invention, FIG. 2 is a conceptual diagram of a conventional optical head device, and FIG. 3 is a diagram of a focus error signal generation circuit. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 1a... 1st photodetector, 2... Hologram element, 3... Condenser lens,
4... Optical disk, 7... Incident light, 8...
・Hollow, 9...Reflected light, 10...Reflected light,
11... Second photodetector, 12... Second photodetector, 13.15° 17... Differential amplifier, 18... Focus error signal FE.

Claims (1)

[Claims] (1) In an optical head device in which light from a semiconductor laser is incident on an information recording surface, the reflected light from the information recording surface is diffracted and separated by a hologram element, and guided to a photodetector to reproduce or record information. A first photodetector that monitors light emitted in the opposite direction to the light emitted to the information recording surface of the semiconductor laser, and a semiconductor substrate that is the same as the semiconductor substrate constituting the first photodetector and detects changes in the diffracted light. An optical head device characterized in that it is integrally configured with at least two second photodetectors for detection.