JPH05250716A - Optical head - Google Patents

Abstract

PURPOSE:To obtain an optical head in which an optical output of a semiconductor laser can be accurately monitored without lens and a stray light of a photodetector of a reproduced signal system is eliminated. CONSTITUTION:A light receiving surface 24 of a monitoring photodetector 23 for receiving a light output from a semiconductor laser and becoming a parallel beam is inclined with respect to an optical axis of the parallel beam, and a latticelike P-N junction elements 24a are formed on the surface 24 to receive a light. Thus, the element 24a itself can be increased in an area, and hence an optical output of the laser can be accurately monitored even without condensing on the elements 24a by using a condensing lens, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device utilizing the magneto-optical effect, and more particularly to a photodetector used for controlling the light output intensity of a light emitting source.

[0002]

2. Description of the Related Art FIG. 7 is a diagram showing a schematic structure of a conventional optical head device, and FIG. 8 is a diagram showing a main part thereof. In the figure, 1 is a semiconductor laser (hereinafter referred to as “LD”) that generates a recording / reproducing light beam, 2 is a collimating lens that converts a divergent light beam emitted from the semiconductor laser 1 into a parallel light beam, and 3 is a tracking sub-beam. Is a diffraction grating, 4 is an optical disc that is an information recording medium, and 5 is a beam splitter that separates the reflected light from the optical disc 4.
It has a characteristic as a polarizing prism that transmits 50 to 90% of the incident light and reflects the rest.

Reference numeral 6 denotes a monitor photodetector (hereinafter, referred to as "monitor PD") for detecting the light output intensity of the LD1, 7 is a light receiving surface of the monitor PD6, and 8 is a part of light emitted from the LD1. A condenser lens for condensing on the light receiving surface 7 of the monitor PD6, and 9 is an objective lens, which is converted into a parallel light flux by the collimator lens 2 and is transmitted through the beam splitter 5 to be a parallel light flux, which is emitted light from the LD1. To
The light is focused on the optical disc 4.

Reference numeral 10 denotes a polarization beam splitter, which guides the light beam reflected by the optical disk 4 and bent by 90 degrees in the traveling direction by the beam splitter 5 to a signal detection system 11 and a part of the signal detection system 11 to focus servo. And the tracking servo signal detection system 12 and the other to the information signal reproduction system 13.

Reference numeral 14 in the signal detection system 11 is an analyzer for converting the information signal contained in the reflected light from the optical disk 4 into rotation of the polarization plane into light intensity change, and 15 is converted into light intensity change by the analyzer 14. An information signal reproducing photodetector (hereinafter, referred to as "TSdet") that receives information signal light and converts it into an electric signal
), 16 is a converging lens for converging and irradiating the TSdet 15 with the information signal light converted into the light intensity change by the analyzer 14.

The focus servo / tracking servo signal detection system 12 is composed of a converging lens 17, a cylindrical lens 18, and a 6-segment photodetector 19 for focus servo and tracking servo. 20 is the light receiving surface of the 6-division photodetector 19 for the focus sensor, 21 is T
A light receiving surface of Sdet 15 and a bias magnetic field generating coil 22. FIG. 9 is an enlarged front view of the monitor PD6 of the conventional optical head device, and FIG. 10 is an enlarged perspective view of the monitor PD6.

Next, the operation will be described. In the operating state, the divergent light flux emitted from the LD 1 is converted into a parallel light flux by the collimator lens 2, passes through the diffraction grating 3, the beam splitter 5, and is focused on the optical disc 4 by the objective lens 9. A magnetic thin film is vapor-deposited on the optical disc 4, and information recording pits having a width of about 1 μm are recorded on the magnetic thin film. In the information recording pit, the direction of perpendicular magnetization is opposite to the direction around it, and the polarization direction of reflected light is + θk or − depending on the direction of this magnetization.
It rotates by the magneto-optical effect by a rotation angle of θk. Then, the reflected light from the optical disk 4 passes through the beam splitter 5 and the polarization beam splitter 10 and the analyzer 14
The change in the rotation angle of the plane of polarization of the light is converted into a change in the light intensity, which is condensed by the converging lens 16 on the TSdet 15 and converted into an electric signal.

On the other hand, a part of the light that has passed through the diffraction grating 3 is reflected by the beam splitter 5 and condensed by the lens 8 on the light receiving surface 7 of the monitor PD 6. Since the output of monitor PD6 is proportional to the optical output of LD1,
By negatively feeding back the electric output from the monitor PD to the light output control circuit (not shown) of the LD 1, the irradiation light amount onto the optical disc 4 can be controlled.

[0009]

Since the conventional device is configured as described above, as shown in FIG. 8, the light receiving surface 7 of the monitor PD6 for detecting the light output of the LD1 is a condensing lens 8. Since it is placed in the vicinity of the light condensing point, a part of the light applied to the light receiving surface 7 is reflected as shown by the broken line and is focused and irradiated on the light receiving surface 21 of the TSdet 15. That is, the light receiving surfaces 20 and 21 of the two photodetectors 15 and 19 are
Each has a relationship of conjugate points.

Therefore, in the operating state of the conventional apparatus, the information signal light from the optical disk 4 and the light receiving surface 7 of the monitor PD 6 are used.
The reflected light at is superimposed on the same optical path, and this reflected light is TSd.
There is a problem that the shot noise of the reproduction signal and the light source noise are increased by being incident on the light receiving surface 21 of et15. This phenomenon becomes a factor of lowering the signal-to-noise ratio (S / N) at the time of reproduction in a magneto-optical disk device which must reproduce an information signal from a minute Kerr rotation angle (1 degree or less).

Further, since the monitor PD 6 system requires the condenser lens 8, it hinders downsizing of the apparatus itself.
There are the following problems with respect to omitting. Since the beam diameter with which the monitor PD 6 is irradiated becomes large and the light intensity distribution within the beam diameter may not be uniform, the LD
In order to accurately control the light output of No. 1, it is necessary to receive the entire luminous flux diameter, the area of the light receiving surface 7 of the monitor PD 6 becomes large, and the junction capacitance of the element of the light receiving surface becomes large, so that the light detector There was a problem that the output frequency characteristics deteriorated.

The present invention has been made in order to solve the above-mentioned problems, and has a simplified structure and is capable of highly reliable optical output control to obtain a high quality reproduced signal. The purpose is to obtain a head device.

[0013]

In an optical head device according to the present invention, a lattice-shaped PN junction element is provided on the light receiving surface of a monitor PD for detecting the light output intensity of an LD, and a parallel light beam is incident on the light receiving surface. Is tilted with respect to the optical axis of.

The optical head device according to the present invention is L
The light receiving surface of the monitor PD for detecting the light output intensity of D is provided with a plurality of small PN junction element intervals, which are the light receiving surfaces, and the light receiving surface is inclined with respect to the optical axis of incident parallel light. The electrical signal is taken out from a plurality of small PN junction elements.

[0015]

According to the present invention, the junction capacitance can be reduced while ensuring the outer surface area of the light receiving surface, and a high-speed and highly accurate electric signal can be fed back to the circuit for controlling the light output intensity of the LD. ..

[0016]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of the optical head device of the first embodiment, FIG. 2 is a perspective view of the monitor PD of this embodiment, FIG. 3 is a front view of the monitor PD, and FIG. 4 is a light receiving surface of the monitor PD. It is a partially expanded perspective view. In the figures, the same or corresponding parts are designated by the same reference numerals and the description thereof will be omitted.

In the figure, reference numeral 23 is a monitor PD, and 24 is a light receiving surface of the monitor PD 23, which are arranged so as to be inclined with respect to the optical axis of incident light. The light-receiving surface 23 has a region 24 in which a plurality of PN junctions are not provided between the PN junction elements 24a.
b is provided and the PN junction element 24a is formed in a lattice shape. 25 is a cathode terminal of the monitor PD 23, 26
Is an anode terminal of the monitor PD 23, and 27 is a light receiving surface 24
And wire bonding that electrically connects the anode terminal 26 with the anode terminal 26.

Next, the operation will be described. In FIG. 1, the divergent light beam emitted from the LD 1 is made into a parallel light beam by the collimator lens 2, a part of this parallel light beam is reflected by the beam splitter 5 in the parallel light beam state, and is received by the light receiving surface 24 of the monitor PD 23. .. This monitor PD
The current generated from 23 is fed back to the output control circuit (not shown) of LD1 to control the optical output of LD1.

Example 2. An embodiment of the present invention will be described below with reference to the drawings. FIG. 5 shows a monitor PD according to the present invention.
6 is an enlarged perspective view of FIG. 6, and FIG. 6 is an enlarged view of the light receiving surface of the monitor PD according to the embodiment of the present invention. In the figures, the same or corresponding parts are designated by the same reference numerals and the description thereof will be omitted.

Reference numeral 23 is a monitor PD of the present invention, 28 is a light receiving element surface of the monitor PD 23, and a plurality of PN junction elements 28 are provided.
a is electrically connected. 25 is the cathode terminal of the monitor PD 23, 26 is the monitor PD 2
An anode terminal 3 of the reference numeral 3 is wire bonding for electrically connecting the light receiving surface 28 and the anode terminal 26.

Next, the operation will be described. In FIG. 1, the divergent light beam emitted from the LD 1 is made into a parallel light beam by the collimator lens 2, and a part of the light intensity of this parallel light beam is
The parallel light beam is reflected by the beam splitter 5 as it is and is received by the light receiving surface 24 of the monitor PD 23. The current generated thereby is fed back to the output control circuit (not shown) of the LD1 to control the optical output of the LD1.

The monitor PD in the first embodiment
Reference numeral 23 denotes the one arranged to be inclined with respect to the optical axis of the incident light, but this inclination angle may be any number as long as it is within a range where an electric output can be obtained as a monitor of the light output intensity.

If a non-reflective coating is applied to the PN junction element 24a and the region 24b where the PN junction is not applied, the inclination angle of the monitor PD 23 is eliminated, and even if the monitor PD 23 is arranged perpendicularly to the optical axis, the light receiving surface of the TSdet 15 is removed. It has the effect of not being affected by reflected light.

Further, P on the light receiving surface 24 of the monitor PD 23
Although the region 24b not subjected to N-junction is shown to have a quadrangular shape, it may have a round shape or any other shape, and the light-receiving surface 24 may have a shape that facilitates manufacture, similar to the first embodiment. Has a great effect.

[0025]

As described above, according to the present invention, the monitor system for monitoring the optical output of the semiconductor laser, which is the light emitting source, can be constructed without a condenser lens, and the monitor PD
The light receiving surface of can be configured with a large area, and the junction capacitance can be suppressed to a small value despite the large area of the light receiving surface, so that the frequency characteristic of the output signal of the monitor PD is improved and the optical output of the semiconductor laser is more accurate. The effect is that it can be accurately monitored even if the intensity distribution within the light beam diameter changes.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical head device showing a first embodiment of the present invention.

FIG. 2 is an enlarged perspective view of the monitor photodetector of the first embodiment.

FIG. 3 is a front view of the monitor photodetector of the first embodiment.

FIG. 4 is a partially enlarged perspective view of the light receiving surface of the monitor photodetector of the first embodiment.

FIG. 5 is an enlarged perspective view of a monitor photodetector according to a second embodiment of the present invention.

FIG. 6 is a partially enlarged perspective view of a light receiving surface of the monitor photodetector of the second embodiment.

FIG. 7 is a diagram showing a configuration of a conventional optical head device.

FIG. 8 is a diagram showing a configuration of a main part for explaining a problem of the conventional optical head device.

FIG. 9 is a front view of a photodetector for a monitor of a conventional optical head device.

FIG. 10 is a perspective view of a monitor photodetector of a conventional optical head device.

[Explanation of symbols]

1 Semiconductor Laser (LD) 2 Collimating Lens 3 Diffraction Grating 4 Optical Disc 5 Beam Splitter 9 Objective Lens 10 Polarizing Beam Splitter 11 Signal Detection System 12 Focus Servo and Tracking Servo Signal Detection System 13 Information Signal Reproduction System 14 Analyzer 15 For Information Signal Reproduction Photodetector 16 Converging lens 17 Converging lens 18 Cylindrical lens 19 6-division photodetector for focus servo 20 Light-receiving surface of 6-division photodetector for focus servo 21 Light-receiving surface of 2-division photodetector 22 Bias magnetic field generating coil 23 Monitor Photodetector (monitor PD) 24 Light-receiving surface of photodetector for monitor 24a PN junction element 24b PN junction-free region 25 Cathode terminal 26 Anode terminal 27 Wire bonding

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Morihiro Karaki No. 1 Baba Institute, Nagaokakyo City, Kyoto Prefecture Mitsubishi Electric Corporation Electronic Product Development Laboratory

Claims (2)

[Claims] 1. An information signal is recorded by using light from a light source.
An information recording medium having a reproducible information recording surface, an optical system for recording / reproducing an information signal by condensing and irradiating light from the light source onto the information recording surface of the information recording medium, and light from the light source. In an optical head device having a monitor photodetector for controlling output, a light-receiving surface of the monitor photodetector is arranged to be inclined with respect to an optical axis of incident parallel light, and a grating is provided on the light-receiving surface. An optical head device comprising a PN junction element formed in a shape of a circle. 2. An information signal is recorded by using light from a light source.
An information recording medium having a reproducible information recording surface, an optical system for recording / reproducing an information signal by condensing and irradiating light from the light source onto the information recording surface of the information recording medium, and light from the light source. In an optical head device having a monitor photodetector for controlling output, the light-receiving surface of the monitor photodetector is arranged to be inclined with respect to the optical axis of incident parallel light, and a space is provided on the light-receiving surface. A plurality of small PN junction elements formed by providing the plurality of small PN junction elements.
An optical head device characterized in that an electric signal is taken out from a junction element.