JPH0636326A - Optical head - Google Patents

Abstract

PURPOSE:To provide the optical head including a front automatic light quantity controller which reduces the quantity of return light and attains sufficiently stable laser oscillation. CONSTITUTION:A semiconductor laser which oscillates laser light, optical systems 12, 13, and 14 which lead this laser light to an optical disk 15, and a light quantity detector 18 which receives a part of laser light led to the optical disk 15 by optical systems 12, 13, and 14 and detects the quantity of light are provided. A condenser lens 19 provided on the laser light incidence side of the light quantity detector 18 and a light shielding body 20 which is provided between the condenser lens 19 and the light quantity detector 18 and has a transmission hole 20a, which permits the laser light condensed by the condenser lens 19 to pass through, and intercepts laser light reflected from the light quantity detector are provided besides to constitute the optical head.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used in, for example, an optical disk device, and more particularly to an automatic light quantity control device for a semiconductor laser.

[0002]

2. Description of the Related Art A semiconductor laser is widely used as a light source for an optical head used in an optical disk device because it is small and inexpensive and consumes little power. An automatic light amount control device is used for this semiconductor laser, but in recent years, fast light amount control is required when reading / writing information from / to an optical disk.

By the way, as a method of controlling the light quantity,
There is a method of controlling the amount of light using a laser beam emitted backward from a semiconductor laser, but this method has a problem of phase shift. Therefore, a front automatic light amount control device that controls the light amount by using the laser beam on the side that is actually used is drawing attention. FIG. 4 shows a configuration of an optical system of an optical head including a most basic conventional forward automatic light amount control device.

That is, the laser light emitted from the semiconductor laser 1 passes through the collimator lens 2 and enters the beam splitter 3. The light incident on the beam splitter 3 is divided into two directions, and one of the two passes through the objective lens 4 and forms an image on the information surface of the optical disc 5. The reflected laser light returns to the beam splitter 3, is reflected in another direction, enters the photodetector 7 via the optical system 6 of the light receiving section, and necessary information is read.

The other of the laser beams split into two directions by the beam splitter 3 enters a light amount detector 8. The output of the semiconductor laser 1, which is the light source, is controlled by using the information on the measured light amount. When writing or reading information to or from the optical disc, the optical disc 5 is irradiated with laser light while controlling the light amount by the front automatic light amount control device.

With such a configuration, it is possible to measure the laser light amount without phase shift, but it has been considered to increase the detection speed in order to further speed up the light amount control. The light amount detector has a characteristic that the detection speed becomes faster as the area of the light receiving surface becomes smaller.

Therefore, a structure as shown in FIG. 5 has been considered. Here, a lens 9 is placed in front of the light amount detector 8 to squeeze the laser light and make it enter the light amount detector 8. Therefore, the light receiving area of the light amount detector 8 can be reduced,
Faster automatic light intensity control is possible.

However, here, there is a problem that a part of the laser light diffusedly reflected on the light receiving surface of the light quantity detector 8 travels in the reverse optical path through the lens 9 and returns to the semiconductor laser 1 to hinder stable laser oscillation. Occurred.

Since the reflection on the light receiving surface of the light quantity detector 8 is irregular reflection, the amount of returning light did not matter so much in the structure shown in FIG. 4, but the lens is placed in the structure shown in FIG. This increased the effect of returning light.

Therefore, as shown in FIG. 6, the light amount detector 8
A method to attach the lens at an angle to the optical axis was considered. Although the reflection on the light receiving surface of the light quantity detector is irregular reflection, the returning light is reduced by diverting the reflection component having the highest density from the optical axis. However, the returning light was not reduced to a satisfactory level, and sufficiently stable laser oscillation was not obtained.

[0011]

As described above, the conventional forward automatic light quantity control device cannot obtain sufficiently stable laser oscillation due to the influence of the return light reflected by the light receiving surface of the light quantity detector. There was a problem.

Therefore, an object of the present invention is to provide an optical head in which the amount of returning light reflected by the light receiving surface of the light amount detector is further reduced and a sufficiently stable laser oscillation can be obtained. To do.

[0013]

In order to solve the above-mentioned problems, the present invention solves the above problems by using a laser light oscillating means for oscillating a laser light and a laser light oscillated from the laser light oscillating means. To the optical information medium, a light amount detector that receives a part of the laser light guided to the optical information medium by this optical system, and detects the light amount, and the laser light incidence of this light amount detector. And a light-transmitting hole that is provided between the light-collecting lens and the light-quantity detector and that transmits the laser light collected by the light-collecting lens. And a light blocking body for blocking the laser light reflected from the container.

[0014]

Most of the laser light diffusely reflected by the light receiving surface of the light quantity detector is shielded by the light shield and does not return to the semiconductor laser, so that sufficiently stable laser oscillation can be performed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in FIG. FIG. 1 is a diagram showing an optical system of an optical head used in an optical disk device.

In the figure, reference numeral 11 denotes a semiconductor laser, and a collimating lens 12 for collimating the laser light into a parallel light in the optical path of the laser light emitted from the semiconductor laser 11, and this collimating lens. A beam splitter 13 that splits the laser light, which is made into parallel light by 12, into two directions is provided. An objective lens 14 is provided in one optical path of the laser light divided into two by the beam splitter 13, and a lens 19 is provided in the other optical path. An optical disk 15 is opposed to the objective lens 14. A light amount detector 18 is opposed to the lens 19 via a shield plate 20.

A small through hole 2 is formed in the approximately central portion of the shielding plate 20.
The laser light passing through the lens 19 is received by the light amount detector 18 through the through hole 21. The light quantity detector 18 is provided as close as possible to the focal point of the laser light. On the other hand, the laser light reflected from the optical disk 15 is reflected by the beam splitter 13 as indicated by an arrow. A lens 16 and a photodetector 17 that receives light via the lens 16 are arranged in the reflected light path. Then, the laser light emitted from the semiconductor laser 11 passes through the collimator lens 12 and enters the beam splitter 13. One of the laser beams split into two directions by the beam splitter 13 passes through the objective lens 4 and forms an image on the information surface of the optical disc 15.

Further, the laser light reflected from the optical disk 15 returns to the beam splitter 13 and is reflected in another direction, passes through the lens 16 and enters the photodetector 17, and necessary information is read.

On the other hand, the other of the laser beams split into two directions by the beam splitter 13 is incident on the light quantity detector 18 after passing through the through hole 20a of the shield plate 20 which is focused by the lens 19 and placed at the focal position. To do.

Of the laser light diffusedly reflected by the light receiving surface of the light quantity detector 18, only the laser light that can pass through the through hole 20 returns to the semiconductor laser 11 through the lens 19, but the quantity thereof is drastically reduced as compared with the case where the light shielding plate 20 is not provided. To do.

Further, since the light quantity detector 18 is placed near the focal point, it is distributed in a relatively narrow range, so that a light quantity detector having a small light receiving area can be used, and the light quantity can be measured at high speed. Is. Therefore, with the configuration shown in FIG. 1, stable laser oscillation and high-speed forward automatic light amount control are possible.

In the above embodiment, the light amount detector 18 is provided in a state orthogonal to the optical axis. However, the present invention is not limited to this, and as shown in FIG. 2, the light amount detection for the front automatic light amount control is performed. The device 28 may be installed obliquely with respect to the optical axis. According to this embodiment, the amount of light returning to the semiconductor laser can be further reduced, and stable laser oscillation and high-speed forward automatic light amount control are possible. Further, as shown in FIG. 3, the light shielding plate 20 may be installed at a position deviated from the focal position of the lens 9.

With such a setting, it is considered that the returning light becomes larger than that in the first embodiment, but the effect of the light shielding plate 20 can be expected sufficiently, and the light quantity of the returning light can be reduced to achieve stable laser oscillation. Thus, a high-speed automatic front light quantity control device becomes possible.

[0024]

As described above, the present invention guides the laser light oscillating means for oscillating the laser light and the laser light oscillated from the laser light oscillating means to the optical information medium. Optical system,
A light amount detector that receives a part of the laser light guided to the optical information medium by this optical system and detects the light amount, and a condenser lens provided on the laser light incident side of the light amount detector, It has a through hole provided between the condenser lens and the light quantity detector for transmitting the laser light condensed by the condenser lens, and shields the laser light reflected from the light quantity detector. Since it is provided with a light-shielding member, the amount of laser light returning to the laser light oscillating means can be drastically reduced, stable laser oscillation and high-speed forward automatic light amount control become possible. When used in an optical disk device, writing to an optical disk is possible. Thus, there is an effect that reading can be performed quickly and reliably.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a first other embodiment of the present invention.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing a first conventional example.

FIG. 5 is a configuration diagram showing a second conventional example.

FIG. 6 is a configuration diagram showing a third conventional example.

[Explanation of symbols]

11 ... Semiconductor laser (laser light oscillation means), 12, 1
3, 14 ... Optical system, 15 ... Optical disk (optical information medium),
18 ... Light amount detector, 19 ... Condensing lens, 20a ... Through hole,
20 ... A light shield.

Claims (1)

[Claims] 1. A laser light oscillating means for oscillating laser light, an optical system for guiding the laser light oscillated from the laser light oscillating means to an optical information medium, and an optical system for activating the laser light. A light amount detector that receives a part of the laser light guided to the information medium and detects the light amount, a condenser lens provided on the laser light incident side of this light amount detector, and this condenser lens A light blocking body which is provided between the light amount detector and has a through hole for transmitting the laser light condensed by the condenser lens, and which shields the laser light reflected from the light amount detector; An optical head comprising: