JP2907759B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for controlling the amount of emitted light by accurately measuring the amount of light emitted from a light source of an optical head device for reproducing, recording, or erasing an optical disk.

[0002]

2. Description of the Related Art Conventionally, a method using a beam splitter has been generally used as a method for monitoring the amount of emitted light used in an optical disk head. FIG. 4 shows a conventional method of monitoring the amount of emitted light. A light beam 102 emitted from a semiconductor laser 101 is converted into substantially parallel light by a collimating lens 103. Part of the parallel light is split by the beam splitter 104 and is incident on a detector 105 for monitoring the amount of light. Detector 10 for light intensity monitor
The output of 5 is controlled via the laser control circuit 113 so that the output of the semiconductor laser is maintained at a required value.
The light beam transmitted through the beam splitter 104 is reflected by a reflection mirror 108, transmitted through an objective lens 106, and collected on an information carrier 109.

The light beam reflected on the information carrier 109 follows the original path in reverse, is reflected by the beam splitter 104, passes through the detection lens 110, and enters the signal detection detector 111. Although the focus servo signal, the tracking servo signal, and the information signal can be obtained by the signal detection detector, detailed description of the operation is omitted because it is not directly related to the present invention.

[0004] A method using a parallel plate glass instead of the beam splitter is also conceivable. FIG. 5 shows an embodiment using a parallel plate glass. The light beam 202 emitted from the semiconductor laser 201 is collimated by a collimator lens 203. Part of the parallel light passes through the parallel flat glass 207 and enters the detector 205 for monitoring the amount of light. The light beam reflected on the surface of the parallel plate glass is
6 and condensed on the information carrier 209. Information carrier 2
The light beam reflected on 09 reverses its original path,
The light is diffracted by the detection hologram 212, passes through the collimator lens, and is incident on a signal detection detector (details not shown) near the semiconductor laser. Although the focus servo signal, the tracking servo signal, and the information signal can be obtained by the signal detection detector, detailed description of the operation is omitted because it is not directly related to the present invention.

In both cases of using a beam splitter and parallel plate glass, in order to keep the intensity of the light beam converged on the information carrier constant, the output of the detectors 105 and 205 is used. The amplifier circuit is driven to control the output power of the semiconductor laser.

[0006]

The beam splitter used in the conventional example has a large size and a high cost because a multilayer film is deposited and adhered to at least two triangular prisms. Considering these facts, it seems that the parallel flat glass is easy to use, but when using a parallel flat glass having a surface reflection of 70 to 95% and a transmittance of about 5 to 30%, interference between the back surface and the front surface is problematic. Becomes That is, even if the reflectance is reduced to 0.5% or less by applying a non-reflection coating on the back surface, interference occurs. As a result, the transmitted light amount fluctuates about 2.5 times between the brightest case and the darkest case. . In an optical system using a semiconductor laser, the wavelength changes due to the output of the semiconductor laser or a change in temperature, the interference fringes move, and the light amount of the light beam incident on the detector changes. As a result, the amount of light beam incident on the information carrier cannot be controlled accurately. FIG. 3 shows the result of plotting the current flowing through the semiconductor laser and the output of the light quantity monitoring detector as an example. An anti-reflection coating was applied to the back surface to reduce the reflectance to 0.5% or less. At this time, the output of the light amount monitoring detector, that is, the light output is an output having a swelling fluctuation like 21.

If the variation ratio is to be 5% or less, the reflectance of the back surface must be 0.006% or less, and must be substantially 0%. This is not only practically difficult but also theoretically impossible depending on the direction of polarization.

[0008]

As described above, in order to solve the problem in the case of using a parallel plate glass, there is a method of deteriorating spatial coherence so as not to cause interference of transmitted light. That is, instead of applying the non-reflective coating on the back surface, there is a method of intentionally deteriorating the surface accuracy of the reflecting surface on the back surface or changing the optical path length between the front surface and the back surface. For example, the back surface can be made into a ground glass shape so that the wavefront of the light has a random phase so that no interference occurs.

[0009]

[Function] When the surface accuracy of the back surface of a parallel plate glass is intentionally degraded to form a ground glass, etc., the interference of light generated between the back surface and the front surface becomes fine, and the influence of interference due to wavelength fluctuation and optical path length fluctuation substantially occurs. Is gone. Accordingly, the output of the detector does not fluctuate due to the movement of the interference fringe caused by the change in the wavelength of the light due to the temperature change and the change in the output power.
The output power of the objective lens can be accurately controlled.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. FIG.
FIG. 1 is a schematic diagram showing a configuration of an optical head device according to the present invention. The light beam 2 emitted from the semiconductor laser 1 is collimated by a collimating lens 3. Part of the parallel light passes through the parallel flat glass 7 and enters the detector 5 for monitoring the amount of light. The light beam reflected on the surface of the parallel plate glass passes through the objective lens 6 and is focused on the information carrier 9. The light beam reflected on the information carrier 9 reverses its original path, is diffracted by the detection hologram 12, passes through the collimating lens, and is a signal detection detector near the semiconductor laser 1a (see FIG. 2). Incident on. A focus servo signal can be obtained from the differential detection of the signal detection detectors 1c1 and 1c2, and a tracking servo signal and an information signal can be obtained from the differential detection of the signal detection detectors 1b1 and 1b2, but the details are omitted because they are not directly related to the present invention. I do. The outline and the output configuration of the light amount monitoring detector will be described later with reference to FIG. The output of the light amount monitoring detector 5 is controlled via the laser control circuit 13 so that the output of the semiconductor laser 1 is maintained at a required value.

The collimating lens 3 is not always necessary, and is an effective means for improving the accuracy of a light spot in a recording film, such as a device for recording. A collimating lens may be omitted in an optical head device or the like used in a device for exclusive use for reproduction or a recording device that does not require light spot accuracy. In the embodiment of the present invention, the laser unit 201 of the laser unit 201 is divided into two parts 1b1, 1b2, 1 on the left and right sides.
c1 and 1c2 are provided. The reflected light from the information carrier 9 is split by the hologram 12 and guided to the detectors 1b1, 1b2, 1c1, and 1c2. The sum signal of each detector is used to read the information signal, and the difference signal between the left and right detectors is read. In combination, they are used for focus error signal detection and tracking error detection. Each input / output signal is connected to the outside by terminals T1 to T8.

The light beam reflected on the surface of the parallel plate glass passes through the objective lens 6 and is focused on the information carrier 9.
The configuration of the optical system is almost the same as that of the example of FIG. 5, but a random phase is added to the wavefront of the transmitted light by making the rear surface of the parallel plate glass 7 into the ground glass 13. When the ground glass is rough, scattering increases and transmittance decreases. In the embodiment of the present invention, a semiconductor laser having a wavelength of 790 nm was used. In such a case, spatial coherence of light is lost if there is a surface roughness that causes an optical path difference of at least 波長 wavelength or more. However, when the surface roughness is made fine as a problem in manufacturing, the productivity is deteriorated. In this example, it was found experimentally that it was necessary to coarsen particles with a size of about # 800 or more in order to improve the performance. However, in the case of # 800, the loss due to scattering increased. In order to increase the transmittance and stabilize the control system, particles of # 3000 were used in the second embodiment. At this time, the light beam incident on the detector could obtain an output of about 80% as compared with the average output of the parallel plate glass coated with the back anti-reflection coating.

[0013] In the case of coarse particles of # 800 particles, the output was about 60 to 70% of the average output of the parallel flat glass coated with the back anti-reflection coating. FIG. 3 shows a measurement comparison result in the embodiment in which the output current of the detector 5 which is an optical output monitor is plotted against the current flowing through the semiconductor laser. The output waveform 21 is an example in which a non-reflective coating 0.5% is applied to the back surface of a parallel plate glass, and the output waveform 22 is an embodiment in which a coarse ground glass is formed on the back surface of a parallel plate glass using about # 3000 seria. . When the output current of the semiconductor laser is increased by increasing the injection current, the wavelength changes to the longer wavelength side. Due to this wavelength variation, the anti-reflection coating 0.5
In the output waveform 21 when% is applied, a sine-shaped change is seen in conjunction with the wavelength fluctuation period. On the other hand, the output waveform 22 of the second embodiment using the ground glass roughened using about 3000 seria on the back surface of the parallel plate glass shows no such fluctuation at all, and has very good linearity. It became clear that it could be obtained. Therefore, if the semiconductor laser is controlled by measuring the light quantity based on the output waveform 22 and amplifying the current, the light quantity of the light beam emitted from the objective lens can be accurately controlled.

In addition to the present embodiment, it is possible to mix a phase object that causes a micro optical path length change inside the parallel plate. Also, in order to avoid interference from the parallel plate glass back surface, it is also possible to use a wedge-shaped plate glass instead of pure parallel plate glass, in which case, instead of changing the accuracy between the front and back surfaces, continuously By changing the thickness, interference occurs partially at any wavelength, but the occurrence of intensive interference at a specific wavelength is suppressed, and periodic nonlinearity is unlikely to occur as shown by the curve 21 in FIG. Can be. Wedge glazing is somewhat expensive, but provides the same effect.

In addition to the above-mentioned ground glass parallel plate and wedge plate glass, as another example of a shape in which the distance between the front surface and the back surface is not constant, a hologram lens is formed on the back surface of a plano-convex lens or a parallel plate glass, and the light amount monitor described above is provided. It is also possible to adopt a configuration in which light is condensed on the detector. Further, in the embodiment, the case where the light source is a semiconductor laser has been described. However, the present invention is not limited to this. The light source can be replaced with another light source such as a gas laser or a solid laser, which is within the scope of the present invention.

[0016]

As described above, as can be seen from the measurement results of the embodiment shown in FIG. 3, the rear surface of the parallel flat glass is made to have a structure in which the distance between the front surface and the rear surface is not constant, such as a ground glass, a wedge-shaped glass plate, or a plano-convex lens. By doing so, the influence of interference on the transmitted light amount can be eliminated, the linearity of the output signal of the detector used for the light amount monitor can be improved, and the light power control characteristics of the objective lens output can be greatly improved. It can be realized with such an extremely simple configuration.

[Brief description of the drawings]

FIG. 1 shows an embodiment according to the present invention.

FIG. 2 is a diagram showing a configuration example of a semiconductor laser according to the present invention;

FIG. 3 shows the effect of the embodiment according to the present invention.

FIG. 4 is a diagram for explaining Conventional Example 1;

FIG. 5 is a diagram for explaining a modification of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 3 Collimating lens 5 Detector for light quantity monitoring 6 Objective lens 7 Parallel plate glass 9 Information carrier

Continuation of the front page (56) References JP-A-61-148642 (JP, A) JP-A-63-86123 (JP, A) JP-A-2-208836 (JP, A) JP-A-5-6917 (JP) , U) Hiroshi Kubota et al., Published by Asakura Shoten Co., Ltd. “Optical Technology Handbook Supplemental Edition” s50.7.20pp667 ~ 6689.3.13 Coating Section (58) Fields surveyed (Int.Cl. ⁶ , DB name) ) G11B 7/135

Claims (8)

(57) [Claims] And 1. A radiation source, an objective lens for converging on receiving the information carrier the light beam from the radiation source, Ri mania between the radiation source and the objective lens, the first of said light beam is incident substantially deflected perpendicularly to the light beam on the surface, also reflecting film that transmits part of the incident light is formed
Cage, and the first surface and substantially the same flat plate the distance between the second surface thereof opposing to receive light transmitted through the plate
A photodetector disposed and in the vicinity of the radiation source;
The reflected light beam of the information carrier deflected again by the recording plate
A detector for detecting a signal, the surface accuracy of the second surface of the flat plate being lower than that of the first surface, and light incident on the photodetector being detected by the second surface of the flat plate. An optical information recording / reproducing apparatus characterized by being transmitted and scattered. 2. An optical information recording / reproducing apparatus according to claim 1, further comprising a collimating means provided between the radiation light source and the flat plate to receive a light beam emitted from the radiation light source and convert the light beam into substantially parallel light. 3. The optical information recording / reproducing apparatus according to claim 1, wherein the second surface of the flat plate is processed into a ground glass shape. 4. The optical information recording / reproducing apparatus according to claim 1, wherein the reflection film is a multilayer film having a reflectance of 0.7 to 0.95 for light polarized in a horizontal direction with respect to the first surface of the flat plate. apparatus. 5. The optical information recording / reproducing apparatus according to claim 3, wherein a surface roughness of the ground glass on the second surface of the flat plate is equal to or less than a wavelength. 6. The optical information recording / reproducing apparatus according to claim 1, wherein a wedge glass plate having a first surface and a second surface having a constant inclination is used in place of the flat plate. 7. The optical information recording / reproducing apparatus according to claim 1, wherein a flat-convex lens structure having a flat reflecting surface is used instead of the flat plate. 8. A reflection film formed on a first surface of the flat plate has a reflectance of 0.7 to 0.95 for light polarized in a direction perpendicular to the first surface of the flat plate. 2. The optical information recording / reproducing apparatus according to claim 1, wherein the optical information recording / reproducing apparatus comprises a film having a reflectance of 0.9 or more with respect to light polarized in the horizontal direction.