JPS62285234A - Reflective optical disc reader - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Industrial Application Field] The present invention detects a focus error signal representing the condensation state of incident light on the optical disc from the reflected light of the optical disc. The present invention relates to a reflective optical disc reading device which can correct astigmatism of the incident light.

[Prior Art] Conventionally, a beam splitter provided between an optical disk and a semiconductor laser is used to change the reflected optical path of light irradiated from the semiconductor laser to the optical disk, and the changed optical path is changed. An optical component such as a cylindrical lens is installed on the disc to generate astigmatism in the reflected light, and this is detected by a photodetector to provide a focus error signal indicating the convergence state of the incident light on the optical disc. A reflective optical disc reading device having such a configuration is known.

By the way, the semiconductor laser used in this type of device has
The focal point of light is different between the semiconductor junction surface and a surface perpendicular to the semiconductor junction surface, and the irradiated laser light may have astigmatism. Therefore, in a reading device using such a semiconductor laser, the beam shape of the irradiated light on the optical disk changes to a flat vertically long or horizontally long beam depending on the distance between the optical disk and the semiconductor laser, and the irradiated light straddles adjacent tracks. There was a problem that reading ability decreased.

Therefore, in recent years, Japanese Patent Application Laid-Open No. 143443/1983 has proposed a method in which a plane parallel plate is provided at a predetermined angle on the optical path of irradiation from the semiconductor laser to the optical disk, thereby correcting the astigmatism of the laser light irradiated from the semiconductor laser. is proposed.

[Problems to be Solved by the Invention] However, although the device according to this proposal can satisfactorily correct the astigmatism of the laser beam irradiated onto the optical disk, the above-mentioned problem is required to obtain a highly accurate focus error signal. As in the past, it was necessary to install an optical component to generate astigmatism on the reflected optical path whose optical path was changed by a beam splitter, and it was not possible to simplify the optical system by using a parallel plane plate. . That is, if astigmatism is simply generated in the reflected light from the optical disk, it is possible to generate astigmatism in the reflected light by the amount of astigmatism of the semiconductor laser by using the above-mentioned plane-parallel plate. However, a good focus error signal that is not affected by noise etc.
In order to achieve this, it is desirable to generate as much astigmatism as possible in the reflected light, and for this purpose, it is necessary to provide an optical component for generating astigmatism on the reflected light path, as in the conventional method. It was not possible to do so.

Therefore, the present invention can generate large astigmatism in reflected light without providing an optical component for generating astigmatism on the reflected optical path formed by a beam splitter.
Moreover, it is an object of the present invention to provide a reflective optical disc reading device that can satisfactorily correct astigmatism of laser light irradiated onto an optical disc from a semiconductor laser.

[Means for Solving the Problems] That is, the configuration of the present invention for solving the above problems is such that the focal point of the laser beam is different between the semiconductor junction surface and the plane perpendicular thereto, resulting in astigmatism. A semiconductor laser, a focusing optical system that focuses laser light incident from the semiconductor laser onto a predetermined area on a reflective optical disk, and returns reflected light from the optical disk in the direction of incidence; reflective optical path changing means for guiding the reflected light from the optical disk returning via the light optical system in a direction different from the direction of incidence from the semiconductor laser; astigmatism generating means for generating astigmatism, and receiving the reflected light transmitted through the astigmatism generating means,
A reflective optical disc reading device comprising: a light receiving unit that generates a focus error signal indicating a condensation state of laser light on the optical disc, between the semiconductor laser and the reflective optical path changing unit; In order to magnify the astigmatism of the semiconductor laser, a first parallel plane plate is disposed, and between the reflection optical path changing means and the converging optical system, the first parallel plane plate is Summary of a reflective optical disk reading device, characterized in that it corrects astigmatism magnified by , and is provided with a second parallel plane plate that functions as astigmatism generating means. It is said that

[Function] In the reflective optical disk reading device of the present invention configured as described above, the astigmatism of the laser beam from the semiconductor laser is magnified once by the first parallel plane plate, and then the astigmatism of the laser beam from the semiconductor laser is magnified by the first parallel plane plate. Corrected by a parallel plane plate. Therefore, astigmatism of the laser beam focused on the optical disk via the focusing optical system is eliminated, and a light beam having a predetermined shape is always focused on the optical disk. In addition, astigmatism is generated in the reflected light from the optical disk by the second parallel plane plate.
The light is transmitted to the light receiving means via the reflective optical path changing means. Therefore, in this reflected light, astigmatism is generated which is the sum of the astigmatism generated by the first parallel plane plate and the astigmatism caused by the semiconductor laser, and the focus error signal obtained by the light receiving means is detected. Accuracy will be improved.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of the entire optical system of the reading device of this embodiment, in which (a) is a plan view taken along the junction surface of a semiconductor laser 1 used therein, and (b) is a right side view thereof.

As shown in the figure, the focal point of the laser beam is different from a and b between the cemented surface of the semiconductor laser 1 and the surface orthogonal thereto, resulting in astigmatism. Therefore, in this embodiment, the Raded light is incident on the optical path from the semiconductor laser 1 to the optical disk 2 via the first parallel plane plate 3 and the parallel plane plate 3 for magnifying the astigmatism. A second parallel plane plate 4 for correcting astigmatism is provided, and these two parallel plane plates 3, 4
After completely correcting the astigmatism of the laser beam from the semiconductor laser 1, the laser beam is condensed onto the optical disk 2 via the collimating lens 5 and the objective lens 6 as the condensing optical system. There is. Incidentally, each of the parallel plane plates 3 and 4 is disposed so as to be orthogonal to the bonding surface of the semiconductor laser 1 and to form predetermined angles α and β with respect to the plane orthogonal to the bonding surface. This is because the plane parallel plate 3 magnifies the astigmatism of the laser beam emitted by the semiconductor laser 1 as described above, and the plane parallel plate 4 corrects the astigmatism. It is determined by the thickness of the flat plates 3 and 4 and the amount of astigmatism to be enlarged or corrected. The reason why astigmatism can be enlarged or corrected using a parallel plane plate is well known and is also detailed in the above-mentioned Japanese Patent Application Laid-Open No. 143443/1983, so the explanation will be omitted here.

Further, in this embodiment, a beam splitter 7 as the reflective optical path changing means is provided between each of the parallel plane plates 3 and 4, and an objective lens 6, a collimating lens 5. Parallel plane plate 4
The reflected light from the optical disk 2 transmitted through the optical disc 2 is guided to a photodetector 8 serving as the light receiving means. Therefore, astigmatism will be generated in the reflected light from the optical disk 2 that is incident on the photodetector 8 due to the parallel plane plate 4, and the laser beam on the optical disk 2 will be detected using the photodetector 8. It becomes possible to detect the condensed state of the light. That is, as shown in FIG. 2, the photodetector 8 includes four photodiodes PLP2. P3. The photodetector 8 has a dotted line, a dotted line and Since the reflected light in the beam shape shown by the solid line and the dashed-dotted line is incident, the photodiodes PI, P3, P2 . By inputting the output signals from P4 to the differential amplifier 9, a single error signal can be obtained.

In this way, in the reading device of this embodiment, the semiconductor laser 1
The astigmatism of the laser beam from the two parallel plane plates 3 and 4
Since the laser beam with no astigmatism is corrected by and focused on the optical disk 2, the reading accuracy is improved without changing the beam shape of the laser beam on the optical disk 2.

In addition, the reflected light from the optical disk 2 has astigmatism generated by the parallel plane plate 4 and then enters the photodetector 8, so that astigmatism is generated on the optical path from the beam splitter 7 to the photodetector 8. The focus error signal can be generated without providing any optical components to generate the focus error signal, which simplifies the configuration.Furthermore, the astigmatism of the reflected light generated by the parallel plane plate 4 is caused by the semiconductor laser 1 and the plane parallel to each other. Since the value is the sum of the astigmatism caused by the face plate 3, the amount of astigmatism of the reflected light can be increased, and the detection accuracy of the -cus error signal can be improved.Furthermore, the plane parallel plate 3 can be replaced with a semiconductor. Laser 1
If the film is directly applied to the semiconductor laser 1 as a protective glass, the structure can be made simpler.

In the above embodiment, the plane parallel plate 4 and the beam splitter 7 were formed separately, but as shown in FIG.
If a plate-shaped beam splitter 7' in which a dielectric material or the like is vapor-deposited between two glass plates is used to correct astigmatism, a plane-parallel plate is not required and the configuration can be made simpler. can. Further, since there is no need for a space for providing a parallel plane plate, the device can be made smaller.

[Effects of the Invention] As detailed above, according to the reflective optical disc reading device of the present invention, the astigmatism of the laser beam from the semiconductor laser can be corrected, and the optical disc reading ability can be improved. In order to reduce the focus error signal by 1q, there is no need to provide an optical component to generate astigmatism in the reflected light from the optical disk, and the configuration can be simplified. In addition, the astigmatism generated in the reflected light is the sum of the astigmatism of the semiconductor laser and the astigmatism caused by the first parallel plane plate, so its ω is large, improving the detection accuracy of the focus error signal. You can also.

[Brief explanation of the drawing]

FIG. 1 shows the optical system of the entire reading device of the embodiment, (A) is a plan view along the junction surface of the semiconductor laser, (A) is a right side view thereof, and FIG. 2 is the configuration of the photodetector 8. An explanatory diagram representing
FIG. 3 is a plan view showing the optical system of the reading device according to another embodiment. 1... Semiconductor laser 2... Optical disk 3.4
...Parallel plane plate 5...Collimating lens 6...
Objective lens 7...Beam splitter 8...Photodetector

Claims (1)

[Claims] A semiconductor laser whose convergence point differs between the semiconductor junction surface and a plane perpendicular to it, causing astigmatism, and a semiconductor laser that directs the laser beam incident from the semiconductor laser onto a reflective optical disk. a condensing optical system that condenses light onto a predetermined area and returns reflected light from the optical disk in the incident direction; reflected light path changing means for guiding the reflected light in a direction different from the direction of incidence thereof; astigmatism generating means provided on the optical path of the reflected light and causing astigmatism in the reflected light; a light receiving means for receiving the reflected light transmitted by the semiconductor laser and generating a focus error signal representing a focusing state of the laser light on the optical disc; and the reflection optical path changing means, a first
A plane-parallel plate is disposed between the reflective optical path changing means and the condensing optical system, and the astigmatism magnified by the first plane-parallel plate is corrected, and the astigmatism occurs. A reflective optical disc reading device, characterized in that a second parallel plane plate functioning as a means is disposed.