JPH07182690A - Optical recorder/reproducer - Google Patents

Abstract

PURPOSE:To suppress aberration and to obtain a reproduced signal of high quality by detecting the difference of thicknesses of a base material of an optical recording medium, and inserting or removing a conversion lens in an optical recorder/reproducer for optically recording or reproducing a signal on or from the medium. CONSTITUTION:A conversion lens 6 is provided between an objective lens 2 and a semiconductor laser 1 so as to be inserted or removed, and the difference of the thickness of a base material of an optical information recording medium 10 is detected to decide an inserted or removed state of the lens 6. Thus, an excellent optical recorder/reproducer which can form an optical spot in a state having a small aberration on a recording surface of the medium 10 with the different thickness of the base material by one optical head and record or reproduce in an optimum state can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for optically recording or reproducing a signal on an optical information recording medium.

[0002]

2. Description of the Related Art A general optical recording / reproducing apparatus using a semiconductor laser is shown in FIG. In FIG. 6, the light beam 42 emitted from the semiconductor laser 41 is partially reflected by the half mirror 43. The reflected light beam 42 is bent at a right angle by a reflection mirror 44, and is condensed by a condenser lens 45 into a substantially parallel light beam. The substantially parallel light flux 42 is reflected by the objective lens 46.
The light spot 48 is narrowed down by the laser beam to form a light spot 48 on the recording surface of the optical information recording medium 47. Then, the light flux 49 reflected by the optical information recording medium 47 passes through the objective lens 46, the condenser lens 45, and the reflection mirror 44 again, and enters the half mirror 43. A part of the light flux 49 is obliquely transmitted through the half mirror 43 to become a light flux having astigmatism, passes through the concave lens 50, is focused, and is received by the photodetector 51. The photodetector 51 is configured to detect a reproduction signal and a control signal for controlling the position of the light spot 48 at the same time.

The objective lens 46 used in the optical head having such a structure is designed in consideration of the substrate thickness of the optical information recording medium 47, and the optical information recording medium having a substrate thickness different from the designed value. On the other hand, spherical aberration occurs on the recording surface and the imaging performance deteriorates, making it difficult to record and reproduce information. Conventionally,
The optical information recording media used in compact discs (CDs), video discs, magneto-optical disc devices for data, etc. all had the same substrate thickness of 1.2 mm. Therefore, one optical head is used for different types of optical information recording media.
It was possible to record and reproduce (CD, video disc, magneto-optical disc, etc.).

On the other hand, in recent years, in order to achieve higher density,
Increasing the numerical aperture of the objective lens has been studied. Increasing the numerical aperture of the objective lens improves the optical resolution and widens the spatial frequency band for recording and reproduction, but the convergent performance of the converged light spot 48 becomes sensitive to aberrations and deteriorates the performance. There is a problem that it is easy. The optical information recording medium 47 and the objective lens 46 are tilted due to the surface deflection of the optical information recording medium 47 and the surface deflection of the turntable to which the optical information recording medium is attached. Due to this inclination, coma aberration occurs in the light spot 48, and the convergence performance does not improve even if the numerical aperture is increased. Therefore, an attempt has been made to use an optical information recording medium having a thin base material so that the coma aberration does not increase even if the numerical aperture of the objective lens is increased. The coma aberration due to the inclination of the optical information recording medium 47 and the objective lens 46 is improved as shown in FIG. 7 when the substrate thickness of the optical information recording medium is reduced. The horizontal axis of FIG. 7 represents the substrate thickness of the optical information recording medium, and the vertical axis represents the numerical aperture. The optical spot 48 when the optical information recording medium and the objective lens are inclined by 0.2 °
This is a calculation of the point where the deterioration of the light intensity at the center of is equal. From the figure, the numerical aperture is 0.5 and the substrate thickness of the optical information recording medium is
It can be seen that the deterioration of the light intensity at the center of the light spot is almost the same when the numerical aperture is 1.2 mm and when the numerical aperture is 0.62 and the substrate thickness of the optical information recording medium is 0.6 mm. Therefore, when the numerical aperture is increased, by reducing the thickness of the base material of the optical information recording medium, the coma aberration caused by the inclination of the optical information recording medium can be suppressed as in the conventional case. However, when the substrate thickness of the optical information recording medium is reduced, the problem of the coma occurs, and it becomes difficult to record and reproduce the conventional optical information recording medium with the objective lens for recording and reproducing the optical information recording medium. It becomes impossible to maintain compatibility with the conventional optical information recording medium. Therefore, there is no choice but to use two optical heads to record and reproduce an optical information recording medium having a thin base material and an optical information recording medium having a base thickness of 1.2 mm by separate optical heads.

[0005]

However, in the above-mentioned structure, when the substrate thickness of the optical information recording medium is different, the aberration on the recording surface becomes large and an appropriate reproduction signal cannot be obtained. Had a point. In view of the above problems, the present invention detects a difference in the base material thickness of an optical information recording medium and suppresses the aberration due to the difference in the base material thickness by inserting / removing the conversion lens based on the detection signal, which is of high quality. It is an object of the present invention to provide an optical recording / reproducing device capable of obtaining a recording or reproducing signal.

[0006]

In order to achieve the above object, an optical recording / reproducing apparatus of the present invention is provided with a conversion lens between an objective lens and a semiconductor laser in a freely attachable / detachable manner. The configuration is such that the insertion / removal state of the conversion lens is determined by detecting the difference.

[0007]

With the above-described structure, the present invention can reduce the spherical aberration generated on the recording surface of the optical information recording medium having a different substrate thickness with one optical head, and can obtain an optimum recording or reproducing signal. .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical recording / reproducing apparatus according to a first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the optical configuration of an optical recording / reproducing apparatus according to the first embodiment of the present invention. In FIG. 1, 1 is a semiconductor laser, 2 is light emitted from the semiconductor laser 1, and the optical information recording medium 10
Objective lens 3 for converging light on the recording surface, a collimator lens 3 for converting the divergent light emitted from the semiconductor laser 1 into a substantially parallel light beam, and 4 a light reflected by the optical information recording medium 10. Is a beam splitter for branching the reflected light from the optical information recording medium 10 to the beam detecting system 4, and 6 is provided between the objective lens 2 and the beam splitter 5. The conversion lens is a concave lens that converts the converging state of the light beam that goes toward the objective lens 2. Further, FIG. 2 is a diagram showing an optical information recording medium and a converged state of a light spot. Reference numeral 10a is an optical information recording medium having a substrate thickness thinner than that of the conventional one, and 10b is an optical information recording medium having a conventional substrate thickness.

The operation of the optical recording / reproducing apparatus configured as described above will be described below with reference to FIGS. 1 and 2. First, in order to increase the information density, the divergent light emitted from the semiconductor laser 1 is inserted into the collimator lens 3 with the optical information recording medium 10a having a thinner base material than the conventional one inserted.
Is converted into a substantially parallel light flux and travels toward the objective lens 2. The light flux passing through the objective lens 2 is focused on the recording surface of the optical information recording medium to form a light spot 15a. The objective lens 2 is designed so that the state of the light spot 15a on the recording surface having a substrate thickness of a specific thickness smaller than that of the conventional one has the smallest aberration. In the case of reproduction, the light reflected by the modulation of the light intensity again passes through the objective lens 2 and enters the beam splitter 5. The beam splitter 5 is reflected in the direction of the detection optical system 4 and is received by the photodetector 16 to detect a reproduction signal and a control signal for controlling the position of the light spot 15a. When the optical information recording medium 10b having a normal substrate thickness is inserted, the type of the inserted optical information recording medium is determined based on the signal detected by the optical information recording medium type detection unit (not shown). Then, the insertion / extraction of the conversion lens 6 is determined by specifying the base material thickness. As shown in FIG. 2B, by inserting the conversion lens 6, the light spot 15b can be converged on the recording surface of the optical information recording medium 10b having the conventional substrate thickness with a small amount of aberration.

As described above, according to the first embodiment of the present invention, the conversion lens 6 for converting the converging state of the light beam traveling from the semiconductor laser 1 toward the objective lens 2 and changing the converging state of the light beam is inserted and removed. The recording surface is freely provided and determines the insertion / extraction state of the conversion lens 6 on the basis of the detection signal of the type of the optical information recording medium, so as to correspond to the optical information recording medium having different base material thicknesses and the recording surface with a small aberration. The light spot can be converged on, and a high quality recording or reproducing signal can be obtained. In addition, in the first embodiment of the present invention, the objective lens 2 is designed according to the optical information recording medium having a specific thickness smaller than the conventional base material thickness. It may be designed according to the information recording medium and the conversion lens may be a convex lens.

A second embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram of an optical recording / reproducing apparatus showing a second embodiment of the present invention. In FIG. 3, 1
Is a semiconductor laser, 2 is an objective lens, 3 is a collimator lens, 4 is a detection optical system, and 5 is a beam splitter. The above is the same as the configuration of the first embodiment of the present invention. The difference from the first embodiment of the present invention is that the conversion lens 13 provided between the semiconductor laser 1 and the objective lens 2 so as to be freely inserted and removed is a convex lens having a positive refractive power.

The operation of the optical recording / reproducing apparatus having the above structure will be described below. The light emitted from the semiconductor laser 1 is converted into a substantially parallel light flux by the collimator lens 3. When the optical information recording medium 10b having the conventional base material thickness is inserted, the conversion lens 13 is inserted and the substantially parallel light flux exiting the collimator lens 3 is once converged and becomes a divergent light flux, and then enters the objective lens 2. . By this action, the light emitted from the objective lens 2 can form the light spot 15b on the recording surface of the optical information recording medium 10b having the conventional base material thickness with little aberration. Although the concave lens is used as the conversion lens in the first embodiment of the present invention, the convex lens is used as the conversion lens in the second embodiment of the present invention, so that the light toward the objective lens is free from vignetting and there is no light amount loss. The light transmission efficiency is improved. Therefore, the emission power of the semiconductor laser can be small and an inexpensive optical recording / reproducing device can be realized. Further, the beam diameter toward the photodetector does not change due to the insertion and removal of the conversion lens, and the beam diameter on the photodetector becomes almost the same, so that the light receiving area of the photodetector can be effectively used.

Although the conversion lens 6 is a concave lens in the first embodiment of the present invention, the conversion lens 6 may be a hologram having a negative refractive power. Further, although the conversion lens 13 is a convex lens in the second embodiment of the present invention, the conversion lens 13 may be a hologram having a positive refractive power. As a result, it is possible to provide a conversion lens that is cheaper than a concave lens or a convex lens, and it is possible to provide an optical recording / reproducing device that is inexpensive as a system.

A third embodiment of the present invention will be described below with reference to the drawings. In FIG. 4, the optical configuration included in the optical head 20 is the same as that of the first or second embodiment, but the conversion lens 13 is attached to the lens holder 17, and the optical head 20 has optical information. The recording medium 10 is configured so that it can be moved by a transfer system 21 in order to move it to a predetermined position for recording or reproducing information. Reference numeral 14 is a type detection unit for detecting the type of the optical information recording medium in order to specify the thickness of the base material of the optical information recording medium.

The operation of the optical recording / reproducing apparatus having the above structure will be described below. When the optical information recording medium 10b having a conventional substrate thickness is inserted, the transfer system 21 is moved to a predetermined position based on the signal detected by the type detection unit 14 of the optical information recording medium, and the transfer system is moved. The lens holder 17 is moved by interfering the projection 22 provided independently of 21 with the lens holder 17, and the conversion lens 13 is moved into the optical path of the optical head. Further, the lens holder 17 can be rotated or reciprocated so that the lens holder 17 can be returned to the original state by a similar operation. According to this configuration, the lens holder 17 can be moved only by moving the conventional transfer system 21 to a predetermined position, and an inexpensive optical recording / reproducing apparatus can be realized without using another driving means. In the third embodiment, the projection 22 is provided independently of the transfer system 21, but the projection 22 may be a cam or a gear.

A fourth embodiment of the present invention will be described below with reference to the drawings. FIG. 5 (a) shows a reproduction signal when the objective lens 2 is designed for an optical information recording medium having a substrate thickness thinner than that of the conventional one, and is reproduced without inserting the conversion lens 6 or the conversion lens 13. Shows the eye pattern of.
According to FIG. 5A, the spherical aberration of the light spot on the recording surface of the optical information recording medium becomes large and the jitter of the reproduced signal deteriorates, which makes it difficult to reproduce. In this case, the degree of deterioration of the reproduction signal is detected, and when the value exceeds a predetermined value, a conversion lens is inserted and reproduction is restarted to obtain the optimum reproduction signal as shown in FIG. 5 (b). You can According to this configuration, a special detection device is not required, and the signal processing circuit that detects the signal component of the reproduction signal can be used for the determination.
It is possible to provide a smaller optical recording / reproducing device.

[0017]

As described above, according to the present invention, the conversion lens for converting the converging state of the light beam directed to the objective lens and changing the converging state of the light beam is detachably provided so that one optical head can be used as the base material. Optical information recording media having different thicknesses can be recorded or reproduced with little aberration, and an inexpensive optical recording / reproducing device can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical head of an optical recording / reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an optical information recording medium of an optical recording / reproducing apparatus according to a first embodiment of the present invention and a condensed state of a light spot.

FIG. 3 is a configuration diagram of an optical head of an optical recording / reproducing apparatus according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical recording / reproducing apparatus for explaining an operation in a third embodiment of the present invention.

FIG. 5 is a diagram of reproduced signals of an optical recording / reproducing apparatus in a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical head of a conventional optical recording / reproducing apparatus.

FIG. 7 is an explanatory diagram of the substrate thickness and the imaging performance of the optical information recording medium.

[Explanation of symbols]

1, 41 ... Semiconductor laser, 2, 46 ... Objective lens, 3 ...
Collimator lens, 4 ... Detection optical system, 5 ... Beam splitter, 6,13 ... Conversion lens, 10, 47 ... Optical information recording medium, 14 ... Kind detection section, 15, 48 ... Optical spot,
16, 51 ... Photodetector, 17 ... Lens holder, 20 ... Optical head, 21 ... Transfer system, 22 ... Projection part, 42, 49 ... Luminous flux,
43 ... Half mirror, 44 ... Reflecting mirror, 45 ... Condensing lens, 50 ... Concave lens.

Claims (9)

[Claims] 1. A semiconductor laser, an objective lens for condensing light emitted from the semiconductor laser on an optical information recording medium, and a condensing light flux provided between the semiconductor laser and the objective lens. A conversion lens that changes the state and changes the state in which the light beam is condensed, a beam splitter provided between the semiconductor laser and the conversion lens, and reflected light from the optical information recording medium is reflected by the beam splitter. An optical recording / reproducing apparatus, comprising: a photodetection optical system provided in a predetermined direction; and a photodetector that receives light emitted from the photodetection system. 2. The optical recording / reproducing apparatus according to claim 1, wherein a conversion lens for converting a condensed state of a light beam directed toward the objective lens is provided so as to be insertable and removable. 3. A conversion lens for converting a condensed state of a light beam toward an objective lens is provided on a fixed side of an optical head and is not driven integrally with an objective lens whose position is controlled by focus control and tracking control. The optical recording / reproducing apparatus according to claim 1. 4. An optical recording / reproducing apparatus, characterized in that a difference in substrate thickness of an optical information recording medium or a difference in type of the optical information recording medium is detected, and a conversion lens is inserted / removed based on the detection signal. 5. The type of the optical information recording medium is detected by reproducing the signal of the optical information recording medium with or without the conversion lens inserted, and when the reproduction is difficult in the reproduction state, the conversion is performed. An optical recording / reproducing apparatus characterized in that signal reproduction is started again by inserting or removing a lens. 6. An optical recording / reproducing apparatus characterized in that the conversion lens is inserted and removed by moving a transfer system of an optical head to a specific position. 7. An optical recording / reproducing apparatus, wherein the conversion lens is a concave lens. 8. An optical recording / reproducing apparatus, wherein the conversion lens is a convex lens. 9. An optical recording / reproducing apparatus, wherein the conversion lens is composed of a hologram.