JPH0449536A - Optical device for optical pickup - Google Patents

Abstract

PURPOSE:To make the whole of a device small-sized and thin by arranging a film-shaped half mirror tilted on the optical axis of emitted light of a light emitting element and providing an objective lens and arranging a light receiving element in the direction in which return light from a disk is reflected by the half mirror. CONSTITUTION:Since a film-shaped half mirror 10 is used, astigmatism does not occur by light transmission, and the output from a semiconductor laser 1 can be condensed on a disk 5 by an objective lens 4. Since the half mirror is used as the transmission system, it is held by a rigid frame-shaped holder to sufficiently secure the face precision for transmission light. Since the light emitting element can be arranged in the transmission direction, the optical axis of emitted light can be arranged in the vicinity of a disk driving motor, and the whole of the device is easily miniaturized. When the half mirror is bent, astigmatism occurs for reflected light to obtain a focus error signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical pickup used in compact disc players, magneto-optical disc devices, etc. The present invention relates to an optical device for a pickup.

[Prior Art 1] Optical pickups installed in compact disc players and the like are desired to have lower costs for the optical components used, and to be smaller and thinner overall.

FIG. 10 shows the structure of a conventional optical device for an optical pickup that aims to reduce costs, reduce size, and reduce thickness.

This pickup uses a flat half mirror 3. This half mirror 3 has a semi-reflective film deposited on the surface of a flat glass to form a semi-reflective surface 3a.

Laser light emitted from the semiconductor laser 1 is reflected by the semi-reflective surface 3a and focused onto the recording surface of the disk 5 by the objective lens 4. The return light from the disk 5 passes through the half mirror 3 and is received by the bin photodiode 6. The returned light is modulated by the bits recorded on the recording surface of the disk 5, and the modulated light is converted into an electrical signal by a vinyl photodiode, thereby reading the information recorded on the disk.

Since the half mirror 3 made of flat glass with a certain thickness is used, the return light from the disk passes through this half mirror 3, causing astigmatism, and this astigmatism is utilized. A focus error signal is obtained by the four-divided light receiving section of the bin photodiode 6. Further, reference numeral 2 is a diffraction grating.

This diffraction grating 2 forms three beam spots on the disk 5. E-F detection outputs are obtained by two of the three beam spots, and tracking errors are detected.

[Problem to be solved by the invention]

In the optical device shown in FIG. 10, since the half mirror 3 made of flat glass is used, it is possible to realize a reduction in size and cost compared to an optical device using a cubic type half mirror. However, when using a half mirror 3 made of flat glass, astigmatism occurs due to the return light from the disk passing through it.
There is an advantage that a focus error signal can be obtained using this astigmatism, but on the other hand, the laser beam emitted from the semiconductor laser 1 is transmitted through the half mirror 3 and the objective lens 4
cannot be sent to. Such structural constraints cause the following problems.

(1) The output from the semiconductor laser l is reflected and sent toward the disk, but the error in surface accuracy when reflecting light is amplified twice as much as when transmitting light. It is necessary to make the surface precision of the reflective surface 3a very high.

(2) The pickup needs to be adjusted so that the positional deviation of the light emitting point of the semiconductor laser 1 is minimized. This results in a position shift of the point. Therefore, it is necessary to improve the positioning accuracy of the half mirror 3, and it is also necessary to adjust the inclination angle.

(3) FIG. 9 is a plan view showing a state in which a pickup P using the optical device shown in FIG. 1O is mounted on an actual compact disc player. In FIG. 9, a semiconductor laser l and a half mirror 3 are installed inside the pickup P.
In addition, a bin photodiode 6 and the like are provided in a planar arrangement, and the light reflected by the half mirror 3 is reflected by a total reflection prism 7 in a direction perpendicular to the plane of the paper, and is condensed by an objective lens 4 to be focused on a disk 5. The recording surface is irradiated with light. In the current compact discs, etc., the pickup P plays back the innermost signal.
When moving to the inner peripheral position of the disk 5, it is necessary to bring the disk drive motor M and the pickup P as close as possible. Furthermore, bringing the optical axis of the returned light closer to the motor M in this close state is an essential condition for signal reproduction. In the optical device shown in FIG. 10, the bin photodiode 6 is located on the optical axis, but since the bin photodiode 6 has terminals 6a extending left and right,
A dimension in the left-right direction in FIG. 9 is required for the length of this terminal 6a. Therefore, in order to reduce the distance δ between the optical axis and the motor M, it is necessary to fold the terminal 6a and attach it to the board 8, which makes the attachment structure complicated. In addition, in order to accurately detect the light received by the photodiode 6, it is necessary to adjust the board 8 to the pickup P in the left-right direction in the figure. It will not be possible to secure it.

The present invention solves the above conventional problems, and provides an optical pickup that uses light from a light emitting element as light that passes through a half mirror to improve space efficiency and can be manufactured at low cost. The purpose is to provide equipment.

[Means for Solving the Problems 1] In the optical device of the optical pickup according to the present invention, a film-like half mirror is arranged obliquely on the optical axis of light emitted from a light emitting element, and the light emitted from the light emitting element is emitted from the half mirror.
An objective lens is provided to condense the light transmitted through the disk onto the disk, and the return light from the disk is focused on the half mirror.
It is characterized in that the light receiving element is arranged in the direction in which the light is reflected by the light.

Furthermore, in the above means, a film-like half mirror
is curved in a shape that causes astigmatism in the returning light to the light-receiving element.

[Step 1] In the above means, since a film-like half mirror is used, astigmatism does not occur due to light passing through this half mirror.

Therefore, the output from the semiconductor laser can be transmitted through the half mirror and focused onto the disk by the objective lens. By using a half mirror as a transmission method, there is no problem with the surface accuracy of the anti-Q= surface as in the anti-QJ method, and for example, a film-like half mirror can be held in a rigid frame-like holder. By doing so, sufficient surface precision for transmitted light can be ensured. In addition, since a light emitting element such as a semiconductor laser can be placed in the transmission direction to the half mirror, the optical axis of the light emitted from the light emitting element can be placed close to the disk drive motor, making it possible to easily downsize the pickup and the entire device. In the second method, by curving a film-like half mirror, astigmatism can be generated in the reflected light, and a focus error signal can be obtained without using a cylindrical lens or a knife. become.

[Example] Examples of the present invention will be described below with reference to the drawings of FIGS. 1 to 8.

FIG. 1 shows an optical device for an optical pickup according to a first embodiment of the present invention.

In this embodiment, a film-like half mirror 10 is used. This half mirror 10 is a transparent film with a thickness of about 0.1 mm, and its surface is coated with a semi-reflective film. Alternatively, the film-like half mirror 10 can be constructed by overlapping two transparent films with different refractive indexes. As shown in FIG. 2, a film-like half mirror 10 is held between two rigid rod-shaped holders 11 and 12.
1.12 is fixed to the pickup chassis.

Moreover, by being held by the frame-shaped holders 11 and 12,
The flatness of the film half mirror 10 is maintained.

Laser light output from the semiconductor laser 1 is used after being transmitted through the film-like half mirror 10. Thickness is 0
．． In the case of a film of about 1 mm, no astigmatism occurs in the transmitted light.The light transmitted from the semiconductor laser 1 through the half mirror 10 is focused by the objective lens 4 and focused on the recording surface of the disk 5. Reference numeral 2 is a diffraction grating, and by using this diffraction grating 2, three
A spot is formed. The return light from the disk 5 passes through the objective lens 4, returns to its original path, and is reflected by the half mirror 1O. The light is then received by the vinyl photodiode 6. Since astigmatism does not occur even when the return light from the disk 5 is reflected by the half mirror 10, a cylindrical lens or a knife lens is provided between the half mirror 10 and the bin photodiode 6 in order to obtain a focus error signal. It is necessary.

In the above embodiment, since the light from the semiconductor laser 1 is used in the transmission direction with respect to the half mirror 10, the surface accuracy of the semi-reflection surface 10a is improved compared to the conventional example shown in FIG. Can be done roughly.

Furthermore, as shown in FIG. 8, even if the optical axis La of the semiconductor laser I is arranged so as to be close to the motor M when the pickup P moves to a position close to the disk drive motor M, this The mounting space for the semiconductor laser 1 located on the optical axis La can be more generous than that for mounting the vinyl photodiode 6. That is, the semiconductor laser 1 is smaller than the vinyl photodiode 6, and the semiconductor laser 1 can be directly attached to the chassis of the pickup P without using the substrate 8 shown in FIG. Furthermore, the mounting and adjustment of the semiconductor laser 1 is easier than that of a vinyl photodiode. Therefore, a pickup configuration is possible in which the distance δ between the optical axis La and the motor M is set to the shortest value. Also, since the vinyl photodiode 6 is installed on the side, there is plenty of space for its installation.
Also, the position can be adjusted widely.

FIG. 3 shows a second embodiment of the invention.

In this embodiment as well, the arrangement is such that the laser light emitted from the semiconductor laser 1 is transmitted through the film-like half mirror 20.

In this embodiment, the film-like half mirror 20 is curved so as to cause astigmatism Δ in the returned light.

As shown in FIG. 5, the half mirror 20 is attached to the pickup while being held between rigid frame-shaped holders 21 and 22. As shown in FIG. Holding surfaces 21a of these holders 21 and 22
, 22a into curved surfaces, the half mirror 2
0 is held in a curved state. With this curved surface shape, as shown in FIG. 6, it becomes a curved surface in the a-axis direction and does not deform in the b-axis direction, and the light component in the a-axis direction is a half mirror.
20, and the light component in the b-axis direction is focused by a half mirror.
20 and is focused only by the objective lens 4. This difference in focusing distance causes astigmatism Δ.

Due to this astigmatism, a focus error signal can be obtained by the four-divided light receiving section of the bin photodiode 6.

Here, the curved surface of the half mirror 20 in the a-axis direction will be explained with reference to FIG. The curved surface in the a-axis direction is set so that its cross section becomes a hyperbola. In FIG. 7, if O-0 is the coordinate axis (X-axis), the light emitting point of the semiconductor laser 1 is located at the focal point F1, and the light receiving point of the bin photodiode 6 is located at the focal point F2. The hyperbola in this coordinate becomes the curved surface of the half mirror 20 in the a-axis direction.

When the return light of the diverging light emitted from the focal point F1 is reflected by a surface including a hyperbola, it is focused at the focal point F8. As shown in Fig. 7, the optical axis length from the light emitting point F1 to the reflecting surface is , and the optical axis length from the reflecting surface to the light receiving point F2 is , and the light component in the a-axis direction is However, the light component in the b-axis direction converges to an apparent focal point F+' located at a position Ll from the reflecting surface. Therefore, -L* becomes astigmatism Δ. In actual start-up, since the astigmatism Δ necessary for detecting the focus error signal is small, the amount of curvature of the film half mirror 20 in the a-axis direction is small.

In FIG. 3, the curved state of the half mirror 20 is a hyperbola because it is a finite system configuration that sends diffused light to the objective lens 4, but an infinite system that uses a collimating lens and sends a parallel beam to the objective lens 4. In the case of this structure, an elliptically curved half mirror 20 is placed in the parallel light beam. By changing the curvature in the a-axis direction and the b-axis direction in this half mirror, it is possible to produce astigmatism at the light receiving point of the bin photodiode 6.

FIG. 4 shows a third embodiment.

In this embodiment, a curved film-like half mirror 20
A lattice 20a is formed on the outer surface of the lattice 20a by means of vapor deposition, printing, or the like. That is, the diffraction grating 2 for forming three beams shown in FIG. 3 is integrated with a half mirror 20.

In the embodiments shown in FIGS. 3 and 4, since the semiconductor laser 1 is arranged in the transmission direction with respect to the half mirror 20, the light emitting optical axis La is aligned with the disk when placed inside the pickup, similar to the embodiment shown in FIG. The structure can be made close to the motor M (see FIG. 8), which is advantageous in terms of construction. Furthermore, since astigmatism is generated by the half mirror, a cylindrical lens or the like is not required. Further, since the half mirror 20 is in the form of a film, by forming the holding surfaces 21a and 22a of the holders 21 and 22 shown in FIG. 5 with high precision, a curved surface can be formed easily and accurately.

[Effect] As described above, according to the present invention, since the light emitting element is positioned in the transmission direction with respect to the half mirror, there is no need to form the reflective surface of the half mirror with high precision as in the conventional reflection method. . Also, when installing a half mirror, the position and angle of inclination are rougher than when using a mirror in the reflective direction.
As shown in the figure, the arrangement structure inside the pickup is also simplified, making it easier to downsize. Furthermore, since the film is inexpensive, the pickup can be manufactured at a lower cost than before.

In the invention according to claim 2, even without using a cylindrical lens or a knife lens for producing astigmatism,
A focus error signal can be obtained.

[Brief explanation of the drawing]

1 is a front view showing an optical device according to a first embodiment of the present invention, FIG. 2 is a perspective view showing an 11-hole structure of a film-like half mirror, and FIGS. 3 and 4 are a front view showing an optical device according to a first embodiment of the invention. FIG. 5 is a perspective view showing the mounting structure of the curved film-like half mirror, and FIGS. 6 and 7 are illustrations of the curved state of the half mirror. figure,
FIGS. 8 and 9 are plan views showing the state in which the optical devices according to the embodiment of the present invention and the conventional example are mounted on a pickup, and FIG. 10 is a front view showing the conventional optical device. l...Semiconductor laser, 2...Diffraction grating, 4...Objective lens, 5...Disk, 6...Bin photodiode 20...Film-like half mirror H-S ψ 8 Σ Ward

Claims (1)

[Claims] 1. An objective lens in which a film-like half mirror is arranged obliquely on the optical axis of light emitted from a light emitting element, and focuses light emitted from the light emitting element and transmitted through the half mirror onto a disk. An optical device 2 for an optical pickup characterized in that a light receiving element is arranged in a direction in which the return light from the disk is reflected by the half mirror, and the film-like half mirror has a light receiving element. Claim 1 wherein the returning light is curved into a shape that causes astigmatism.
Optical device of the optical pickup described