JPH0444003A - Optical device for optical pickup - Google Patents

Abstract

PURPOSE:To eliminate the malfunction of APC and the generation of back-talk noise due to return light detection by arranging an optical branching element, formed by sandwiching a polarizing film between flat plate type transparent plates, slantingly to the optical axis of a light emitting and a light receiving element. CONSTITUTION:The two both-side flat glass plates 11 between which the optical branching element 10 is sandwiched are equal in refractive index, so the element 10 can be arranged at 45 deg. to the optical axes La and Lb extending to the semiconductor laser 1 and pin photodiode 9 for collimated light. Then when the light emitted by the semiconductor laser 1 is used in the direction of a P- polarized light wave, the polarizing film 12 transmits about 80% of the light and reflects 20% of the light, and this reflected light passes through the flat plate glass 11 arranged at 45 deg. and is reflected in a direction irrelevant to the optical axis La of the semiconductor laser 1. Consequently, the generation of the back-talk noise due to the return of the reflected light to the semiconductor laser 1 is eliminated and the malfunction of the APC by a monitor element in the semiconductor laser 1 can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical pickup used in a magneto-optical disk device, etc., and in particular, to prevent backtalk noise caused by detection light returning to a light emitting element. The present invention relates to a protected optical device.

[Prior Art] FIG. 4 shows an optical device of a conventional optical pickup for a magneto-optical disk device.

The laser beam output from the semiconductor laser 1 is converted into a parallel beam by a collimating lens 2, passes through a cubic-quib beam splitter 3, and is focused on the recording surface of a disk 5 by an objective lens 4, thereby forming a minute spot.

In this conventional example, since the laser beam output from the semiconductor laser 1 is configured to pass through the beam splitter 3, the linearly polarized wave emitted from the semiconductor laser 1 is
It is used as a polarized light wave. When used as P-polarized light, about 80% of the light is transmitted and about 20% is reflected by the polarizing film 3a of the beam splitter 3. disk 5
The return light reflected from the recording surface of the beam splitter 3
is reflected by the polarizing film 3a of the Oraston prism 6.
The light passes through, is condensed by a condenser lens 7, passes through a cylindrical lens 8, and is received by a bin photodiode 9.

The above-mentioned Oraston prism 6 allows the return light from the disk 5 to be converted to P polarized light L+, S polarized light L2, and leaked light L.
The leakage light L3 is used to obtain error signals such as focusing.

[Problem to be solved by the invention]

FIG. 5 shows an enlarged view of the collimating lens 2 and the beam splitter 3 in the conventional example. Since the cubic type beam splitter 3 has surfaces (a), (b), (c), and (d) that are perpendicular or parallel to the optical axis, reflection of light on these surfaces becomes a problem. . That is, a portion of the laser light output from the semiconductor laser 1 is reflected toward the semiconductor laser 1 at the (a) plane. Further, other light passes through the polarizing film 3a, is reflected on the (c) plane, and a part of it passes through the (a) plane and returns to the semiconductor laser 1. Furthermore, the light that passes through the (a) plane, is reflected to the left by the polarizing film 3a, is also reflected by the (a) plane, and is further reflected by the polarizing film 3a, and then returns to the direction of the semiconductor laser 1. Since there is light returning to the semiconductor laser 1 side in this way, this returning light is detected by the monitoring light receiving element provided in the semiconductor laser 1, causing a malfunction of the APC that controls the output of the semiconductor laser 1. Furthermore, the light that returns to the light emitting section of the semiconductor laser causes backtalk noise.

Further, since the laser light emitted from the semiconductor laser 1 is reflected by each surface of the beam splitter and goes directly to the bin photodiode 9, this causes an offset such as focus error detection.

Further, in order to prevent reflection on each surface of the beam splitter 3, each surface may be inclined by approximately ±1° with respect to a surface perpendicular to or parallel to the optical axis. However, it is very difficult to create a beam splitter 3 in which each surface is inclined by a minute angle, and mass production is poor.

The present invention is intended to solve the above-mentioned conventional problems, and it is an object of the present invention to provide an optical device for an optical pickup that can prevent detection light emitted from a light emitting element from going directly toward the light emitting element or the light receiving element. The purpose is

[Means to solve the problem]

The present invention provides a light-emitting element and a light-receiving element located on different optical axes, an objective lens that focuses detection light from the light-emitting element onto a recording surface of a disk, and a light-emitting element and a light-receiving element that are located on different optical axes. In the optical device, the light branching element is provided with a light branching element that transmits or reflects light in the direction of the light receiving element and reflects or transmits return light from the disk in the direction of the light receiving element. It is characterized in that a polarizing film is interposed between the transparent plates.

[Effect]

In the above means, since a light branching element configured in a flat plate shape is used, the light emitted from the light emitting element is reflected by surfaces such as (A) and C), as in the conventional example shown in FIG. Therefore, backtalk noise and offset problems do not occur. Further, in this light branching element, since the polarizing film is interposed between the flat transparent plates, the polarizing film can be arranged at an angle of approximately 45° with respect to the light emitting element and the light receiving element.

〔Example〕

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

FIG. 1 is a front view showing the element configuration of an optical device for an optical pickup according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 is a semiconductor laser, 2 is a collimating lens, 4 is an objective lens, 5 is a disk, 6 is an Oraston prism, 7 is a condenser lens, 8 is a cylindrical lens, and 9 is a bin photodiode.

Reference numeral 10 is a light branching element. This element IO is a flat beam splitter. As shown enlarged in FIG. 2, this light branching element has a polarizing film 12 between two flat glasses 11
It is constructed by sandwiching the Although the two flat glasses 11 are made of the same material, their thicknesses t1t2 do not necessarily have to be the same. As the light transmission path is shown in FIG. 2, in a light branching element in which a polarizing film 12 is sandwiched between two flat glasses 11, the layers on both sides of the polarizing film 12 have the same refractive index. Therefore, for collimated light, the optical axes La and Lb extending in the direction of the semiconductor laser 1 and the bin photodiode 9 are
Can be placed at an angle of 5°. In other words, the conventionally used flat plate beam splitter has a polarizing film formed on the surface of a single flat glass plate, and the refractive index on both sides of the polarizing film is different, so there is a strong angular dependence. It was impossible to do so, and it was necessary to set an incident angle of about 60 to 70 degrees. On the other hand, the optical branching element IO according to the above embodiment allows incidence and reflection at 45°.

In the embodiment shown in FIG. 1, the light emitted from the semiconductor laser 1 is used in a P-polarized wave direction. That is, the laser beam emitted from the semiconductor laser 1 is used with its plane of polarization oriented in a direction perpendicular to the meridian plane (direction along the plane of the paper in FIG. 1). When used as a P-polarized wave,
About 80% of the light is transmitted through the polarizing film 12 and about 20% is reflected. However, this approximately 20% of reflected light is 45
The light passes through the flat glass 11 disposed at an angle of 1.degree. and is reflected in a direction unrelated to the optical axis La of the semiconductor laser 1. Therefore, the problem of this reflected light returning to the semiconductor laser 1 and generating backtalk noise does not occur.Therefore, there is no malfunction of the 8PC caused by the monitor light receiving element in the semiconductor laser 1. The laser light emitted from the laser 1 is not reflected toward the bin photodiode 9, and there is no problem of offset such as a focus error signal.

A laser beam emitted from a semiconductor laser 1 is collimated by a collimating lens 2, passes through a light branching element 10, and is condensed by an objective lens 4 to form a minute spot on a disk 5. The reflected light is reflected by the polarizing film 12 at 90°
reflected in the ° direction. Then, the Oraston prism 6 converts the light into P-polarized light waves, S-polarized light waves L2, and leakage light L3, which are received by the pin photodiode 9.

FIG. 3 is a perspective view showing the structure of an optical device according to a second embodiment of the present invention.

In this embodiment as well, the optical branching element 10 is arranged at an angle of 45'' with respect to the light emission side optical axis La of the semiconductor laser 1 and the light reception side optical axis Lb of the bin photodiode 9. In this embodiment, The laser beam emitted from the semiconductor laser 1 is used as an S-polarized wave. That is, the direction of the polarization plane of the laser beam is the meridian direction (vertical plane direction including La). In this case, the polarizing film 12 Approximately 8
0% is reflected light and about 20% is transmitted light.

Therefore, the light reflected by the polarizing film 12 is sent in the -C direction. Reference numeral 21 is a reflecting plate of a galvano mirror.

A total reflection prism 22 and an objective lens 23 held in the pickup movable section are provided in the direction of reflection by the reflection plate 21. Since the movable part of the pickup moves in the radial direction of the disk, the prism 22 and objective lens 23 move in the direction of reflection of the reflection plate 21, as shown by solid lines and broken lines in FIG. . Galvano mirror
The reflecting plate 21 is swung in the α direction in FIG. 3, thereby swinging the optical axis and performing tracking correction.

Also in the embodiment shown in FIG. 3, the optical branching element 10 has an optical axis La
Since the semiconductor laser 1 is disposed at an angle of 45° to the semiconductor laser 1, the light emitted from the semiconductor laser 1 is not returned in the direction of the semiconductor laser 1. Further, the light emitted from the semiconductor laser 1 is not directly reflected toward the focus photodiode 9.

[Effect] As described above, according to the present invention, since a light branching element in which a polarizing film is sandwiched between flat transparent plates is used, this element is placed obliquely to the optical axes of the light emitting element and the light receiving element. , the light from the light emitting element will not be reflected in the return direction and detected by the monitor light receiving element, and backtalk noise will not occur.

In addition, since both sides of the polarizing film are flat transparent plates with the same refractive index, this light branching element is connected to the light emitting element and the light receiving element by 45 cm.
It can be placed at 100 degrees, improving placement efficiency and making the placement space more efficient.

[Brief explanation of drawings]

FIG. 1 is a front view showing the element configuration of an optical device of an optical pickup according to a first embodiment of the present invention, FIG. 2 is an enlarged front view of an optical branching element, and FIG. 3 is an element of an optical pickup according to a second embodiment of the present invention. FIG. 4 is a front view showing the element structure of an optical device of a conventional optical pickup, and FIG. 5 is a front view showing the beam splitter and collimating lens in FIG. 4. 1... Semiconductor laser, 2... Collimator lens, 6
... Oraston prism, 7... Condensing lens, 9
... Bin photodiode, 10 ... Optical branching element, 1
DESCRIPTION OF SYMBOLS 1...Flat glass, 12...Polarizing film, 23...Objective lens.

Claims (1)

[Claims] 1. A light emitting element and a light receiving element located on different optical axes, an objective lens that focuses the detection light from the light emitting element onto the recording surface of the disk, and a direction of the detection light from the light emitting element toward the objective lens. In an optical device, the light branching element is provided with a light branching element that transmits or reflects light and reflects or transmits return light from the disk in the direction of the light receiving element. An optical device for an optical pickup, characterized in that a polarizing film is interposed between plates.