JP2933396B2 - Polarization separation optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization splitting optical system for splitting a light beam incident from one side into a P-polarized component and an S-polarized component, and more particularly, to an optical system capable of adjusting the light amount balance between both polarized lights. About.

[0002]

2. Description of the Related Art A polarization separation optical system of this type is used as an optical system for reproducing a signal in a head of a magneto-optical disk device, for example. The magneto-optical disk device separates the linearly polarized light reflected by the disk into a P-polarized component and an S-polarized component,
By detecting the difference between the two light amounts, the rotation of the polarization plane due to the magnetic Kerr effect is detected, and a signal recorded on the disk as an array of magnetization directions is reproduced.

The rotation of the plane of polarization due to the magnetic Kerr effect is 0.5
Since it is a very small value of about ゜, the change in the light amount difference is small, and in order to accurately detect the difference, it is important to adjust the balance of the detection system. Conventionally, the balance has been adjusted by electrically adjusting the output signal from the light receiving element that receives each polarized light component.

[0004]

However, when a signal is electrically balanced as in the prior art,
There is a problem that the circuit becomes complicated.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and is intended to adjust the balance of the amount of light reaching a light receiving element by optical means without providing an electric adjusting means. It is an object of the present invention to provide a polarization separation optical system capable of performing the above-mentioned.

[0006]

In order to achieve the above object, a polarization beam splitting optical system according to the present invention converts incident light to P light.
A polarized light separating unit that separates the polarized light component into an S polarized light component and emits the light with a predetermined angle difference, and is set near a critical angle of a light beam emitted from the polarized light separating unit and reflects at least one polarized light component. A reflecting surface to be adjusted, and a light amount balance adjusting means for adjusting the balance between the amounts of the two polarized lights by adjusting at least one of the amounts of the polarized light components by changing the angle of the reflecting surface. Features.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment in which the polarization separation optical system of the present invention is used in a recording signal reproducing system of a magneto-optical disk.

As shown in FIG. 1A, a divergent light beam emitted from a semiconductor laser 10 is converted into a parallel light beam by a collimator lens 11, and the two half mirror surfaces 31, 32 are provided.
To the composite prism 30 having Composite prism 3
The luminous flux incident on the laser beam 0 is shaped in a cross section, a part of the luminous flux is reflected by the second half mirror surface 32, and is collected by the condenser lens 33 on the light receiving element 40 for automatic output adjustment of the semiconductor laser. Light. The light beam emitted from the composite prism is reflected by the mirror 20 in a direction perpendicular to the plane of FIG. 1A, and the objective lens 21 is turned on as shown in FIG.
Converges on the magneto-optical disk MOD via The objective lens 21 and the mirror 20 are provided in a head (not shown) that slides in the radial direction of the magneto-optical disk MOD. The objective lens 21 is provided on an actuator provided in the head, and is driven in the optical axis direction.

The light beam reflected by the disk MOD enters the composite prism 30 again and is separated by the first and second half mirror surfaces 31 and 32. The light beam reflected by the first half mirror surface 31 is reflected again by the routine prism 41 and is condensed on a servo sensor 44 for detecting an error signal via a condenser lens 42 and a cylindrical lens 43.

The servo sensor 44 has a light receiving area divided into four in the shape of a "field" and calculates the output of each area to obtain a focus error signal by the astigmatism method and a push-pull method. And a tracking error signal.

The light beam reflected by the second half mirror surface 32 has its polarization direction rotated by 45 ° by the λ / 2 plate 34, and enters the polarization splitting prism 50. On a slope 50a of the polarization separation prism 50, a multilayer film for polarization separation is coated, and a wedge prism 51 is attached. The P-polarized light component of the light beam incident on the polarization splitting prism passes through the slope 50a and is reflected by the wedge prism 51, and the S-polarized light component is reflected by the slope 50a. Both polarization components exit the polarization splitting prism 50 with an angle difference corresponding to the apex angle of the wedge prism 51, enter the adjusting prism 53 via the condenser lens 52, are deflected by approximately 45 ° by the adjusting prism 53, and Guided on 54.

A portion including the adjustment prism 53 and the data sensor 54 surrounded by a broken line in the drawing is provided so as to be integrally rotatable about an axis perpendicular to a plane (equivalent to a paper surface) containing both light beams. I have.

As shown in FIG. 1C, the data sensor 54 has a first light receiving region 54a for receiving the S-polarized light component and a second light receiving region 54b for receiving the P-polarized light component. . Since the polarization direction of the laser beam incident on the magneto-optical disk MOD is rotated by the magnetic Kerr effect in accordance with the magnetization direction of the disk at the position where the spot is imaged, it is rotated by 45 ° to obtain P, S. The recording signal can be read out from the difference in intensity by separating the light into components and detecting the light in separate light receiving regions.

By providing an angle difference between the two polarized light components using a wedge prism, the light receiving area can be made closer as compared with the case of using a cube-type polarized beam splitter. Thus, two light receiving areas can be provided on the same substrate. Therefore, the arrangement space can be reduced as compared with the case where a separate light receiving element is provided.

The adjusting prism 53 is, as shown in FIG.
Initially, the minimum incident angle θs of the S-polarized light on the inclined surface is set to be substantially equal to the critical angle, and the minimum incident angle θp of the P-polarized light to the inclined surface is set to be larger than the critical angle. When convergent light is incident on the adjusting prism, the incident angle with respect to the slope is different even within the same polarization component. Therefore, initially, the minimum incident angle is set so that the S polarization component also satisfies the condition of total reflection. It is set to be substantially equal to the critical angle. If the adjustment prism 53 is rotated in the direction of arrow A within a range not smaller than the critical angle, the reflection intensity of P-polarized light is not changed and S
The intensity of polarized light can be changed, and the intensity balance of both polarized light components can be adjusted. Since the adjustment is performed in the direction of decreasing the S-polarized light component, the λ / 2 plate 33 is adjusted.
Is previously attached to the compound prism 30 in the axial direction such that the intensity of the S-polarized component is slightly increased. The intensity of the polarization component may be adjusted by rotating only the adjustment prism.

Assuming that the refractive index of the adjusting prism 53 is 1.5 and the refractive index of air is 1, the relationship between the incident angle θ with respect to the inclined surface of the adjusting prism and the reflection intensities Rs and Rp of the respective polarization components is as shown in FIG. Becomes The S polarization component is adjusted by increasing or decreasing the S polarization component because the change of the reflection intensity with respect to the angle change near the critical angle is smaller in the S polarization component, and the adjustment is easier.

FIG. 4 shows an optical path when the converging lens attached to the polarization splitting prism is removed from the optical system shown in FIG. In this case, it is necessary to provide a condenser lens between the adjustment prism 53 and a data sensor (not shown).

Next, an example of a polarization separation optical system using a cube-type polarization beam splitter will be described. FIGS. 5A and 5B show an example in which convergent light is made incident on the re-polarization beam splitter 61 by the condenser lens 60.
(A) shows an example in which the intensity of the P-polarized light component is adjusted by rotating the adjustment prism 61, and (B) shows an example in which the intensity of the S-polarized light component is adjusted.

FIGS. 6A and 6B show an example in which a light beam is converged by condensing lenses 60, 60 after exiting a polarizing beam splitter 61 and an adjusting prism 62. FIG. An example in which the intensity of the P-polarized light component is adjusted by the rotation of 62, and (B) shows an example in which the intensity of the S-polarized light component is adjusted.

When a cube-type polarization beam splitter is used, the convergence points of the respective polarization components are farther apart than when a wedge prism is used, so that light must be received by two independent sensors.

[0021]

As described above, according to the polarized light separating optical system of the present invention, the light amount balance of each of the separated polarized light components can be adjusted by a simple means of adjusting the angle of the adjusting prism. Can be avoided.

[Brief description of the drawings]

FIG. 1 shows an optical system of a magneto-optical disk device including a polarization separation optical system according to the present invention, wherein (A)
Is a plan view, (B) is a side view of the objective lens portion, and (C) is a plan view of the sensor.

FIG. 2 is an enlarged view of a polarization splitting prism and an adjustment prism of FIG.

FIG. 3 is a graph showing a relationship between an incident angle and a reflection intensity.

FIG. 4 is an enlarged view similar to FIG. 2 when a parallel light beam is incident on a prism for polarization.

5A and 5B are explanatory diagrams of an optical system in a case where convergent light is incident on a cube-type polarization splitting prism. FIG. 5A illustrates an example in which the intensity of a P-polarized component is adjusted, and FIG. The example which adjusts is shown.

6A and 6B are explanatory diagrams of an optical system in a case where parallel light is incident on a cube-type polarization splitting prism. FIG. 6A is an example in which the intensity of a P-polarized component is adjusted, and FIG. The example which adjusts is shown.

[Explanation of symbols]

 Reference Signs List 10 semiconductor laser 50 polarization separation prism 51 wedge prism 53 adjustment prism 54 data sensor

Claims (3)

(57) [Claims] 1. A polarized light separating means for separating incident light into a P-polarized light component and an S-polarized light component and emitting the light with a predetermined angle difference, and near a critical angle of a light beam emitted from the polarized light separating means. Set, a reflecting surface that reflects at least one polarization component, by changing the angle of the reflecting surface,
A polarization separation optical system comprising: a light amount balance adjusting unit that adjusts at least one of the amounts of the polarized light components and adjusts the balance between the amounts of the two polarized lights. 2. The polarization splitting optical system according to claim 1, wherein said polarization splitting means comprises a polarization splitting surface and a wedge prism joined to the polarization splitting surface. 3. The polarization separation optical system according to claim 1, wherein said light amount balance adjusting means adjusts an S-polarized light component.