JPH06274925A - Beam separating optical element and optical pickup - Google Patents

Abstract

PURPOSE:To embody a new beam separating optical element capable of using as a beam deflecting element and a beam shaping optical element while embodying an ultraresolution effect with a simple structure and to embody an optical pickup using the beam separating optical element. CONSTITUTION:A reflecting film 10B whose boundary part is linear is formed on one part of one face of a transparent parallel plate 10A having a prescribed thickness, and a reflecting face 10C is formed on the other face. Also, the parallel plate 10A is arranged so as to be inclined at a prescribed angle against a laser beam flux L to be divided. Half the incident laser beam flux L is reflected on the reflecting film 10B on one face with the linear boundary part P as a boundary, and the other half of the laser beam flux made incident to the parallel plate 10A is made incident on the reflecting face 10C formed on the other face. Then, the laser flux is made to exit from the other face side, and divided into two parallel laser beam fluxes L2 and L3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam splitting optical element and an optical pickup.

[0002]

2. Description of the Related Art There are various optical pickups that focus a laser beam on a recording medium as a light spot to write information on the recording medium or reproduce information recorded on the recording medium. The system type is widely known.

In order to increase the recording density of the information written / reproduced by the optical pickup, it is intended to reduce the diameter of the light spot. As one of the methods, the "super-resolution effect" is used.
Has been proposed (US Pat. No. 5,025).
No. 438).

That is, a parallel laser beam is divided into two, and the two obtained beams are condensed at the same position by the same objective lens. At this time, if the phases of the laser light beams are aligned at the converging position (which is said to be phase-matched),
The formed light spot has a smaller spot diameter than that obtained when the laser light flux is not split and is condensed by the objective lens. This is called the super-resolution effect.

As a "beam separation optical element" which divides a laser beam into two in order to utilize the super-resolution effect, the one disclosed in the above-mentioned US Patent is known, but it does not cause a loss of light quantity. Since all of them are quite large, they are obstacles when compacting the optical pickup, and since the beams are separated by using refraction, extremely high precision is required for the element.

A semiconductor laser generally used as a light source in an optical pickup has an elliptical far-field pattern of a laser beam emitted from it. Therefore, if this laser beam is directly focused as a light spot, the light spot shape is also elliptical. Be in shape. The light spot shape is preferably “circular or elliptical close to a circle”. In order to obtain such a preferable light spot shape, a “beam shaping prism” is usually used for the optical pickup, and the light flux of the laser light flux is used by refraction. The beam is “beam-shaped” in cross section into a circular shape or an elliptical shape close to a circle.

Since the beam shaping prism bends the optical path of the laser beam by refraction, it is troublesome to adjust the position with other optical elements, and there are various problems such as occurrence of aberration due to refraction.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a simple structure and a novel structure which can be used as a beam deflecting element or a beam shaping optical element while realizing a super-resolution effect. An object of the present invention is to provide a beam splitting optical element and an optical pickup using this element.

[0009]

A beam splitting optical element according to claims 1 and 2 is an "optical element which splits a parallel laser beam into two beams in the vicinity of the optical axis of the beam to form two parallel beams. .

A beam separating optical element according to a first aspect of the present invention is "a reflecting film having a linear boundary is formed on a part of one surface of a transparent parallel plate having a predetermined thickness, and a reflecting surface is formed on the other surface. It is arranged at a predetermined angle with respect to the laser beam to be split, and half of the incident laser beam is reflected by the above-mentioned one-sided reflecting film with a linear boundary as a boundary, and is incident on a parallel plate. The other half of the laser light flux is reflected by the reflection surface formed on the other surface and emitted from the one surface side. "

A beam separating optical element according to claim 2 is
“The ridge of the right-angled prism is chamfered in parallel to the bottom surface at a predetermined distance from the bottom surface, and a reflection film is formed on the plane formed by the chamfer, and a reflection surface is formed on the bottom surface. On the other hand, a half of the incident laser light flux is reflected at a predetermined angle with respect to the linear boundary between the prism surface and the prismatic surface by the reflection film formed by the chamfering, and then the prism surface is introduced into the prism. The other half of the incident laser beam is reflected by the reflecting surface formed on the bottom surface and emitted from the other prism surface. "

A beam separating optical element according to a third aspect of the present invention is an "optical element which divides a parallel laser light beam into two parallel two light beams which are parallel to each other" and has a "predetermined thickness and parallel surfaces". A transparent plate having an exit surface inclined at 45 degrees with respect to the reflecting surface, and a right-angle prism having an inclined surface joined to the entrance surface are provided for splitting. Is arranged so that the desired laser beam is incident on the prism surface of the right-angled prism at right angles, the incident surface is formed on a half mirror surface, and the laser beam transmitted through the incident surface is reflected by the reflecting surface and the exit surface. To be ejected from. "

In the beam separating optical element according to any one of claims 1 to 3, the transparent parallel plate or the transparent plate has a "predetermined thickness", and the ridge portion of the prism has a "predetermined distance from the bottom surface". By the way, the chamfering and the fact that each beam separation optical element is tilted by a "predetermined angle" with respect to the laser light flux to be split means that these "thicknesses" and "angles" are It is meant to be set to be "phase matched".

In the beam splitting optical element according to any one of claims 1 to 3, the reflective film is a reflector having a film structure literally, and the "reflective surface" is the reflective film and all of the parallel plate, the transparent plate and the prism. Including a reflective surface.

The beam separating optical element according to claim 1, 2 or 3 can be used as a beam shaping optical element or a beam deflecting element. In the optical pickup described in claim 4, the beam separating optical element is used as a beam shaping optical element and / or a beam deflecting element. The “beam deflecting element” is an optical element for deflecting the parallel laser beam traveling direction by 90 degrees. For example, a separation type optical pickup (the light source section and the signal processing section are fixed, and the objective lens is moved in the tracking direction). The movable optical pickup) is used by being integrated with an objective lens.

[0016]

As described above, the beam separating optical element of the present invention has two reflecting surfaces (including a reflecting film, a total reflecting surface and a half mirror surface), and the reflecting surfaces are parallel to each other. Half of the parallel laser light flux is reflected by one reflection surface, and the other half is reflected by the other reflection surface.

[0017]

FIG. 1 shows an embodiment of the beam splitting optical element according to the first aspect. The beam separation optical element 10 is used as a beam deflection element in the above-mentioned "separation type optical pickup".

The beam separating optical element 10 has a reflecting film 10 on one surface of a transparent parallel plate 10A having a predetermined thickness.
B, a reflection film 10C is formed on the other surface, and the reflection film 10C is arranged at a predetermined angle, that is, 45 degrees with respect to the traveling direction of the parallel laser beam L to be divided. The portion of the reflection film 10B indicated by the symbol P is the "boundary portion" of the reflection film 10B, which is linear in the direction orthogonal to the drawing.

When the laser light flux L is made incident on the beam separation optical element 10 so that its optical axis (light flux center line) coincides with the boundary P, the lower half of the laser light flux L is linearly formed by the reflecting film 10B. Is reflected at the boundary P of the boundary. The other half of the laser light flux enters the parallel plate 10A and is reflected by the reflection film 10C formed on the other surface, and the reflection surface 10 on the side where the reflection surface 10B is formed.
It is injected from the part where B is not formed.

In this way, the two pieces separated in parallel to each other are
Two parallel laser beams L2 and L3 are obtained. A light spot is obtained by condensing these with the objective lens 100. When the laser light fluxes L2 and L3 are phase-matched at the condensing portion of the laser light fluxes L2 and L3, "the laser light flux L is directly reflected by the objective lens 100" due to the super-resolution effect.
The light spot having a smaller spot diameter can be obtained than the light spot obtained by condensing the light spot.

To achieve phase matching, a parallel plate 10A is used.
According to the refractive index of the two separated laser beams L2,
The thickness of the parallel plate 10A may be set so that the optical path difference of L3 is an integral multiple of the wavelength of the laser light.

The reflective film 10C may be formed only on a necessary portion or on one whole surface of the parallel plate. If the parallel plate 10A is made of a material having a large refractive index, the other surface can be used as a reflecting surface and total reflection can be used instead of providing the reflecting film 10C.

FIG. 2 shows an embodiment of the beam separating optical element according to the present invention. The beam separation optical element 20 is used as a beam deflection element in the above-mentioned "separation type optical pickup".

The main body 20A of the beam splitting optical element 20 is one in which the ridge of the rectangular prism is chamfered parallel to the bottom surface at a predetermined distance from the bottom surface. A reflection film 20B is formed on the flat surface formed by chamfering, and a reflection film 20C is formed on the bottom surface.

The beam splitting optical element 20 is composed of the reflection film 2 described above.
0B and 20C are arranged so as to be inclined by 45 degrees with respect to the incident parallel laser light flux L. When the laser light flux L is made incident on the beam separation optical element 20 so that its optical axis "matches with the boundary portion between the reflection film 20B and the prism surface 20a", half of the laser light flux L is formed by the reflection film 20B on the prism surface. The light is reflected at the straight boundary with 20a. The other half of the laser light flux that has entered the prism 20A (main body) from the prism surface 20a is reflected by the reflection film 20C formed on the bottom surface and exits from the other prism surface 20b.

[0026] In this way, the two separated
Two parallel laser beams L2 and L3 are obtained. A light spot is obtained by condensing these with the objective lens 100. In the condensing part of the laser light beams L2 and L3,
When the laser light fluxes L2 and L3 are phase-matched, the laser light flux L is directly reflected by the objective lens 10 due to the super-resolution effect.
It is possible to obtain a light spot having a smaller spot diameter than the “light spot obtained by converging at 0”.

To achieve the phase matching, the prism 20A is used.
According to the refractive index of the two separated laser beams L2,
The distance between the reflection films 20B and 20C, that is, the prism 20A, so that the optical path difference of L3 is an integral multiple of the wavelength of the laser light.
The distance between the bottom surface and the plane formed by chamfering may be set.

If a material having a large refractive index is used as the prism 20A, the bottom surface itself can be used as a reflecting surface instead of providing the reflecting film 20C, and reflection can be performed by total reflection of the bottom surface. When the reflection film 20C is provided on the bottom surface, the reflection film 2 is formed by the prism 20A and the rectangular prism 22 shown by a broken line.
The reflective film 20C may be protected by sandwiching 0C.

FIG. 3 shows an embodiment of the beam separating optical element according to the present invention. The beam separation optical element 30 is used as a beam deflection element in the above-mentioned "separation type optical pickup".

The beam separating optical element 30 is formed by joining a transparent plate 31 and a rectangular prism 32, and the joining surface is formed as a half mirror surface HF. The transparent plate 31 has a predetermined thickness and is formed with one of parallel surfaces as an incident surface and the other as a reflecting surface 31b, and has an exit surface 31a inclined by 45 degrees with respect to the reflecting surface 31b. The oblique surface of the right-angled prism 32 is joined to the incident surface of the transparent plate 31, and the parallel laser light flux L to be split is a prism surface 32 a of the right-angled prism 32.
It is arranged so as to be incident at a right angle to.

When the laser light flux L is incident from the prism surface 32a as described above, a part of the laser light flux is reflected by the half mirror surface HF and emitted from the prism surface 32b as a parallel laser light flux L3. The component transmitted through the half mirror surface HF is totally reflected by the reflecting surface 31b of the transparent plate 31 and emitted as a parallel laser beam L2 from the emitting surface 31a.

In this way, the two parts separated in parallel with each other are
Two parallel laser beams L2 and L3 are obtained. A light spot is obtained by condensing these with the objective lens 100. When the laser light fluxes L2 and L3 are phase-matched at the condensing portion of the laser light fluxes L2 and L3, "the laser light flux L is directly reflected by the objective lens 100" due to the super-resolution effect.
The light spot having a smaller spot diameter can be obtained than the light spot obtained by condensing the light spot.

In order to realize phase matching, the transparent plate 31 and the prism 32 are transparent so that the optical path difference between the two separated laser beams L2 and L3 is an integral multiple of the wavelength of the laser beam. The thickness of the plate 31 may be set.

In this example, the reflection by the reflecting surface 31b of the transparent plate 31 uses total reflection, but a reflecting film may be formed on this surface, and in this case, the transparent plate 31 and the right angle shown by a broken line. The prism 33 may sandwich the reflection film to protect the reflection film.

FIG. 4 schematically shows an optical pickup using the beam separating optical element 10 of the type shown in FIG. 1 as a beam shaping optical element. Since the optical pickup itself is already well known, the structure is conceptually drawn.

The laser light beam from the semiconductor laser 1 is collimated by the collimator lens 3, enters the beam splitter 7 through the beam splitting optical element 10 and the deflecting prism 5, and passes through the beam splitter 7, and is recorded by the objective lens 9. It is condensed as a light spot on the recording surface 13 of the medium. The reflected light from the recording surface 13 is the objective lens 9
The component reflected by the beam splitter 7 is guided to the optical sensor 17 by the condenser lens 15 via the beam splitter 7.

The beam splitting optical element 10 is used as a beam shaping optical element. The beam cross section of the parallel laser beam emitted from the collimator lens 3 has an elliptical shape at the position indicated by reference numeral A in the figure, but the beam separation optical element 10
After being separated by, the elliptical shape at the position A is divided into two in the minor axis direction at a position near the optical axis, as in the position B, and becomes a shape close to a circular shape as a whole.

Therefore, a light spot close to a circle is obtained on the recording surface 13. The beam separation optical element 10 is configured so that the two separated light beams are in a phase-matched state, and therefore the spot diameter of the light spot becomes extremely small due to the super-resolution effect.

FIG. 5 schematically shows a modification of the optical pickup shown in FIG.

The laser light flux from the semiconductor laser 1 is collimated by the collimator lens 3, enters the beam splitter 7, passes through the beam splitter 7, and is split into two beams while being reflected by the beam splitting optical element 10 and the objective lens. The light is focused as a light spot on the recording surface 13 of the recording medium by 9. The reflected light from the recording surface 13 returns to the beam splitter 7 via the objective lens 9 and the beam splitting optical element 10, and the component reflected by the beam splitter 7 is passed through the condensing lens 15 to the optical sensor 17.
Be led to.

The beam separating optical element 10 is used as a "beam shaping optical element and a beam deflecting element". The beam cross section of the parallel laser beam emitted from the collimator lens 3 is elliptical at the position indicated by reference numeral C in the drawing and has a light beam diameter D ₁ in the vertical direction of the drawing.
After being separated by, for example, at position D, the elliptical shape at position C is divided into two in the minor axis direction at a position near the optical axis,
The overall shape is close to a circle, and the luminous flux diameter is D ₂ (>
D ₁ ).

Therefore, the recording surface 13 is the same as in the embodiment of FIG.
A light spot close to a circle is obtained above. Of course, the beam separation optical element 10 is constructed so that the two separated light beams are in a phase-matched state, and therefore the spot diameter of the light spot becomes extremely small due to the super-resolution effect.

In the embodiment of FIG. 5, the beam separating optical element 1 is used.
0 is provided immediately before the objective lens 9, and the optical path portion from the semiconductor laser 1 to the beam separation optical element 10 has a flat luminous flux shape with the vertical direction in the drawing as the minor axis direction. From beam separation optical element 10
The size of the optical element on the optical path leading to the above can be reduced in the vertical direction in the drawing in accordance with the flatness of the light flux, so that the optical pickup can be made thin. Of course, the optical pickup of FIG. 5 can be configured as the above-described separation type optical pickup by making the objective lens 9 and the beam separation optical element 10 integrally movable and fixing the other parts.

[0044]

As described above, according to the present invention, a novel beam separation optical element and optical pickup can be provided. Since the beam separation optical element of the present invention separates the light beams by the reflection surfaces parallel to each other as described above, it is possible to easily realize the separation accuracy required for the phase matching for realizing the super-resolution effect, and the configuration is also Since it is simple, it can be realized at a small size and at low cost. Therefore, an optical pickup using these as a beam deflecting element or a beam shaping optical element can realize a small-sized light spot with a super-resolution effect at a small size and low cost.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of a beam splitting optical element according to claim 1;

FIG. 2 is a diagram for explaining one embodiment of the beam separation optical element according to claim 2;

FIG. 3 is a diagram for explaining one embodiment of the beam separation optical element according to claim 3;

FIG. 4 is a diagram for explaining one embodiment of the optical pickup according to claim 4;

FIG. 5 is a diagram for explaining a modified embodiment of the optical pickup according to claim 4;

[Explanation of symbols]

 10 Beam Separation Optical Element 10A Transparent Parallel Plate 10B Reflective Film 10C Reflective Film that constitutes a reflective surface. L parallel laser beam L2, L3 split laser beam

Claims (4)

[Claims] Claim: What is claimed is: 1. An optical element for splitting a parallel laser light beam into two parallel light beams in the vicinity of the light beam optical axis, wherein the parallel laser light beam has a predetermined thickness and a boundary on a part of one side of a transparent parallel plate. It has a linear reflection film on its other side and a reflecting surface on the other side, and it is arranged at a predetermined angle with respect to the laser beam to be split. Half of the incident laser beam is reflected on one side. The film is reflected at a linear boundary, and the other half of the laser light flux that has entered the parallel plate is reflected by the reflecting surface formed on the other surface so that it is emitted from the one surface side. Configured beam separation optics. 2. An optical element for splitting a parallel laser light beam into two parallel light beams in the vicinity of the light beam optical axis, wherein the ridge line portion of a right-angle prism is formed on the bottom surface at a predetermined distance from the bottom surface. Chamfered in parallel, a reflective film is formed on the flat surface formed by chamfering, a reflective surface is formed on the bottom surface, and it is arranged at a predetermined angle with respect to the laser beam to be split, and half of the incident laser beam is The reflection surface of the other half that is reflected by the flat reflection film formed by the chamfering at the boundary of the straight line with the prism surface as a boundary, and the other half of the laser light flux that has entered the prism from the prism surface is formed on the bottom surface. A beam separation optical element configured to be reflected by the other prism surface and emitted from the other prism surface. 3. An optical element for splitting a parallel laser beam into two parallel two beams which are parallel to each other and have a predetermined thickness, and one of the mutually parallel surfaces is an incident surface and the other is a reflecting surface. A transparent plate having an exit surface inclined by 45 degrees with respect to the reflecting surface and a right-angled prism having an inclined surface joined to the entrance surface are provided, and a laser beam to be split is formed on the prism surface of the right-angled prism. Beam separation optics arranged so as to be incident at right angles, and configured such that the incident surface is formed on a half mirror surface, and the laser light flux transmitted through the incident surface is reflected by the reflecting surface and emitted from the emitting surface. element. 4. An optical pickup using the beam splitting optical element according to claim 1, 2 or 3 as a beam shaping optical element and / or a beam deflecting element.