JPH04232915A - Beam shaping element - Google Patents

Abstract

PURPOSE:To offer a beam shaping element which can be made in a small size at low cost and can be easily used without a complicated procedure for positioning. CONSTITUTION:A thin film 13 comprising a dielectric material or metal having dependency opn angle is provided. By making a beam to be shaped enter this thin film 13, the beam is shaped into a desired cross section.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam shaping element used for shaping a beam from a semiconductor laser, for example.

0002

2. Description of the Related Art For example, as shown in FIG.
The light has an elliptical cross-section with a short axis in the direction parallel to (x direction) and a long axis in the thickness direction (y direction) of the active layer 2, and is linearly polarized light parallel to the x direction. Further, assuming that the center ray of the beam orthogonal to the x and y directions is in the z direction, the light amount distribution in the z-x section and the z-y section is as shown in FIG. As a beam shaping element for shaping such a beam having an elliptical cross section into a beam having a substantially circular cross section, a beam shaping element as shown in FIG. 11 has been proposed. This beam shaping element 3 is designed to shape the beam from the semiconductor laser 1 into a substantially circular cross-sectional shape by transmitting the beam. It is constructed by providing a thin film 5 as shown in FIG. The thin film 5 has a constant transmittance with respect to the incident angle in the x direction as shown in FIG. 13, and in the y direction, the incident angle increases as shown in FIG. 14 by blocking light from the center to the periphery. The structure is configured such that the transmittance decreases accordingly, thereby suppressing the intensity distribution and phase distribution due to Fresnel diffraction, and shaping the transmitted light into a beam with a substantially circular cross section and a light intensity distribution as shown in FIG. There is. A beam shaping element having such a light transmittance distribution is also disclosed in, for example, Japanese Patent Laid-Open No. 2-199423. In addition, as another conventional beam shaping element, Japanese Patent Application Laid-Open No. 2-220240 discloses that two right-angled isosceles triangular prisms having different refractive indexes are joined, and a beam from a semiconductor laser is refracted and transmitted through these two prisms. Accordingly, a beam has been proposed in which the beam is shaped into a substantially circular cross section.

0003

[Problem to be solved by the invention] However, FIG.
In the beam shaping element 3 shown in , it is difficult to control the film thickness in order to give the thin film 5 a light transmittance distribution, and in general, vacuum evaporation is performed on the surface of the parallel plate 4 opposite to the surface on which the thin film 5 is provided. However, since a mask or the like is used to provide a light transmittance distribution when forming the thin film 5, these anti-reflection films and the thin film 5 must be created in completely different processes. Therefore, there is a problem in that the cost is high. In addition, since the transmittance in the y direction is decreased from the center toward the periphery, alignment with the semiconductor laser 1 is required in actual use, making assembly and adjustment troublesome. Furthermore, the beam shaping element disclosed in Japanese Unexamined Patent Publication No. 2-220240 is constructed by joining two right-angled isosceles triangular prisms with different refractive indexes, so there is a problem that it is large and expensive. be. The present invention has been made in view of these conventional problems, and provides a beam shaping element that can be made small and inexpensive, and is suitably configured so that it can be easily used without requiring troublesome alignment. The purpose is to

0004

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a thin film made of a dielectric or metal having angular dependence is provided, and the beam is shaped into a predetermined cross-sectional shape by this thin film. .

[0005]

[Operation] That is, in this invention, the dielectric or metal thin film is made to have angular dependence on reflectance or transmittance,
By making the beam to be shaped incident on this thin film and causing it to be reflected or transmitted, the incident beam is shaped into a predetermined cross-sectional shape.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the present invention. In this embodiment, a beam from a semiconductor laser 1 is shaped by passing through a beam shaping element 11, and the beam shaping element 11 is a transparent parallel plate 12.
dielectric thin film 1 whose transmittance is angularly dependent on one surface of
3 to form a coating. When the parallel plate 12 is made of BK7, the dielectric thin film 13 is constructed by alternately laminating TiO2 with a high refractive index and MgF2 with a low refractive index, as shown in an enlarged cross-sectional view in FIG. 2, for example. , P-polarized light transmittance (Tp), and S-polarized light transmittance (Ts) are made to have angular dependence such that the transmittance decreases as the incident angle increases, as shown in FIGS. 3 and 4, for example. In addition,
In this embodiment, the angle dependence of Ts is made steeper than that of Tp.

In FIG. 1, a semiconductor laser 1 is arranged so that the polarization direction (x direction) of its emitted beam is within the plane of the paper and the center ray is perpendicularly incident on the beam shaping element 11, and the normal line between the incident light and the incident surface is If the in-plane direction including the P polarization direction is the P polarization direction, and the direction perpendicular thereto is the S polarization direction, then the light rays within the plane of the paper enter the beam shaping element 11 as P polarization, and the light rays in the direction perpendicular to the plane of the paper enter the S polarization direction. I will do it. here,
As shown in FIGS. 3 and 4, the dielectric thin film 13 of the beam shaping element 11 has an angle-dependent structure in which the transmittance of both P-polarized light and S-polarized light differs depending on the angle of incidence, and the transmittance decreases as the angle of incidence increases. Therefore, the beam emitted from the semiconductor laser 1 and having the elliptical light intensity distribution shown in FIG. 10 is transformed into a beam having an approximately circular light intensity distribution as shown in FIG. formatted into.

As described above, according to this embodiment, the beam shaping element 11 is formed by coating one surface of the transparent parallel plate 12 with the dielectric thin film 13 whose transmittance is angularly dependent. In addition to being able to make it smaller,
The dielectric thin film 13 can also be formed in the same process as a normal dielectric coating, and therefore can be made at low cost. Further, in actual use, since troublesome positioning is not required, it is easy to use, and since the element itself can be made small and inexpensive, the device itself that uses it can also be made small and inexpensive.

FIG. 5 shows a second embodiment of the invention. In this embodiment, a dielectric thin film 1 whose transmittance is angularly dependent is placed on the surface of a cover glass 16 of a semiconductor laser 15.
7 to form a cover glass 16 as a beam shaping element having the same structure as shown in FIG. By configuring the cover glass 16 of the semiconductor laser 15 as a beam shaping element in this way, it is possible to obtain emitted light from the semiconductor laser 15 with no variation in the divergence angle.

FIG. 6 shows a third embodiment of the invention. In this embodiment, the emitted light from the semiconductor laser 1 is
The incident surface of the beam splitter 21 is coated with a dielectric thin film 22 whose transmittance is angularly dependent, so that the beam splitter 21 also functions as a beam shaping element. Note that this dielectric thin film 22 is
The exit surface of the beam splitter 21 can also be coated.

FIG. 7 shows a fourth embodiment of the invention. In this embodiment, a dielectric thin film 26 whose transmittance is angularly dependent is coated on the back surface of a grating 25 for obtaining a plurality of beams from the light emitted from the semiconductor laser 1, and the grating 25 can also be used as a beam shaping element. It was made to work.

FIG. 8 shows an example of how the beam shaping element according to the present invention is used. This example is used in an optical pickup that records and/or reproduces information on an optical recording medium, and the light emitted from the semiconductor laser 1 is incident on a grating 25 having a beam shaping function shown in FIG. As a result, 0th-order light and ±1st-order diffracted light having a substantially circular cross section are obtained, and after these three beams are reflected by a parallel plate 31, they are focused onto an optical recording medium 33 by an objective lens 32. In addition, the three beams of reflected light from the optical recording medium 33 pass through the objective lens 32 and pass through the parallel plate 31, thereby causing astigmatism and detecting the photodetector 3.
4, an RF signal and a focus error signal based on the astigmatism method are detected in a known manner based on the received light output of the 0th-order light, and a tracking error signal is detected based on the received light output of the ±1st-order diffracted light. To detect. As described above, if the grating 25 having the beam shaping function according to the present invention is used in an optical pickup, the grating 25 itself can be made small and inexpensive, and it can be easily incorporated without troublesome alignment. , the optical pickup itself can be made smaller and cheaper.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be modified or changed in many ways. For example, in the above-described embodiments, a dielectric thin film is coated, but a similar structure may be formed by coating a metal thin film. Further, the angular dependence is not limited to the transmittance, but it is also possible to configure a reflective beam shaping element by giving the reflectance an angular dependence.

[0014]

As described above, according to the present invention, a thin film made of a dielectric or metal having angular dependence is provided,
Since the beam is thereby shaped into a predetermined cross-sectional shape, it is possible to obtain a beam shaping element that can be made small and inexpensive, and can be easily used without requiring troublesome alignment.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the invention.

FIG. 2 is an enlarged cross-sectional view showing the structure of an example of the dielectric thin film shown in FIG. 1;

FIG. 3 is a diagram showing the angular dependence of the P-polarized light transmittance of the dielectric thin film shown in FIG. 1;

4 is a diagram showing the angular dependence of the S-polarized light transmittance of the dielectric thin film also shown in FIG. 1. FIG.

FIG. 5 is a diagram showing a second embodiment of the invention.

FIG. 6 is a diagram similarly showing a third embodiment.

FIG. 7 is a diagram showing a fourth embodiment.

FIG. 8 is a diagram showing an example of how the beam shaping element according to the present invention is used.

FIG. 9 is a diagram showing a cross-sectional shape of light emitted from a semiconductor laser.

FIG. 10 is a diagram showing a light amount distribution of light emitted from a semiconductor laser.

FIG. 11 is a diagram showing an example of a conventional beam shaping element.

12 is a plan view showing the structure of the thin film shown in FIG. 11. FIG.

13 is a diagram showing the transmittance in the x direction of the thin film similarly shown in FIG. 11. FIG.

FIG. 14 is a diagram similarly showing the transmittance in the y direction.

15 is a diagram showing a light amount distribution after beam shaping by the beam shaping element also shown in FIG. 11. FIG.

[Explanation of symbols]

1 Semiconductor laser 11 Beam shaping element 12 Parallel plate 13 Dielectric thin film 15 Semiconductor laser 16 Cover glass 17 Dielectric thin film 21 Beam splitter 22 Dielectric thin film 25 Grating 26 Dielectric thin film 31 Parallel plate 32 Objective lens 33 Optical recording medium 34 Photodetector

Claims (1)

[Claims] 1. A beam shaping element comprising a thin film made of a dielectric or metal having angular dependence, the thin film shaping a beam into a predetermined cross-sectional shape.