JPS59228612A - Polarizing prism - Google Patents

Abstract

PURPOSE:To facilitate manufacture and to improve yield by adhering a triangular prism made of a birefringent material to a cylindrical type distributed index lens in one body. CONSTITUTION:The cylindrical type distributed index lens 2 which has a slanting end surface conforming to the slanting surface of a triangular prism 1 made of a birefringent material is adhered to said triangular prism 1 with an adhesive 3. The refractive index of the cylindrical type distributed index lens 2 to an extraordinary light beam (e) is different according to the radial distance from the cylinder axis, and even if light is made incident slantingly to the cylinder axis, its light beam track is bent and the projection light is projected from the end surface of the cylindrical type distributed index lens 2 in parallel to the incident light. Thus, the cylindrical type distributed index lens 2 uses the transparent material such as glass, so the workability is excellent, the nonreflective coating of the end surface is facilitated, and only one triangular prism made of the birefringent material which is inexpensive and superior in workability is used; the yield is improved, the manufacture is facilitated, and the cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in polarizing prisms, and more specifically to a polarizing prism having a structure in which a triangular prism made of a birefringent material and a triangular prism made of an isotropic transparent material such as glass are bonded and integrated. It is related to.

For example, in an optical communication system, an optical isolator is incorporated in order to prevent equipment (semiconductor, etc.) on the transmitting side from being interfered with by reflected light from the receiving side. This optical isolator is a two-terminal element with irreversibility that transmits light only in one direction and not in the opposite direction, and has a configuration in which polarizing prisms are placed at each end of a Faraday rotator. Common.

The polarizing prism used here is configured to obtain plane polarized light by optically bonding two triangular prisms with the optical axis of a birefringent material in a certain direction. Polarizing prisms used in optical isolators for optical communication systems include:
Extremely high performance is required, and for this reason natural calcite crystals (calcite), which is generally very difficult to work with, are used as the birefringent material. Therefore, they are extremely expensive, for example several hundred thousand yen per piece, and
Optical isolators, which require individual polarizing prisms, are much more expensive than semiconductor lasers, and this has been a huge problem in the widespread development of optical communication systems in various fields.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing prism that can eliminate the drawbacks of the prior art as described above, has a high yield, is easy to manufacture, and can significantly reduce costs.

The present invention focuses on the fact that with the recent development of optical communication technology, a light source with a constant wavelength such as a laser beam is often used, and that the polarization effect occurs at the joint surfaces of triangular prisms. This was done after learning that one side of the scale could be replaced with another material. That is, the present invention
Basically, it has a structure in which a triangular prism made of a birefringent material and a cylindrical distributed index lens are bonded together.

Hereinafter, the present invention will be explained in more detail based on the drawings. FIG. 1 is an explanatory diagram showing an embodiment of a polarizing prism according to the present invention, and is an example of a case where the polarizing prism is applied to a Glan-Thompson type prism. This type of prism utilizes extraordinary rays. That is, the polarizing prism shown in this embodiment includes a triangular prism 1 made of polymorphic material, and a cylindrical distributed index lens 2 having an inclined end surface that matches the slope of the triangular prism 1, attached to an adhesive 3. It is integrated with adhesive. In this case, the triangular prism 1 is a right-angled prism, and one angle thereof is about 20 degrees. As the birefringent material, various materials such as calcite crystal (calcite) and rutile crystal (rutile) can be used. The cylindrical distributed index lens 2 has a refractive index gradient in the radial direction from the cylinder axis, and is therefore capable of changing the ray trajectory of light incident in the cylinder axis direction.

Now, FIG. 2 shows the case where light is incident on the triangular prism 1 made of a birefringent material. A ray of light incident on the triangular prism 1 travels straight through the triangular prism 1 and is separated into an ordinary ray O and an extraordinary ray e at the interface between the triangular prism 1 and the adhesive 3.

The refractive index of the adhesive 3 is selected to be smaller than that of the ordinary ray O and larger than that of the extraordinary ray e.

Therefore, the extraordinary ray e passes through the layer of adhesive 3, but
Since the incident angle of the ordinary ray 0 exceeds the critical angle, it is totally reflected at the boundary surface, so that it can be separated into both rays. The refractive index for the extraordinary ray e in the cylindrical distributed index lens 2 varies depending on the distance in the radial direction from the cylinder axis, but even if the ray enters at an angle with respect to the cylinder axis, the trajectory of the ray will be bent and the outgoing light will be The light can be emitted from the end face of the cylindrical distributed index lens 2 in a state parallel to the incident light.

If ordinary rays are to be used, a Rotchon prism as shown in FIG. 3 may be used. In this case as well, the triangular prism 1 is made of a birefringent material, and the other member is made of a cylindrical distributed index lens 2. The angle and crystal orientation of the joint surfaces in the triangular prism 1 are the same as in the Rothon prism. In this case, the incident light entering the triangular prism 1 and the ordinary ray 0 exiting from the cylindrical distributed index lens 2
can be considered parallel. What should be noted here is that in the conventional Rotchon prism, the extraordinary ray e, which is emitted at an angle to the optical axis, is also emitted parallel to the optical axis. That is, the extraordinary ray e also has its ray trajectory bent by the cylindrical distributed index lens 2, and therefore exits parallel to the optical axis at the end face. In other words, in this embodiment, the ordinary ray 0 and the extraordinary ray e can be separated and both can be emitted parallel to the incident light.
This is a particularly suitable device if you want to use both.

The polarizing prism according to the present invention can be widely applied to various optical devices that utilize laser light, such as optical switches and optical circulators, in addition to the optical isolators described above.

Since the present invention is a polarizing prism configured as described above, one member, the cylindrical distributed index lens, is made of a transparent material such as glass, so it is easy to process, and the end face can be easily coated with anti-reflection coating. Since only one triangular prism is required, which is made of expensive and difficult-to-process birefringent material, the yield is improved, manufacturing is easy, and costs can be significantly reduced.The output light and the input light are parallel to each other. Because of this, it can be installed in the same place where conventional polarizing prisms are used, and therefore, the conventional optical system can be used as is, providing many excellent effects.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of a polarizing prism according to the present invention, FIG. 2 is an explanatory diagram showing its operation, and FIG. 3 is an explanatory diagram showing another embodiment. 1... Triangular prism, 2... Cylindrical distributed index lens, 3... Adhesive. Patent applicant: Fuji Electrochemical Co., Ltd. Agent: Yuki Omata
Shigeru's brother Sedo Ara
Tomonosuke Ki Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A cylindrical distributed index lens having an inclined end surface that matches the slope of the triangular prism is adhered to a triangular prism made of a birefringent material, so that polarized output light is emitted parallel to the optical axis. A polarizing prism featuring