JPS59228611A - Polarizing prism - Google Patents

Abstract

PURPOSE:To facilitate manufacture and to improve yield by adhering the 1st triangular prism made of a birefringent material and the 2nd triangular prism made of an isotropic transparent material in one body. CONSTITUTION:The 1st triangular prism 1 made of the birefringent material and the 2nd triangular prism 2 made of the isotropic transparent material which has a refractive index from the refractive index of the birefringent material to specific light wavelength of an extraordinary light beam are united together by adhering their slanting surfaces to each other with an adhesive 3. Then, one end surface 2a of the triangular prism 2 is formed into a convex surface which has a focus (f) right at the intersection of an optical axis x-x and the slanting surface (adhered surface) of the prism. This convex surface may be cylindrical or spherical. The isotropic transparent material uses various kinds of optical glass or plastic, etc. Thus, the triangular prism 2 uses the isotropic transparent material such as glass, so the workability is improved, the nonreflective coating of the end surface is facilitated, and only one triangular prism of the birefringent material which is expensive and inferior in workability is used; the yield is improved, the manufacture is facilitated, and the cost is reduced greatly.

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 a transmitting side device (such as a semiconductor laser) from being interfered with by reflected light from a 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. By replacing one of the triangular prisms with an isotropic transparent material such as glass, we learned about scales.
It has been done. That is, the present invention basically has a structure in which a first triangular prism made of a birefringent material and a second triangular prism made of an isotropic transparent material are bonded and integrated, and is easy to use in practice. Various other measures have been taken to achieve this.

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 two-polarizing prism shown in this embodiment includes a first triangular prism 1 made of a birefringent material, and an isotropic transparent prism having a refractive index different from the refractive index for a specific light wavelength of the extraordinary ray of the birefringent material. A second triangular prism 2 made of a material is integrally bonded to each other with an adhesive 3 at their inclined surfaces. In this case, the first triangular prism 1
is a right-angled prism, and one angle is about 20 degrees. As the birefringent material, various materials such as calcite crystal (calcite) and rutile crystal (rutile) can be used. The second triangular prism 2 has one end surface 2a formed into a convex surface such that the intersection of the optical axis XX and the slope (adhesive surface) of the prism is exactly the focal point f, and has a cylindrical surface. It may be shaped or spherical. The isotropic transparent material may be various optical glasses or plastics.

FIG. 1 shows a case where light is incident on a first triangular prism 1 made of a birefringent material. First triangular prism 1
The incident light ray travels straight through the first triangular prism 1 and is separated into an ordinary ray 0 and an extraordinary ray e at the interface between the first 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 0 and larger than that of the extraordinary ray e. Therefore, the extraordinary ray e passes through the layer of adhesive 3, but the ordinary ray 0, whose incident angle exceeds the critical angle, is totally reflected at the boundary surface and can be separated into both rays. Since the refractive index for the extraordinary ray e at the second triangular prism 2 is different from the refractive index at the first triangular prism 1 as described above, it is refracted there, but the refracted light is
The light passes through the focal point f of the convex end surface 2a of the triangular prism 2, and is therefore refracted at the end surface 2a so as to be parallel to the optical axis. As a result, the emitted light is emitted from the end surface 2a of the second triangular prism 2 in a state parallel to the incident light.

If ordinary rays are to be used, a Rotchon prism as shown in FIG. 2 may be used, for example. In this case as well, the first triangular prism 1 is made of a birefringent material, and the second triangular prism 2 is made of an isotropic transparent material. Here, the second triangular prism 2 has one end surface formed into a cylindrical or spherical convex surface such that the intersection of the optical axis XX and the slope (adhesive surface) of the prism is exactly the focal point f. This point is also similar to the case of the previous embodiment. Incidentally, the angle and crystal orientation of the cemented surface in the first triangular prism 1 are the same as those of the Rochon prism. In this case, the first
Incident light entering the triangular prism 1 and the second triangular prism 2
It is parallel to the ordinary ray 0 that comes out from. 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. In other words, the extraordinary ray e is also light that passes through the focal point f of the convex end surface 2a of the second triangular prism 2,
Therefore, it is refracted so as to be parallel to the optical axis at the end surface 2a. That is, in this embodiment, the ordinary ray 0 and the extraordinary ray e can be separated and both can be emitted in parallel to the incident light, so the apparatus is particularly suitable when it is desired to use both.

The polarizing prism according to the present invention has no light wavelength dependence, and even if the wavelength of the incident light changes slightly, the light is emitted parallel to the optical axis. It can be widely applied to various optical devices that use laser light, such as circulators.

Since the present invention is a polarizing prism configured as described above, one of the triangular prisms is made of an isotropic transparent material such as glass, so it is easy to process, anti-reflection coating on the end face is easy, and expensive processing is required. Since only one triangular prism is required, which is made of a birefringent material with poor properties, the yield is improved, manufacturing is easy, and costs can be significantly reduced.The output light and the input light are parallel, so It offers a number of superior effects, such as being able to be installed in locations where conventional polarizing prisms have been used, and thus allowing the use of conventional optical systems as is.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of a polarizing prism according to the present invention, and FIG. 2 is an explanatory diagram showing another embodiment. DESCRIPTION OF SYMBOLS 1... First triangular prism, 2... Second triangular prism, 2a... End surface, 3... Adhesive.

Claims (1)

[Claims] 1. A second triangular prism made of an isotropic transparent material having a refractive index different from the refractive index for ordinary rays or extraordinary rays of the birefringent material is adhered to a first triangular prism made of a birefringent material, A polarizing prism in which one end surface of the second triangular prism is formed into a convex surface such that the intersection of the optical axis and the adhesive surface serves as a focal point.