JPS61198101A - Polarizing separation element - Google Patents

Abstract

PURPOSE:To prevent an increase of a loss of light on a reflecting surface due to a sticking of dust and a deterioration of characteristics of the titled element by coating the reflecting surface of a prism with a substance, having a refractive index lower than that of a birefringence substance, thereby totally reflecting the incident light on the reflecting surface. CONSTITUTION:The substance 5 having the lower refractive index than that of the birefringence substance is vapor-deposited on the reflecting surface 3 of the prism 1 composed of the birefringence substance. The total reflection is carried out due to the difference of the refractive index of the birefringence substance and that of the substance vapor-deposited on the reflecting surface 3. When silicon dioxide is vapor-deposited on the reflecting surface 3 of the prism 1 composed of a titanium dioxide single crystal, the total reflection may be sufficiently carried out by the difference of the refractive index of the titanium dioxide single crystal and that of silicon dioxide.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical isolator constituting an optical communication system, and particularly to a polarization splitting element made of a birefringent material used in an optical isolator.

When forming an optical communication network, reflected light or the like in the middle of the network is transmitted in the opposite direction by an optical fiber, and when it enters a semiconductor laser used as a light source, noise is mixed into the optical signal. Therefore, in order to prevent the light transmitted in the opposite direction from entering the semiconductor laser and stabilize the operation of the semiconductor laser, an optical isolator is inserted in front of the semiconductor laser, and the light rays in the forward direction form a circuit network. The light beam enters the optical fiber, but the light rays in the opposite direction are deflected out of the optical fiber.

Such an optical isolator incorporates a polarization separation element, and the polarization separation element is made of a composite material such as a calcite crystal or a single crystal of titanium dioxide (T i 02 ), which has a different refractive index for ordinary rays and for extraordinary rays. Composed of refractive material. In addition, the polarization separation element includes a transmission type polarization separation element that separates light by transmitting it from the front side of a plate-shaped birefringent material to the back side, and a transmission type polarization separation element that separates the light by transmitting it from the front to the back side of a plate-shaped birefringent material. There is a prism-type polarization separation element, etc., in which the light is reflected, the polarization is separated, and the light is emitted from the other surface.

Among them, a prism-type polarization splitting element made of a single crystal of titanium dioxide has a large refractive index and a large separation angle, and is used as an extremely effective polarization splitting element because it allows miniaturization of optical devices.

[Conventional technology]

FIG. 2 is a cross-sectional perspective view showing a conventional example of a prism-type polarization splitting element made of a single crystal of titanium dioxide.

In the figure, the prism 1 is made of a single crystal of titanium dioxide, and the light shown by the arrow that enters from the entrance surface 2 of the prism 1 is reflected by the reflection surface 3 formed at the boundary between the prism 1 and air, and is reflected from the exit surface. It emits from 4. Titanium dioxide single crystal has a high refractive index of 2.463 for ordinary rays and 2.721 for extraordinary rays. Therefore, the light incident from the entrance surface 2 is totally reflected by the reflection surface 3, and the two light beams having different polarization directions are separated and exit from the exit surface 4.

[Problem that the invention seeks to solve]

As long as the reflective surface of the prism is clean, the light incident on the prism is totally reflected by the reflective surface. However, since no dust-proofing measures such as a protective film are applied to the reflective surface, dust particles floating in the air adhere to the exposed reflective surface. When dust or the like adheres to the reflective surface, light incident on the prism is diffusely reflected by the dust or the like, which increases the loss of light at the reflective surface and deteriorates the characteristics of the polarization separation element.

[Means for solving problems]

The above problem is that the reflective surface of the prism made of birefringent material
This problem is solved by the polarization splitting element of the present invention, which is coated with a substance whose refractive index is lower than that of the birefringent substance.

[Effect]

By coating the reflective surface of a prism made of a birefringent material with a material whose refractive index is lower than that of the birefringent material, the light incident on the prism is totally reflected on the reflective surface, and dust and other particles are prevented from adhering to the reflective surface. This makes it possible to avoid problems such as increasing light loss at the reflecting surface and deteriorating the characteristics of the polarization separation element.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional perspective view showing one embodiment of a polarization splitting element according to the present invention, and the same objects as in FIG. 2 are represented by the same symbols.

In the figure, a substance 5 whose refractive index is lower than that of the birefringent material is deposited on the reflective surface 3 of a prism 1 made of a birefringent material, and the difference in refractive index between the birefringent material and the deposited material is total internal reflection is performed. For example, a single crystal of titanium dioxide has a high refractive index of 2.463 for ordinary rays.
2.721 for extraordinary rays, and the reflective surface 3 of the prism 1 made of a single crystal of titanium dioxide has a refractive index of 1.
．． When silicon dioxide (Si02) of No. 5 is vapor-deposited, sufficient total reflection can be achieved due to the difference between the refractive index of the single crystal of titanium dioxide and the refractive index of silicon dioxide.

Moreover, the surface of the reflective surface 3 of the prism 1 is covered with a deposited material 5.
This avoids problems such as dust floating in the air adhering to the reflective surface, increasing light loss on the reflective surface and deteriorating the characteristics of the polarization separation element. I can do it.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a polarization separation element that prevents dust and the like floating in the air from adhering to the reflecting surface and deteriorating the characteristics.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional perspective view showing an example of a prism-type polarized light splitting element according to the present invention formed of a single crystal of titanium dioxide. FIG. 2 is a cross-sectional perspective view showing a conventional example of a prism-type polarized light splitting element. , is. In the figure, 1 represents a prism, 2 represents an entrance surface, 3 represents a reflection surface, 4 represents an exit surface, and 5 represents a deposited material.

Claims (1)

[Scope of Claims] 1) A polarization separation element characterized in that the reflecting surface of a prism made of a birefringent substance is coated with a substance whose refractive index is lower than that of the birefringent substance. 2) A polarization splitting element according to claim 1, which uses a single crystal of titanium dioxide as the birefringent substance.