JPH03135512A - Faraday rotator - Google Patents

Abstract

PURPOSE:To obtain a small-sized optical isolator which is easily assembled by forming polarization separating films on the incidence and projection surfaces of a magnetooptic element which has its light incidence surface slanted by 45 deg. to the optical axis, and its projection surface slanted by 45 deg. to both the optical axis and incidence surface. CONSTITUTION:The magnetooptic element 7 is formed in a cylindrical shape, then the incidence surface 9 is polished optically by 45 deg. to the optical axis 8. Then the projection surface 10 is polished optically by 45 deg. to the optical axis and by 45 deg. to the incidence surface 9. At such a time, the distance between the incidence and projection surfaces on the optical axis is so set that the polar izing direction is rotates by 45 deg.. Then the polarization separating films are formed on the incidence surface 9 and projection surface 10 to obtain the Fara day rotator. Further, this Faraday rotator is fixed in a magnet 11 to form the optical isolator. Thus, the polarization separating films are formed to obtain the small-sized optical isolator which has neither a polarizer nor an analyzer and is easily assembled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a Faraday rotator used in optical isolators and the like.

Conventional Technology When a semiconductor laser is used as a light source in an optical signal transmission system such as optical communication, a portion of the light emitted from the semiconductor laser is reflected at the transmission line or at each connection of the transmission optical components, causing the semiconductor laser to emit light. This causes oscillation characteristics to become unstable and noise to increase. An optical isolator is generally used to prevent this reflected return light from returning to the semiconductor laser. A Faraday rotator is an optical rotation element that utilizes the Faraday effect, and is used in optical isolators because it has non-reciprocity.

A conventional optical isolator, for example, as shown in FIG.
Polarizer 1. Magneto-optical element 2. The configuration includes an analyzer 3 and a magnet 4. The principle of an optical isolator is shown in Figure 4 (a
As shown in FIG. 1, the emitted light 5a from the semiconductor laser first passes through the polarizer 1 and becomes linearly polarized light 5b. Subsequently, when passing through the magneto-optical element 2 in the saturation magnetic field H, its polarization direction is rotated by 45 degrees, and the linearly polarized light 5C is transmitted through the polarizers 1 and 4.
The linearly polarized light 5d passes through the analyzer 3 placed at an angle of 5 degrees.
becomes. Conversely, as shown in FIG. 4(b), the reflected return light 6a first passes through the analyzer 3 and becomes linearly polarized light 6b.

Subsequently, when passing through the magneto-optical element 2 in the saturation magnetic field H,
Due to the non-reciprocity of the Faraday effect, the polarization direction is further rotated by 45 degrees to become linearly polarized light 6C, which is perpendicular to the polarizer 1 and cannot pass through. Based on the principle described above, reflected return light can be prevented from returning to the semiconductor laser.

Problems to be Solved by the Invention In such a conventional optical isolator configuration, a polarizer and an analyzer are required, which creates extra space inside the case and makes it difficult to downsize the optical isolator. had its limits. Furthermore, there is a drawback that fine adjustment of the polarization direction of the light is required during assembly.

The present invention solves these problems and aims to provide an optical isolator that is small and easy to assemble.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a magnetic sensor in which the light incident surface is tilted at 45 degrees with respect to the optical axis, and the light exit surface is tilted at 45 degrees with respect to both the optical axis and the incident surface. The present invention provides a Faraday rotator in which a polarization separation film is formed on the entrance/exit surface of an optical element.

Function: According to the Faraday rotator of the present invention, the polarization separation film is formed directly on the magneto-optical element, and the light entrance and exit surfaces are tilted at 45 degrees, so that linearly polarized light can be obtained. The polarizer and analyzer can be removed, resulting in an optical isolator that is compact and easy to assemble.

EXAMPLE Hereinafter, an example of the present invention will be explained based on FIGS. 1 and 2.

FIG. 1 shows the structure of a Faraday rotator according to the present invention.

First, the magneto-optical element 7 (for example, YIG) is formed into a cylindrical shape, and then the entrance surface 9 is optically polished so as to form an angle of 45 degrees with respect to the optical axis 8 . Next, the output surface 10 is optically polished so that the angle is 45 degrees with respect to the optical axis and 45 degrees with respect to the input surface 9. At that time, the distance between the input and output planes on the optical axis changes the polarization direction by 4
Make the length so that it rotates 5 degrees. Next, a polarization separation film (for example, 5iO=
and TiO2) to form a Faraday rotator. Furthermore, as shown in FIG. 2, this Faraday rotator is fixed in a magnet 11 to form an optical isolator.

Here, the emitted light 12a from the semiconductor laser first passes through the incident surface 9 on which the polarized light separation film is formed, and then the linearly polarized light 12b
becomes. Subsequently, when passing through the magneto-optical element 7, its polarization direction is rotated by 45 degrees, and the linearly polarized light 12c passes through a polarization separation film formed on the output surface 10, which has an angle of 45 degrees with the input surface 9. It becomes linearly polarized light 12d. Conversely, the reflected return light 13a first passes through the output surface 10 on which the polarization separation film is formed, and becomes linearly polarized light 13b. Next, magneto-optical element 7
When passing through, the polarization direction is further rotated by 45 degrees due to the non-reciprocity of the Faraday effect, so that the linearly polarized light 13c cannot pass through the polarization separation film formed on the incident surface 9.

With such a configuration, a polarizer and an analyzer can be omitted, and an optical isolator that is small and easy to assemble can be realized.

Note that a lens and an optical fiber may be added to the optical isolator of the above embodiment to form a semiconductor laser module with an optical isolator.

Effects of the Invention As described above, according to the present invention, the input surface of the magneto-optical element is tilted at 45 degrees with respect to the optical axis, and the output surface is tilted at 45 degrees with respect to both the optical axis and the incidence surface. By forming a polarized light separation film on the output surface, it is possible to obtain an optical isolator that is small and easy to assemble without a polarizer or analyzer.

[Brief explanation of the drawing]

FIG. 1 is a side view of a Faraday rotator according to the present invention, FIG.
The figures are explanatory diagrams for explaining the optical isolator according to the present invention, Figure 3 is an exploded perspective view of a conventional optical isolator, and Figure 4 is an exploded perspective view of a conventional optical isolator.
The figure shows the principle of an optical isolator. 7...Magneto-optical element, 8...Optical axis, 9
...Incidence surface, 10...Output surface, 11.
...Magnet, H...Saturation magnetic field.

Claims (1)

[Claims] A polarization separation film is formed on the input and output surfaces of a magneto-optical element whose light input surface is tilted at 45 degrees with respect to the optical axis and whose output surface is tilted at 45 degrees with respect to both the optical axis and the input surface. Faraday rotator.