JPS5944606B2 - light switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical path switching moonlight switch used in optical communications or optical experimental systems.

A conventional device of this type is shown in FIG.

Here, 1 and 2 are light input ports, and 3 and 4 are light output ports. Further, 1 is a mirror whose front and back surfaces have a total reflection function, and is rotatable about an axis 2. Now, considering the situation shown in FIG. 1, light from port 1 is reflected by mirror 1 and goes to port 4, while light from port 2 is also reflected by mirror 1 and goes to port 3. Next, considering mirror 1 rotated by 900 degrees around axis 2, light from port 1 is reflected by mirror 1 and goes to port 3, while light from port 2 is also reflected by mirror 1. and will proceed to port 4. Therefore, the optical circuit shown in FIG. 1 functions as a 2×2 optical switch with ports 1 and 2 as input sections and ports 3 and 4 as output sections. However, in the optical switch constructed in this manner, the operation is achieved by mechanically rotating the mirror 1, which has the disadvantage that it is subject to significant deterioration over time and that satisfactory accuracy cannot be obtained. In order to eliminate such drawbacks, the present invention enables the traveling direction of light to be controlled by the direction of a magnetic field applied from the outside, and will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which numerals 3 and 4 are polarizing prisms whose end faces are processed perpendicular to the direction in which light travels;
5 is a Faraday element whose thickness is determined so that the polarization directions of the incident light and the output light differ by 450 by an external magnetic field H;
6 is a compensating plate whose thickness is determined so that the polarization directions of the incident light and the output light differ by 450, and 7 and 8 are reflecting mirrors.

In the figure, dotted lines indicate positions where an optical path may exist, and □, [F], 0, and 0 indicate light input/output terminals corresponding to these. YIG, which is a magneto-optical material, is suitable for the Faraday element 5, and an optical rotator can be used for the compensator 6. That is, two polarizing prisms 3 and 4 are provided before and after the optical system consisting of the Faraday element 5 and the compensating plate 6, the end faces of which are processed to be perpendicular to the traveling direction of the incident light and the outgoing light. Of the four end faces of the polarizing prism 3, the light incident on the two end faces that do not face the optical system exits from the two end faces that face the optical system, and is emitted from the Farade element 5 and the compensator plate 6, respectively.
After passing through, the light enters two of the four end faces of the other polarizing prism 4 that face the optical system, and then exits from the two end faces that do not face the optical system.

Now, when the direction of the external magnetic field H and the crystal axis of the compensator plate 6 are appropriately selected, when light passes through both the Farade element 5 and the compensator plate 6, it travels from the left to the right in Fig. 2. for,
The polarization direction of the light does not change due to mutual canceling effects, but when the light travels from the right to the left, the optical rotations of the light overlap and the polarization direction of the light can be rotated by 90 degrees.

At this time, the light incident on the terminal 4 is separated into mutually orthogonal polarized lights while traveling, but eventually these are combined again and appear at the terminal 6. Similarly, light from terminal 8 appears at terminal 0. This situation is shown in FIGS. 3 and 4. In these figures, black dots and arrows indicate polarized light that is orthogonal to each other, with black dots indicating polarized light perpendicular to the plane of the paper, and arrows indicating polarized light parallel to the plane of the paper. Next, consider a case where the direction of the external magnetic field H is reversed by some method.

In this case, unlike the case described above, when the light travels from the left to the right, the optical rotations of the Farade element 5 and the compensation plate 6 overlap, and the polarization direction of the light changes when it passes through both. rotates by 90 degrees, but when the light travels from right to left, the polarization direction of the light does not change due to mutual canceling effects. This situation is shown in FIGS. 5 and 6. Because of this operation, the optical circuit according to the configuration method shown in Figure 2 changes the optical path of light (4→
It has a function of switching between the case of 6,0→O) and the case of ((A)→9,6→O), and can therefore be used as a 2×2 optical switch.

FIGS. 7 and 8 are diagrams showing specific means for changing the direction of the external magnetic field. In FIG. 7, a permanent magnet 9 is provided in the vicinity of the Farade element 5, and by rotating it, the external magnetization is changed. In FIG. 8, an electromagnet 10 is provided near the Farade element 5, and the external magnetization is changed by switching the direction of the current therein. In the embodiment shown in FIG. 2, one Farade element and one compensation plate are used, but two of these may be used for each optical path. An example thereof is shown in FIG. In the figure 11,
12 is a Farade element, and 13 and 14 are compensation plates. Furthermore, the order of these may be changed, and an example thereof is shown in FIG. In the polarizing prisms shown in FIGS. 2, 9, and 10, the main axis of the birefringent crystal, which is the material of the prism, is set perpendicular to the plane of the paper, but the above-described operation is possible even if the main axis is set parallel to the plane of the paper. Further, as the polarizing prism, a Glan-Thompson prism or a Glan-Taylor prism is suitable.
Furthermore, by adding a lens system to the optical circuit shown in the above embodiment, it is possible to couple it to an optical waveguide such as an optical fiber.

Note that the embodiment is not limited to the above embodiment, and the light that has passed through the Farade element and the compensation plate may be reflected by a reflecting mirror to change the optical path. It may be made to pass through the plate.

As explained above, the device of the present invention can switch the optical path by changing the direction of external magnetization, so mechanical vibrations are not transmitted to the optical system, so it is stable and accurate with little deterioration over time. This has the advantage that a 2×2 optical switch with good performance can be realized.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional optical switch, Fig. 2 is a block diagram of an embodiment of the present invention, Figs. 3 to 6 are diagrams explaining the operation of the device shown in Fig. 2, Fig. 7, FIG. 8 is a block diagram showing a specific example for changing external magnetization in the device of the present invention, and FIG.
10 are configuration diagrams showing other embodiments of the present invention. 1... Rotating mirror, 2... Rotating shaft, 3, 4
...Polarizing prism, 5...Fuarade element, 6...Compensation plate, 7, 8...Reflector, 9...Permanent Magnet, 10... Electromagnet, 11, 12... Furade element, 13, 14
...Compensation board.

Claims (1)

[Claims] 1 Due to external magnetization, the polarization direction of the incident light and the output light is 45
An optical system consisting of a Faraday element whose thickness is determined so that the polarization directions of the incident light and the output light differ by 45 degrees, and a compensation plate whose thickness is determined so that the polarization directions of the incident light and the output light differ by 45 degrees, and a compensator that is installed in front of this optical system. a first polarizing prism that separates the incident light into mutually orthogonal polarized lights, and a second polarizing prism that is provided after the optical system and combines the incident light separated into the mutually orthogonal polarized lights, The external magnetization direction of the Faraday element and the crystal axis of the compensator are set so that when the light passes through the optical system, the polarization direction of the light does not change due to mutual canceling effects when the light travels in one direction. , an optical switch characterized in that when the lights travel in opposite directions, their optical rotations overlap with each other and the polarization directions of the lights are rotated by 90°.