JPS6255766B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an optical isolator that separates light traveling in the opposite direction from light traveling in the forward direction.

(2) Background of the technology In optical communication systems, forward light is An optical isolator is used to separate the light in the opposite direction, which returns to the laser direction.

(3) Conventional technology and problems Conventionally, when separating light in opposite directions using an optical isolator, the light is directed into a birefringent crystal material such as calcite whose entrance and exit planes are formed at right angles to the optical path. Previously, the light was diffused by a lens and entered at a predetermined angle, but this required a lens for light diffusion in front of the birefringent crystal material, and the length of the optical isolator in the optical path direction This has the disadvantage that the length of the line becomes longer and the device becomes larger accordingly.

(4) Object of the Invention In order to eliminate the above-mentioned drawbacks, the present invention aims to provide an optical isolator that does not require a diffusion lens and has a small length in the optical path direction.

(5) Configuration of the Invention That is, the present invention is configured by providing a birefringent crystal material such that the entrance/exit surface is inclined with respect to the optical path.

(6) Embodiments of the Invention The present invention will be specifically described below based on embodiments shown in the drawings.

1 and 2 are front views showing one embodiment of the optical isolator according to the present invention, FIG. 3 is a diagram showing the relationship between the incident angle of light in the forward direction and the amount of shift of light in the reverse direction, and FIG. FIG. 4 is a diagram showing the relationship between the incident angle of light in the forward direction and the exit angle of light in the reverse direction.

As shown in FIGS. 1 and 2, the optical isolator 1 has an inner core 2 and a magnet 3 provided to surround the inner core 2, and the inner core 2 has a Faraday rotation angle of 45 degrees. A magneto-optical material 5 having a set circular cross section is provided. A birefringent crystal material 6 such as rutile or calcite is provided on the left side of the substance 5 in the figure, with its entrance/exit surface 6a tilted by a certain angle β with respect to the optical path 7. On the right side, a birefringent crystal material 10 is provided with an entrance/exit surface 10a inclined by a certain angle β with respect to the optical path 7, with a compensating plate 9 made of quartz interposed therebetween.

Since the present invention has the above-described configuration, the forward light 11 emitted from a laser or the like to the optical isolator 1 enters the birefringent crystal material 6 at an incident angle with respect to the optical path 7, as shown in FIG. The light enters at ω, and the optical paths of the ordinary and extraordinary light deviate from each other. In FIG. 2, only the path of ordinary light is shown by a solid line, and light 11, which will only be explained below, then enters the magneto-optical material 5, and its polarization direction is rotated by 45 degrees with respect to the direction of travel of the light. , becomes circularly polarized light, is further rotated by 45 degrees in the opposite direction by the compensator 9, becomes linearly polarized light, passes through the birefringent crystal material 10, and exits from the entrance/exit surface 10a at an exit angle γ equal to the entrance surface ω. go. That is, since the deflection at the magneto-optical material 5 is canceled by the deflection in the opposite direction at the compensator 9, as a result, only the birefringent materials 6 and 10 are tilted by a certain angle β in opposite directions with respect to the optical path 7. This means that it has passed through. In other words, when light of the same polarization passes through a material tilted at a certain angle in opposite directions, the angle of incidence and angle of exit are:
They are each equal. Note that the light 12 traveling in the opposite direction, which is generated as a result of the light 11 being reflected by the fiber end face, travels from the point D from the substance 6 at an exit angle δ with respect to the optical path 7, following a process opposite to the above process. It is emitted. Here, light 12 is light 1
1, the birefringent material 10 is transmitted along an optical path parallel to the light 11. Further, the light 12 is rotated by 45 degrees by the compensating plate 9, and further rotated by 45 degrees in the same direction by the magneto-optic material 5.
In other words, since the magneto-optical material 5 rotates the incident light in the same direction regardless of the traveling direction, the light 11
and the light 12 has a rotation angle difference of 90° in the birefringent substance 6. The plane of deflection of the light 12 in the birefringent material 6 is different from the plane of deflection of the light 11 by 90°, so its refractive index is also different from that of the light 11. Therefore, the point P when the light 12 is emitted is shifted from the optical path 7, but the light 1 in the opposite direction with respect to the light 11 in the forward direction
The amount of deviation d of the point P from the optical path 7 at the time of emission of 2 is:
As shown in Figure 3 (birefringent crystal material 6,1
0 is rutile and the radius of the cross section of the magneto-optical material 5 is 0.5
mm, the thickness in the optical path 7 direction is 2.0 mm, and the thickness of the compensator plate 9 in the optical path 7 direction is 0.07 mm). In addition, the emission angle δ of the light 12 at that time is as shown in FIG.
2.0 mm, when the thickness of the compensator plate 9 in the optical path 7 direction is 0.07 mm). As is clear from Figures 3 and 4,
Even when the incident angle ω with respect to the optical path 7 is 0°, the angle β of the entrance and exit surfaces 6a and 10a of the birefringent crystal materials 6 and 10 is set appropriately (for example, when β = 20°, d is approximately
100 [μm], δ is about 7°. ), the backward light 12 can be separated from the forward light 11 to a practically sufficient extent.

In addition, although the above-mentioned embodiment described the case where the angle β of the entrance/exit surfaces 6a, 10a of the first and second birefringent crystal materials 6, 10 with respect to the optical path 7 is equal, the angle β of each entrance/exit surface 6a, 10a is The angle β does not necessarily have to be equal; it is perpendicular to the optical path 7 (β
= 0°), it is possible to set it independently as necessary.

(7) Effects of the Invention As explained above, according to the present invention, since the entrance/exit surfaces 6a and 10a of the birefringent crystal materials 6 and 10 are provided in a manner tilted with respect to the optical path 7, forward light is 1
Even if the light 12 in the opposite direction is not diffused before entering the substances 6 and 10, it becomes possible to sufficiently separate the light 12 in the opposite direction, eliminating the need for a conventional diffusion lens, and making the spectral isolator 1 It becomes possible to shorten the length in the optical path direction and make it more compact.

[Brief explanation of the drawing]

1 and 2 are front views showing one embodiment of the optical isolator according to the present invention, FIG. 3 is a diagram showing the relationship between the incident angle of light in the forward direction and the amount of shift of light in the reverse direction, and FIG. FIG. 4 is a diagram showing the relationship between the incident angle of light in the forward direction and the exit angle of light in the reverse direction. DESCRIPTION OF SYMBOLS 1... Optical isolator, 2... Inner core, 5... Magneto-optical material, 6, 10... Birefringent crystal material, 6
a, 10a...input/output surface, 7...optical path.

Claims (1)

[Claims] 1. An optical isolator having an inner core in which birefringent crystal material is provided on both sides of a magneto-optical material, wherein the optical isolator is characterized in that the entrance/exit surface of the birefringent crystal material is provided in a form inclined with respect to the optical path.