JPH04149406A - Optical isolator - Google Patents

Abstract

PURPOSE:To decrease the number of components and to improve the performance by arranging a 1st and a 2nd magnetooptic material between a 1st and 2 2nd birefringent element, and providing he 2nd birefringent element between the 1st and 2nd magnetooptic materials. CONSTITUTION:The optical isolator is formed of flat plate type birefringent crystals 1 - 3 and the magnetooptic materials 4 and 5 in combination. Namely, the optical isolator is equipped with the 1st and 2nd flat plate type birefringent element 1 and 2 which are provided between two optical waveguides 6 and 7 at intervals, the 1st magnetooptic material 4 and 2nd magnetooptic material 5 which are interposed between the 1st and 2nd birefringent elements 1 and 2 respectively and have their lengths determined so that the polarizing directions of incident light and projection light are almost 45 deg. different by magnetism, and a 3rd flat plate type birefringent element 3 arranged between the 1st and 2nd magnetooptic materials 4 and 5. Consequently, the optical isolator which consists of a small number of components and has high performance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a polarization-independent optical isolator.

(Prior Art) Conventionally, various optical isolators without polarization dependence have been proposed, such as Japanese Patent Publication No. 58-28561 and Japanese Patent Publication No. 60-49297.

Therefore, a conventional example will be explained with reference to FIG. 2. As shown in FIG. 2(A), the optical isolator consists of two birefringent crystal plates 8 of the same thickness, a magneto-optical material 10 having a Faraday rotation angle of 9.45 degrees, and a polarization direction of the incident light and a polarization direction of the output light. It is composed of an optically active crystal plate 11 whose optical axis and thickness are set so that the polarization direction differs by 45 degrees, and is placed between two opposing optical fibers 12 and 13.

The incident light is split into ordinary light and extraordinary light by the first birefringent crystal plate 8 on the optical fiber 12 side, and then the polarization direction of the light that passes through the magneto-optic material 10 is counterclockwise when viewed from the optical fiber 13 side. It is rotated by 45 degrees in the direction (counterclockwise), further rotated by 45 degrees by the optically active crystal plate 11, and enters the second birefringent crystal plate 9, where the ordinary light and the extraordinary light are combined again to form both light beams. Both are incident on the optical fiber 13.

When the light in the opposite direction emitted from the optical fiber 13 passes through the second birefringent crystal plate 9 and the optically active crystal plate 11, its polarization direction is the same as the polarization direction of the light in the forward direction. When the light enters the magneto-optic material 10, it is rotated by 45 degrees counterclockwise when viewed from the optical fiber 13 side, so the polarization direction differs by 90 degrees from that of the forward direction light, and the first birefringent crystal The ordinary light and the extraordinary light that have entered the plate 8 remain branched and are not combined, and are emitted toward the optical fiber 12 at a position different from the forward incident axis.

Point P in the forward direction traveling from the optical fiber 12 to the optical fiber 13
I, P2. P3. P4. The change in polarization direction at P5 will be explained with reference to FIG. 2(B).

At the time of incidence, the vertically polarized light component F1 is shown by a dotted line, the horizontally polarized light component F2 is shown by a solid line, the component center C1°C2 is shown by a dot, and the central axis O along which the incident light travels is shown by an open circle.

In the first birefringent crystal plate 8, the vertically polarized component Fl of the incident light travels straight as ordinary light, and the horizontally polarized component F2 moves horizontally and exits as extraordinary light. The center C2 moves to a different position from the center C1 of the component F1.

When the light component exiting the first birefringent crystal plate 8 passes through the magneto-optic material 10, its polarization direction is rotated by 45 degrees counterclockwise when viewed from the optical fiber 13 side, so that the light component is rotated 45 degrees counterclockwise to point P.
As shown in FIG. 3, the component F1 and the component F2 are tilted by 45 degrees.

Further, as shown at point P4, these light components enter the optically active crystal plate 11 and are rotated by 45 degrees, so that the polarization direction is rotated by 90 degrees when compared with the polarization direction at point P2.

Then, these light components enter the second birefringent crystal plate 9, and the component F1 moves horizontally, and the component F2 moves straight, so that the component Fl as shown at point P5.

The center CI of F2 and C2 coincide.

In addition, as shown in FIG. 2(C), the component Fl of the light in the opposite direction
a, F2a is point P5. P4. As shown at P3, the light travels to point P3 in the same way as the forward direction light. Then, as shown at point P2, the components Fla and F2a are 4 by the magneto-optical material ]O.
After being rotated by 5 degrees, the component Pla and the component P2a at the point P1 have their centers C1a and C2a at the axis of incidence 0.
located far away from.

Point P2. P3. In P4, the center C1a of component Fla
is located on the central axis 0, so that the light in the opposite direction passes along the central axis O of the forward incident light until it enters the first polarization refracting crystal plate 8.

(Problem to be Solved by the Invention) In the upper optical isolator, the above two birefringent crystal plates are used as a means to enhance the function of preventing light incident from the opposite direction from returning to the light source side optical fiber. It is easily possible to combine the magneto-optical material and the magneto-optical material into one unit. However, even if the performance is improved by simply increasing the number of units, the number of parts will increase accordingly, resulting in higher costs, and furthermore, there will be problems in that miniaturization is not possible. Return light (
Since the light (in the opposite direction) passes along the central axis of the forward incident light until it is incident on the first polarization refracting crystal plate, the performance is likely to deteriorate.

An object of the present invention is to provide an optical isolator with a small number of parts and high performance.

(Means for Solving the Problems) The optical isolator of the present invention is characterized by a first birefringent element and a second birefringent element in the form of a flat plate, which are provided at intervals between two optical waveguides; A first magneto-optical material is inserted between the first and second birefringent elements and has a length determined so that the polarization directions of the incident light and the output light differ by approximately 45 degrees due to magnetization. and a second magneto-optical material, and a flat third birefringent element disposed between the first and second magneto-optic materials.

Another feature of the invention is that the thickness of the third birefringent element is /7 times the thickness of the first birefringent element; This is equivalent to that of a refractive element.

(Example) Embodiments of the present invention will be described below with reference to FIG.

The optical isolator in this invention is constructed by combining plate-shaped birefringent crystals 1, 2.3 and magneto-optic materials 4, 5. These components 1 to 5 are arranged between two leading waveguide optical fibers 6.7. The arrangement order is from the first birefringent crystal 1 on the optical fiber 6 side to the first magneto-optic material 4 and the third
birefringent crystal 3 , second magneto-optical material 5 and second birefringent crystal 2 . The birefringent crystals 1 to 3 are made of rutile, and if the first and second birefringent crystals 1.2 each have a thickness t, the third birefringence crystal 3 has a thickness f t.

The polarization plane of the third birefringent crystal 3 (the plane perpendicular to the transmission end face and containing the optical axis of the crystal) is rotated by 45 degrees with respect to the polarization plane of the first birefringence crystal 1.

The polarization plane of the second birefringent crystal 2 is rotated by 45 degrees with respect to the polarization plane of the third birefringence crystal 3, and is rotated by 90 degrees with respect to the polarization plane of the first birefringence crystal 1. It is.

The first and second magneto-optical materials 4 and 5 are made of garnet, and their lengths are determined so that the polarization directions of the incident light and the outgoing light differ by approximately 45 degrees.

Next, the operation of the optical isolator will be explained.

Light from a light source first enters the first birefringent crystal 1 through an optical fiber 6, where it is split into ordinary light and extraordinary light, and passes through the magneto-optic material 4 of the apprentice 1, where the polarization direction is changed. It rotates 45 degrees clockwise (clockwise) when viewed from the optical fiber 7 side, is further moved horizontally by the third birefringent crystal 3, enters the second magneto-optic material 5, and the polarization direction is rotated 45 degrees. In the second birefringent crystal 2, the light whose polarization direction has been rotated by 45 degrees (rotated by 90 degrees from the first birefringent crystal 1) is split into ordinary light and extraordinary light. Both lights are combined and enter the optical fiber 7.

The light returning from the optical fiber 7 (in the opposite direction) passes through the second birefringent crystal 2, and the ordinary light and extraordinary light split by the second birefringent crystal are sent to the second magneto-optic material 5. The light beam is rotated by 45 degrees, passes through the third birefringent crystal 3, moves horizontally, is further rotated by 45 degrees by the first magneto-optic material 4, and enters the first birefringent crystal 1. Here, the ordinary light and the extraordinary light each travel toward the optical fiber 6 at a position that is far away from the central axis 0.

Here, each point Pl, P2 . of the light traveling from the optical fiber 6 to the optical fiber 7. Pa, P4. P5. The change in the polarization direction at Pa will be explained based on FIG. 1(B), and the change in the polarization direction at each of the above points of light in the opposite direction will be explained based on FIG. 1(C).

Note that the symbols corresponding to those in FIGS. 2(B) and 2(C) are the same.

In the incident light, at points PI and P2, the vertically polarized component F1 travels straight through the first birefringent crystal 1 as ordinary light, and the horizontally polarized component F2 moves horizontally as extraordinary light, so the component Fl
The center CI of the component F2 and the center C2 of the component F2 are at different positions.

As shown at point P3, the polarization directions of the light components Fl and F2 exiting the first birefringent crystal 1 are rotated by 45 degrees in the first magneto-optic material 4.

As shown at point P4, the component F1 that has entered the third multi-refraction crystal 3 moves straight, and the component F2 moves horizontally.

As shown at point P5, in the second magneto-optical material 5, the polarization directions of components Fl and F2 are further rotated by 45 degrees due to the Faraday effect, and as shown at point P6,
The centers CI and C2 of the component F1 and the component F2 incident on the second birefringent crystal 2 coincide on the central axis O.

Further, the change in the direction of the light emitted from the optical fiber 7 in the opposite direction is as follows.

Point P6. As shown in P5, the light in the opposite direction passes through the second birefringent crystal 2 and returns to the center C2a of the component F2a.
moves.

As shown at point P4, when the components Fl and F2 are incident on the second magneto-optic material 5, they are rotated by 45 degrees, so their polarization directions are 90 degrees different from the respective polarization directions of the forward components Fla and F2a. It will be different.

As shown at point P3, the component F2a incident on the third birefringent crystal 3 moves straight, and the component Fla moves horizontally, so the center C1a of the component Fla moves.

As shown at point P2, the polarization directions of the components Fla and F2a are rotated by 45 degrees in the first magneto-optical material 4, and as shown at point P1, the components Fla and F2a are rotated by 45 degrees in the first magneto-optical material 4. Since the vehicle moves straight and the component F2g moves horizontally, the center C2a of the component F2a moves.

To explain the relationship between the light components Fla and F2a in the direction opposite to the central axis O, from the point P3 to the point P1, the component Fla
, the center C1a and the center C2a of F2a are both the central axis O
Not located above. At point P1, other points P6 to P2
Compared to the center C1a, C2a of both components Fla, F2a
and the central axis O are further apart.

(Effects of the Invention) As explained above, according to the present invention, the first and second magneto-optical materials are arranged between the first and second birefringent elements,
By providing the second birefringent element between the first and second magneto-optical materials, it is possible to provide an optical isolator with fewer parts and higher performance than the conventional example. Also, since the forward emitted light that has passed through the second birefringent element is located on the central axis,
Alignment with the leading waveguide becomes easy.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram according to the present invention, in which an optical fiber 7
FIG. 2 is an explanatory diagram showing a conventional example, in which the optical fiber 13
It is a diagram seen from the side. 1... first birefringent element (first birefringent crystal), 2...
...Second birefringent element (second birefringent crystal), 3...
Third birefringent element (third birefringent crystal), 4...first
5... Second magneto-optical material, 6.7... Optical waveguide (optical fiber), Fl, F
la, F2, F2tx-...component, 0...
central axis. Above (A) Figure 1 (B) (C) Figure 2

Claims (1)

[Scope of Claims] 1. A first birefringent element and a second birefringent element in the form of a flat plate, which are provided at intervals between two optical waveguides; and the first and second birefringent elements. a first magneto-optical material and a second magneto-optic material each having a length determined such that the polarization directions of the incident light and the outgoing light differ by approximately 45 degrees due to magnetization; 1. An optical isolator characterized by comprising a third flat birefringent element disposed between a second magneto-optical material. 2. The thickness of the third birefringent element is √2 times the thickness of the first birefringent element, and the thickness of the first birefringent element is equal to that of the second birefringent element. The optical isolator according to claim 1, characterized in that: