JPS5828561B2 - optical isolator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in optical isolators used in the field of optical communication or optical transmission.

Conventionally, an optical isolator, which is a type of non-reciprocal circuit, has been constructed as shown in FIG. 1ab.

In other words, this is the permanent magnet 1 (Figure a) attached to the outside.
Alternatively, the shape of the magneto-optical material 5 is determined so that the polarization directions of the incident light 3 and the outgoing light 4 differ by 45 degrees due to Faraday rotation due to the influence of magnetization caused by the external coil 2 (Figure b) in which a direct current is passed. In this case, a polarizer 6 and a polarizer 7 are provided at the entrance part and the output part, respectively.

In this case, since the polarizer 7 is rotated by 45 degrees with respect to the polarizer 6, the incident light that has passed through the polarizer 6 undergoes Faraday rotation and then passes through the polarizer 7 without loss. Regarding the light that is incident from the output section and travels in the opposite direction, it is blocked because the polarization direction of the polarizer 6 and the polarization direction of the light are perpendicular to each other.

Therefore, this configuration has the function of an optical isolator, but as it is, the transmission loss varies from zero to infinity depending on the polarization of the incident light. When dealing with light containing all types of polarized light, there is a limit to the reduction of passing loss, resulting in a loss of at least 3 dB.

This loss amount of 3 dB corresponds to the transmission loss of approximately 1 km of optical fiber length, and was extremely problematic.

The present invention has been made in view of the above points, and in order to eliminate the above-mentioned conventional drawbacks, the present invention has been made by using two or three tabular birefringent crystals and a magneto-optical material having optical rotation or anisotropy. By selectively combining crystals and using the imaging effect of lenses, we provide an extremely good optical isolator that functions even for different polarized lights that are perpendicular to each other and can be configured to be inserted between optical waveguides. The purpose is to

An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, in FIG. 2, 89 is an optical fiber serving as an optical waveguide, 10 is a lens, 11.12 is a flat birefringent crystal,
13 is a magneto-optical material, and 14 is a crystal having optical rotation or anisotropy.

The lens 10 has the function of converging and focusing light from one optical fiber and making it enter the other optical fiber.

In addition, the birefringent crystal 1112 is made of calcite, for example, and has the function of separating and combining ordinary light and extraordinary light, and these optical axes are hereinafter located within 72 planes of the coordinate axes shown in the figure. Assume that there is.

Further, the magneto-optical material 13 is suitably made of, for example, YIG, exhibits the Faraday effect when magnetized B from the outside, and has a length determined so that the polarization directions of the incident light and the outgoing light differ by 45 degrees. .

Similarly, the length of the crystal 14 having optical rotation or anisotropy is determined so that the polarization directions of the incident light and the outgoing light differ by 45 degrees, and quartz or the like is suitable for this material. There is.

Next, the operation of the optical isolator having the above-mentioned configuration will be explained.Here, for the light traveling to the optical fiber 8 or the optical fiber 9, the magneto-optic material 13 and the crystal 14 having optical rotation or anisotropy Both change the polarization direction by 45° clockwise, and two birefringent crystals 11.
120 Optical axes are parallel to each other by θ(0<θ<
900) and the crystal thicknesses are the same.

FIG. 3 shows each point Z1. in the light traveling direction in FIG. Z2゜・・
..., polarization direction F1 at Z5. F2 or F1
'.

This figure shows how F2' and the center points 01, 02 or 01', 02' of the light change. First, the light traveling from the optical fiber 8 to the optical fiber 9 will be explained using Fig. 3a. shall be.

That is, the 21 points show the state of the light immediately after exiting from the optical fiber 8, and the polarized light F1 . Center points 01 and 02 of F2 coincide.

Next, the extraordinary light F2 is displaced by passing through the birefringent crystal 11, so that its center point 02 is the ordinary light F1, as shown at point 22.
move to a position different from the center point 01.

Further, when passing through the magneto-optical material 13 and the crystal 14 having optical rotation or anisotropy, F, , F2 are each rotated by 90° clockwise, passing through 33 points and becoming as shown in the phase diagram at 24 points.

After that, when passing through the birefringent crystal 12, the extraordinary light F1 is displaced, so that the center points 01 and 02 of both polarized lights finally coincide at the 25th point.

Therefore, in this case the side polarized light F1. F2 enters the optical fiber 9 without loss.

Next, the light traveling from the optical fiber 9 to the optical fiber 8 will be explained with reference to FIG. 3. Since the magneto-optic material 13 has directionality, the light in this case is Rotate the polarization by 45° counterclockwise.

Therefore, the final result is circularly polarized light F1' as shown in the phase diagram at 21 points.

Center points 01' and 02' of F2' are located at different locations.

Here, as can be seen by comparing FIG. 3a and FIG. It is located at a different position from the center point 01°02 of F2.

Therefore, in this case, the side polarized lights F1' and F2' are transmitted through the optical fiber 8.
It will not be incident to.

As can be seen from the above explanation, according to the configuration shown in FIG. 2, the light from the optical fiber 8 enters the optical fiber 9, but since the light from the optical fiber 9 does not enter the optical fiber 8, it operates as an optical isolator. It is possible to do so.

Figure 4 shows the above situation viewed from within the y-2 plane. In the figure, 15 is the ordinary light based on the birefringent crystal that the light passes through first, and 16 is the extraordinary light. There is.

4a shows the light traveling from the optical fiber 8 to the optical fiber 9, and FIG. 4(a) shows the light traveling from the optical fiber 9 to the optical fiber 8.

That is, according to this, light emitted from one optical waveguide enters the other optical waveguide in a state of convergence within the plate-shaped birefringent crystal, and light emitted from the other optical waveguide enters the plate-shaped birefringent crystal. It can be seen that the birefringent crystal exhibits a diverging state and can function as an isolator configured so that it does not enter one of the optical waveguides.

In addition, in the above, the rotation direction given to polarized light by the magneto-optical material 13 and the crystal 14 having optical rotation or anisotropy,
Furthermore, even if the inclination of the optical axis of the birefringent crystal is different from the state described here, the operation can be explained, but it will be omitted here.

Further, the configuration according to the present invention can be applied not only to light but also to electromagnetic waves in general (for example, Mi-IJ waves, etc.).

FIG. 5 shows another embodiment of the present invention, in which 1
7 is a birefringent crystal with one side polished into a spherical surface.

And the other 8 9 13 1412 (the same applies hereafter)
The principle of operation is the same as that of the structure shown in Figure 2, but the structure is simplified by giving the birefringent crystal 17 (or 13, 14, or 12) a lens function. is a feature of this configuration.

FIG. 6 also shows another embodiment of the present invention, in which reference numeral 18 denotes a total reflection mirror attached to the end face of the magneto-optical material 13, which has the function of multiple-reflecting light internally.

Here, if the Faraday effect of the magneto-optical material 13 is small, a large rotation angle can be obtained by using such a structure.

That is, in this case, as shown in FIG. 10a, the magnetic field is applied approximately parallel to the optical path within the crystal.

By doing this, the state of deflection passing through the inner crystal surfaces A and B changes as shown in bc of the figure.

In other words, as can be seen from these figures, even if sufficient polarization rotation is not achieved with one pass through the crystal, the rotation angle increases in proportion to the number of passes through multiple passes (multiple reflections). It is.

This can be similarly applied to the embodiment shown in FIG. 7, which will be described later.

FIG. 7 also shows another embodiment of the present invention, in which reference numeral 19.20 indicates a tabular birefringent crystal.

FIG. 8 shows the positional relationship of planes A, B, and C formed by the optical axes and optical axes (Z-axes) of each of the birefringent crystals 11, 19, and 20 in the embodiment of FIG. 7.

That is, B and C are set to be perpendicular to each other and inclined by 45 degrees with respect to A.

Moreover, as can be seen from FIGS. 9a and 9b, in this embodiment,
The light from the optical fiber 8 enters the optical fiber 9, but
Conversely, the light from optical fiber 9 does not enter optical fiber 8.

Incidentally, since FIG. 9 ab can be explained in accordance with the case of FIGS. 3 a and b described above, the explanation will be omitted here.

As explained above, according to the present invention, two or three birefringent crystals, a magneto-optical material, a crystal having optical rotation or anisotropy are selectively combined, and further, the imaging effect of a lens is used. As a result, it can function even for different polarized lights that are orthogonal to each other, and because it has a configuration that can be inserted between optical waveguides, it is possible to create an optical isolator that has no loss and is suitable for, for example, multimode optical fibers. There are advantages.

[Brief explanation of the drawing]

Figures 1a and b are block diagrams showing a conventional optical isolator, Figure 2 is a block diagram showing an embodiment of the optical isolator according to the present invention, and Figure 3ab is for explaining the operating principle of Figure 2. Figures 4a and 4b are diagrams showing the operating state of Figure 2, Figures 5, 6 and 7 are configuration diagrams showing other different embodiments of the present invention, The figure is a diagram showing the positional relationship between the optical axes of the birefringent crystal and the plane formed by the optical axis in the embodiment of FIG. 7, and FIGS. 9a and b are diagrams for explaining the operation of the embodiment of FIG. 7. , FIG. 10 abc are diagrams for explaining the operation of the embodiment shown in FIG. 8.9... Optical fiber, 10... Lens, ii. 12...Birefringent crystal, 13...Magneto-optical material, 14...Optical rotation crystal, 15...
・Ordinary light at the incident part, 16... Extraordinary light at the incident part, 17... Birefringent lens, 18... Total reflection mirror, 19, 20... ...Birefringent crystal.

Claims (1)

[Claims] First and second plate-shaped birefringent crystals are provided between the 12 optical waveguides, and the polarization directions of the incident light and the outgoing light are changed by magnetization between the first and second birefringent crystals. Insert a magneto-optical material whose length is determined so that the polarization direction of the incident light and the output light differ by approximately 45 degrees, and a crystal having optical rotation or anisotropy whose length is determined so that the polarization directions of the incident light and the output light differ by approximately 45 degrees. Furthermore, one or more lenses are added between the two optical waveguides, or the end surface of at least one of birefringent crystals, magneto-optical materials having optical rotation or anisotropy is curved. By providing this function, the light emitted from one optical waveguide exhibits a state of convergence within the flat birefringent crystal and enters the other optical waveguide, and the light emitted from the other optical waveguide enters the flat birefringent crystal. The optical axis of each of the first and second plate-shaped birefringent crystals is included in the same plane. An optical isolator characterized in that the optical isolator is set so that the A first and second plate-shaped birefringent crystal is provided between the two optical waveguides, and the polarization directions of the incident light and the output light differ by approximately 45 degrees due to magnetization between the first and second birefringent crystals. A magneto-optical material with a predetermined length and a crystal with optical rotation or anisotropy with a predetermined length such that the polarization directions of the incident light and the output light differ by approximately 45° are inserted, and the above two light guides are One or more lenses are added between the wave paths, or the end surface of at least one of the above birefringent crystals, magneto-optical materials having optical rotation or anisotropy is curved to have a lens function. As a result, the light emitted from one optical waveguide enters the other optical waveguide in a state of convergence within the plate-shaped birefringent crystal, and the output light from the other optical waveguide enters the plate-shaped birefringent crystal. The first optical waveguide is configured such that the first optical waveguide exhibits a state of divergence within the optical waveguide and does not enter one of the optical waveguides.
The optical axes of each of the second tabular birefringent crystals are set to be included in the same plane, and a total reflection mirror is added to the end face of the magneto-optic material to internally reflect light multiple times. Features of optical isolators. 3. First, second, and third plate-shaped birefringent crystals are provided between the two optical waveguides, and the polarization directions of the incident light and the output light are set to about 45 by magnetization between the first and second birefringent crystals.
Insert magneto-optical materials whose lengths are determined to differ by °, and further add one or more lenses between the two optical waveguides, or at least one of the birefringent crystals and magneto-optic materials described above. By making one end face curved to have a lens function, the light emitted from one optical waveguide appears to be converging within the plate-shaped birefringent crystal and enters the other optical waveguide, and The configuration is such that the light emitted from the optical waveguide exhibits a state of divergence within the planar birefringent crystal and does not enter one of the optical waveguides, and each of the second and third planar birefringent crystals The two planes formed by the optical axes are set to be perpendicular to each other and are inclined by approximately 45° with respect to the plane formed by the optical axes of the first tabular birefringent crystal. Features of optical isolators. First, second, and third plate-shaped birefringent crystals are provided between the 42 optical waveguides, and the polarization direction of the incident light and the output light is set to about 45 by magnetization between the first and second birefringent crystals.
Insert magneto-optical materials whose lengths are determined to differ by °, and add one or more lenses between the two optical waveguides, or At least one end face is curved to have a lens function, so that the light emitted from one optical waveguide enters the other optical waveguide while being converged within the plate-shaped birefringent crystal; The second and third planar birefringent crystals are configured such that the light emitted from the other optical waveguide is in a state of divergence within the planar birefringent crystal and does not enter one of the optical waveguides. The two planes formed by the respective optical axes of the first plate-shaped birefringent crystal are set to be perpendicular to each other and are inclined by approximately 45° with respect to the plane formed by the optical axes of the first tabular birefringent crystal. An optical isolator further comprising a total reflection mirror that internally reflects light multiple times on the end face of the magneto-optical material.