JPH0526172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical isolator device, and in particular:
The present invention relates to an optical isolator device that can be used for light having various wavelengths.

Generally, in an optical isolator device, a magnetic field is applied to a Faraday rotation element in a predetermined direction, and light that has passed through a polarizer is incident on the Faraday rotation element in the direction of the magnetic field, thereby rotating the plane of polarization of the incident light by 45 degrees. After that, it passes through another polarizer to obtain the emitted light. In this configuration, since the rotation angle by the Faraday rotation element is determined by the optical path length within the Faraday rotation element and the wavelength of the incident light,
It is necessary to prepare a separate optical isolator device each time the wavelength of the incident light changes.

On the other hand, an optical isolator device that can be adjusted according to light of different wavelengths is disclosed in Japanese Utility Model Application Publication No. 56-55803. Referring to Figure 1,
The optical isolator device described in the above-mentioned publication includes a polarizer 1, a magnet 2 (the direction of the magnetic field is the direction indicated by arrow h in FIG. 1), and a magnet 2 interposed between the polarizer 1 and the magnet 2. A Faraday rotation element 3 having a slope 3a formed on one side, and a magnetic field direction h of this Faraday rotation element 3.
A prism 4 having a slope 4a parallel to the slope 3a of the Faraday rotator 3 attached to a side surface 3b parallel to ). Further, the slope 3a of the Faraday rotation element 3 and the slope 4a of the prism 4 each form an angle θ (=45°) with respect to the optical axis A, and the magnet 2, the Faraday rotation element 3, and the prism 4 are placed in a magnetic field. It has a configuration that allows it to move in a direction perpendicular to the direction h (arrow Z shown in FIG. 1).

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

First, the light incident on the polarizer 1 becomes linearly polarized light having a specific polarization direction, is guided to the prism 4, is reflected by the slope 4a of the prism 4, and enters the Faraday rotation element 3. Furthermore, the light incident on the Faraday rotation element 3 is reflected by the slope 3a and propagates within the Faraday rotation element 3 in parallel to the light incident on the polarizer. During propagation, the plane of polarization is rotated by the magnetic field applied by the magnet 2, and the Faraday rotation element 3
Emits from.

In this configuration, the light incident on the Faraday rotation element 3 is affected by the rotation of the plane of polarization by the Faraday rotation element 3 when it passes through the optical axis parallel to the magnetic field direction h. The magnet 2, Faraday rotation element 3, and prism 4 are moved in the direction of arrow Z in accordance with the wavelength of the light incident on the rotation element 3, and the rotation angle of the polarization plane due to the magnetic field is 45
degree.

Here, the light emitted from the Faraday rotation element 3 enters the analyzer 5, and the light is emitted from the analyzer 5 because the polarization direction of the polarization plane matches that of the analyzer 5.

On the other hand, the light incident from the analyzer 5 is
By passing through the Faraday rotation element 3 and the prism 4, it becomes linearly polarized light with a plane of polarization tilted 90 degrees with respect to the plane of polarization of the polarizer 1, and enters the polarizer 1, so it does not pass through the polarizer 1. .

The optical isolator device described above changes the optical path length according to the wavelength of the light used by moving the Faraday rotation element 3 in a direction perpendicular to the direction of the magnetic field.
That is, by adjusting the length of the optical axis parallel to the magnetic field direction h within the Faraday rotation element, the rotation angle of the polarization plane can be adjusted. However, the illustrated optical isolator device has the following drawbacks.

First, each of the slopes 3a and 4a of the Faraday rotation element 3 and the prism 4 must have high surface accuracy. This is because if the surface accuracy is poor, the direction of light emitted from the Faraday rotation element will not be constant, and the direction of reflection on each slope will be unspecified, so even if the Faraday rotation element 3 is moved in the Z direction, This is because it is not possible to determine the optical path length according to the wavelength of the light used. In addition, the Faraday rotation element 3
The prism 4 and the prism 4 are usually attached using an adhesive, but there is a drawback that the thickness of the adhesive must be uniform. In other words, if the adhesive film thickness is not uniform, the adhesive will cause the light to be refracted when it enters the Faraday rotator element from the prism, and the light reflected on the slope 3a of the Faraday rotator element 3 will be The direction cannot be made constant, and as a result, the desired optical path length cannot be achieved simply by moving the Faraday rotation element 3 in the Z direction. All of the above drawbacks are caused by adjusting the optical path length.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide an optical isolator device that can be adjusted to work appropriately for light of various wavelengths by varying the magnetic field strength applied to the Faraday rotation element. It is to be.

Another object of the present invention is to provide an optical isolator device that can be easily combined with other optical systems by having the optical axis of the output light on an extension of the optical axis of the incident light.

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

Example 1 This example will be described in detail based on FIG. Note that FIG. 3A is a cross-sectional view, FIG. 1B is a side view, and FIG.

The optical isolator device of this example includes a case 11 having a circular cross section (this case 11 is divided into two parts as shown in FIG. 2b, and is formed integrally after fixing a permanent magnet 12). , and a ring-shaped permanent magnet 12 fixed to the inner wall of this case 11, and the permanent magnet 12 has a magnetic field of sufficient strength to rotate the plane of polarization of light incident on a Faraday rotation element 14 (to be described later) by 45 degrees. occurs. Furthermore, side plates 11a and 11b are positioned in the incident and output directions of light from the case 11, respectively.
1a and 11b are through holes 11c and 11d that face each other
have. Further, a tube 13 (cylindrical body) made of aluminum or the like is inserted into the through holes 11c, 11d and the hole 12a which is the space of the permanent magnet 12.

The tube 13 is connected to the through holes 11c and 11d of the case 11.
As shown in Fig. 2a and c, the through hole 11c side is the N pole and the through hole 11d side is the S pole.
The magnetic field direction h in the hole 12a of the permanent magnet 12 which is a pole
It slides freely in parallel. Further, inside the tube 13, there is a Faraday rotation element 14 made of a known material, for example, paramagnetic glass (FR-5, trade name of Hoya Glass Co., Ltd.), and a Faraday rotation element 14 fixed to the incident side of the Faraday rotation element 14. First beam splitter 1
5 and a second beam splitter 16, and a polarizer 17 that faces the first beam splitter 15 and is fixed to the output side of the Faraday rotation element 14. The first beam splitter 15 and the second beam splitter 16 act as a single polarizer, and the first beam splitter 15
is on the bottom surface of the tube 13 in FIG. 2a, while the second
The beam splitters 16 are each fixed above the first beam splitter 15. Further, the polarizer 17 is fixed on the extension of the optical axis of the light incident on the first beam splitter 15, and is relative to the polarization plane of the polarizer by the first beam splitter and the second beam splitter. It has a polarization plane tilted at 45 degrees. Further, in the Faraday rotation element 14, a first reflective film 14a is deposited on the side surface on the output side at a position facing the second beam splitter 16, and on the other hand, a polarizer on the side surface on the input side of the Faraday rotation element 14 is coated. A position opposite to 17 is coated with a second reflective film 14b.

Next, the operation of the optical isolator device of this example will be explained.

First, the tube 1 in which the Faraday rotation element 14 is installed
3 in parallel to the direction of the magnetic field h, and adjust the position of the Faraday rotation element 14 with respect to the magnetic field H so that an optimal magnetic field can be obtained depending on the wavelength of the incident light 18 and the operating temperature.

In this state, the light 18 entering the tube 13 is
The beam is bent by the beam splitter 15 toward a second beam splitter 16 , and further polarized by the second beam splitter 16 before entering the Faraday rotation element 14 . The light 18 that has entered the Faraday rotation element 14 is reflected by the first reflection film 14a toward the second reflection film 14b, further reflected by the second reflection film 14b, and exits from the Faraday rotation element 14. At this time, the plane of polarization of the light 18 within the Faraday rotation element 14 is rotated by 45 degrees due to the influence of the magnetic field of the permanent magnet 12. next,
The light 18 emitted from the Faraday rotation element 14 is incident on the polarizer 17. At this time, since the inclination of the polarization plane of the light 18 emitted from the Faraday rotation element 14 and the inclination of the polarization plane of the polarizer 17 match, the light 18 is emitted from the polarizer 17.

Generally, the Faraday rotation angle θ obtained by a Faraday rotation element is given by θ=VHl, (where V is the Verdet constant, H is the magnetic field, and l is the length of the optical path parallel to the direction of the magnetic field.) . Since V changes depending on the wavelength of light, in conventional optical isolator devices,
As mentioned above, in order to obtain a predetermined rotation angle (45 degrees), the optical path length l is changed as the wavelength of the incident light changes.

On the other hand, in the first embodiment described above, by adjusting the strength of the magnetic field H, a rotation angle of 45 degrees can be obtained for various wavelengths of light used, and the drawbacks caused by changing the optical path length l can be overcome. Can be removed. Further, even if a Faraday rotation element made of a temperature-dependent material such as paramagnetic glass is used, adjustment can be made according to the operating temperature. Furthermore, the light incident on the optical isolator device is coaxial with the light emitted from the optical isolator device, making it easy to couple it with an external optical system. Furthermore, in this example, since the optical axis within the Faraday rotation element is substantially constant, the uniformity of the curvature of the Faraday rotation element, which is necessary to prevent light scattering, is at the optical axis. Unlike the conventional Faraday rotation element of an optical isolator device in which the optical axis is unspecified, uniformity is not required throughout the Faraday rotation element. Therefore, the manufacturing yield of the material forming the Faraday rotation element can be improved.

Example 2 This example is shown in FIG. Note that this figure is a cross-sectional perspective view. The difference between this example and the first embodiment is that rubber bushes 20 are fixed to the through holes 11c and 11d of the case 11, respectively, and the other configurations are the same as the first embodiment. The rubber bush 20 is provided with a hole, and the tube 13 is fitted into the hole of the rubber bush 20 and is slidably held therein.

Example 3 This example is shown in FIG. Note that this figure is also a cross-sectional perspective view. The difference between this example and the first embodiment is that a thread 13a is cut on the outer peripheral surface of the tube 13 that contacts each of the side surfaces 11a and 11b of the case 11, and when the tube 13 is rotated, the tube 13 follows this thread 13a. moves parallel to the direction of the magnetic field within the hole 12a of the permanent magnet 12, allowing fine adjustment of the tube 13.

Example 4 This example will be explained based on FIG. Note that figure a is a cross-sectional perspective view, and figure b is a side view.

First, the case 21 of this example has a left outer side plate 21a and a left inner side plate 2 on both sides of the permanent magnet 12, respectively.
1b, a right outer side plate 21c, and a right inner side plate 21d, and each side plate 21a, 21b, 2
1c and 21d have through holes having circular cross-sections whose central axes coincide with each other. And between the left inner side plate 21b and the right inner side plate 21d of this case 21,
A permanent magnet 12 similar to that in the first embodiment is fixed. Also, inside this case 21, a guide 30 is provided.
a, a spring 30b, and a collar 30c, and one end of this first tube 30 (permanent magnet 12
side) and has a screw 31a on the outer peripheral surface.
A second pipe 31, which has been cut off, is installed inside.

The guide 30a of the first tube 30 is the left outer side plate 21
The spring 30b is fitted into the notch 21e of the spring 30b.
is the first part between the left inner side plate 21b and the collar 30c.
It is wound around the outer peripheral surface of the tube 30, and one end is pressed against the left inner side plate 21b and the other end is pressed against the collar 30c. Furthermore, the first tube 30 is inserted into the hole 12a of the permanent magnet 12, and inside this tube 30 there is provided a Faraday rotation element similar to that in the first embodiment.
First and second beam splitters and a polarizer are installed inside.

According to this example, the second tube 31 can be rotated along the screw 31a, and the spring 30b of the first tube 30 can smoothly move the first tube 30 forward and backward. The Faraday rotation element inside can be moved back and forth in the hole 12a of the permanent magnet 12 in parallel to the direction of its magnetic field, and as a result, the strength of the magnetic field applied to the Faraday rotation element can be adjusted. Further, according to this example, the guide 30a is the first
Notch 2 formed in the tube 30 of the left outer side plate 21a
1e, the first tube 30 does not rotate even if the first tube 31 rotates. Therefore, when using the optical isolator device in combination with other optical systems, the incident light and It becomes easy to adjust the optical axis, polarization plane, etc. of the emitted light.

The present invention is not limited to the above embodiments, but may be as follows.

First, in the above embodiment, the tube with the Faraday rotation element inside was moved parallel to the magnetic field direction with respect to the magnet, but the magnet may also be moved relative to the tube, or both the tube and the magnet may be moved. It's okay. Further, although ring-shaped permanent magnets are used as magnets, magnets of other shapes may be used, and electromagnets may be used instead of permanent magnets. That is, any magnet may be used as long as it has a space into which a cylindrical body in which a Faraday rotation element is fixedly installed is inserted. The direction of magnetization of the magnet is as shown in Figure 2, that is, the incident side is the north pole,
The direction is not limited to the direction in which the emission side is the S pole, but may be the opposite direction. Furthermore, although two beam splitters, the first and second beam splitters, act as one polarizer, one beam splitter may be used as a polarizer and the other may be used as a mirror. However, using two beam splitters has a better extinction ratio than using one beam splitter, and
Since one beam splitter having an extinction ratio equivalent to that of two beam splitters is very expensive, it is better to use two inexpensive beam splitters. Further, the case and the tube do not have to be cylindrical or tubular, and may be, for example, a cylindrical body with a polygonal cross section. Furthermore, an antireflection film may be coated on the light incident surface and the light exit surface of the Faraday rotation element.

As described above, the present invention adjusts the magnetic field strength for the Faraday rotation element by moving the cylindrical body in which the Faraday rotation element is internally fixed in parallel to the magnetic field direction in the space of the magnetic field application means such as a magnet. Therefore, the Faraday rotation angle can be adjusted sufficiently according to various wavelengths of light without increasing the surface precision of the prism and each slope of the prism and Faraday rotation element, which is required in conventional optical isolator devices that adjust the optical path length. can be adjusted. In addition, since the incident light to the optical isolator device and the output light from the optical isolator device are on the same axis, it is very easy to adjust the optical axis when using this optical isolator device in combination with other optical systems. Therefore, it has a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional optical isolator device, FIG. 2 is a diagram showing an embodiment of the optical isolator device of the present invention, and FIG.
Figure b is a side view, and figure c is a diagram showing the magnetic field distribution of the magnet. 3 and 4 are cross-sectional perspective views showing other embodiments of the optical isolator device of the present invention, respectively. FIG. 5 is a diagram showing still another embodiment of the optical isolator device of the present invention, in which FIG. 5A is a cross-sectional perspective view and FIG. 5B is a side view. 11, 21...Case, 12...Permanent magnet, 1
3... tube, 14... Faraday rotation element, 15...
...First beam splitter, 16...Second beam splitter, 17...Polarizer, 20...Rubber bushing, 30...First tube, 31...Second tube.

Claims (1)

[Scope of Claims] 1. A Faraday rotation element, a magnetic field application means having a space inside that applies a magnetic field to the Faraday rotation element, and at least one of the Faraday rotation element and the magnetic field application means, the magnetic field application means an adjusting means for adjusting the magnetic field strength for the Faraday rotation element by moving parallel to the direction of the magnetic field in the space, and the adjustment means has a cylindrical body with the Faraday rotation element fixed therein;
An optical isolator device comprising means for mechanically moving the cylindrical body together with a Faraday rotation element within a space of the magnetic field applying means and relative to the magnetic field. 2. A Faraday rotation element, a magnetic field application means having a space therein that applies a magnetic field to the Faraday rotation element, and at least one of the Faraday rotation element and the magnetic field application means, and a magnetic field direction in the space of the magnetic field application means. Adjustment means for adjusting the magnetic field strength for the Faraday rotation element by moving it in parallel, means for inputting light into the Faraday rotation element from a predetermined direction, and means for emitting light from the Faraday rotation element. The adjustment means includes a cylindrical body in which the input means, the Faraday rotation element, and the output means are sequentially arranged and fixed, and the cylindrical body is moved together with the Faraday rotation element into the space of the magnetic field application means. It has a means for moving mechanically relative to the magnetic field, and the emitting means is arranged and fixed on an extension of the predetermined direction, and has an optical axis of the incident light and an optical axis of the emitted light. An optical isolator device characterized by having the same axis.