JPS63220109A - Deflection separation/synthesis prism - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] ``-1'' The first . It consists of a second birefringent plate and a compensating plate that is inserted at a predetermined position between them and rotates the polarization plane of transmitted light by 90 degrees.
Despite its relatively simple structure, a polarization separation/synthesis prism that separates each of the incident light rays and then sends them out from the same part of the second birefringent plate, has a relatively simple structure. It can be used in various multi-boat type optical devices that require a high degree of polarization separation.

TECHNICAL FIELD The present invention relates to the structure of a polarization separation/synthesis prism particularly suitable for use in a multi-boat type optical device.

For example, an example of an optical switch that changes and switches the optical path using an appropriate control signal is one that uses a pair of polarization separation/synthesis prisms and controls the polarization state of the signal light between them. can. A polarization separation/composition prism is used to separate incident light into two optical paths (usually consisting of linearly polarized light whose polarization planes are orthogonal to each other), or conversely, to combine the two optical paths. In addition to optical switches, it is also applied to optical isolators, optical circulators, etc. As described above, polarization separation/synthesis prisms are widely used in a variety of optical devices, and there is a need for something with a simple configuration and reliable operation.

As conventional polarization separation/composition prisms, those constructed using a polarization separation film and those constructed using a birefringent plate are mainly put into practical use.

Among these, those using a polarization separation film have the advantage that the optical path can be set freely depending on the shape of the prism on which the film is formed, and are said to be applicable to a variety of devices and have high versatility. On the other hand, a device using a birefringent plate can obtain a high degree of polarization separation, and is said to be suitable for use in high-performance devices such as optical isolators by taking advantage of this feature.

FIG. 6 shows an example of the configuration of an optical switch as an example of the use of a polarization separation/synthesis prism using a polarization separation film.

This optical switch is constructed by arranging polarization separation/synthesis prisms 1.1' of the same configuration at positions rotationally symmetrical to each other, and providing a polarization control means 5 between them. The polarization separation/synthesis prism 1 (1') is a parallelogram prism 2 (2').
It has a configuration in which a polarization splitter 114 (4') such as a dielectric multilayer film is inserted between a triangular prism 3 (3') and a triangular prism 3 (3').

The polarization control means 5 is configured using, for example, a magneto-optic crystal and a half-wave plate, and depending on the polarity of the magnetic field applied to the magneto-optic crystal, the polarization control means 5 rotates the polarization plane of the transmitted light by 90 degrees or polarizes the light so that it does not rotate. can be controlled.

Now, the light that is incident on the polarization separation/synthesis prism 1 toward the polarization separation WA4 is polarization separation! ! I4 separates the light into a component P having a plane of polarization parallel to the plane of the paper and a component S having a plane of polarization perpendicular to the plane of the paper. These separated lights are polarized 11
When the plane of polarization is not rotated by the i control means 5, it is combined in the polarization separation/synthesizing prism 1' and emitted in the six directions of arrows, and when the plane of polarization is rotated by 90 degrees by the polarization control means 5, it is emitted in the direction of arrow B. be done. In this way, the direction of the emitted light can be switched by the polarization mail by the polarization control means 5.

FIG. 7 shows an example of the configuration of an optical isolator as an example of the use of a polarized light separating/combining prism using a birefringent plate. This optical isolator has birefringent plates 6 and 6' arranged in parallel with their principal axes in the same direction, and a polarization plane rotation means 7 provided between them.

The polarization plane rotating means 7 is constructed using a magneto-optical crystal with a fixed applied magnetic field and a half-wave plate, and rotates the polarization plane of transmitted light in the forward direction (from left to right in the paper) in the traveling direction. It functions to rotate the light 90 degrees clockwise toward the viewer, and not to rotate the light in the opposite direction.

Now, the light incident on the birefringent plate 6 from a light source (not shown) is
It is separated into a component p having a plane of polarization parallel to the plane of the paper and a component S having a plane of polarization perpendicular to the plane of the paper, and the plane of polarization of each component is rotated 90 degrees clockwise in the forward direction by the plane of polarization rotation means 7. After that, they are combined by a birefringent plate 6' and emitted as a single beam. For example, if a part of this emitted light is reflected by a reflecting object (not shown) and enters the birefringent plate 6' from the emitted optical axis, this reflected light is separated by the birefringent plate 6' and is then transferred to a polarization plane rotating means. 7
The light enters the birefringent plate 6 without rotating its plane of polarization, is further separated as shown by the dotted line in the figure, and is prevented from returning to the light source.

One problem that Ming is trying to solve.

However, the two types of polarization separation/synthesis prisms mentioned above are
I had the following problem fish.

First, a polarization separation/synthesis prism constructed using a polarization separation film has a high degree of freedom in setting the optical path and is said to be highly versatile, but due to the characteristics of the polarization separation film itself, it has a high degree of polarization separation over a wide wavelength band. The problem is that it is difficult to obtain If a high degree of polarization separation cannot be obtained, the wavelength range in which this prism can reliably operate will become narrower when, for example, an optical switch is constructed using this prism.

On the other hand, a polarization separation/synthesis prism constructed using a birefringent plate can obtain a high degree of polarization separation over a relatively wide wavelength band, but the polarization separation angle of the birefringence plate itself is extremely small. (For example, the thickness of the prism is about 111I11.) Therefore, if this prism is applied to a multi-boat type optical device, it has a problem that it will have a complicated structure.

The present invention was created in view of these problems, and its purpose is to provide a polarization separation/synthesis prism that has a relatively simple configuration, can operate reliably over a wide wavelength band, and is suitable for multi-boat type optical devices. It is about providing.

The problems of the prior art described above are solved by the structure of the polarization separation/synthesis prism shown below.

A first birefringent plate and a second birefringent plate, whose incident and exit surfaces are polished parallel to each other, are arranged parallel to each other. - A compensation plate is provided at a predetermined position between both birefringence plates to rotate the polarization plane of transmitted light by 90 degrees.

This predetermined position is on the optical path of one of the linearly polarized light components having mutually orthogonal polarization planes that are separated for each light ray when the two parallel light rays are made incident on the first ?1y refracting plate.

The thickness of the second birefringent plate and the distance between the two parallel rays are:
The separated linearly polarized light component is the second polarized light component for the two light beams.
The beams are set to be emitted from the same part of the birefringent plate.

Function When two parallel light rays are incident on the first birefringent plate, each light beam is separated into two linearly polarized light components having planes of polarization perpendicular to each other, and one of these components is divided into two linearly polarized light components by the compensator. The plane is rotated 90 degrees. Therefore, the separated light for one incident light ray has the same polarization plane and the second
The light is incident on the birefringent plate. The thickness of the second birefringent plate and the distance between the two parallel light beams are set as described above so that each separated light beam is emitted from the same location on the second birefringent plate. When used as
By switching the polarization state of the incident separated light beam,
This is to ensure that the output positions of the combined light are interchanged.

EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the configuration of a polarization separation/synthesis prism manufactured by applying the present invention. This polarization separating/combining prism 10 has a first birefringent plate 11 and a second birefringent plate 12 of the same configuration arranged in parallel, and a compensating plate 13, 14 between them.
It is configured with . The crystal axis 11a of the first birefringent plate 11 (which coincides with the principal axis, the same applies hereinafter) and the crystal axis 128 of the second birefringent plate 12 are set to face in the same direction. These birefringent plates 11.12 are, for example, 1
It can be cut out from a sheet of rutile (T10□ single crystal) plate and used. For example, a compensator plate 1 consisting of a 172 wavelength plate
3.14 functions to rotate the polarization plane of incident light by 90 degrees, and may be directly formed as a film on the first birefringent plate 11 or the second birefringent plate 12 depending on the case.

Now, the two parallel light rays 101 and 102 are passed through the first birefringent plate 11.
Suppose that it is made incident on . The light ray 101 is divided into a linearly polarized light component (hereinafter referred to as an S-wave component) having a polarization plane perpendicular to the plane of paper as an ordinary ray and a linearly polarized light component (hereinafter referred to as an S-wave component) having a polarization plane parallel to the plane of paper as an extraordinary ray in the first birefringent plate 11. The P-wave component is separated and emitted. Of these, the S-wave component is converted into a P-wave component by the compensator 14, refracted as an extraordinary ray within the second birefringence plate 12, and emitted from the point. Since the P-wave component of the separated light beam does not pass through the compensator 14, it enters the second birefringent plate 12 in its polarized state as it is, is refracted as an extraordinary light beam, and is emitted from point C.

On the other hand, the light ray 102 also passes through the first birefringent plate 11.
Similarly, it is separated into an S wave component and a P wave component and is emitted. S
The wave component enters the second birefringent plate 12 in its polarized state and exits from the point. The P-wave component has its polarization plane rotated by 90 degrees by the compensator 13 to become an S-wave component, and the second
The light is emitted from the point C as an ordinary ray of the birefringent plate 12.

FIG. 2 shows a modification of FIG. 1, and the same members as in FIG. 1 are denoted by the same reference numerals (the same applies hereinafter). Here, the second birefringent plate 15 is an inverted version of the second birefringent plate 12 in the previous example, and one compensating plate 16 is placed between the first birefringent plate 11 and the second birefringent plate 15. I try to let them do it. Now, two parallel rays 201.20
2 is made incident on the first birefringent plate 11. The S wave component of the light 111201 separated by the first birefringent plate 11 is
It is emitted from point F as an ordinary ray of the second birefringent plate 15, and P
The wave component is also emitted from point E by the compensating plate 16 as an ordinary ray of the second birefringent plate 15 .

The S-wave component of the light ray 202 separated by the first birefringent plate 11 is converted into a P-wave component by the compensator 16 and is emitted from the point F as an extraordinary ray of the birefringent plate 15.

The P-wave component remains at point E as an extraordinary ray of the birefringent plate 15.
It is emitted from. The polarization separating/combining prism 15 having such a configuration can be applied to optical devices that do not require phase matching because the optical path lengths of the light beams 201 and 202 are different.

FIG. 3 is a block diagram of a two-man power two-output optical switch constructed using the polarization separation/synthesis prism shown in FIG. 1.

This optical switch has a magneto-optic crystal 17 between the polarization separation/synthesis prism 10 and a polarization separation/synthesis prism 10' which is arranged at a rotationally symmetrical position when viewed from the top of the page.
and a 1/2 wavelength plate 18 are arranged. A magnetic field of a predetermined intensity is applied to the magneto-optic crystal 17 by a magnetic field applying means (not shown), and the polarity of this applied magnetic field can be switched by, for example, an electrical switching signal. The light passing through the magneto-optic crystal 17 is rotated 45 degrees clockwise or 45 degrees counterclockwise in the forward direction and then output. The thickness of the half-wave plate 18 is set so that the polarization plane of transmitted light always rotates 45 degrees clockwise toward the traveling direction.

Here, it is assumed that two mutually parallel light beams 301 and 302 are incident on the polarization separation/synthesis prism 10. Assuming that the rotation direction of the polarization plane of the magneto-optic crystal 17 is counterclockwise toward the forward direction, this rotation is caused by the rotation of the half-wave plate 18.
The polarization plane of the light transmitted through both optical elements 17 and 18 is not rotated. At this time, the light 1i301 separated into two P-wave components by the polarization separation/synthesis prism 10 remains in its polarized state, that is, as two P-wave components at the polarization separation/synthesis prism 10'.
and only one P wave component is converted into S by the compensator plate 14.
It is considered to be a wave component. These P wave components and S wave components are combined and emitted from point G.

On the other hand, the light ray 302 separated into two S-wave components by the polarization separation/synthesis prism 10 travels straight through the second birefringent plate 12 of the polarization separation/synthesis prism 10' in the same polarization state as shown by the dotted line in the figure. ), only one S-wave component is made into a P-wave component by the compensation plate 13. These S wave components and P
The wave components are combined and emitted from point H.

Next, assuming that the magneto-optic crystal 17 rotates the polarization plane of the transmitted light by 45 degrees clockwise in the forward direction, the transmitted light is transmitted by the magneto-optic crystal 17 and the half-wave plate 18 by a total of 90 degrees. It will rotate. At this time, the light ray 301 separated into two P-wave components by the polarization separation/synthesis prism 10 becomes an S-wave component when the light ray 301 enters the polarization separation/synthesis prism 10'. The light is emitted from point H via the same path as light [1302. Also, 911302 is a polarization separation/synthesis prism 10'
The light beam is emitted from point G via the same path as the light beam 301 in the precondition. In this way, since the output positions of the two input lights can be switched by the rotation direction of the polarization plane of the magneto-optic crystal 17, in other words, the polarity of the magnetic field applied to the magneto-optic crystal 17, the traveling direction of the light can be electrically controlled. It is something that can be done.

In the above description, it has been assumed that the first birefringent plate 11 and the second birefringent plate 12 constituting the polarization separation/synthesizing prism have the same thickness, but the present invention is not necessarily limited to this. For example, as shown in FIG.
A two-manufactured two-output optical switch may be constructed by a polarization separating/combining prism 20, 20' constructed using a second birefringent plate 22 having a different thickness. In this case, the distance d1 between the two incident rays 401 and 402 is set so that the optical path of the two polarized components separated from the incident ray 401 and the optical path of the two polarized components separated from the incident ray 402 coincide. be done. In the embodiment shown in FIG. 3, the distance between the incident light rays and the distance between the separated polarized light components are the same. Also, the second birefringent plate 22 of the polarization separation/synthesis prism 20
The thickness of the second birefringent plate 22 of the polarization separation/synthesis prism 20' does not necessarily have to match. If these thicknesses do not match, only the distance between the incident light rays, dl, and the distance d2 between the light ray exit points, M, differ.

What should be noted here is that the first ? This means that the thicknesses of the I-refracting plates 11 and 11 must be made the same. If these thicknesses are not made to match -C, the emitted light cannot be made into a single beam, resulting in a disadvantage that the coupling efficiency to an optical fiber (not shown) or the like is reduced.

FIG. 5 is a block diagram of a two-man power one-output optical switch constructed using the polarization separation/synthesis prism 10. This optical switch has a birefringent plate 26 provided with a compensating plate 25 at a predetermined position on one side of the polarization separating/combining prism 10' of the two-manufactured two-output optical switch shown in FIG. The incident light 11501 is converted into two P wave components by the 1/2 wavelength plate 1.
8, these components are emitted from the birefringent plate 2.
6 and are combined and emitted from point I as a single beam. At this time, the incident light beam 502 is emitted from the half-wave plate 18 as two S-wave components, so these components are further separated within the birefringence plate 26 and emitted from points J and K.

On the other hand, when the rotation direction of the polarization plane of the magneto-optic crystal 17 is reversed, the incident light ray 502 is emitted as a single beam from the point I of the birefringent plate 26, completely opposite to the above, and the incident light ray 501 is emitted from the point J and the birefringent plate 26. It will be separated from K and emitted. In this way, the light beam emitted as a single beam from point I can be selected by the direction of the magnetic field applied to magneto-optic crystal 17.

Effects of the Invention As detailed above, according to the structure of the polarization separation/synthesis prism of the present invention, it is possible to apply a birefringent plate having a high degree of polarization separation over a wide wavelength band to a multi-boat type optical device. This has the effect that the performance (for example, extinction ratio) of this device can be improved.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a polarization separation/composition prism showing a preferred embodiment of the present invention, Fig. 2 is a configuration diagram showing a modified example of the polarization separation/composition prism, and Fig. 3 is a configuration diagram of the polarization separation/composition prism. Figure 4 is a block diagram of a two-man power two-output optical switch constructed using the same two-man power two-output optical switch.
A configuration diagram showing a modified example of an output optical switch. Figure 5 is a configuration diagram of a two-man power one-output optical switch configured using the same polarization separation/synthesis prism, and Figure 6 is a configuration diagram using a polarization separation film. A configuration diagram of an optical switch showing an example of the use of a conventional polarization separation/composition prism. Figure 7 shows a conventional polarization separation/composition prism constructed using a birefringence plate.
FIG. 2 is a configuration diagram of an optical isolator showing an example of the use of a synthetic prism. 1.1', 10.10'. 20.20'...Polarization separation/synthesis prism, 4...
Polarization separation film, 6.11.12.15゜22.26... Birefringence plate, 13.14.16... Compensation plate, 17... Magneto-optic crystal, 18... 1/2 wavelength plate . Illustration 1 of the book's pods and flowers

Claims (1)

[Claims] A first birefringent plate (11) and a second birefringent plate (12) whose entrance and exit surfaces are polished parallel to each other are arranged parallel to each other, and the distance between the two birefringent plates (11, 12) is Set the polarization plane of the transmitted light at a predetermined position at 90
It is configured by providing compensating plates (13, 14) that rotate by degrees, and the predetermined positions are such that when two parallel light rays are incident on the first birefringent plate (11), the two light beams are separated and mutually orthogonal. The thickness of the second birefringent plate (12) and the distance between the two parallel light rays are such that the separated linear polarization component is on the optical path of one of the linearly polarized light components having a plane of polarization. A polarized light separating/combining prism characterized in that the polarized light is set to be emitted from the same part of the second birefringent plate (12).