JPH06324289A - Polarization beam splitter and optical circulator using this splitter and optical switch - Google Patents

Abstract

PURPOSE:To provide the optical circulator or optical switch which decreases the directions of incident and exit ports of a 4-port optical circulator, etc. CONSTITUTION:This polarization beam splitter 1 having a triangular columnar shape is constituted by respectively optically polishing quadrangular prism glass 2 having a trapezoidal shape and triangular columnar glass 3 having a rectangular triangular shape, depositing polarized light separating films 4 by evaporation on the surfaces corresponding to the upper base of the trapezoidal shape or the base of the triangular shape, joining both with optical adhesives and forming antireflection films on the light incident and exit faces a to f. This optical switch is constituted by arranging two polarization beam splitters in such a manner that the slopes thereof are paralleled, inserting a 45 deg. Faraday rotor and a half-wave plate therebetween and using a permanent magnet as a means for impressing the magnetic field to the Faraday rotor and an electromagnet in place of the optical circulator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization beam splitter capable of miniaturizing an optical circulator and an optical switch, an optical circulator using the same, and an optical switch.

[0002]

2. Description of the Related Art Optical circulators are widely used for two-way communication and optical measurement. Conventional four-port optical circulators have two triangular prism-shaped polarization beam splitters 21 and 22 as shown in FIG. Are arranged at right angles, and a 45 ° Faraday rotator 23 and a ½ wavelength plate 24 are inserted between them, and the respective light input / output ports are radially emitted in four directions. .

[0003]

However, in such a form in which the input / output ports of the optical circulator go out in four directions, the optical circulator main body becomes large. In addition, since the minimum bending radius of the optical fiber is about 20 mm when it is mounted on the substrate, a space that does not cause optical loss due to bending is required to process the optical fiber at each input / output port. Further, in order to effectively utilize the substrate surface, the optical circulator must be installed in the center of the substrate, and there is almost no degree of freedom in designing the substrate.

The present invention has been made in view of the above background, and an object of the present invention is to provide an input / output port for an optical circulator, an optical switch, etc., which has been conventionally provided in four directions.
It is to provide a polarization beam splitter capable of emitting light in two directions or two directions. Further, another object of the present invention is to use such a triangular prism-shaped polarization beam splitter,
An object of the present invention is to provide an optical circulator and an optical switch in which the input / output ports are arranged in two directions or one direction.

[0005]

In order to achieve the above object, in a polarizing beam splitter according to the present invention, a square prism glass having a trapezoidal cross section and a triangular prism glass having a right triangle shape in cross section are optically polished, A polarization splitting film was vapor-deposited on the upper base of the trapezoid or the surface corresponding to the bottom of the triangle, and the two were joined by an optical adhesive, and an antireflection film was applied to the light input / output surface.

In the optical circulator according to the present invention,
Two polarization beam splitters described above are used and are arranged so as to face each other so that their slopes are parallel to each other, or symmetrically arranged so as to face each other. Then, a 45 ° Faraday rotator, 1/2
A wave plate was inserted, an optical fiber and a condenser lens were arranged in each of the entrance / exit ports, and a permanent magnet was arranged around the Faraday rotator. When the two polarization beam splitters are symmetrically arranged, it is preferable to further insert the polarization dispersion compensator on the short optical path side.

Further, by disposing an electromagnet instead of the permanent magnet arranged around the Faraday rotator used in the optical circulator having each of the above-mentioned constitutions, the optical switch according to the present invention is constituted.

[0008]

The polarizing beam splitter according to claim 1 is a bonded body of a trapezoidal quadrangular prismatic glass and a right-angled triangular triangular prismatic glass, which has a polarization separating film on the bonding surface and antireflection films on both sides thereof. Since it has an entrance / exit surface, two ports can be arranged in parallel on the same side. Therefore, by using this, the direction of the input / output port can be reduced from the conventional 4 directions to 2 directions or 1 direction, and the optical circulator and the optical switch can be downsized.

Further, when two polarization beam splitters according to the present invention are arranged so as to face each other so that their slopes are parallel to each other to constitute an optical circulator (optical switch), the directions of the input / output ports are two directions. Decrease. For this reason, it is possible to reduce the size and mount it on the side portion of the substrate.
Therefore, it is possible to reduce the space for mounting on a substrate, and to provide an optical circulator (optical switch) with a high degree of freedom in substrate design.

Further, when an optical circulator (optical switch) is constructed by arranging the two polarization beam splitters symmetrically, the direction of the input / output ports is reduced to one direction, and the installation space is further increased. Is reduced, and it is possible to mount it on the corner portion of the substrate. Further, in the above configuration, when the polarization dispersion compensator is inserted on the short optical path side between the two polarization beam splitters, there is no optical path difference and no polarization dispersion, and an optical circulator in which all ports are arranged in parallel in the same direction ( Optical switch) is obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a polarization beam splitter according to the present invention. As shown in the figure, the polarization beam splitter 1 includes a rectangular column glass 2 having a trapezoidal cross section and a triangular column glass 3 having a right triangle shape in cross section.
And are optically polished, and the polarization separation film 4 is vapor-deposited on the surface c corresponding to the upper base of the trapezoid or the bottom of the triangle, and the two are bonded with an optical adhesive to form a larger right triangular prism having a right triangular cross section. is doing. Square column glass 2 after this bonding
The two surfaces (a total of four surfaces) a, b, d, and e of the triangular prism glass 3 excluding the inclined surfaces c and f are used as the light incident and outgoing surfaces, and the four light incoming and outgoing surfaces a and b. , D, and e are each provided with an antireflection film.

Next, the operation of the above embodiment will be described. First, as shown in FIG. 2A, when non-polarized light is incident on the surface d, it is totally reflected by the slope f and S-polarized and P by the surface c.
Divided into polarized light, P-polarized light is directly reflected from the surface b, and S-polarized light is totally reflected by the inclined surface f and emitted from the surface e. Both polarized lights emitted from the polarization beam splitter 1 are parallel light beams. Further, as shown in FIG. 7B, when unpolarized light is incident on the surface a, it is split into S-polarized light and P-polarized light on the surface c as described above, and the S-polarized light is reflected on the surface c, so that the surface b remains unchanged. Emitted from the surface, the P-polarized light passes through the surface c and is totally reflected by the inclined surface f, and then the surface e
Exit from.

By the way, in order to construct an optical circulator and an optical switch, two polarization beam splitters and polarization rotating means are required as is well known. In order to configure with these minimum components, the polarized beam splitter must have the same polarized light position even if they are incident on different incident positions (planes shown in FIGS. 2A and 2B). (surface)
It is desirable that the polarized light is emitted at a wavelength of 1, and the separated polarized lights are parallel to each other. This facilitates optical axis adjustment and reduces the number of parts.

Then, in the relationship of FIGS. 2 (A) and 2 (B),
Two incident ports can be arranged in parallel while satisfying these conditions. Therefore, this polarization beam splitter
If one is used, four incident ports can be arranged in one direction or two directions. Further, this can be expected to reduce the size of the main body, save space when implemented on a board, and increase the degree of freedom in board design.

FIG. 3 shows an embodiment of the optical circulator according to the present invention. As shown in the figure, the two polarization beam splitters 1 each having the above-mentioned triangular prism shape are arranged so as to face each other so that their slopes are parallel to each other, and a 45 ° Faraday rotator 5 and a half wave plate 6 are inserted between them. An optical fiber 7 and a condenser lens 8 are arranged at each of the input / output ports, and a permanent magnet 9 is used as a magnetic field applying means for applying a magnetic field to the Faraday rotator.
Is used. An optical switch can be configured by using an electromagnet instead of the permanent magnet 9 as a magnetic field applying unit for the Faraday rotator 5.

The two polarization beam splitters 1,
1, the surfaces b and e of one splitter face the surfaces e and b of the other splitter, and the surfaces d and d of one splitter are
The surface a and the surfaces a and d of the other splitter are the entrance and exit surfaces.

In FIG. 3A, port 1 to port 2, FIG.
(B) shows a path through which light travels from port 2 to port 3. The Faraday rotator 5 and the half-wave plate 6 are arranged so that the plane of polarization does not rotate when the light travels from left to right on the paper surface, and the polarization plane rotates by 90 ° when the light travels from right to left on the paper surface. Is set to. As shown in FIG. 3, the ports 1 and 3 are on the front side, the ports 2 and 4 are on the other side, and the ports project in two directions from the main body. Therefore,
The positions of the four ports are reduced in two directions from the conventional four directions.

By thus arranging the positions of the four ports in two directions, the size of the main body of the optical circulator and the optical switch can be reduced. Further, when the optical fiber is mounted on the board, it can be installed on the side of the board, so that the processing of the optical fiber is facilitated and the degree of freedom in board design is increased.

FIG. 4 shows another embodiment of the optical circulator according to the present invention. As shown in the figure, this example is different from the above-described embodiment in that two polarization beam splitters 1 having the above-mentioned triangular prism shape are symmetrically arranged to face each other.
A 45 ° Faraday rotator 5 and a half-wave plate 6 are inserted between the two polarization beam splitters 1, and an optical fiber 7 and a condensing lens 8 are arranged at each input / output port to perform Faraday rotation. Arranging the permanent magnet 9 around the child 5 is similar to the above-described example. Also in this example, it goes without saying that the optical switch can be constructed by using an electromagnet instead of the permanent magnet.

FIG. 4A shows a path of light traveling from port 1 to port 2, and FIG. 4B shows a path of light traveling from port 2 to port 3. The Faraday rotator 5 and the half-wave plate 6 are set so that the plane of polarization is rotated by 90 ° when the light travels from left to right on the paper surface. Circulation is performed as shown in this figure, and all the ports are arranged in the same direction.

As described above, by making the positions of the ports the same as shown in FIG. 4, the size of the main body of the optical circulator or the optical switch can be reduced. Further, when the optical fiber is mounted on the board, it can be installed at the corner of the board, so that the processing of the optical fiber is facilitated, and the freedom of board design is increased.

FIG. 5 shows still another embodiment of the optical circulator according to the present invention. That is, the configuration of FIG. 4 has a problem that the optical path lengths of S-polarized light and P-polarized light differ. Therefore, in this example, the optical path length difference is eliminated. Specifically, in addition to the basic configuration in which a 45 ° Faraday rotator 5 and a half-wave plate 6 are inserted between two symmetrically arranged triangular polarization beam splitters 1, further on the short optical path side. The polarization mode dispersion compensating plate 10 is inserted.

That is, as shown in FIG. 6, apparently,
An optical path length difference L occurs in one polarization beam splitter 1, and 2
Since it is used in some places, the optical path length difference is 2L, and assuming that the refractive index of the glass material is ng, an optical path length difference of 2ng · L occurs. Since the optical paths of the polarized lights thus separated are different from each other, polarization dispersion occurs. To compensate for polarization dispersion, the optical path lengths should be equal. Therefore, by selecting the thickness of the polarization dispersion compensating plate 10 or a glass material having an appropriate refractive index,
There will be no polarization dispersion, and an optical circulator will be constructed in which all ports are arranged in parallel in the same direction.

To explain the point that the difference in optical path length is zero, both polarized lights dispersed by the polarization beam splitter pass through the Faraday rotator 5 and the half-wave plate 6, so Ignore and think. One of the separated polarized lights propagates in space as it is, and the other polarized light travels through the polarization dispersion compensating plate 10 to the opposite polarization beam splitter 1. Assuming that the refractive index of the space is 1, the refractive index of the polarization dispersion compensator is nc, and the thickness is d, the optical path length at this time is one optical path length d and the other polarized light is the optical path length n.
c · d. Therefore, if the refractive index and the thickness of the polarization dispersion compensating plate are appropriately selected so as to satisfy (nc-1) d = 2ng.L, the optical path length difference becomes zero. Since the other configurations and operations are the same as those of the above-described respective embodiments, the same reference numerals are given and the description thereof will be omitted.

In each of the above-described embodiments, the bonding positions of the trapezoidal quadrangular prismatic glass and the right triangular triangular prismatic glass are determined by the ratio of the side lengths of the surfaces a and d (or the surfaces b and e). In the present invention, the two input / output ports are adjacent to each other in the same polarization beam splitter, so that the adjoining input / output ports are spaced apart from each other widely. It is preferable that the side length of the entrance / exit surface a (or b) is shorter than the exit surface d (or e).

[0026]

As described above, in the polarization beam splitter according to the present invention, four input / output ports can be arranged in one direction or two directions in the optical circulator, the optical switch, etc., and the size of the main body can be reduced and the substrate can be reduced. It can be expected to save space and increase the degree of freedom in board design.

In the optical circulator and the optical isolator constructed by appropriately arranging the polarization beam splitter, the main body can be downsized and at the same time,
When the board is mounted, the fiber can be easily processed, and the degree of freedom in design is increased. Moreover, when the two polarization beam splitters are symmetrically arranged and the polarization dispersion compensator is arranged at a predetermined position between them, all the ports are arranged in parallel in the same direction, and polarization dispersion does not occur. Therefore, it is advantageous for long distance and large capacity transmission.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a polarization beam splitter according to the present invention.

FIG. 2 is a diagram showing an operation of the polarization beam splitter of FIG.

FIG. 3 is a diagram showing an embodiment of an optical circulator according to the present invention.

FIG. 4 is a diagram showing another embodiment of the optical circulator according to the present invention.

FIG. 5 is a diagram showing still another embodiment of the optical circulator according to the present invention.

6 is a diagram for explaining an optical path length difference of the optical circulator shown in FIG.

FIG. 7 is a diagram showing a conventional polarization beam splitter.

[Explanation of symbols]

 1 polarization beam splitter 2 trapezoidal quadrangular prism glass 3 right-angled triangular prismatic glass 4 polarization separation film 5 Faraday rotator 6 1/2 wavelength plate 7 optical fiber 8 condenser lens 9 permanent magnet (magnetic field applying means) 10 polarization dispersion Compensation plate a, b, d, e Light input / output surface

Claims (5)

[Claims] 1. A prismatic glass having a trapezoidal cross section and a triangular prismatic glass having a right triangle in cross section are optically polished to form a polarization separation film on the upper base of the trapezoid or the surface corresponding to the base of the triangle. A polarizing beam splitter, characterized in that the two glasses are bonded together with an optical adhesive, and an anti-reflection film is applied to the light entrance / exit surface. 2. The two polarization beam splitters according to claim 1, which are arranged so as to face each other with their slopes parallel to each other,
Moreover, a 45 ° Faraday rotator and a 1/2 wavelength plate are inserted between both polarization beam splitters arranged opposite to each other, and an optical fiber and a condenser lens are arranged at each input / output port, and the Faraday rotator is provided. An optical circulator characterized by using a permanent magnet as a means for applying a magnetic field. 3. The two polarization beam splitters according to claim 1 are used, which are symmetrically opposed to each other, and a 45 ° Faraday rotator, 1 /, is disposed between the opposed polarization beam splitters. An optical circulator characterized in that a two-wave plate is inserted, an optical fiber and a condenser lens are arranged at each of the entrance and exit ports, and a permanent magnet is used as a means for applying a magnetic field to the Faraday rotator. 4. Two polarization beam splitters according to claim 1 are arranged symmetrically opposite each other, and a 45 ° Faraday rotator, 1 /, is arranged between the polarization beam splitters oppositely arranged. As a means for applying a magnetic field to the Faraday rotator, a two-wave plate is inserted, a polarization dispersion compensator is further inserted on the short optical path side, an optical fiber and a condenser lens are arranged at each input / output port, An optical circulator characterized by using a permanent magnet. 5. An optical switch, characterized in that an electromagnet is used instead of a permanent magnet as means for applying a magnetic field to the Faraday rotator according to claim 2, 3, or 4.