JPH06242401A - Three-port type optical circulator - Google Patents

Abstract

PURPOSE:To increase the coupling efficiency of light by making emitting light of a single beam to a 3rd port. CONSTITUTION:This optical circulator is equipped with a nonreciprocal part 10, a 2nd fiber collimator 32 and a 3rd fiber collimator 34 which are arranged at a 2nd port P2 and a 3rd port P3 on both sides of the nonreciprocal part 10, and a 1st fiber collimator 30 which is arranged at a 1st port P1 nearby the 3rd port P3. Then a triangular prism 20 is arranged between the nonreciprocal part 10 and 1st port P1 and a 1st birefringent parallel flat plate 22 and a 2nd birefringent parallel flat plate 24 are arranged between the nonreciprocal part 10 and 3rd port P3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a non-reciprocal portion in which wedge-shaped birefringent prisms are arranged on both sides of a 45-degree Faraday rotator, one side of which has a second port and the other side of which has first and third ports. The present invention relates to the arranged 3-port type optical circulator. More specifically, by inserting two birefringent parallel plates or a combination of a half-wave plate and a birefringent parallel plate between the non-reciprocal part and the third port, the light emitted to the third port The present invention relates to a three-port type optical circulator in which the beam is a single beam. This technique is useful in fields such as optical communication systems and optical measurement.

[0002]

2. Description of the Related Art Although a 4-port type optical circulator using a birefringent prism has been known for a long time, only 3 out of 4 ports are used in a normal application.
Therefore, recently, a small 3-port type optical circulator has been proposed (for example, Japanese Patent Laid-Open No. 1-287528). This utilizes the fact that the optical axis shifts laterally when extraordinary light passes through a birefringent plate whose optical axis forms an angle of about 45 degrees with the plane, and the non-reciprocity of the Faraday rotator. Here, at least four birefringent plates are used, and at least one 45-degree Faraday rotator is interposed between them.
Then, two optical fibers are juxtaposed on one side of the combined body, and one optical fiber is provided on the other side via a lens. Each of the three optical fibers serves as a port.

[0003]

However, the above-mentioned three-port type optical circulator uses a parallel-plane birefringent plate as a polarizing element, which causes a problem that the port interval becomes very narrow. This is because the birefringent plate shifts the light rays, that is, the separation distance between the ordinary ray and the extraordinary ray is extremely small. Therefore, a collimator lens cannot be provided at the tip of the fiber. To increase the amount of light beam shift, it is conceivable to increase the thickness of the birefringent plate, but this would not only increase the size of the device but also increase the cost.

Therefore, wedge-shaped birefringent prisms are positioned on both sides of the 45 ° Faraday rotator and are combined so that their thick and thin portions face each other to form a non-reciprocal portion, and a second port is provided on one side thereof. , A configuration in which the first and third ports are arranged on the opposite side was considered. In this configuration, since the wedge-shaped birefringent prism is used, the first port and the third port are not parallel but form an angle, so that a space can be provided to the extent that a fiber collimator can be installed. However, in this configuration, the light emitted from the second port to the third port becomes a double beam, the insertion loss is not reduced, and the isolation cannot be sufficiently increased. In addition, by increasing the apex angle of the wedge-shaped birefringent prism (for example, about 11 to 31 degrees when a rutile single crystal is used),
The angle formed by the first port and the third port can be made larger to increase the degree of freedom in fixing the fiber collimator and facilitate assembly and adjustment, but the wedge-shaped birefringent prism becomes thicker, resulting in an increase in cost.

A configuration in which the non-reciprocal portions are cascaded in two stages is also conceivable. With this configuration, the light emitted from the second port to the third port becomes a substantially single beam, and the isolation can be sufficiently large. Further, even if the apex angle of the wedge-shaped birefringent prism is not extremely increased, the angle formed by the first port and the third port can be increased, and the fiber collimator can be easily arranged. However, since the non-reciprocal parts are combined in two stages, the size is increased and the cost is increased.

An object of the present invention is to provide a three-port type optical circulator capable of increasing the light coupling efficiency by making the light emitted to the third port a single beam.

[0007]

The present invention comprises a non-reciprocal portion,
A second fiber collimator and a third fiber collimator respectively arranged at positions of the second port and the third port on both sides thereof, and a first fiber collimator arranged at a position of the first port adjacent to the third port. Equipped with 3
A port type optical circulator is assumed. Here, the non-reciprocal part is a combination of wedge-shaped birefringent prisms on both sides of a 45-degree Faraday rotator, such that the thick-walled portion and the thin-walled portion face each other and both optical axes form approximately 45 degrees. It has a different structure. The first fiber collimator has a polarization-maintaining optical fiber, the linearly polarized signal light from the first port passes through the non-reciprocal portion, is coupled to the second port, and the signal light from the second port is non-reciprocal. To the third port through the section. Particularly, the present invention has a structure in which the first birefringent parallel plate and the second birefringent parallel plate are inserted between the non-reciprocal portion and the third fiber collimator, and is characterized in this respect. Here, the optical axis of the first birefringent parallel plate is orthogonal or parallel to the optical axis of the wedge-shaped birefringent prism adjacent to it,
The optical axes of the first and second birefringent parallel plates are orthogonal to each other. The first birefringent parallel plate is one of the two separated lights that have reached the first birefringent parallel plate from the non-reciprocal part.
The thickness is such that extraordinary light is refracted and emitted on an extension of the polarization direction of ordinary light. The second birefringent parallel plate has a thickness such that the extraordinary light of the two separated lights reaching from the first birefringent parallel plate is refracted and emitted in a single layer with the ordinary light.

A half-wave plate and a birefringent parallel plate may be inserted between the non-reciprocal portion and the third fiber collimator. Here, the optical axis of the half-wave plate is 1 / of the angle formed by the direction connecting the incident points of the two separated lights reaching the half-wave plate from the non-reciprocal part and the polarization plane of one of the separated lights. The optical axis of the birefringent parallel plate is set to the direction connecting the incident points of the two separated lights. The birefringent parallel plate has such a thickness that extraordinary light of the two separated lights that have arrived from the half-wave plate is refracted and is emitted as a single layer with the ordinary light.

Further, in addition to the above circulator structure, a prism having a substantially triangular cross section is disposed between the non-reciprocal portion and the first fiber collimator so that the top of the prism faces the direction of the third port. preferable.

[0010]

The light beam entering from the first port through the polarization maintaining optical fiber is emitted to the second port while the refraction or polarization plane of each optical component in the non-reciprocal portion rotates. The light beam incident from the second port is separated at the non-reciprocal portion and becomes two separated lights whose polarization directions are orthogonal to each other, and reaches the first birefringent parallel plate. Since the optical axis of the first birefringent parallel plate is orthogonal or parallel to the optical axis of the adjacent wedge-shaped birefringent prism, one of the split lights becomes ordinary light and the other becomes extraordinary light. Of the rays incident on the birefringent parallel plate, the ordinary ray goes straight and the extraordinary ray is refracted in the polarization direction. First
When it passes through the birefringent parallel plate, the extraordinary ray is refracted and its emission point is shifted on the extension line of the polarization direction of the ordinary ray. Since the polarization directions of the first and second birefringent parallel plates are orthogonal to each other,
The second birefringent parallel plate converts ordinary light into extraordinary light and extraordinary light into ordinary light. When passing through the second birefringent parallel plate,
The extraordinary light is refracted and overlaps with the ordinary light to be emitted to the third port. Further, the light ray incident from the third port is opened at the non-reciprocal portion and is emitted, so that it is not coupled to the second port. Therefore, in the present invention, the optical circulation operation of the first port → the second port and the second port → the third port is performed.

When a half-wave plate and a birefringent parallel plate are used in place of the first and second birefringent parallel plates, a light beam incident from the second port has two polarization directions orthogonal to each other. It becomes separated light and reaches the half-wave plate. Since the polarization directions of the two separated lights rotate symmetrically around the optical axis of the half-wave plate, the polarization directions of the two separated lights are parallel and perpendicular to the direction connecting the incident points. This reaches the birefringent parallel plate. Since the optical axis of the birefringent parallel plate is set in the direction connecting the incident points of both separated lights, both separated lights are ordinary light and extraordinary light. When passing through the birefringent parallel plate, the extraordinary ray is refracted, becomes a single layer with the ordinary ray, and is emitted to the third port. The other circulation operations are the same as those described above.

When a prism having a substantially triangular cross section is arranged between the non-reciprocal portion and the first fiber collimator,
The linearly polarized signal light that is obliquely incident on the optical axis from the port is refracted by passing through this prism. Since the top of this prism is arranged in the direction of the third port, the signal light is refracted in the direction in which the angle formed with the optical axis is reduced. Therefore, the angle formed by the first port and the third port can be increased, and the distance can be increased.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing an embodiment of a 3-port type optical circulator according to the present invention. This optical circulator comprises a non-reciprocal portion 10, and a second fiber collimator 32 and a third fiber collimator 34 which are respectively arranged at the positions of the second port P ₂ and the third port P ₃ on both sides thereof.
And a first fiber collimator 30 arranged at a position of the first port P ₁ close to the third port P ₃ . The triangular prism 20 is arranged between the non-reciprocal portion 10 and the first port P ₁ , and the first birefringent parallel plate 22 and the second birefringent parallel plate are disposed between the non-reciprocal portion 10 and the third port P _3. Place 24.

The non-reciprocal portion 10 has a first wedge-shaped birefringent prism 16 and a second wedge-shaped birefringent prism 18 on both sides of a 45 ° Faraday rotator 15, and their inclined surfaces are outward and their thicknesses are the same. This is a structure in which the thin portion and the thin portion are arranged to face each other. The 45-degree Faraday rotator 15 has a magneto-optical element 14 housed in a cylindrical permanent magnet 12. The magneto-optical element 14 is, for example, an LPE (liquid phase epitaxial growth) film of a magneto-optical crystal formed on a substrate. The wedge-shaped birefringent prisms 16 and 18 are made of rutile single crystal, for example. The optical axes of the wedge-shaped birefringent prisms 16 and 18 used in this embodiment are shown in FIG. Both wedge-shaped birefringent prisms 16 and 18 have the same structure, and their optical axes are both in a plane without inclination. As shown in FIG. 2, when the y-axis is taken in the direction perpendicular to the wedge-shaped surface and the x-axis is taken in the direction perpendicular to the y-axis in the plane without inclination, the optical axis is -y with respect to the x-axis direction. It is tilted 67.5 degrees in the axial direction. When the first and second wedge-shaped birefringent prisms 16 and 18 are arranged such that their thick and thin portions face each other, their optical axes form an angle of 45 degrees with each other.

The triangular prism 20 is a prism in the shape of a triangular prism made of glass or the like. The top of the triangular prism 20 faces the direction of the third port P ₃ so that the light emitted from the first port P ₁ enters the second port P _2. To install. Since the light may be refracted at a certain angle, the cross section is not limited to the triangular shape and may be a wedge shape.

First and second birefringent parallel plates 22, 24
Is, for example, a rutile single crystal. Here, the optical axis of the first birefringent parallel plate 22 is orthogonal to the optical axis of the adjacent second wedge-shaped birefringent prism 18. The optical axis 22c of the first birefringent parallel plate 22 and the second birefringent parallel plate 2
The four optical axes 24c are orthogonal to each other. Also, the first and second
The optical axes 22c and 24c of the birefringent parallel plates 22 and 24 are inclined by 45 degrees with respect to the optical axis direction.

The first, second and third fiber collimators 30, 32 and 34 have a structure in which a lens and an optical fiber with a ferrule are housed in a metal sleeve. The optical fibers 33 and 35 of the second and third fiber collimators 32 and 34 arranged at the second and third ports P ₂ and P ₃ are both single mode fibers (SMF). A polarization maintaining fiber (PMF) is used as the optical fiber 31 of the first fiber collimator 30 arranged at the first port P ₁ . The second and third fiber collimators 32 and 34 are both parallel to the optical axis, while the first fiber collimator 30 is arranged obliquely to the optical axis.

FIG. 3 shows the first port P ₁ to the second port P ₁ .
FIG. 3 is an optical path diagram of a light beam emitted to ₂ . As shown in the figure,
Three orthogonal axes of X, Y and Z are set. The linearly polarized signal light, which is obliquely incident from the first port P _{1 with} respect to the Z axis, for example, extraordinary light, is refracted by passing through the triangular prism 20. The triangular prism 20 has a third triangular top portion with a third cross section.
Since the light is arranged in the direction of the port P ₃ , the signal light is refracted in the direction in which the angle formed with the Z axis is reduced. Then, in the second wedge-shaped birefringent prism 18, the signal light is refracted as extraordinary light and reaches the 45 ° Faraday rotator 15. Four
The polarization plane is rotated by 45 degrees (rotated from the X axis to the Y axis direction) by the 5 degree Faraday rotator 15, and the optical axis of the first wedge-shaped birefringent prism 16 is relative to the optical axis of the second wedge-shaped birefringent prism 18. Since it is rotated by -45 degrees (rotated from the X axis to the -Y axis direction), the polarization direction of the light beam is orthogonal to the optical axis of the first wedge-shaped birefringent prism 16. That is, extraordinary light is converted into ordinary light. The light rays thus converted into ordinary rays are refracted by the first wedge-shaped birefringent prism 16 and are then refracted into the second rays.
Emit to the port P ₂ . Conversely speaking, the positions of the triangular prism and the first port P ₁ are determined so that the converted light beam is exactly emitted to the second port P ₂ . Therefore, the first
When the light is emitted from the port P ₁ to the second port P _2, it depends on the polarization.

FIG. 4 shows the second port P ₂ through the third port P ₂ .
FIG. 6 is an optical path diagram of a light beam emitted to ₃ . The incident light from the second fiber collimator 32 is separated by the first wedge-shaped birefringent prism 16 into ordinary light and extraordinary light whose polarization directions are orthogonal to each other. The two separated lights have their polarization directions rotated by 45 degrees (rotated from the X axis to the Y axis) by the 45 degree Faraday rotator 15 and reach the second wedge-shaped birefringent prism 18. Since the optical axis of the second wedge-shaped birefringent prism 18 forms an angle of 45 degrees with the first wedge-shaped birefringent prism 16, the two separated lights are refracted as ordinary light and extraordinary light, and the separation distance is increased. Spreads further. Both of these separated lights 40, 42
Pass through the first birefringent parallel plate 22 and the second birefringent parallel plate 24 to form a single third port P.
Emit to ₃ . The first and second birefringent parallel plates 2
Operations 2 and 24 will be described in detail below.

FIG. 5 is an explanatory view of the signal light on the end face of each component viewed from the second port P ₂ side. Here, the angle formed between the optical axis and the polarization direction and the X-axis direction is + for the Y-axis side and − for the −Y-axis side. As described above, the light rays are separated at the non-reciprocal portion 10 and separated into the first separated light 40.
And becomes the second separated light 42. In FIG. 5A, the exit side end face 18a of the second wedge-shaped birefringent prism 18 is shown. The angle formed by the optical axis 18c of the second wedge-shaped birefringent prism 18 is 6
It is 7.5 degrees. The first separated light 40 is ordinary light in the second wedge-shaped birefringent prism 18, and the angle formed by the polarization direction of the first separated light 40 and the X axis is −22.5 degrees. The second separated light 42 is extraordinary light, and its polarization direction forms an angle of −2 with the X axis.
It is 2.5 degrees. The separated lights 40 and 42 are emitted from the emission points 40a and 4
The parallel light is emitted from 2a and reaches the first birefringent parallel plate 22.

The incident side end face 22a of the first birefringent parallel plate 22 is shown in FIG. 5B, and the first birefringent parallel plate 22 is shown in FIG. 5C.
The incident side end surface 22b of is shown. First birefringent parallel plate 22
The optical axis 22c is orthogonal to the second wedge-shaped birefringent prism 18, and the angle formed with the X-axis direction is -22.5 degrees. Therefore, the first separated light 40 becomes extraordinary light and is refracted,
The second separated light 42 becomes ordinary light and goes straight on. Now, the extraordinary ray is refracted in the polarization direction in the first birefringent parallel plate 22, and is emitted in parallel with the ordinary ray that has gone straight. Here, the optical axis 22c of the first birefringent parallel plate 22
Is tilted by 45 degrees with respect to the Z-axis, and therefore, assuming that the thickness of the first birefringent parallel plate 22 is t _A , in the case of a rutile single crystal, the incident point and the emission point of extraordinary light are about 0.1 t. Only _B shifts. Utilizing this property, the extraordinary light (first separated light 40) reaches the extension of the polarization direction of the ordinary light (second separated light 42).
The emission point 40c of is moved. To this end, the separation distance between ordinary light and extraordinary light (distance between the incident points 40b and 42b of both lights)
Is L, the thickness t of the first birefringent parallel plate 22 is
_A requires t _A = 10 · L · cos 22.5 °. Thus, on the emission side end face 22b of the first birefringent parallel plate 22, the ordinary light (the second separated light 42) goes straight, and the positions of the incident point 42b and the emission point 42c do not change. Further, the extraordinary light (first separated light 40) is refracted to shift the emission point 40c of the extraordinary light (first separated light 40) to an extension line of the polarization direction of the ordinary light (second separated light 42). It will be.

FIG. 5D shows the incident side end face 24a of the second birefringent parallel plate 24, and FIG. 5E shows the second birefringent parallel plate 24.
The incident side end surface 24b of is shown. Second birefringent parallel plate 24
Since the optical axis 24c of the above is orthogonal to the optical axis 22c of the first birefringent parallel plate 22, the first separated light 40 becomes extraordinary light and the second separated light 42 becomes ordinary light. Ordinary light travels straight, and extraordinary light is refracted in its polarization direction. Here, since the optical axis of the first birefringent parallel plate 22 is tilted by 45 degrees with respect to the Z axis, when the thickness of the first birefringent parallel plate 22 is t _A , in the case of a rutile single crystal, The incident point and the exit point of extraordinary light deviate by about 0.1 t _B. By utilizing this property, the emission point 40e of the extraordinary light (first separated light 40) is shifted to the position of the emission point 42e of the ordinary light (second separated light 42). For this purpose, the thickness t _B of the second birefringent parallel plate 24 needs to be t _B = 10 · L · sin22.5 °. In this way, the emission points 40e and 42e of the extraordinary light (first separated light 40) and the ordinary light (second separated light 42) overlap. Therefore, the first separated light 40 and the second separated light 4
2 becomes a single beam and is emitted to the third port P ₃ .

FIG. 6 shows the third port P ₃ to the second port P _2.
It is an optical-path figure of the light ray which goes to. The light ray incident from the third port P ₃ passes through the second birefringent parallel flat plate 24 and the first birefringent parallel flat plate 22 and is separated into ordinary light and extraordinary light, becoming parallel light and the second wedge-shaped birefringent light. It reaches the refraction prism 18.
Since the optical axes of the second wedge-shaped birefringent prism 18 and the first birefringent parallel plate 22 are orthogonal to each other, the ordinary light is converted into the extraordinary light and the extraordinary light is converted into the ordinary light, and the 45 degree Faraday rotator 15
Reach The polarization direction of the light beam is rotated by 45 degrees by the Faraday rotator 15 (rotation from the X axis to the Y axis direction). First
Since the optical axis of the wedge-shaped birefringent prism 16 is rotated by −45 degrees (rotated from the X axis to the −Y axis direction) with respect to the optical axis of the second wedge-shaped birefringent prism 18, the polarization direction of the separated light is changed. Is orthogonal to the optical axis of the first wedge-shaped birefringent prism 16. Therefore, the ordinary light refracts as extraordinary light in the first wedge-shaped birefringent prism 16, and the extraordinary light refracts as ordinary light.
After passing through, the distance between the separated lights is further expanded. For this reason, the light beam is not coupled to the second port P ₂ , so the third port P 2
High isolation is obtained for light rays incident from ₃ .

In the above embodiment, the non-reciprocal portion 10
The two birefringent parallel plates 22 and 24 located between the third port P ₃ and the third port P ₃ may be interchanged. In that case, the birefringent parallel plate adjacent to the second wedge-shaped birefringent prism 18 is
The optical axis thereof is parallel to the optical axis of the second wedge-shaped birefringent prism 18, and the birefringent parallel plates 22 and 24 have their optical axes orthogonal to each other.

FIG. 7 is an explanatory view of another embodiment of the 3-port type optical circulator according to the present invention. The non-reciprocal part 10, the first port P ₁ , the second port P ₂ , the third port P ₃ , the first fiber collimator 30, the second fiber collimator 32, and the third fiber collimator 34 of this three-port type optical circulator. The arrangement / configuration of is the same as that of the above-mentioned embodiment. The difference from the above example is that a wedge prism 21 is arranged between the non-reciprocal portion 10 and the first port P ₁ , and the half-wave plate 26 and the birefringence parallel are provided between the non-reciprocal portion 10 and the third port P _3. That is, the flat plate 28 is arranged.

The wedge-shaped prism 21 is made of glass or the like as in the above example, and has a shape obtained by cutting off the top of a triangular prism. The half-wave plate 26 is made of, for example, quartz, and the birefringent parallel plate 28 is made of rutile single crystal as in the above embodiment. Here, the X axis, the Y axis, and the Z axis are set in the same direction as in FIG. The optical axis of the half-wave plate 26 forms an angle of -11.25 degrees with respect to the X-axis direction. The optical axis of the birefringent parallel plate 28 is the same as the X-axis direction.

FIG. 8 is an explanatory diagram of the signal light on the end face of each component viewed from the second port P ₂ side. Here, the angle formed between the optical axis and the polarization direction and the X-axis direction is + for the Y-axis side and − for the −Y-axis side. As described above, the light rays are separated at the non-reciprocal portion 10 and are separated into the first separated light 50.
And becomes the second separated light 52. In FIG. 8A, the exit side end face 18a of the second wedge-shaped birefringent prism 18 is shown. The angle formed by the optical axis 18c of the second wedge-shaped birefringent prism 18 is 6
It is 7.5 degrees. The first separated light 40 is ordinary light in the second wedge-shaped birefringent prism 18, and the angle formed by the polarization direction of the first separated light 40 and the X axis is −22.5 degrees. The second separated light 42 is extraordinary light, and its polarization direction forms an angle of −2 with the X axis.
It is 2.5 degrees. The separated lights 50 and 52 are output points 50a and 5
The parallel light from 2a reaches the half-wave plate 26.

The incident side end face 26a of the half-wave plate 26 is shown in FIG. 5B, and the incident side end face 2 of the half-wave plate 26 is shown in FIG. 5C.
6b is shown. The direction connecting the incident point 50b of the first separated light 50 and the incident point 52b of the second separated light 52 is parallel to the X axis. Since the optical axis 26c of the half-wave plate 26 forms -11.25 degrees with respect to the X-axis direction, it is 1/2 of the angle formed by the optical axis of the first separated light 50 with respect to the X-axis direction. . Therefore, when passing through the half-wave plate 26, the polarization directions of the first and second separated lights 50 and 52 are rotated to positions symmetrical about the optical axis 26c. Therefore, the polarization direction of the first separated light 50 rotates in the X axis direction, and the polarization direction of the second separated light 52 rotates in the Y axis direction. At this time, since both separated lights go straight, 1/2
On the exit side end face 26b of the wave plate, the exit points 50c and 52c
Is the same as the incident points 50b and 52b.

Next, when the two separated lights 50 and 52 reach the birefringent parallel flat plate 28, as shown in D of FIG.
In 8a, the optical axis 28c of the birefringent parallel plate 28 is in the X-axis direction. Therefore, the first separated light 50 becomes extraordinary light and is refracted, and the second separated light 52 becomes ordinary light and travels straight. Now,
In the birefringent parallel plate 28, the extraordinary light is polarized in the polarization direction, that is, X.
The light is refracted in the axial direction and is emitted in parallel with the straight ordinary light. Here, since the optical axis 28c of the birefringent parallel plate 28 is inclined by 45 degrees with respect to the Z-axis, letting the thickness of the first birefringent parallel plate 22 be t _C , in the case of a rutile single crystal, the incident point is And the emission point shifts by about 0.1t _C. Utilizing this property, up to the emission point 52e of the ordinary light (second separated light 52),
The emission point 50e of the extraordinary light (first separated light 50) is shifted. For this purpose, if the separation distance between the ordinary light and the extraordinary light (distance between the incident points 50d and 52d of both lights) is L, the thickness t _C of the birefringent parallel flat plate 28 is required to be t _c = 10 · L. Become. Thus, as shown in E of FIG. 8, at the emission side end face 28b of the birefringent parallel plate 28, the emission points 50e and 52e of the extraordinary light (first separated light 50) and the ordinary light (second separated light 52) are Overlapping one. Therefore, the first separated light 5
The 0 and the second separated light 52 become a single beam and are emitted to the third port P ₃ .

The signal light incident from the first port P ₁ is emitted to the second port P ₂ as in the above embodiment. Also, the third
The signal light incident from the port P ₃ is received by the birefringent parallel plate 28.
And the half-wave plate 26, and in the non-reciprocal portion 10, the distance between the separated lights is further expanded in the same manner as in the above embodiment, and both light rays are not coupled to the second port P _2. Therefore, the third port P ₃ High isolation can be obtained for the light rays incident from.

[0031]

According to the three-port type optical circulator of the present invention, two birefringent parallel flat plates or a half-wave plate and a birefringent parallel flat plate are arranged between the nonreciprocal portion and the third port. Since the two separated lights that have arrived from the portion are overlapped with each other and the influence of lens aberration can be reduced, the light coupling efficiency can be increased.

If a prism having a substantially triangular cross section is arranged between the non-reciprocal portion and the first port, the distance between the first port and the third port arranged on the same side of the non-reciprocal portion can be widened. Assembly adjustment and fixing can be easily performed.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a 3-port type optical circulator according to the present invention.

FIG. 2 is an explanatory diagram of a wedge-shaped birefringent prism used therein.

FIG. 3 is an optical path diagram of a light beam emitted from a first port P ₁ to a second port P ₂ .

FIG. 4 is an optical path diagram of a light beam emitted from a second port P ₂ to a third port P ₃ .

FIG. 5 is an explanatory diagram of signal light on an end surface of each component viewed from the second port P ₂ side.

FIG. 6 is an optical path diagram of a light beam incident from a third port P ₃ toward a second port P ₂ .

FIG. 7 is an explanatory view showing another embodiment of the 3-port type optical circulator according to the present invention.

FIG. 8 is an explanatory diagram of signal light on an end face of each component viewed from the second port P ₂ side.

[Explanation of symbols]

10 non-reciprocal part 15 45 degree Faraday rotator 16 wedge-shaped birefringent prism 18 wedge-shaped birefringent prism 20 triangular prism 22 first birefringent parallel plate 24 second birefringent parallel plate 30 first fiber collimator 32 second fiber Collimator 34 Third fiber collimator P ₁ First port P ₁ P ₂ Second port P ₂ P ₃ Third port P ₃

Claims (3)

[Claims] 1. A non-reciprocal part, a second fiber collimator and a third fiber collimator respectively arranged at positions of a second port and a third port on both sides of the non-reciprocal part, and a first port close to the third port. A first fiber collimator arranged at a position, and the non-reciprocal portion has wedge-shaped birefringent prisms on both sides of the Faraday rotator of approximately 45 degrees, and the thick portion and the thin portion face each other. The first fiber collimator has a polarization maintaining optical fiber, and the linearly polarized signal light from the first port passes through the non-reciprocal portion. In the 3-port type optical circulator, which is coupled to the second port and the signal light from the second port passes through the non-reciprocal portion and is coupled to the third port, the first port is provided between the non-reciprocal portion and the third fiber collimator. A birefringent parallel plate and a second birefringent parallel plate are inserted, and the optical axis of the first birefringent parallel plate is orthogonal or parallel to the optical axis of the wedge-shaped birefringent prism adjacent to the first and second birefringent parallel plates. The optical axes of the birefringent parallel flat plates are orthogonal to each other, and the first birefringent parallel flat plate extends the polarization direction of the ordinary light by refracting the extraordinary light out of the two separated lights reaching from the nonreciprocal part. The thickness of the second birefringent parallel plate is set so that the extraordinary light is refracted by the extraordinary light of the two separated lights that have arrived from the first birefringent parallel flat plate, and is emitted as a single layer with the ordinary light. 3 port type optical circulator characterized by. 2. A non-reciprocal part, a second fiber collimator and a third fiber collimator respectively arranged at positions of a second port and a third port on both sides of the non-reciprocal part, and a first port close to the third port. A first fiber collimator arranged at a position, and the non-reciprocal portion has wedge-shaped birefringent prisms on both sides of the Faraday rotator of approximately 45 degrees, and the thick portion and the thin portion face each other. The first fiber collimator has a polarization maintaining optical fiber, and the linearly polarized signal light from the first port passes through the non-reciprocal portion. In a three-port type optical circulator that is coupled to the second port and the signal light from the second port passes through the non-reciprocal portion and is coupled to the third port, the distance between the non-reciprocal portion and the third fiber collimator is 1/2. Inserting a wave plate and a birefringent parallel plate, the optical axis of the half wave plate is the direction connecting the incident points of the two separated lights reaching the half wave plate from the non-reciprocal part and the polarization of one of the separated lights. It is set to 1/2 of the angle formed by the plane, and the optical axis of the birefringent parallel plate is set in the direction connecting the incident points of both separated lights.
The birefringent parallel plate is a three-port type optical circulator characterized in that extraordinary light, out of the two separated lights that have arrived from the half-wave plate, is refracted and overlaps with ordinary light to be emitted. 3. A three-port type according to claim 1, wherein a prism having a substantially triangular cross section is arranged between the non-reciprocal portion and the first fiber collimator so that the top of the prism faces the direction of the third port. Optical circulator.