JP2001021750A - Optical multiplexer/demultiplexer module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive optical multiplexer/demultiplexer module of samll size excellent in a temperature characteristic. SOLUTION: A pair of polarization face-conservative optical fibers 2a, 2b is held in parallel by a guide member 8. A lens 1, a prism 3, a parallel plate 4, a double refraction crystal 5 and a lens 6 are arrayedly arranged in series, in this order from the optical fibers 2a, 2b, between the polarization face- conservative optical fibers 2a, 2b and a single mode optical fiber 7. A normal beam 15o emitted from the optical fiber 2a and an abnormal bean 15e emitted from the optical fiber 2b are associated in an emission face of the double refraction crystal 5, and a resultant composite beam is introduced into a core of the single mode optical fiber 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multiplexing / demultiplexing module applied to an optical communication system and an optical measurement field.

[0002]

2. Description of the Related Art In recent years, a semiconductor laser (LD) has been widely used as a light source in the field of optical communication, and further improvement in its output is required. However, in reality, it is difficult to provide a high-output semiconductor laser that can meet the demand.

On the other hand, a laser beam emitted from an LD combines laser beams orthogonal to each other whose polarization plane (polarization plane) is parallel to the joint surface of the LD. It has been found that the light output can be improved. By using this technique, the optical output of the laser beam can be improved without increasing the output of the LD itself. For example, by synthesizing a laser beam of 100 mW, an output of 200 mW can be expected in theory. . Such high-power laser light can be used as an excitation light source for an erbium-doped optical fiber.

FIG. 6 shows a conventional optical multiplexer / demultiplexer that combines mutually orthogonal polarized waves using a birefringent crystal. In this optical multiplexer / demultiplexer, a pair of polarization-maintaining optical fibers (PMFs) 102
Ray 105o and extraordinary ray 105 respectively emitted from
e is condensed by the juxtaposed lens 107, then enters the birefringent crystal 106, only the optical path of the extraordinary ray 150e changes, and the opposite surface (output end face) of the birefringent crystal 106 The light is emitted as combined light (multiplexed / demultiplexed light). Then, the combined light 150c is condensed by the lens 108 and enters the end face of the single mode optical fiber (SMF) 110,
The single mode optical fiber 110 is transmitted.

In this type of optical multiplexer / demultiplexer, the ordinary ray and the extraordinary ray are combined and extracted on the crystal face on the output end side of the birefringent crystal 106. It is necessary to set the separation width (incidence interval) z between the 150o and the extraordinary ray 150c and the crystal length (the length of the birefringent crystal 106) to predetermined values.

In the case where a collimating lens is arranged on the end face of an optical fiber arranged in parallel, if the processing accuracy of the ferrule for fixing the fiber, the assembly accuracy of the lens, and the accuracy for fixing these are poor, the above-mentioned multi-layered structure is required. It is difficult to keep the incident distance (separation width) z between the ordinary ray and the extraordinary ray on the incident surface of the refraction crystal 106 at a set value.
Further, since the birefringent crystal 106 has individual variations in characteristics such as the refractive index, there is a case where the combined light of the ordinary ray and the extraordinary ray cannot be efficiently extracted even if the incident interval z and the crystal length are set as designed. is there. In consideration of such circumstances, conventionally, a lens 107 is juxtaposed between the respective output ends of the pair of polarization-maintaining single-mode fibers 102 and the birefringent crystal 106 so that the birefringent crystal 106 has The lens 107 is adjusted so that the combined light is emitted.

[0007]

However, in the case of the above-mentioned optical multiplexer / demultiplexer, a pair of polarization-maintaining optical fibers 102
In this configuration, a pair of individual lenses 107 are arranged side by side on the output end side of the optical fiber, so that the interval between the two polarization-maintaining single-mode fibers 102 can be reduced to shorten the interval between incidence on the birefringent crystal 106. However, as a result, there is a problem that the crystal length of the birefringent crystal becomes long, for example, about 50 mm, and the size of the device becomes large.

Further, as shown in FIG. 7, an improved optical system in which one direction of the polarized light converged by the lens 107 is shifted by the parallel prism 120 and the interval z of incidence on the birefringent crystal 106 is reduced to about 1 mm, for example. Although a duplexer has been proposed, this device can shorten the crystal length of the birefringent crystal 106, but requires a space for incorporating the prism 120, and the lens 107 is also arranged side by side. It was not enough.

On the other hand, as shown in FIG. 8, an optical multiplexer / demultiplexer using a PBS (polarizing beam splitter) 106 instead of a birefringent crystal is widely used. There is a possibility that the organic adhesive for fixing the resin may deteriorate and the reliability of the multiplexing / demultiplexing may decrease. In addition, the adhesive is made of PBS due to the difference in thermal expansion coefficient and Young's modulus between materials.
In addition, there is a problem that the prism that forms the pixel moves and temperature dependency occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a small-sized, inexpensive, high-performance optical multiplexing / demultiplexing module having excellent temperature characteristics. is there.

[0011]

Means for Solving the Problems In order to achieve the above object, the present invention has the following structure to solve the problems. That is, in the first invention, a lens, a prism, a birefringent crystal, and a lens are arranged between a pair of polarization-maintaining optical fibers and a single-mode optical fiber having polarization planes orthogonal to each other from the polarization-maintaining optical fiber side. An incident end face of the birefringent crystal, which is disposed, of an ordinary ray incident from one of the pair of polarization-maintaining optical fibers and an extraordinary ray incident from the other polarization-maintaining optical fiber. a plane perpendicular to the separation width d, the ordinary refractive index of the birefringent crystal n _o, a refractive index of the extraordinary ray of the birefringence crystal n _e, the transmission direction of the optical axis and the ordinary ray of the birefringence crystal in when the angle of the theta, substantially the thickness of the birefringent crystal in the transmission direction of the ordinary ^{_{ray, (n o 2 × (tanθ}} ) 2
× is the ^{_{d / ((n o 2 -n}} e 2) tanθ)) and the means for solving the problems with the configuration.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, an ordinary ray between the pair of polarization-maintaining optical fibers and the single-mode optical fiber is provided between the prism and the birefringent crystal. This is a means for solving the problem with a configuration in which a parallel plane plate for equalizing the optical path length of the extraordinary ray is arranged.

Further, a third aspect of the present invention is directed to the first or second aspect.
And the angle θ between the optical axis of the birefringent crystal and the plane perpendicular to the transmission direction of the ordinary ray is set to an angle in the range of 40 to 60 degrees. Means.

Further, a fourth aspect of the present invention is the first or second aspect.
Alternatively, with the configuration of the third invention, the polarization-maintaining optical fiber is fixed by a guide member, and the guide member is a group of a synthetic resin mold, ceramics, stainless steel, glass, silicon, zirconia, and quartz. The guide member has two round holes or a bar-shaped hole having the same diameter as the outer diameter of the polarization-maintaining optical fiber, and has a core interval between the pair of polarization-maintaining optical fibers. As a means for solving the problem, the pair of polarization-maintaining optical fibers guided by these holes is fixed to the guide member while being kept parallel within a range of an angle deviation of ± 10 degrees. I have.

Further, a fifth aspect of the present invention is directed to the first to fourth aspects.
Wherein the pair of polarization-maintaining optical fibers each have a stress applying portion extending in the axial direction on both sides of the core, and each of the polarization-maintaining optical fibers when viewed from the face. The straight line connecting the stress applying parts in
It is a means for solving the problem by being parallel or orthogonal to each other within a range of 5 degrees or less.

Further, the sixth invention is characterized in that the first to fifth inventions
Wherein the birefringent crystal is rutile (TiO ₂ ), calcite (CaC
O ₃ ), YVO ₄ , and BBO.

Further, a seventh invention is directed to the first to sixth embodiments.
Wherein the lens comprises any one of an aspherical lens, a ball lens, a plano-convex lens, and a distributed index lens.

In the present invention, the light beams emitted from the pair of polarization-maintaining optical fibers are converged by one lens and guided to the birefringent crystal. The side end is guided by a guide member to increase the parallelism between the polarization-maintaining optical fibers, and
Since it is possible to set a pair of polarization-maintaining optical fibers by extremely narrowing the core spacing of the polarization-maintaining optical fiber, the crystal length of the birefringent crystal used for polarization synthesis can be set shorter. Is achieved.

Further, by moving the pair of polarization-maintaining optical fibers and the lens integrally in the distance direction with respect to the prism, a light beam emitted from one side of the pair of polarization-maintaining optical fibers (for example, a normal This makes it possible to variably adjust the separation width (interval between both light beams) of the light beam (the light beam) and the light beam (for example, the extraordinary light beam) emitted from the other fiber on the plane of incidence of the birefringent crystal.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an embodiment of the optical multiplexing / demultiplexing module. In the figure, the optical multiplexing / demultiplexing module according to the present embodiment includes polarization-maintaining optical fibers 2a, 2a between the exit end faces of a pair of polarization-maintaining optical fibers 2a, 2b and the incident end face of single-mode optical fiber 7.
a lens 1, a prism 3, a parallel plate 4, and a
The birefringent crystal 5 and the lens 6 are arranged and arranged in series along a substantially straight line (cascade arrangement).

The pair of polarization maintaining optical fibers 2a, 2a
b has an outer diameter of 120 to 130 μm. As shown in FIG. 3, a core 10 is arranged at the center of the cross section, and stress applying parts 9 are provided on both sides of the core 10 with the core 10 interposed therebetween. The stress applying section 9 extends along the core 10 in the length direction of the fiber. This polarization-maintaining optical fiber 2
As a and 2b, a bow-tie fiber or an elliptical jacket fiber can be used, but in the illustrated example,
Panda fibers are used.

The pair of polarization maintaining optical fibers 2a, 2a
b has its exit end region held and fixed by a guide member 8. The guide member 8 is made of a synthetic resin mold,
It is formed by selecting any material of ceramics, stainless steel, glass, silicon, zirconia and quartz. The shape of the guide member 8 is not particularly limited. For example, a configuration may be used in which a block body having a V-groove is used and the polarization-maintaining single-mode fibers 2a and 2b are accommodated and held in a pair of parallel V-grooves. In this embodiment, FIG.
A ferrule made of a filler-containing epoxy resin as shown in FIG. The guide member 8 of this ferrule is provided with a through hole 8b at the center of its cross section, and through holes 8a, 8c formed on both sides of the hole 8b.

The straight line connecting the centers of the equally spaced holes 8a, 8b, 8c is on the line of the diameter of the guide member 8, and
a, 8b and 8c are formed such that their length directions are parallel to each other. The distance d between the holes 8a, 8b, 8c is 250 μm in the example shown in FIG. In addition, each hole 8a, 8b,
The diameter of the polarization-maintaining optical fiber 2b is equal to the diameter of the polarization-maintaining optical fibers 2a, 2b. In this embodiment, the polarization-maintaining optical fiber 2b is inserted into the center hole 8b, and the polarization-maintaining optical fiber 2b is inserted into the adjacent one-side hole 8a. The wavefront-maintaining optical fiber 2a is inserted, and the polarization-maintaining optical fibers 2a and 2b are held and fixed to the corresponding holes 8a and 8b by an adhesive or the like.

In this holding and fixing state, the core spacing between the polarization-maintaining single-mode fibers 2a and 2b is as narrow as 250 μm, and the polarization-maintaining single-mode fibers 2a and 2b have holes 8a and 8b.
b and is parallel to the length direction. Ideally, the parallelism of the pair of polarization-maintaining single-mode fibers 2a and 2b is desirably completely parallel. However, the parallelism with an angle shift of ± 10 degrees or less is sufficient. In order to secure the angle, it is preferable that the angle is kept within a parallelism with an angle shift within ± 3 degrees.

Although the hole for accommodating the polarization-maintaining optical fibers 2a and 2b is a round hole in the example of FIG. 2, it may be a square hole, an elliptical hole, or a ball-shaped hole. When fixing the optical fibers 2a and 2b with an adhesive, it is desirable that the hole shape is such that the extinction ratio of the polarization-maintaining single-mode fibers 2a and 2b does not decrease due to the curing shrinkage of the adhesive.

FIG. 3 shows the regulation of the position of the pair of polarization-maintaining single-mode fibers 2a and 2b held by the guide member 8 in the rotation direction. The face (the face of the panda's face appearing in a cross section (end face)) is shown. 3, the line ma on the polarization-maintaining optical fiber 2a side connecting the stress applying unit 9 and the center of the core 10 and the line mb on the polarization-maintaining optical fiber 2b side are parallel to each other within a range of ± 5 degrees (FIG. (A), (b)) or orthogonal (see (c) in FIG. 3).

As the lenses 1 and 6, any one of an aspherical lens, a ball lens, a plano-convex lens, and a gradient index lens is selectively used. In the example of FIG.
Are coincident with the center of the core of the polarization-maintaining optical fiber 2b (the center of the core of the polarization-maintaining optical fiber 2b, the center of the lens 1, and the center of the lens 6 are on a straight line). In this embodiment, the polarization-maintaining optical fiber 2
Polarized light is input to the polarization-maintaining optical fibers 2a and 2b so that the ordinary ray 15o is emitted from b and the extraordinary ray 15e is emitted from the polarization-maintaining optical fiber 2a.

The prism 3 is made of the most popular BK7. The transmitted ordinary ray 15o is made to go straight to enter the incident surface of the birefringent crystal 5 at a right angle, and the transmitted extraordinary ray 15e exits the prism 3. After that, the angle α of the prism 3 is set so as to be parallel to the ordinary ray 15o and to enter the incident surface of the birefringent crystal 5 at right angles. For example, as in the above example, the core interval between the pair of polarization-maintaining single-mode fibers 2a and 2b is 250 μm, and the focal length of the lens 1 is 1.3.
mm, the prism angle α is about 20 degrees.

A parallel plate 4 functioning as a plane parallel plate is provided between the prism 3 and the birefringent crystal 5. This parallel plate 4
Is provided to equalize the optical path length (optical path length considering the refractive index) of the ordinary ray 15o and the extraordinary ray 15e from the polarization-maintaining single-mode fibers 7 to the single-mode optical fiber 7. In the present embodiment, the spot size of the ordinary ray 15o and the spot size of the extraordinary ray 15e converged on the single mode optical fiber 7 are made the same (more specifically, at the exit surface position of the birefringent crystal 5; The spot size of the extraordinary ray 15e is made the same) to improve the coupling efficiency of the two rays 15o and 15e.

Further, the extraordinary ray 15e and the ordinary ray 15o passing through the parallel plate 4 are prevented from overlapping each other to cause crosstalk, and the extraordinary ray 15e is connected to the prism 3 so as not to hit the prism edge. Parallel plate 4
The interrelationships are designed. In the example of FIG.
The beam diameter of o and the extraordinary ray 15e is about 300 μm,
To satisfy the above condition, the ordinary ray 15 exiting the prism 3
500 μm as the parallel beam interval between o and extraordinary ray 15e
Is secured.

The reason why the position of the parallel plate 4 is after the prism 3 and before the birefringent crystal 5 is as follows. That is, when the parallel plate 4 is not provided at this position, the ordinary ray 15o and the extraordinary ray 15e pass through the prism 3 so that the ordinary ray 15o and the extraordinary ray 15e enter the incident surface of the birefringent crystal 5. This causes a problem of deviation. Therefore, the parallel plate 4 is arranged between the prism 3 and the birefringent crystal 5 in order to prevent this displacement by providing the parallel plate 4 and reduce the diffraction loss to the lens 6.

The birefringent crystal 5 is made of rutile (TiO ₂ ) or calcite (CaC) whose beam incident surface and beam output surface are parallel.
O ₃ ), a uniaxial birefringent crystal selected from YVO ₄ and BBO, and the pair of polarization-maintaining single-mode fibers 2
a, the separation width at the incident end face of the birefringent crystal 5 between the ordinary ray 15o incident from the polarization-maintaining optical fiber 2b and the extraordinary ray 15e incident from the other polarization-maintaining optical fiber 2a. (see FIG. 5) d, the refractive index n _o of the ordinary ray 15o birefringent crystal _5, the refractive index n _e of the extraordinary ray 15e birefringent crystal _5, the transmission of the optical axis and the ordinary ray of the birefringence crystal 5 when the the angle between the plane perpendicular to the direction theta, thickness L _m of the birefringent crystal in the transmission direction of the ordinary ray has a thickness (crystal length) which is obtained by (1).

[0033] ^{_{L m = (n o 2 ×}} (tanθ) 2 × d / ((n o 2 -n e 2) tanθ)) · ··· (1)

[0034] The crystal length L _m of the birefringent crystal 5 by setting the thickness, the ordinary ray 15o and the extraordinary ray 15e to lens 6 is matched synthesized without displacement in the exit end surface side of the birefringent crystal 5 It will be emitted toward it. At this time, the combined beam (combined light beam) is a light beam parallel to the incident light beams 15o and 15e.

When rutile or the like is used as the birefringent crystal 5, for example, the optical axis of the birefringent crystal 5 is coplanar with the transmission directions of the ordinary ray 15o and the extraordinary ray 15e, and the angle θ is 47.8 degrees. This is the angle that maximizes the separation width d. From this, when the separation width d is considered, θ is 40
A range of 60 degrees is desirable. In the example of FIG. 1, θ is 45 degrees and the crystal length of the birefringent crystal 5 is 5 mm.

The lens 6 has an ordinary ray 15o and an extraordinary ray 15e.
Is converged and introduced into the core of the single mode optical fiber 7.

In practice, when a light beam is incident on the incident surface at right angles, a problem arises in that return light is generated by reflection. In order to prevent such a problem, the prism 3, the parallel plate 4, and the birefringent crystal 5 are used. The incident surface of the beam (light ray) is inclined by about 2 degrees so as not to be a normal incidence.

By the way, as shown in FIG. 4, the first mode field diameter is d ₁ , and the second mode field diameter is d.
₂ , the mode field diameters d ₁ and d 1 are set by a lens (aspherical lens in the example of FIG. 4) 1 having a focal length f.
_{In order} to perform the conversion of ₂ , it is necessary to satisfy the relationship of the following expression (2).

1 / a + 1 / b = 1 / f (2)

Here, a is the first mode field diameter d.
The distance between the ₁ and the lens 1, b is the distance between the lens 1 and the second mode field diameter d _2. In this case, the magnification m of the lens 1 is _{m = d} 1 / d _2.

Therefore, this relationship is applied to the present embodiment, where d ₁ is the mode field diameter (for example, 10 μm) of the end face of the polarization-maintaining optical fibers 2 a and 2 b, and d ₂ is the mode of the exit surface of the birefringent crystal 5. By using the same lens as the lens 1 for the lens 6, the mode field diameter of the single mode optical fiber 7 becomes d ₁ , and the section of L ₁ and the optical section of L _{2 become} the mode field diameter d ₂ (The position of the exit surface of the birefringent crystal 5) is symmetrical.

That is, the position of d1 is set as the exit end surface position of the polarization-maintaining _single- mode fibers 2a and 2b, and the lens 1 is set at a position that is optically separated by a from the position.
Is set at a position optically separated by b from the output surface of the birefringent crystal 5, a lens 6 is placed at a position optically separated by b from this output surface, and is separated by an optical distance a from the lens 6. By arranging the incident end face of the single mode optical fiber 7 at the position, the polarization preserving optical fibers 2a and 2b of the optical multiplexing / demultiplexing module in this embodiment and the lens 1
The arrangement positions of the birefringent crystal 5, the lens 6, and the incident end face of the single mode optical fiber 7 are determined.

FIG. 5 shows that the ordinary ray 15o and the extraordinary ray 15e are output from the birefringent crystal 5 even if the length of the birefringent crystal 5 (the length of the crystal length) fluctuates with respect to the design length due to a processing error or the like. The figure shows an adjustment method that enables synthesis without deviation on the (outgoing end) side. FIG. 5A shows a state in which the length of the birefringent crystal 5 is processed as designed. FIG. 3B shows a case where the length of the birefringent crystal 5 is shorter than the design length. In this case, the unit 11 in which the polarization maintaining optical fibers 2 a and 2 b and the lens 1 are integrated is brought closer to the prism 3 side. Thereby, the ordinary ray 15 incident on the birefringent crystal 5
The separation width (interval) d between the extraordinary ray 15e and the extraordinary ray 15e becomes narrower on the exit surface side of the birefringent crystal 5.
They are combined without any loss.

FIG. 5C shows a case where the length of the birefringent crystal 5 is longer than the design length. In this case, the unit 11 in which the polarization maintaining optical fibers 2 a and 2 b and the lens 1 are integrated is moved from the prism 3. keep away. Thereby, the separation width (interval) between the ordinary ray 15o and the extraordinary ray 15e incident on the birefringent crystal 5
d is widened, and the ordinary ray 15o on the exit surface side of the birefringent crystal 5
And the extraordinary ray 15e are synthesized without deviation.

As described above, by adjusting the movement of the unit 11 in the distance direction with respect to the prism 3, the ordinary ray 15o and the extraordinary ray 15e can be synthesized without displacement even if the birefringent crystal 5 has a different length. Becomes Note that FIG. 5 shows a case where the length (crystal length) of the birefringent crystal 5 is extremely changed with respect to the design length of the birefringent crystal 5, but this is for the sake of easy understanding of the description. In fact, a change in the length (crystal length) of the birefringent crystal 5 due to an error in processing or the like with respect to the design length of the birefringent crystal 5 is very small. Further, in the example of FIG. 5, the lens 6 and the single mode optical fiber 7 are also integrated into a unit, but it is a matter of course that the configuration may not be unitized.

The optical multiplexing / demultiplexing module of this embodiment is configured as described above. Next, the operation will be described. Extraordinary ray 15e from polarization-maintaining optical fiber 2a
However, the ordinary ray 15o is emitted from the polarization-maintaining single-mode fiber 2b, and the ordinary ray 15o goes straight, and the lens 1,
The light passes through the prism 3, the parallel plate 4, the birefringent crystal 5, and the lens 6 linearly (transmits), and enters the single mode optical fiber 7. On the other hand, the extraordinary ray 15e incident on the lens 1 at a position shifted from the center of the lens 1
Due to the convergence action, the optical path is corrected by the prism 3 so as to be parallel to the ordinary ray 15o, and the light enters the birefringent crystal 5.

The extraordinary ray 15e is refracted by the birefringent crystal 5 and is combined with the ordinary ray 15o on the exit surface of the birefringent crystal 5. The combined light having a high output due to the combination of the ordinary light 15o and the extraordinary light 15e is then converged by the lens 6 and introduced into the core of the single mode optical fiber 7, and transmitted to a desired position through the single mode optical fiber 7. Is done.

According to the optical multiplexing / demultiplexing module of this embodiment, one common lens 1 is disposed on the exit side of the polarization-maintaining single-mode fibers 2a and 2b.
As shown in FIG.
As compared with the case where individual lenses 107 are juxtaposed on the emission side of b, the space for disposing the lenses can be reduced, and the interval (core interval) between the polarization-maintaining optical fibers 2a and 2b can be narrowed. The separation width d between the ordinary ray 15o and the extraordinary ray 15e incident on the lens can be narrowed (smaller), and accordingly, the length (crystal length) of the birefringent crystal 5 is reduced (shorter).
Therefore, the size of the apparatus can be significantly reduced.

The length of the birefringent crystal 5, the birefringent crystal 5
Even if the optical path lengths of the ordinary ray 15o and the extraordinary ray 15e become different due to the refractive index of each ray 15o, 15e passing through the
Since the parallel plate 4 is interposed between the birefringent crystal 5 and the birefringent crystal 5, the optical lengths of the light beams 15o and 15e are adjusted to be the same by the parallel plate 4. The spot of the ordinary ray 15o and the spot of the extraordinary ray 15e are made the same on the exit surface side, and the ordinary ray 15o and the extraordinary ray 15
Since e can be combined, it is possible to provide a high-performance optical multiplexing / demultiplexing module with high optical multiplexing / demultiplexing accuracy.

The present invention is not limited to the above-described embodiment, but can adopt various embodiments.

[0051]

According to the present invention, since one common lens is arranged on the emission side of the pair of polarization-maintaining optical fibers, the interval between the cores of the pair of polarization-maintaining optical fibers can be reduced. Along with this, the interval between the light beams (ordinary ray and extraordinary ray) incident on the birefringent crystal from each of the pair of polarization maintaining optical fibers can be narrowed, so that the crystal length of the birefringent crystal can be shortened, As a result, the size of the device (optical multiplexing / demultiplexing module) can be significantly reduced, and the cost of the device can be reduced.

Further, by providing a plane-parallel plate for making the optical path lengths reaching the single-mode optical fiber the same for the beams (light rays) respectively emitted from the pair of polarization-maintaining optical fibers, the respective beams are made identical. Since the light can be combined into a single mode optical fiber without displacement at the spot, it is possible to provide a high-performance optical multiplexing / demultiplexing module with high optical multiplexing / demultiplexing accuracy.

Further, even if the length (crystal length) of the birefringent crystal is not as designed due to a processing error or the like and the length is shortened, the pair of polarization-maintaining single-mode fibers and the lens on the exit side thereof are connected. By integrally moving the prism in the distance direction, the beam (light beam) emitted from each of the pair of polarization-maintaining single-mode fibers can be properly combined on the exit surface side of the birefringent crystal. It is.

Further, the PB as shown in FIG.
Since S is not used, it is possible to avoid a temperature dependency problem caused by using PBS and to provide an optical multiplexing / demultiplexing module having excellent temperature characteristics.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory diagram of an embodiment of an optical multiplexing / demultiplexing module according to the present invention.

FIG. 2 shows a polarization-maintaining optical fiber 2 formed by a guide member 8;
It is explanatory drawing of the holding structure example of a and 2b.

FIG. 3 is an explanatory diagram showing a positional regulation relationship in a rotation direction of a pair of polarization-maintaining single-mode fibers 2a and 2b.

FIG. 4 is an explanatory diagram showing an arrangement relationship of each member of the optical multiplexing / demultiplexing module in the embodiment.

FIG. 5 is a diagram illustrating a method of adjusting beam combining according to the length of the birefringent crystal 5;

FIG. 6 is an explanatory diagram of a conventional optical multiplexer / demultiplexer.

FIG. 7 is an explanatory diagram of another conventional optical multiplexer / demultiplexer.

FIG. 8 is an explanatory diagram of still another conventional optical multiplexer / demultiplexer.

[Explanation of symbols]

 1, 6 lens 2a, 2b polarization-maintaining optical fiber 3 prism 4 parallel plate (parallel plane plate) 5 birefringent crystal 7 single-mode optical fiber 8 guide member 15o ordinary ray 15e extraordinary ray

Claims (7)

[Claims] 1. A pair of polarized waves having polarization planes orthogonal to each other.
Between surface-maintaining optical fiber and single-mode optical fiber
In addition, from the polarization preserving optical fiber side,
The refractive crystal and the lens are arranged and arranged, and the pair of polarized waves are arranged.
Polarization-maintaining optical fiber of one of the surface-maintaining optical fibers
Ordinary ray incident from the other and polarization-maintaining optical fiber?
The incident end face of the birefringent crystal with the extraordinary ray incident from
Is d and the refractive index of the ordinary ray of the birefringent crystal is n._o, Multiple
Let the refractive index of the extraordinary ray of the refraction crystal be n _e, Birefringent crystal optics
The angle between the axis and the plane perpendicular to the transmission direction of the ordinary ray is θ.
Sometimes, the thickness of the birefringent crystal in the
Bo, (n_o ²× (tan θ)²× d / ((n_o ²-N_e
²) Tan θ))
Wool. 2. A plane-parallel plate is disposed between the prism and the birefringent crystal for equalizing the optical path lengths of the ordinary ray and the extraordinary ray from the pair of polarization-maintaining optical fibers to the single-mode optical fiber. 2. The optical multiplexing / demultiplexing module according to claim 1, wherein: 3. An angle θ between the optical axis of the birefringent crystal and a plane perpendicular to the transmission direction of the ordinary ray is an angle in the range of 40 to 60 degrees. 3. The optical multiplexing / demultiplexing module according to 2. 4. The polarization-maintaining optical fiber is fixed by a guide member, and the guide member is made of a synthetic resin mold, ceramics, stainless steel, glass, silicon, or the like.
The guide member includes two round holes or a bar-shaped hole having the same diameter as the outer diameter of the polarization-maintaining optical fiber, and the guide member includes one selected from the group consisting of zirconia and quartz. Guided by these holes, the pair of polarization-maintaining optical fibers is provided with a core interval, is kept parallel within a range of angular deviation of ± 10 degrees, and is fixed to the guide member. The optical multiplexing / demultiplexing module according to claim 1, 2, or 3. 5. A pair of polarization-maintaining optical fibers each having a stress applying portion extending in the axial direction on both sides of the core, and a straight line connecting the stress applying portions of each polarization-maintaining optical fiber when viewed from the face is The optical multiplexing / demultiplexing module according to any one of claims 1 to 4, wherein the optical multiplexing / demultiplexing module is parallel or orthogonal to each other within a range of ± 5 degrees. 6. The birefringent crystal is a uniaxial birefringent crystal composed of one selected from the group consisting of rutile (TiO ₂ ), calcite (CaCO ₃ ), YVO ₄ , and BBO. An optical multiplexing / demultiplexing module according to any one of claims 1 to 5. 7. The lens according to claim 1, wherein the lens comprises any one of an aspherical lens, a ball lens, a plano-convex lens, and a gradient index lens.
An optical multiplexing / demultiplexing module according to any one of the above.