JPH0843657A - Dispresion compensator - Google Patents

Abstract

PURPOSE:To provide a dispersion compensator which hardly generates polarization dispersion. CONSTITUTION:A dispersion compensation optical fiber 3 having a negative dispersion characteristic generated by the refractive index distribution of a core is coiled to form a dispersion compensation optical fiber coil 6 and a double refractive optical fiber 8 having the polarization dispersion value of nearly the same quantity as the polarization dispersion value of this dispersion compensation optical fiber coil 6 is connected to the dispersion compensation optical fiber coil 6. A slow axis and fast axis which are polarization component axes varying in propagation rates of light are respectively formed due to the respective polarization dispersion values in the dispersion compensation optical fiber coil 6 and the double refractive optical fiber 8 and, therefore, the dispersion compensation optical fiber coil 6 and the double refractive optical fiber 8 are so connected that the slow axis of the double refractive optical fiber 8 and the fast axis of the dispersion compensation optical fiber coil 6 are aligned to each other and that the fast axis of the double refractive optical fiber 8 and the slow axis of the dispersion compensation optical fiber coil 6 are aligned to each other at the time of connecting the dispersion compensation optical fiber coil and the double refractive optical fiber 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber type dispersion compensator for compensating for wavelength dispersion of an optical fiber or a semiconductor laser.

[0002]

2. Description of the Related Art A communication system in which light from a semiconductor laser or the like is modulated with a pulse signal and incident on an optical fiber, and the optical fiber is used as a transmission line has been put into practical use.

By the way, the optical fiber is usually formed of silica glass, and the refractive index of the silica glass becomes smaller as the wavelength of light becomes longer. Therefore, due to the known material dispersion of light, an optical fiber has a higher propagation speed of light as the wavelength of the light wave propagating through the optical fiber becomes faster, and a shorter wavelength of the light wave causes the propagation speed of the light as much as possible. Is known to have a so-called positive dispersion characteristic (wavelength dispersion). Then, in general, when light of a semiconductor laser having a certain degree of spread with respect to the center wavelength is incident on an optical fiber having such a dispersion characteristic, the light propagates through the optical fiber as compared with the pulse width of the incident light. The pulse width of the subsequently emitted light becomes wider.

Therefore, in order to be able to identify the independent pulses of the emitted light when the emitted light is received at the light receiving side, the pulse interval of the incident light incident on the optical fiber is sufficiently wide. Therefore, if the pulse interval of the incident light is widened, it becomes difficult to perform high-speed communication, and as it is, the construction of a high-speed, large-capacity communication system using a semiconductor laser and an optical fiber is hindered. Will end up.

Therefore, for example, as shown in FIG. 17, a dispersion compensator 4 is provided between a semiconductor laser 1 and a propagation optical fiber 5 for propagation. Communication system (communications system) that compensates the dispersion characteristics of 5 (dispersion compensation) and makes the dispersion value of the entire transmission optical path almost zero.
Is proposed.

In the dispersion compensator 4, due to the structural dispersion of the optical fiber in which the refractive index distribution of the core, which is the portion of the optical fiber that propagates light, has a special distribution structure, the propagation speed of the light wave becomes slower as the wavelength becomes longer, The dispersion compensating optical fiber 3 having a so-called negative dispersion characteristic that is made faster as the length is shorter is constituted by, for example, a dispersion compensating optical fiber coil 6 formed by winding a plurality of times in a coil shape. The negative dispersion value of 3 is equivalent to the positive dispersion value of the propagation optical fiber 5. Further, as described above, by winding the dispersion compensating optical fiber 3 in a coil shape, the space occupied by the dispersion compensating optical fiber 3 is made as small as possible, and the small dispersion compensator 4 is provided.

According to the communication system as shown in FIG. 17, the dispersion compensator 4 compensates for the dispersion characteristic of the propagation optical fiber 5, so that the light is emitted from the propagation optical fiber 5 as described above. It is possible to prevent the pulse width of the emitted light from increasing.

[0008]

However, the dispersion compensator 4 has the dispersion compensating optical fiber coil 6 formed by winding the dispersion compensating optical fiber 3 into a coil having a small diameter, and thus the When the length of the dispersion compensating optical fiber 3 is wound in a coil shape with a small diameter, stress strain due to bending is applied to the optical fiber 3, whereby the cross-sectional structure of the axially symmetric refractive index of the dispersion compensating optical fiber 3 collapses, and the fiber cross section A phenomenon called birefringence occurs in which the refractive index distributions of the X-axis and the Y-axis, which are perpendicular to each other (cross section), change. The birefringence due to the coil winding is mainly caused by the bending due to the coil winding, and is caused by the change in the refractive index of the axis vertical to the bending direction. This birefringence is partly small, but in a long optical fiber, the total amount of the birefringence is large, and therefore, among the optical waves propagating through the optical fiber, X
A phenomenon in which the propagation velocities of the axial polarization component and the Y-axis polarization component are different,
So-called polarization dispersion occurs.

That is, the dispersion compensating optical fiber coil 6 has a polarization component axis in which the propagation speed of the light propagating in the dispersion compensating optical fiber 3 is slow due to the polarization dispersion value of the dispersion compensating optical fiber coil 6. The slow axis and the fast axis, which is the polarization component axis in which the propagation speed of light is faster than the slow axis, are formed orthogonal to each other.

Then, when polarization dispersion occurs in the dispersion compensating optical fiber coil 6 and a slow axis and a fast axis are formed in this way, the dispersion compensating optical fiber coil 6 is made to enter the dispersion compensating optical fiber 3 similarly to the material dispersion. Widening the pulse width of laser light will hinder the construction of high-speed, large-capacity communication systems,
It was a problem.

The present invention has been made to solve the above problems, and an object thereof is to provide a dispersion compensator in which polarization dispersion hardly occurs.

[0012]

In order to achieve the above object, the present invention is constructed as follows. That is, the first aspect of the present invention has a dispersion compensating optical fiber coil formed by winding a plurality of dispersion compensating optical fibers having a negative dispersion characteristic caused by a refractive index distribution of a core, Is the slow axis, which is the polarization component axis where the propagation speed of light is slow, and the fast axis, which is the polarization component axis where the propagation speed of light is faster than the slow axis, due to the polarization dispersion value of the dispersion compensating optical fiber coil. Are formed so as to be orthogonal to each other, and the dispersion compensation optical fiber coil has a polarization dispersion value approximately equal to the polarization dispersion value of the dispersion compensation optical fiber coil, and the slow axis and the fast axis are orthogonal to each other. The formed birefringent optical fiber is connected, the slow axis of the birefringent optical fiber and the fast axis of the dispersion compensating optical fiber coil coincide with each other, and the fast axis of the birefringent optical fiber and the dispersion compensation fiber are matched. It is configured as characterized in that the slow axis of the optical fiber coil are coincident with each other.

The birefringent optical fiber is a stress imparting type birefringent optical fiber, the birefringent optical fiber is a structural type birefringent optical fiber, and the birefringent optical fiber is a dispersion compensating optical fiber coil. It is also a characteristic configuration of the first invention that it is connected to one end side and that the birefringent optical fiber is divided and connected to both end sides of the dispersion compensating optical fiber coil.

Further, the second invention comprises a dispersion compensating optical fiber coil formed by winding a plurality of dispersion compensating optical fibers having a negative dispersion characteristic caused by the refractive index distribution of the core, the dispersion compensating optical fiber coil. Due to the polarization dispersion value of the dispersion-compensating optical fiber coil, the fiber coil has a slow axis that is a polarization component axis with a slow light propagation speed and a polarization component axis with a light propagation speed that is faster than the slow axis. A certain fast axis is formed orthogonally to each other, and a fiber tail of the dispersion compensating optical fiber is extended from at least one end side of the dispersion compensating optical fiber coil and is separated from the dispersion compensating optical fiber coil by the fiber tail. Polarization dispersion compensating coil is formed, and the polarization dispersion compensating coil has a polarization dispersion value approximately equal to the polarization dispersion value of the dispersion compensating optical fiber coil. And paste shaft are orthogonal formed,
Between the polarization dispersion compensation coil and the dispersion compensation optical fiber coil, the slow axis of the polarization dispersion compensation coil and the fast axis of the dispersion compensation optical fiber coil are aligned with each other, and the first axis of the polarization dispersion compensation coil is aligned. And a twisted portion that makes the slow axis of the dispersion-compensating optical fiber coil coincide with each other.

Further, the third invention has first and second dispersion compensating optical fiber coils formed by winding a plurality of dispersion compensating optical fibers having a negative dispersion characteristic caused by the refractive index distribution of the core. However, the first and second dispersion compensating optical fiber coils have a slow axis, which is a polarization component axis in which the propagation speed of light is slow, due to the polarization dispersion value of the unique dispersion compensating optical fiber coil. A first axis, which is a polarization component axis whose light propagation speed is faster than the slow axis, is formed orthogonal to each other, and the first dispersion-compensating optical fiber coil has a One end side of a first birefringent optical fiber having a polarization dispersion value substantially equal to the polarization dispersion value and having a slow axis and a fast axis formed orthogonal to each other is connected to the first birefringent light. Fiber slow axis and the first part The first axis of the compensation optical fiber coil is aligned with each other, the first axis of the first birefringent optical fiber is aligned with the slow axis of the first dispersion compensation optical fiber coil, and the first birefringence is The side of the optical fiber connected to the first dispersion compensating optical fiber coil is connected to the first dispersion compensating optical fiber coil to form a part of the coil, and further to the second dispersion compensating optical fiber coil. Is connected to one end side of a second birefringent optical fiber in which the slow axis and the fast axis are formed orthogonal to each other, having a polarization dispersion value of substantially the same amount as the polarization dispersion value of the second dispersion compensating optical fiber coil. The slow axis of the second birefringent optical fiber and the fast axis of the second dispersion compensating optical fiber coil match each other, and the fast axis of the second birefringent optical fiber and the second dispersion compensation Optical fiber The slow axes of the coils are aligned with each other, and the connection side of the second birefringent optical fiber with the second dispersion compensating optical fiber coil is connected to the second dispersion compensating optical fiber coil. And the other end side of the second birefringent optical fiber is connected to the other end side of the first birefringent optical fiber to connect the slow axis of the first birefringent optical fiber and the second birefringent optical fiber. The first axis of the birefringent optical fiber and the slow axis of the second birefringent optical fiber coincide with each other, and the fast axis of the refraction optical fiber coincides with each other.

Further, the fourth invention has first and second dispersion compensating optical fiber coils formed by winding a plurality of dispersion compensating optical fibers having a negative dispersion characteristic caused by the refractive index distribution of the core. However, the first and second dispersion compensating optical fiber coils have a slow axis, which is a polarization component axis in which the propagation speed of light is slow, due to the polarization dispersion value of the unique dispersion compensating optical fiber coil. A first axis, which is a polarization component axis having a light propagation speed higher than that of the slow axis, is formed orthogonal to each other, and the first and second dispersion-compensating optical fiber coils are provided between the first and second dispersion-compensating optical fiber coils. A birefringent optical fiber in which the slow axis and the fast axis are formed to be orthogonal to each other and which has almost the same amount of polarization dispersion values as the combined polarization dispersion values of the dispersion-compensating optical fiber coil of 2 is interposed and connected. And the slot of the birefringent optical fiber The axis coincides with the fast axis of the first dispersion compensating optical fiber coil and the fast axis of the second dispersion compensating optical fiber coil, and the fast axis of the birefringent optical fiber is the slow axis of the first dispersion compensating optical fiber coil. And the slow axis of the second dispersion-compensating optical fiber coil are matched with each other.

[0017]

In the first, third and fourth inventions of the above construction, one or more birefringent optical fibers are connected to one or more dispersion compensating optical fiber coils. The total of the polarization dispersion values is approximately the same as the polarization dispersion value on the dispersion compensating optical fiber coil side, and the slow axis of the birefringent optical fiber and the dispersion compensating optical fiber coil. The first axis of
Since the fast axis of the birefringent optical fiber and the slow axis of the dispersion compensating optical fiber coil match each other, the propagation time difference between the slow axis and the fast axis generated on the dispersion compensating optical fiber coil side is They are canceled by the propagation time difference between the fast axis and the slow axis, and the polarization dispersion of the dispersion compensator becomes almost zero.

Further, in the second aspect of the present invention having the above-mentioned structure, the twisted portion has a polarization dispersion value of about the same amount as the polarization dispersion value of the dispersion compensating optical fiber coil, and the slow axis and the fast axis are provided. Is made orthogonal to each other, the slow axis of the polarization dispersion compensation coil and the fast axis of the dispersion compensation optical fiber coil are matched with each other, and the fast axis of the polarization dispersion compensation coil and the slow axis of the dispersion compensation optical fiber coil are They are matched with each other, so that the propagation time difference between the slow axis and the fast axis generated on the dispersion compensation optical fiber coil side is
It is canceled by the propagation time difference between the fast axis and the slow axis of the polarization dispersion compensation coil, and the polarization dispersion of the dispersion compensator becomes almost zero.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same reference numerals will be given to the same names as those in the conventional example, and the detailed description thereof will be omitted.
FIG. 1 shows the configuration of the essential parts of a first embodiment of a dispersion compensator according to the present invention. This embodiment is different from the conventional example in that one end of the dispersion compensating optical fiber coil 6 is
A birefringent optical fiber 8 having a polarization dispersion value substantially equal to that of the dispersion compensating optical fiber coil 6 and having a slow axis and a fast axis formed orthogonal to each other is connected, as shown in FIG. Thus, the slow axis of the birefringent optical fiber 8 and the fast axis of the dispersion compensating optical fiber coil 6 coincide with each other, and the fast axis of the birefringent optical fiber 8 and the slow axis of the dispersion compensating optical fiber coil 6 coincide with each other. That is what we are doing.

As shown in FIG. 1, the dispersion compensating optical fiber coil 6 comprises a dispersion compensating optical fiber 3 having a length of 15 km and a barrel diameter of 60 mm.
The dispersion compensating optical fiber 3 has a core 20 doped with germanium and has a special refractive index distribution of the core 20. The dispersion compensating optical fiber 3 has a core 20 doped with germanium and has a diameter of mmφ and a body width of 42 mm. The optical fiber is structured to have a negative dispersion characteristic of −80 psec / nm / km due to the structural dispersion caused by the refractive index distribution of the core 20. Then, the polarization dispersion value of the dispersion compensation optical fiber coil 6 formed by winding the dispersion compensation optical fiber 3 as described above was measured by the Jones matrix method, and the polarization dispersion value was 6.3 psec. .

As shown in FIG. 3, the birefringent optical fiber 8 has a core 10 and a clad 11, and the clad 11 is provided with a circular stress in such a manner that the core 10 is sandwiched from both sides with a gap therebetween. The portion 13 is provided, and the birefringent optical fiber 8
Is a so-called stress-giving birefringent optical fiber (polarization-maintaining optical fiber) in which stress is applied to the core 10 by the stress-applying portion 13 to cause birefringence in the core 10. The birefringence index of this birefringent optical fiber 8 is 4 × 10 ⁻⁴ , its length is 4.8 m, and its polarization dispersion value is 6.3 psec, which is the same as that of the dispersion compensating optical fiber coil 6.

This embodiment is constructed as described above,
When light is incident from the incident end side 22 of the dispersion compensating optical fiber coil 6, the light passes through the dispersion compensating optical fiber coil 6 and emerges from the emitting end side 23, and from the incident end side 24 of the birefringent optical fiber 8. The light enters the birefringent optical fiber 8, passes through the birefringent optical fiber 8, and exits from the exit end side 25. In this embodiment, as shown in FIG. The first axis of the compensating optical fiber coil 6 is aligned with each other, the first axis of the birefringent optical fiber 8 is aligned with the slow axis of the dispersion compensating optical fiber coil 6, and the polarization of the birefringent optical fiber 8 is aligned with each other. Since the dispersion value is almost the same as the polarization dispersion value of the dispersion compensating optical fiber coil 6, the propagation time difference between the slow axis and the fast axis generated on the dispersion compensating optical fiber coil 6 side is Fa Offset by the propagation time difference of stringent axis and slow axis, polarization mode dispersion of the dispersion compensator 4 becomes substantially zero.

Therefore, when pulse-shaped light (light wave) as shown in FIG. 4A is made incident from the incident end side 22 of the dispersion compensating optical fiber coil 6 of the dispersion compensator 4 of this embodiment. The pulse shape of the emitted light emitted from the emission end side 23 of the dispersion compensating optical fiber coil 6 becomes a shape as shown in FIG. 4B, and the pulse shape is changed by the polarization dispersion of the dispersion compensating optical fiber coil 6. Even if it is deformed and the pulse width is widened, the polarization dispersion of the dispersion compensating optical fiber coil 6 is compensated when the light passes through the birefringent optical fiber 8, and the pulse shape and pulse width of the light wave are almost returned to the original values. When the light is emitted from the emission end side 25 of the birefringent optical fiber 8, it is emitted as a pulse-shaped light substantially similar to the incident light as shown in FIG. 4C.

Actually, as a result of measuring the polarization dispersion value of the dispersion compensator 4 of the present embodiment by the Jones matrix method, the polarization dispersion value is 0.13 psec, and the polarization dispersion value of the dispersion compensating optical fiber coil 6 ( It was a very small value compared to 6.3 psec), and the polarization dispersion was close to zero. The chromatic dispersion of the dispersion compensator 4 was -1198 psec / nm, which was the same value as the chromatic dispersion of the dispersion compensating optical fiber coil 6 and was confirmed to have the same compensation effect.

According to the present embodiment, as described above, the birefringent optical fiber 8 cancels the propagation time difference between the slow axis and the fast axis generated on the side of the dispersion compensating optical fiber coil 6 to cancel the deviation of the dispersion compensator 4. Since the wave dispersion can be made substantially zero, when light is incident on the dispersion compensator 4 from, for example, the semiconductor laser 1, the light can be emitted without widening the pulse width.

Moreover, since the dispersion compensator 4 of this embodiment also has a sufficient compensation effect as the conventional dispersion compensator 4, the dispersion compensator 4 of this embodiment is shown in FIG. When used by being incorporated in the communication system as shown in FIG. 3, the material dispersion of the propagation optical fiber 5 can be sufficiently compensated, and the pulse interval of the incident light to be incident from the semiconductor laser 1 to the dispersion compensator 4 can be sufficiently obtained. Even if it is narrowed, when the incident light is made incident on the propagation optical fiber 5 through the dispersion compensator 4 and propagated and the light emitted from the propagation optical fiber 5 is received, an independent pulse is generated on the light receiving side. It is possible to identify. Therefore, by using the dispersion compensator 4 of this embodiment,
It becomes possible to construct a communication system capable of high-speed and large-capacity communication.

FIG. 5 shows a second dispersion compensator according to the present invention.
The configuration of the essential parts of this embodiment is shown. This embodiment is different from the first embodiment in that the birefringent optical fiber 8 is divided and connected to both ends of the dispersion compensating optical fiber coil 6. The birefringent optical fiber 8 of the present embodiment is a birefringent optical fiber having a birefringence of 4 × 10 ⁻⁴ and having a length of 4.8 m, which is configured similarly to the first embodiment. The refraction optical fiber 8 is replaced by a 2.4 m birefringence optical fiber 8a.
And a 2.4 m birefringent optical fiber 8b, one birefringent optical fiber 8a is connected to the incident end side 22 of the dispersion optical fiber coil 6, and the other birefringence optical fiber 8b is a dispersion compensation optical fiber coil. 6 is connected to the emission end side 23.

In this embodiment, the same 4.8 m birefringent optical fiber 8 as that of the first embodiment is used, and 2.4 m each is used for 2 m.
Since the birefringent optical fibers 8a and 8b are divided into two parts, the birefringent optical fibers 8a and 8b each have a polarization dispersion value that is about half that of the birefringent optical fiber 8 of the first embodiment. Therefore, the birefringent optical fibers 8a and 8b each have a polarization dispersion value that is about half the polarization dispersion value of the dispersion compensating optical fiber coil 6.

As shown in FIG. 6 (a), the slow axis of the birefringent optical fiber 8a and the fast axis of the dispersion compensating optical fiber coil 6 coincide with each other, and the fast axis of the birefringent optical fiber 8a and the dispersion compensating light. The slow axis of the fiber coil 6 coincides with each other, and similarly, as shown in FIG. 6B, the slow axis of the birefringent optical fiber 8b and the fast axis of the dispersion compensating optical fiber coil 6 coincide with each other. However, the fast axis of the birefringent optical fiber 8b and the slow axis of the dispersion compensating optical fiber coil 6 coincide with each other.

This embodiment is constructed as described above,
When incident light is made incident on the incident end side 26 of the birefringent optical fiber 8a, the light passes through the birefringent optical fiber 8a and is emitted from the emission end side 27, and from the incident end side 22 of the dispersion compensating optical fiber coil 6. It enters the dispersion compensating optical fiber coil 6, passes through the dispersion compensating optical fiber 6, and emerges from its emission end side 23.
Further, the light enters the birefringent optical fiber 8b from the incident end side 24 of the birefringent optical fiber 8b and is emitted from the exit end side 25 thereof.

In this embodiment, the polarization dispersion value of the birefringent optical fiber 8a is about half the polarization dispersion value of the dispersion compensating optical fiber coil 6, and the birefringence optical fiber 8
Since the slow axis of a and the fast axis of the dispersion compensating optical fiber coil 6 match, and the fast axis of the birefringent optical fiber 8a and the slow axis of the dispersion compensating optical fiber coil 6 match, the birefringent optical fiber 8a The propagation time difference between the slow axis and the fast axis on the side works in the direction of compensating for a part (about half) of the propagation time difference between the slow axis and the fast axis which occurs in advance on the dispersion compensating optical fiber coil 6 side. Then, for example, when light having an incident pulse shape as shown in FIG. 7A is made incident from the incident end side 26 of the birefringent optical fiber 8a, the light is caused by the birefringence of the birefringent optical fiber 8a. The light having the shape shown in FIG. 7B is emitted from the emission end side 27 of the birefringent optical fiber 8a and is incident on the dispersion compensating optical fiber coil 6.

The light incident on the dispersion compensating optical fiber coil 6 propagates through the dispersion compensating optical fiber coil 6 and has a pulse shape as shown in FIG. From the birefringent optical fiber 8b
However, in the dispersion compensator 4 of the present embodiment, the slow axis of the birefringent optical fiber 8b and the fast axis of the dispersion compensating optical fiber coil 6 coincide with each other, and the birefringent optical fiber 8
The fast axis of b and the slow axis of the dispersion compensating optical fiber coil 6 are aligned, and the dispersion compensation value of the birefringent optical fiber 8 is approximately half the polarization dispersion value of the dispersion compensating optical fiber coil 6. From among the propagation time differences between the slow axis and the fast axis generated on the dispersion compensating optical fiber 6 side, the remaining propagation time difference previously compensated by the birefringent optical fiber 8a is compensated by the birefringent optical fiber 8b. The polarization dispersion is almost zero.

As a result, the birefringent optical fiber 8b
From the output end side 25, a pulse-shaped light wave having the same shape as the incident pulse with no pulse width spread is emitted as shown in FIG. 7 (d).

This embodiment also achieves the same effect as that of the first embodiment by the above operation, and as a result of actually measuring the polarization dispersion of this dispersion compensator 4 by the Jones matrix method, the value is 0.12 psec. Yes, it was confirmed that it was very small compared to the polarization dispersion (6.3 psec) of the dispersion compensating optical fiber coil 6. The chromatic dispersion of the dispersion compensator 4 of this embodiment is -1199.
It was psec / nm, and it was confirmed to have the same compensation effect as that of the first embodiment.

FIG. 8 shows a sectional view of a birefringent optical fiber 8 used in a third embodiment of the dispersion compensator of the present invention. The present embodiment is constructed almost in the same manner as the first embodiment, and the characteristic of this embodiment different from the first embodiment is that the birefringent optical fiber 8 and the core 10 have an elliptical shape. The structure-type birefringent optical fiber 8 is formed asymmetrically in the biaxial directions (X, Y axis directions) at right angles on the cross section of the optical fiber. The birefringent optical fiber 8 of this embodiment is an optical fiber having a birefringence of 3.5 × 10 ⁻⁴ and a length of 5.3 m. The polarization dispersion value of the birefringent optical fiber 8 is Similar to the first embodiment, the polarization dispersion value of the dispersion compensating optical fiber coil is 6.3 psec, which is almost the same amount.

This embodiment also operates in the same manner as the first embodiment and has the same effect. The polarization compensator 4 of the present embodiment has a polarization dispersion of -1202 psec / nm, and the chromatic dispersion shows a value almost equal to that of the first embodiment, and it is confirmed that it has an equivalent compensation effect. It was

FIG. 9 shows the essential configuration of a fourth embodiment of the dispersion compensator of the present invention. In the figure, the dispersion-compensating optical fiber coil 6 is -80 psec generated by the refractive index distribution of the germanium-doped core, like the dispersion-compensating optical fiber coil 6 used in the first to third embodiments.
A dispersion compensating optical fiber 3 having a negative dispersion characteristic of / nm / km and a length of 15 km is wound around an aluminum bobbin 19 having a barrel diameter of 60 mmφ and a barrel width of 42 mm and having a polarization dispersion value of 6.3 psec. The dispersion compensating optical fiber coil has a slow axis and a fast axis formed orthogonally to each other. From one end of the dispersion compensating optical fiber coil 6, a fiber tail 9 of the dispersion compensating optical fiber 3 of about 10 m is extended. ing.

The fiber tail 9 forms a polarization dispersion compensation coil 16 separate from the dispersion compensation optical fiber coil 6, and the polarization dispersion compensation coil 16 has a fiber tail of the dispersion compensation optical fiber 3 of about 10 m. 9, body diameter 30mmφ,
The coil is wound around an aluminum bobbin 15 having a body width of 10 mm, and has a smaller diameter than the dispersion compensating optical fiber coil 6. Further, the polarization dispersion compensation coil 16 has a polarization dispersion value which is substantially the same as the polarization dispersion value of the dispersion compensation optical fiber coil 6, and due to the polarization dispersion value, the slow axis and the fast axis The axis is formed orthogonally.

A twisting portion 14 is provided between the polarization dispersion compensating coil 16 and the dispersion compensating optical fiber coil 6, and the twisting portion 14 is used to disperse the polarization dispersion as shown in FIG. Compensation coil
The 16 slow axes and the fast axis of the dispersion compensating optical fiber coil 6 are aligned and fixed to each other, and the polarization dispersion compensating coil
The 16 fast axes and the slow axis of the dispersion compensating optical fiber coil 6 are aligned and fixed.

The present embodiment is configured as described above,
The polarization dispersion compensating coil 16 is the dispersion compensating optical fiber coil 6.
The slow axis and the fast axis are formed to be orthogonal to each other with a polarization dispersion value substantially equal to the polarization dispersion value of the. The first axis of the optical fiber coil 6 is aligned with each other, and the first axis of the polarization dispersion compensation coil 16 and the slow axis of the dispersion compensation optical fiber coil 6 are aligned with each other and fixed. The propagation time difference between the slow axis and the fast axis generated on the dispersion compensating optical fiber coil 6 side is the same as in the third embodiment.
The propagation time difference between the fast axis and the slow axis cancels each other out, and the same operation as in the first and third embodiments and the same effect can be obtained.

Further, if the polarization dispersion compensating coil 16 has a diameter sufficiently smaller than that of the dispersion compensating optical fiber coil 6 as in the present embodiment, even the polarization dispersion compensating coil having an extremely short optical fiber length can be used. A polarization dispersion compensation coil having the same polarization dispersion value as that of the dispersion compensation optical fiber coil 6 can be provided, and the same amount of birefringence as the dispersion compensation optical fiber coil 6 can be generated. Is possible. Therefore, the short-length fiber tail 9 extending from the one end side of the dispersion compensating optical fiber coil 6 forms the polarization dispersion compensating coil 16 having a polarization dispersion value substantially equal to that of the dispersion compensating optical fiber coil 6. As a result, as described above, it is possible to realize a dispersion compensator in which the polarization dispersion is almost zero without lowering the compensation effect.

It has been confirmed that the polarization compensator 4 of this embodiment has a polarization dispersion of 0.15 psec and a chromatic dispersion of -1189 psec / nm, which is the same as in the first and third embodiments. It was confirmed that there was almost no polarization dispersion and that it had a sufficient compensation effect.

FIG. 11 shows the configuration of the essential parts of a fifth embodiment of the dispersion compensator of the present invention. This embodiment is different from the fourth embodiment in that the fiber tails 9a and 9b of the dispersion compensating optical fiber 3 are extended by 10 m from both ends of the dispersion compensating optical fiber coil 6, respectively. Polarization dispersion compensation coil with fiber tails 9a and 9b
16a and 16b are formed.

A twisting portion 14a is provided between the polarization dispersion compensating coil 16a and the dispersion compensating optical fiber coil 6, and is disposed between the polarization dispersion compensating coil 16b and the dispersion compensating optical fiber coil 6. A twisting portion 14b is interposed in the twisting portions 14a and 14b, as shown in FIGS.
As a result, the slow axes of the polarization dispersion compensation coils 16a and 16b and the fast axis of the dispersion compensation optical fiber coil 6 are made to coincide with each other, and the fast axes of the polarization dispersion compensation coils 16a and 16b and the dispersion compensation optical fiber coil 6 are aligned. The slow axis of and is fixed by being matched with each other.

In this embodiment, the polarization compensating coils 16a and 16a are provided on both ends of the dispersion compensating optical fiber coil 6, respectively.
b is provided, the polarization dispersion compensation coils 16a and 16b cause the propagation time difference between the slow axis and the fast axis generated in the dispersion compensating optical fiber coil 6 as in the fourth embodiment. Will be compensated, for example,
When light is incident from the polarization dispersion compensation coil 16a side,
A part of the propagation time difference between the slow axis and the fast axis generated on the dispersion compensating optical fiber coil 6 side is previously compensated by the polarization dispersion compensating coil 16a, and then the polarization dispersion compensating coil is provided.
16b compensates for the remaining propagation time difference of the propagation time difference between the slow axis and the fast axis that occurs on the side of the dispersion compensating optical fiber coil 6 and, as a result, the polarization dispersion is almost zero,
The same effects as those of the first to fourth embodiments are obtained.

In this embodiment, for example, when pulse-shaped incident light as shown in FIG. 7A is made incident from the incident end side of the polarization dispersion compensation coil 16a, the polarization dispersion compensation coil 16a The pulse-shaped light as shown in FIG. 7 (b) is emitted from the emission end side, and the pulse-shaped light as shown in FIG. 7 (c) is emitted from the emission end side of the dispersion compensation optical fiber coil 6. Is emitted, and pulse-shaped light as shown in FIG. 7D is emitted from the emission end side of the polarization dispersion compensation coil 16b.

It has been confirmed that the polarization compensator 4 of this embodiment has a polarization dispersion of 0.10 psec and a chromatic dispersion of -1190 psec / nm.

FIG. 13 shows the configuration of the essential parts of a sixth embodiment of the dispersion compensator of the present invention. In the figure, similar to the dispersion compensating optical fiber coil 6 of the first to fifth embodiments, each has its own polarization dispersion value (6.3 psec), and the slow axis is caused by this polarization dispersion value. A first dispersion-compensating optical fiber coil 6a and a second dispersion-compensating optical fiber coil 6b in which the first axis and the fast axis are formed orthogonal to each other are provided, and the first dispersion-compensating optical fiber coil 6a includes
A first birefringent optical fiber (polarization maintaining fiber) having a polarization dispersion value of the same amount as that of the first dispersion compensating optical fiber coil 6a and having a slow axis and a fast axis formed orthogonally to each other. One end of the optical fiber) 8a is connected by a connecting portion 29.

The slow axis of the first birefringent optical fiber 8a and the fast axis of the first dispersion compensating optical fiber coil 6a coincide with each other, and the first birefringent optical fiber 8a
Fast axis and first dispersion compensating optical fiber coil 6a
Of the first dispersion compensating optical fiber coil 6 of the first birefringent optical fiber 8a.
The connection side with a, that is, the connection section 29 side is connected to the first dispersion compensation optical fiber coil 6a and forms a part of the coil.

On the other hand, the second dispersion compensating optical fiber coil 6b has the second dispersion compensating optical fiber coil 6b.
The one end side of the second birefringent optical fiber (polarization maintaining optical fiber) in which the slow axis and the fast axis are formed orthogonal to each other with the polarization dispersion value of the polarization dispersion value of The second birefringent optical fiber 8b and the slow axis of the second birefringent optical fiber 8b are aligned with the fast axis of the second dispersion-compensating optical fiber coil 6b.
Fast axis and second dispersion compensating optical fiber coil 6b
The slow axes of and match each other.

In addition, the second birefringent optical fiber 8b
Of the second dispersion-compensating optical fiber coil 6b is connected to the dispersion-compensating optical fiber coil 6b.
It is connected to b and forms a part of the coil.

The other end side of the first birefringent optical fiber 8b is connected to the other end side of the first birefringent optical fiber 8a by a connecting portion 31. And the fast axis of the second birefringent optical fiber 8b coincide with each other, and the first birefringent optical fiber 8b
The fast axis of a and the slow axis of the second birefringent optical fiber 8b coincide with each other.

This embodiment is constructed as described above,
By the same operation as in the first and second embodiments, the propagation time difference between the slow axis and the fast axis generated in the first dispersion compensating optical fiber coil 6a becomes slower than the slow axis and the fast axis of the first birefringent optical fiber 8a. Almost offset by the propagation time difference of the axis,
The propagation time difference between the slow axis and the fast axis generated in the second dispersion compensating optical fiber coil 6b is almost canceled by the propagation time difference between the fast axis and the slow axis of the second birefringent optical fiber 8b. Then, further, the first birefringent optical fiber 8a
And the second birefringent optical fiber 8b are connected to each other, the polarization dispersion on the side of the first dispersion-compensating optical fiber coil 6a and the second dispersion-compensating optical fiber coil 6b which are set to approximately zero as described above. The polarization dispersion on the side is almost completely canceled out, and as a result, the polarization dispersion of the dispersion compensator 4 becomes extremely close to zero, and the same effect as that of the above-mentioned embodiment is obtained.

As in this embodiment, one end sides of the first and second birefringent optical fibers 8a and 8b connected to the first and second dispersion compensating optical fiber coils 6a and 6b, respectively, are
The lengths of the first and second birefringent optical fibers 8a and 8b are freely adjusted by connecting and winding the first and second dispersion compensating optical fiber coils 6a and 6b to form a part of the coil. This makes it possible to equalize the polarization dispersion on the side of the first dispersion compensating optical fiber coil 6a and the polarization dispersion on the side of the second dispersion compensating optical fiber coil 6b. When connecting the fiber 8a and the second birefringent optical fiber 8b, as described above, the dispersion compensator 4
It is possible to bring the polarization dispersion of the to very close to zero.

Furthermore, the first dispersion compensating optical fiber coil 6a and the second dispersion compensating optical fiber coil 6b are respectively
By connecting with the second birefringent optical fibers 8a and 8b, even if a temperature change occurs in the environment in which the dispersion compensator 4 is installed, the polarization state changes due to the influence of the temperature change or the like. This can be prevented, and the dispersion compensator 4 that can ignore factors such as temperature that affect the polarization state can be provided.

FIG. 14 shows the essential configuration of the seventh embodiment of the dispersion compensator of the present invention. This embodiment is different from the sixth embodiment in that the first and second dispersion compensating optical fiber coils 6a and 6b are provided between the first and second dispersion compensating optical fiber coils 6a and 6b. That is, the birefringent optical fiber 8 having a polarization dispersion value of about the same amount as the combined polarization dispersion value of 1 is provided and connected by the connecting portions 29 and 30.

Also in this birefringent optical fiber 8, the slow axis and the fast axis are formed orthogonally due to the polarization dispersion value, and the slow axis of this birefringent optical fiber 8 is the first dispersion compensation light. First axis of fiber coil 6a and second axis
Of the dispersion compensating optical fiber coil 6b and the fast axis of the birefringent optical fiber 8 are the slow axis of the first dispersion compensating optical fiber coil 6a and the first axis of the second dispersion compensating optical fiber coil 6b. Aligns with the slow axis.

This embodiment is constructed as described above,
Also in this embodiment, the propagation time difference between the slow axis and the fast axis of the first and second dispersion compensating optical fiber coils 6a and 6b is the same as in the above-described embodiment, and the propagation time between the fast axis and the slow axis of the birefringent optical fiber 8 is the same. They are canceled by the time difference, and the polarization dispersion of the dispersion compensator 4 becomes almost zero, and the same effect as that of the above embodiment is obtained.

The present invention is not limited to the above-mentioned embodiment, and various embodiments can be adopted. For example, in the first and second embodiments, the birefringent optical fiber 8 is
As shown in FIG. 4, the stress-applying birefringent optical fiber is provided in which the circular stress-applying portions 13 are provided so as to sandwich the core 10 with a space therebetween.
A stress imparting type birefringent optical fiber that imparts stress to the core 10 may be used as a mode in which the core 10 is sandwiched by a stress imparting portion 13 having a shape as shown in FIG. 15, and as shown in FIG. It is also possible to provide a stress imparting type birefringent optical fiber in which an oval-shaped stress imparting portion 13 is provided so as to surround the core and the stress imparting portion 13 imparts stress to the core 10. in this way,
In the birefringent optical fiber 8, stress is imparted to the core 10 by the stress imparting portions formed asymmetrically in the biaxial directions (X, Y axis directions) at right angles on the cross section of the optical fiber, whereby the dispersion compensating optical fiber is provided. It suffices that the coil 6 has a polarization dispersion value that is substantially the same as that of the coil 6.

Further, in the third embodiment, the structural type birefringent optical fiber in which the core 10 is formed in an elliptical shape is connected to one end side of the dispersion compensation type optical fiber coil 6, but the structural type The refraction optical fiber 8 may be divided and connected to both ends of the dispersion compensation optical fiber coil 6.

A structural-type birefringent optical fiber 8 having a birefringence of 3.5 × 10 ⁻⁴ , which is similar to the birefringent optical fiber 8 used in the third embodiment, is set to 2.6 as shown in FIG. m birefringent optical fiber 8a and 2.6 m birefringent optical fiber 8b are divided and connected to both ends of the dispersion compensating optical fiber coil 6, and the slow axes of the birefringent optical fibers 8a and 8b and the dispersion compensating optical fiber are connected. Polarization dispersion of the dispersion compensator 4 formed by aligning the fast axis of the coil 6 with each other, and aligning the fast axis of each of the birefringent optical fibers 8a and 8b with the slow axis of the dispersion compensating optical fiber coil 6, As a result of measurement by the Jones matrix method, it was 0.12 psec, and the chromatic dispersion of the dispersion compensator 4 was -1201 psec / nm. Thus, even when the structural birefringent optical fiber 8 is divided into both ends of the dispersion compensating optical fiber coil 6 to form the dispersion compensator 4, the same effects as those of the first to seventh embodiments are obtained. Has been confirmed to play.

Furthermore, in the third embodiment described above, the birefringent optical fiber 8 is the structural type birefringent optical fiber having the elliptical core 10, but the birefringent optical fiber 8 is the core 10.
The shape may be a birefringent optical fiber having a structure other than an elliptical shape and having a difference in structure in the X-axis direction and the Y-axis direction on the cross section of the optical fiber.

Further, in the above embodiment, each dispersion compensating optical fiber 3 forming the dispersion compensating optical fiber coil 6 has a core doped with germanium, and has a −80 psec /
Although the dispersion compensating optical fiber of 15 km having the dispersion characteristic of nm / km is used, the length and the dispersion characteristic of the dispersion compensating optical fiber 3 are not particularly limited.
Any dispersion compensating optical fiber having a negative dispersion characteristic caused by the refractive index distribution of the core 10 may be used. The number of windings of the dispersion compensating optical fiber coil 6 formed by the dispersion compensating optical fiber 3 and the bobbin 19 for winding the coil.
The body diameter, body width, etc. are not particularly limited and may be set appropriately.

Further, in the fourth and fifth embodiments, the polarization dispersion compensation coil 16 formed by the fiber tail 9 of the dispersion compensation optical fiber 3 is the dispersion compensation optical fiber coil 6.
Although the diameter of the coil is smaller than that of the dispersion compensating optical fiber coil 6, the polarization dispersion compensating coil 16 is not necessarily smaller than the dispersion compensating optical fiber coil 6. However, as in the above example,
If the polarization dispersion compensation coil 16 has a diameter sufficiently smaller than that of the dispersion compensation optical fiber coil 6, even if the polarization dispersion compensation coil has a very short optical fiber length, the polarization dispersion value of the dispersion compensation optical fiber 6 is reduced. It is possible to make a polarization dispersion compensation coil having a polarization dispersion value of about the same amount as the above, and by making the polarization dispersion compensation coil 16 a coil having a small diameter, the dispersion compensator can be made smaller accordingly. Therefore, the polarization dispersion compensation coil 16 is preferably a coil having a small diameter.

Further, the number of dispersion compensating optical fiber coils 6 provided in the dispersion compensator of the present invention is not particularly limited. For example, a plurality of dispersion compensating optical fiber coils 6 are provided.
Are provided, and the dispersion compensating optical fiber coil 6 and the birefringent optical fiber 8 are alternately connected, or a plurality of the dispersion compensating optical fiber coil 6 and the polarization dispersion compensating coil 16 are formed and are alternately arranged. However, the dispersion compensator 4 may be formed by interposing the twisting portion 14 between each dispersion compensation optical fiber coil 6 and the polarization dispersion compensation coil 16.

Further, the birefringence and length of the birefringent optical fiber 8 used in the dispersion compensator of the present invention, the length of the fiber tail 9 forming the polarization dispersion compensating coil 16 and the number of coil turns are not particularly limited. Not what they are
The polarization dispersion value on the dispersion compensating optical fiber coil 6 side and the polarization dispersion value on the birefringent optical fiber 8 side or the polarization dispersion compensating coil 16 side are appropriately set so as to be substantially the same.

[0067]

According to the present invention, for example, one or more birefringent optical fibers are connected to one or more dispersion compensating optical fiber coils, and the total polarization dispersion value of the birefringent optical fibers is dispersed. It is configured to have a polarization dispersion value that is almost the same as the polarization dispersion value on the compensating optical fiber coil side, and the slow axis of the birefringent optical fiber and the fast axis of the dispersion compensating optical fiber coil are aligned with each other to ensure birefringence. By making the fast axis of the optical fiber and the slow axis of the dispersion compensating optical fiber coil coincide with each other, the propagation time difference between the slow axis and the fast axis caused by the polarization dispersion value of the dispersion compensating optical fiber coil can be determined. It becomes possible to cancel by the propagation time difference between the slow axis and the fast axis of the fiber.

Further, due to the fiber tail of the dispersion compensating optical fiber extending from at least one end side of the dispersion compensating optical fiber coil, the polarization compensating value having substantially the same amount as that of the dispersion compensating optical fiber coil is polarized. A wave dispersion compensation coil is formed, and the slow axis of the polarization dispersion compensation coil and the fast axis of the dispersion compensation optical fiber coil are matched with each other,
According to the present invention, the fast axis of the polarization dispersion compensating coil and the slow axis of the dispersion compensating optical fiber coil are matched with each other. It is possible to cancel the difference in propagation time between the slow axis and the fast axis.

Therefore, according to the present invention, it is possible to form a dispersion compensator in which polarization dispersion hardly occurs. For example, the light of a semiconductor laser or the like is modulated with a pulse signal, and an optical fiber for propagation is used. If the dispersion compensator according to the present invention is provided in a communication system for transmitting in the same way, the pulse width of the laser light having a certain wavelength spread can be widened by the polarization dispersion of the dispersion compensator as in the conventional dispersion compensator. Not,
High-speed, because it is possible to compensate the material dispersion of the optical fiber for propagation and prevent the spread of the pulse width due to the material dispersion.
It is possible to construct a large capacity communication system.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram showing a first embodiment of a dispersion compensator according to the present invention.

FIG. 2 is an explanatory diagram showing a connection state of the dispersion compensating optical fiber 3 and the birefringent optical fiber 8 of the first embodiment.

FIG. 3 is a cross-sectional explanatory view of the birefringent optical fiber of the first embodiment.

FIG. 4 is a pulse of incident light (a) to the dispersion compensator of the first embodiment, emitted light (b) from the dispersion compensating optical fiber coil 6, and emitted light (c) from the dispersion compensator. It is explanatory drawing which shows a shape.

FIG. 5 is a main part configuration diagram showing a second embodiment of the dispersion compensator according to the present invention.

FIG. 6 is an explanatory diagram showing a connection state of each of the dispersion compensating optical fiber coil 6 and each of the birefringent optical fibers 8a and 8b of the second embodiment.

FIG. 7 shows incident light (a) to the dispersion compensator and outgoing light (b) from the birefringent optical fiber 8a in the second embodiment.
And the light emitted from the dispersion compensating optical fiber coil 6 (c)
3A and 3B are explanatory diagrams showing a pulse shape of emitted light (d) from the dispersion compensator.

FIG. 8 is a cross-sectional explanatory view showing a birefringent optical fiber used in a third embodiment of the dispersion compensator according to the present invention.

FIG. 9 is a main part configuration diagram showing a fourth embodiment of the dispersion compensator according to the present invention.

FIG. 10 is an explanatory diagram showing states of a slow axis and a fast axis of the dispersion compensating optical fiber 3 (fiber tail 9) in the twisting section 14 of the fourth embodiment.

FIG. 11 is a main part configuration diagram showing a fifth embodiment of the dispersion compensator according to the present invention.

FIG. 12 is an explanatory diagram showing the states of the slow axis and the fast axis of the dispersion compensating optical fiber 3 (fiber tail 9) in the twisting portions 14a and 14b of the fifth embodiment.

FIG. 13 is a main part configuration diagram showing a sixth embodiment of the dispersion compensator according to the present invention.

FIG. 14 is a main part configuration diagram showing a seventh embodiment of the dispersion compensator according to the present invention.

FIG. 15 is a cross-sectional explanatory view showing an example of a stress-applying birefringent optical fiber used in another embodiment of the dispersion compensator according to the present invention.

FIG. 16 is a transverse cross-sectional explanatory view showing another example of the stress imparting type birefringent optical fiber used in another embodiment of the dispersion compensator according to the present invention.

FIG. 17 is a communication system (communication system) using a dispersion compensator.
It is explanatory drawing which shows an example.

[Explanation of symbols]

 3 Dispersion compensating optical fiber 6 Dispersion compensating optical fiber coil 8 Birefringent optical fiber 9 Fiber tail 14 Twisting part 16 Polarization dispersion compensating coil

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Haruki Ogoshi Inventor Haruki Ogoshi 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (8)

[Claims] 1. A dispersion compensating optical fiber coil formed by winding a plurality of dispersion compensating optical fibers having a negative dispersion characteristic caused by a refractive index distribution of a core, the dispersion compensating optical fiber coil being provided with the dispersion compensating optical fiber coil. Due to the polarization dispersion value of the fiber coil, the slow axis, which is the polarization component axis in which the light propagation speed is slow, and the first axis, which is the polarization component axis in which the light propagation speed is faster than the slow axis, are orthogonal to each other. The dispersion-compensating optical fiber coil has a polarization dispersion value approximately equal to that of the dispersion-compensating optical fiber coil, and a slow axis and a fast axis are formed orthogonally. A refraction optical fiber is connected, and the slow axis of the birefringence optical fiber and the fast axis of the dispersion compensation optical fiber coil match each other, and the fast axis of the birefringence optical fiber and the dispersion compensation optical fiber coil are connected. A dispersion compensator characterized in that the slow axis of the il matches each other. 2. The dispersion compensator according to claim 1, wherein the birefringent optical fiber is a stress imparting type birefringent optical fiber. 3. The dispersion compensator according to claim 1, wherein the birefringent optical fiber is a structural type birefringent optical fiber. 4. The dispersion compensator according to claim 1, 2 or 3, wherein the birefringent optical fiber is connected to one end side of the dispersion compensating optical fiber coil. 5. The dispersion compensator according to claim 1, wherein the birefringent optical fiber is divided and connected to both ends of the dispersion compensating optical fiber coil. 6. A dispersion compensating optical fiber coil formed by winding a plurality of dispersion compensating optical fibers having a negative dispersion characteristic caused by a refractive index distribution of a core, wherein the dispersion compensating optical fiber coil is provided. Due to the polarization dispersion value of the fiber coil, the slow axis, which is the polarization component axis in which the light propagation speed is slow, and the first axis, which is the polarization component axis in which the light propagation speed is faster than the slow axis, are orthogonal to each other. And the fiber tail of the dispersion compensating optical fiber is extended from at least one end side of the dispersion compensating optical fiber coil, and the fiber tail forms a polarization dispersion compensating coil separate from the dispersion compensating optical fiber coil. The polarization-dispersion compensation coil has a polarization-dispersion value approximately equal to that of the dispersion-compensating optical fiber coil, and the slow axis and the fast axis are formed orthogonally. The slow axis of the polarization dispersion compensating coil and the fast axis of the dispersion compensating optical fiber coil are aligned with each other between the polarization dispersion compensating coil and the dispersion compensating optical fiber coil, and the polarization dispersion compensating coil is compensated for. A dispersion compensator, characterized in that a twisting part for interposing the first axis of the coil and the slow axis of the dispersion compensating optical fiber coil with each other is interposed. 7. A first and second dispersion compensating optical fiber coil formed by winding a plurality of dispersion compensating optical fibers having a negative dispersion characteristic caused by a refractive index distribution of a core,
The first and second dispersion compensating optical fiber coils have a slow axis, which is a polarization component axis in which the propagation speed of light is slow, and a slow axis due to the polarization dispersion value of the unique dispersion compensating optical fiber coil. The fast axis, which is the polarization component axis in which the propagation speed of light is faster than the axis, is formed orthogonal to each other,
The first dispersion-compensating optical fiber coil has a polarization dispersion value approximately equal to that of the first dispersion-compensating optical fiber coil, and a slow axis and a fast axis are formed orthogonally to each other. One end side of the birefringent optical fiber is connected, and the slow axis of the first birefringent optical fiber and the fast axis of the first dispersion-compensating optical fiber coil match each other, and the first birefringent optical fiber And the slow axis of the first dispersion compensation optical fiber coil are aligned with each other,
Further, the connection side of the first birefringent optical fiber with the first dispersion compensating optical fiber coil is connected to the first dispersion compensating optical fiber coil to form a part of the coil. Of the second dispersion-compensating optical fiber coil has a polarization dispersion value substantially equal to that of the second dispersion-compensating optical fiber coil and a slow axis and a fast axis are formed orthogonally to each other. One end side of the refraction optical fiber is connected, and the slow axis of the second birefringence optical fiber and the fast axis of the second dispersion compensation optical fiber coil match each other, and the first axis of the second birefringence optical fiber is matched. The axis and the slow axis of the second dispersion compensating optical fiber coil are aligned with each other,
Moreover, the connection side of the second birefringent optical fiber with the second dispersion compensating optical fiber coil is connected to the second dispersion compensating optical fiber coil to form a part of the coil. The other end of the optical fiber is connected to the other end of the first birefringent optical fiber so that the slow axis of the first birefringent optical fiber and the fast axis of the second birefringent optical fiber coincide with each other. A dispersion compensator in which the first axis of the first birefringent optical fiber and the slow axis of the second birefringent optical fiber coincide with each other. 8. A first and a second dispersion compensating optical fiber coil formed by winding a plurality of dispersion compensating optical fibers having a negative dispersion characteristic caused by a refractive index distribution of a core,
The first and second dispersion compensating optical fiber coils have a slow axis, which is a polarization component axis in which the propagation speed of light is slow, and a slow axis due to the polarization dispersion value of the unique dispersion compensating optical fiber coil. The fast axis, which is the polarization component axis in which the propagation speed of light is faster than the axis, is formed orthogonal to each other,
Between the first and second dispersion compensating optical fiber coils, the first
A birefringent optical fiber in which the slow axis and the fast axis are formed orthogonally and which has a polarization dispersion value of about the same amount as the sum of the polarization dispersion values of the second dispersion compensation optical fiber coil and The slow axis of the birefringent optical fiber coincides with the fast axis of the first dispersion-compensating optical fiber coil and the fast axis of the second dispersion-compensating optical fiber coil, and the slow axis of the birefringent optical fiber is fast. Axis is first
Dispersion compensator, wherein the slow axis of the dispersion compensating optical fiber coil and the slow axis of the second dispersion compensating optical fiber coil are coincident with each other.