JP3029255B2 - Optical circuit and method of controlling polarization state of optical circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit having polarization maintaining characteristics. That is, the present invention uses a light source having a low degree of polarization as a light source and uses an optical waveguide having a polarization maintaining function as an output part of an optical circuit, and simply uses an optical circuit output part without using a polarization state changing unit. Is realized.

Further, in such an optical circuit, the polarization state of propagation light can be easily controlled by inserting a polarization state changing means in front of an optical waveguide having a polarization maintaining function.

[0003]

2. Description of the Related Art In the technical field of transmitting light while maintaining a polarization state, a special optical fiber capable of maintaining a polarization state, that is, a polarization maintaining optical fiber is often used. As a polarization maintaining optical fiber, "Introduction to Optical Fiber Communication" (Yasuharu Suematsu, Ohmsha, 197-199)
Page, published on March 10, 1991, 3rd edition), in addition to the PANDA type fiber which has a structure in which a stress applying portion is provided in the cladding to apply anisotropic strain to the core, the elliptical deformation is increased. Optical fibers with asymmetrical axial pits provided in the refractive index distribution to increase the structural asymmetry, the cladding part is made into a double structure, the intermediate cladding part is deformed elliptically, and stress is applied to the core. And the like.

However, the most frequently used PAN
DA (Polarizationmaintainin)
g and abduction reduction
In the case of a fiber type fiber, as shown in FIG. 11, there are only two directions of the polarization plane that can be held, and the other polarization-maintaining optical fibers are also held only in a specific direction. .

[0005] In FIG. 11, reference numeral 1 denotes a cross section of a PANDA type fiber, in which stress applying portions 3 a and 3 b are provided so as to sandwich a core 2 through which light passes. The directions 4 and 5 in which the polarization maintaining optical fiber can maintain the polarization plane are the direction connecting the centers of the stress applying portions 3a and 3b and the direction orthogonal thereto, as indicated by the dashed line, and the polarization plane is in other directions. It is not retained even if it is incident.

Therefore, conventionally, as shown in FIG. 12, a polarization controller which is a means for arbitrarily changing the polarization direction before the polarization maintaining optical fiber 7 using a light source 6a having a high degree of polarization like a semiconductor laser. 8, it is necessary to adjust the polarization plane of the laser light so as to match the direction in which the polarization-maintaining optical fiber 7 can be held and guide the laser light to the polarization-maintaining optical fiber 7.

In FIG. 12, reference numeral 9 denotes a single mode optical fiber for connecting the light source 6a and the polarization maintaining optical fiber 7,
10 is a polarization maintaining optical fiber 7 and a single mode optical fiber 9
And an optical connector is usually used or fusion-spliced. Reference numeral 11 denotes an output terminal of the polarization maintaining optical fiber 7. Although the polarization controller 8 is installed in the middle of the single mode optical fiber 9 in the figure, it may be installed between the single mode optical fiber 9 and the polarization maintaining optical fiber 7.

FIG. 13 shows the state of propagating light in the optical circuit system of FIG. Even if the light emitted from the light source 6a having a high degree of polarization is elliptically polarized light 12a (13 is its polarization plane) (linearly polarized light / circularly polarized light corresponds to a special case of elliptically polarized light), The polarization controller 8 is inserted in the middle of the one-mode optical fiber 9, and the polarization maintaining surface 4 of the polarization maintaining optical fiber 7 is inserted.
By converting the input signal into a linearly polarized wave 14 parallel to and inputting the same, the state of polarization in the polarization maintaining optical fiber 7 and the state of polarization of the light emitted from the output terminal 11 can be kept constant.

FIG. 14 shows a case where the polarization plane 13 of the polarized light 12a emitted from the light source 6a having a high degree of polarization enters the polarization maintaining optical fiber 7 in a direction completely different from the direction in which the optical fiber can be maintained. This shows the state of the propagating light. That is, this corresponds to a case where the polarization controller 8 is omitted from FIG. In this case, the polarization-maintaining optical fiber 7 does not perform any polarization-maintaining function, and is different from the polarization light 12a.
b propagates through the polarization-maintaining optical fiber 7, and is emitted from the output terminal 11 in a polarization state 15 different from 13. When a perturbation 16 is received at any position of the polarization maintaining optical fiber 7, the polarization state of the emitted light changes from 15 to 17 in accordance with the perturbation.

An optical system in which light controlled by a polarization controller 8 is observed by a polarization analyzer 18 as shown in FIG. This system is obtained by adding a polarization analyzer 18 to the output terminal of FIG. FIG. 16 shows the observed result as a Poincare sphere with the polarization state as a Stokes parameter. Here, 101 is clockwise circular polarization,
102 is -45 ° linear polarization, 103 is vertical linear polarization, 1
04 is + 45 ° linear polarization, 105 is horizontal linear polarization, 10
Reference numeral 6 denotes a left-handed circularly polarized state. Now, the polarization controller 8 changes the polarization plane of the elliptical polarization 12a to the polarization-maintaining optical fiber 7a.
, The polarization plane observed by the polarization analyzer 18 is observed on the equator 107 of the Poincare sphere. That is, it becomes any linearly polarized light. But,
If the polarization plane of the elliptical polarization 12a is not made to coincide with the polarization plane of the polarization maintaining optical fiber 7, the state of polarization is unstable, and if perturbed, the state on the equator 107 of the Poincare sphere cannot be maintained. Fluctuate irregularly like

As described above, when a light source having a high degree of polarization such as a semiconductor laser is used to propagate light while maintaining the polarization state, the light emitted from the semiconductor laser is once transmitted to a polarization controller such as a polarization controller. It was necessary to convert the plane of polarization to a direction in which the polarization-maintaining optical fiber can be held by using means capable of arbitrarily changing the polarization state, and then guide the polarization plane to the polarization-maintaining optical fiber. However, means for matching the polarization state to the polarization maintaining surface of the polarization maintaining optical fiber in this way generally has an expensive and complicated structure. It is also possible to incorporate a polarization maintaining optical fiber in advance as a semiconductor laser module in accordance with the plane of polarization of the emitted light of the laser, but such a semiconductor laser module is very expensive. In addition, in order to use a semiconductor laser incorporating such a polarization maintaining optical fiber in a measuring device requiring high precision, sufficient consideration must be given to its use.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has a simple structure in which a polarization state changing means such as a polarization controller is omitted, but is sufficiently polarized at a predetermined position in an optical circuit. An object of the present invention is to provide an optical circuit capable of maintaining a wave state.

It is another object of the present invention to provide an optical circuit in which the polarization state of propagation light can be easily controlled by inserting a polarization state changing means in front of an optical waveguide having a polarization maintaining function in such an optical circuit. I do.

[0014]

In order to achieve the above object, an optical circuit according to the present invention is an optical circuit comprising a light source, an input section and an output section, which has no polarization state changing means. source consists source degree of polarization of 30% or less (excluding 0%), the input unit, the optical waveguide is not a polarization state holding structure is connected to the light source, only in the optical waveguide is not a polarization state holding structure An optical waveguide that is not configured or does not have a polarization state maintaining structure and an optional optical circuit, and the optional optical circuit is a single
Or multiple optical waveguides without polarization maintaining structure and singular
Or a plurality of optical components (actively changing the polarization state
And the output section is constituted by an optical waveguide having no branch connected to one or more of the input sections, and the optical waveguide having no branch is at least partially polarized. It is characterized by having an optical waveguide of a state holding structure .

According to another aspect of the present invention, there is provided a method for controlling a polarization state of an optical circuit.
Characterized by controlling the polarization state with a constant region of one of or inserted into the input side to the optical waveguide of any of the polarization state holding structure, the Poincare sphere by said polarization state changing means And

Preferably, the light source is an edge emitting light emitting diode.

Here, the optical waveguide is an optical fiber
And the optical waveguide of the integrated circuit.
Optical waveguide with carrier structure maintains polarization state despite perturbation
An optical waveguide with a special structure to enable
Light such as polarization maintaining optical fiber including PANDA type fiber
Refers to a waveguide. In contrast, the polarization state maintaining structure
An optical waveguide without any means other than an optical waveguide with a polarization maintaining structure
In the optical waveguide, even if the polarization state is maintained in the fixed state,
Single mode that cannot maintain polarization state with perturbation
Refers to an optical waveguide such as an optical fiber.

[0018]

FIG. 8 shows an example of the structure according to claim 1 of the present invention. Low degree of polarization (less than 30%
Except for 0%, the same applies to the following in the embodiments and examples.)
The input section 19 of the optical circuit is connected to the light source 6b.
Is connected to the output unit 20.

The input section 19 comprises an optical waveguide 9 having no polarization state maintaining structure and an optional optical circuit 21. The arbitrary optical circuit 21 includes an optical waveguide having no polarization state maintaining structure and an optical component. (side
Excluding those that actively change the wave state) . That is, there is no optical waveguide or optical component that actively changes the state of the polarization incident from the light source 6b in the input unit 19. The output unit 20 includes a plurality of optical waveguides 22a and 22b having no branch. The optical waveguide 22a is different from the input unit 19 in that the optical waveguide 23a is not a polarization maintaining structure and the optical waveguide has a polarization maintaining structure. 7a, polarization state maintenance
The optical waveguides 23c are connected in the order of the optical waveguides 23c not having the holding structure , the optical waveguide 23c has an output terminal 11a, and the optical waveguide 22b is
An optical waveguide 23b having no polarization state maintaining structure, an optical waveguide 7b having a polarization state maintaining structure , a polarization state maintaining
The optical waveguides 23d are not connected in the order of the optical waveguides 23d, and the optical waveguides 23d have output terminals 11b. In FIG. 8, connection portions between the optical waveguide 7a and the optical waveguide 23a, between the optical waveguide 7a and the optical waveguide 23c, between the optical waveguide 7b and the optical waveguide 23b, and between the optical waveguide 7b and the optical waveguide 23d are omitted. 9, and FIG. 10). Each optical waveguide 2 of the output unit 20
2a and 22b, the light source 6b having a low degree of polarization and the polarization
The polarization maintaining function of the combination of the optical waveguides 7a and 7b having the holding structure works, and light having a constant polarization plane is output from the output terminals 11a and 11b unless external perturbation is applied to the optical waveguides 23c and 23d. .

For connection between optical waveguides, an optical connector is usually used or fusion-spliced. For the connection between the optical waveguide and the optical circuit, an optical connector, an optical splitter / coupler, an optical demultiplexer, an optical multiplexer, an optical switch, and the like are usually used, and fusion splicing is used. Regarding the connection between the optical waveguide and the optical circuit 21 in the configuration example of FIG. 8, these optical components are included in the optical circuit 21 (the same applies to the configuration examples of FIGS. 9 and 10).

There are various modifications to the configuration according to the first aspect. The input unit 19 may be composed of only the optical waveguide 9 and the optical demultiplexer which are not a single polarization state maintaining structure . Also, the optical waveguides 22a, 22a having no branch of the output section 20 are provided.
b may be only one, or three or more. Further, each of the optical waveguides 22a and 22b is an optical waveguide 7 having a polarization state maintaining structure.
a, as long as it has 7b least a portion thereof, polarized wave
One or both of the optical waveguides 23a and 23c which are not the state holding structure, and one or both of the optical waveguides 23b and 23d may be omitted. Also in these cases, the input section 19 has no optical waveguide or optical component that actively changes the state of the polarization incident from the light source 6b, and the output section 20 has the same polarization state as the light source 6b with a low degree of polarization. The polarization maintaining function by the combination of the optical waveguides 7 having the structure works, and light having a certain polarization plane is output from the output terminals 11a and 11b.

FIG. 9 shows an example of the configuration of an optical circuit for implementing the knitting wave state control method according to the fourth aspect of the present invention.
This configuration is also one configuration example of the fifth aspect . This configuration is obtained by adding polarization state changing means 25a and 25b to FIG. Polarization state changing means 25a and 25b are in the polarization state
It is inserted in the optical waveguides 23a and 23b which are not the holding structure, that is , on the input unit 19 side with respect to the optical waveguides 7a and 7b of the polarization state holding structure . Polarization state changing means 25
a, 25b and the optical waveguides 7a, 7b having a polarization state maintaining structure act a polarization control function, and the output terminal 11
Light having a controlled polarization plane is output from a and 11b.

There are various modifications in the configuration of the optical circuit for implementing the knitting wave state control method according to the fourth or fifth aspect . The input unit 19 may be composed of only one optical waveguide 9 having no polarization maintaining structure and an optical demultiplexer. Further, the number of the optical waveguides 22a and 22b having no branch of the output unit 20 may be only one, or may be three or more. Each of the optical waveguides 22a and 22b has a polarization state maintaining optical waveguide 7a, 7b.
If at least a part of b has a polarization state,
One or both of the optical waveguides 23a and 23c having no structure ,
One or both of 23b and 23d may be omitted. The polarization state changing means 25a and 25b may be inserted into the optical waveguides of the respective polarization state maintaining structures on the side of the input portion 19, and the optical waveguides 7a and 7b of the polarization state maintaining structures may be used. You may install in the state connected to. Further, regarding claim 4 , one of the polarization state changing means 25a and 25b may be omitted.

FIG. 10 shows a modification of the configuration of the optical circuit for implementing the knitting wave state control method according to the fourth or fifth aspect .
As shown in the figure, the optical waveguides 22a and 22b having no branch are connected to one splitter 24 in an arbitrary optical circuit 21, and the optical waveguide 21 does not have one polarization state maintaining structure. In the configuration where only the optical waveguide 9i is connected to the demultiplexer 24, one polarization state changing means 25 is used to maintain the polarization state.
It may be provided in the middle of the optical waveguide 9i having no structure . Also in these cases, the polarization state changing means 25 has a polarization state holding structure.
The optical waveguides 7a and 7b are inserted on the input unit 19 side, and the polarization state is controlled by the interaction between the polarization state changing means 25 and the optical waveguides 7a and 7b having the polarization state maintaining structure. The function is activated, and light having a controlled polarization plane is output from the output terminals 11a and 11b.

[0025]

Embodiment 1 FIG. 1 is a diagram showing the structure of an embodiment of an optical circuit in the present invention, the polarization state maintained in a low degree of polarization light source 6b
An optical waveguide 9 having no structure is connected, and a polarization state maintaining structure is provided.
The optical waveguide 9 of the polarization state maintaining structure is connected to the optical waveguide 9 which is not . 11 is an optical waveguide 7 having a polarization maintaining structure
Of an output terminal, 10 denotes a connecting portion of the optical <br/> waveguide 9 is not a state of polarization-holding structure and an optical waveguide 7 of the polarization state holding structure, the optical connector or fusion splicing is used. Polarization maintenance
The optical waveguide 9 and the connecting portion 10 which do not have the holding structure are included in the input portion 19, and the optical waveguide 7 having the polarization maintaining structure and the output terminal 11 are included in the output portion 20.

The propagation state of light in this optical system is shown in FIG.
Shown in When the elliptically polarized wave 13 in an arbitrary direction is emitted from the light source 6b having a low degree of polarization and enters the optical waveguide 7 having the polarization state maintaining structure , the polarization can be maintained in the optical waveguide 7 having the polarization state maintaining structure. The polarizations 26 and 27 in the directions 4 and 5 are maintained. At this time, the state of the polarized waves 26 and 27 is always maintained even if the perturbation 16 is received at any position of the optical waveguide 7. In addition, when the light source 6b having a low polarization degree is used, on the Poincare sphere, FIG.
8, a specific polarization state, that is, a meridian 10 connecting the clockwise circular polarization 101 and the counterclockwise circular polarization 106
9, the polarization state does not change even if a perturbation is applied to the optical waveguide 7.

That is, a light source having a low degree of polarization and a polarization state maintaining
By combining the optical waveguides having the polarization structure , even if the polarization plane of the light emitted from the light source does not coincide with the polarization plane of the optical waveguide having the polarization maintaining structure, the polarization of the light propagating in the optical waveguide is not required. It was found that the wave state was maintained.

The degree of polarization is the percentage of the energy of the polarized light component in the total energy of light expressed in%, and the present invention uses a light source having a low degree of polarization. Light emitting diodes are known as light sources having a low degree of polarization. Light-emitting diode (Light-Emitting Dio)
de), Oki Electric Research and Development, January, 1997, No. 173, Vol. 64 No. 1 "Low coherence edge emission type L
ED ", written by Yasumasa Kashima, has current-light output characteristics with excellent linearity, small temperature dependence of light emission characteristics, low light coherence, can be operated with a simple drive circuit,
It has features such as high reliability, and is applied to medium- and short-range optical communication systems, optical local area networks, data communication, and the like.

As described in the above document, light emitting diodes are classified into a surface emitting type and an edge emitting type in terms of structure.
Surface emitting light emitting diodes emit light from the surface of the chip. On the other hand, an edge-emitting light emitting diode that extracts light from an element end face in a direction parallel to the light emitting layer like a semiconductor laser is characterized by a small beam spot diameter and narrow beam emission characteristics. For this reason, the edge-emitting light emitting diode is expected as a light emitting diode that can be coupled to a single mode optical fiber with high efficiency. That is, in the surface emission type, the beam cannot be narrowed because the emission area is large in the light traveling direction. On the other hand, in the edge emission type, the beam is radiated from a narrow area of the end face. Can be narrowed down.

In this embodiment, an edge-emitting light emitting diode is used for the light source 6b having a low degree of polarization, a PANDA type fiber is used for the optical waveguide 7 having a polarization state maintaining structure, and a polarization state maintaining structure is used.
Using no single-mode optical fiber to the optical waveguide 9, an output terminal 11 of the optical circuit, it was confirmed that the polarization state is well retained polarization than 30% of the time. Also, the lower the degree of polarization, the easier it is to maintain the polarization state, and it was confirmed that the stability was good at 10% or less.

[0031]

Second Embodiment FIG. 2 is a diagram showing the configuration of another embodiment of an optical circuit in the present invention, the polarization state coercive low degree of polarization light source 6b
The optical waveguide 9a having no holding structure is connected to maintain the polarization state.
Structure waveguide 7 of the polarization state holding structure is connected to the optical waveguide 9a are not further waveguide polarization state holding structure 7
Is connected to an optical waveguide 9b which is not a polarization state maintaining structure . Reference numeral 11 denotes an output terminal of the optical waveguide 9b which is not a polarization state maintaining structure. Reference numerals 10a and 10b denote polarization state maintaining structures.
An optical connector or a fusion splicing is used at a connection portion between the optical waveguides 9a and 9b and the optical waveguide 7 having the polarization state maintaining structure . Also, no branch has emerged from the connection portion 10b. Polarized
The optical waveguide 9a and the connecting part 10a which are not the state maintaining structure are included in the input part 19, and the optical waveguide 7 and the connecting part 10b of the polarization state maintaining structure and the optical waveguide 9b which is not the polarized state maintaining structure and the output terminal 11 are output. Part 20.

Also in this embodiment, an edge emitting light emitting diode is used as the light source 6b, and a PAN is used as the optical waveguide 7 having the polarization state maintaining structure.
As the DA type fiber, a single mode optical fiber can be used for the optical waveguide 9 having no polarization state maintaining structure . As in the case of the first embodiment, the polarization state is sufficiently maintained at the output terminal 11 of the optical circuit.

[0033]

Third Embodiment FIG. 3 is a diagram illustrating a configuration of still another embodiment of the optical circuit of the present invention, the polarization in a low degree of polarization light source 6b
Waveguide 9a are not in a state holding structure is connected, polarized wave
Optical circuit 21a to the optical waveguide 9a are not state holding structure are connected, the optical waveguide 9c to the optical circuit 21a is not a polarization state holding structure are connected, the polarization state holding structure is not a polarization state holding structure waveguide 9c optical waveguide 7 is connected. Reference numeral 11 denotes an output terminal of the optical waveguide 7 having a polarization maintaining structure, and reference numeral 10c denotes an optical waveguide 9c having no polarization maintaining structure.
An optical connector or a fusion splicer is used at a connection between the optical waveguide 7 and the optical waveguide 7 having the polarization state maintaining structure . The optical circuit 21a includes optical waveguides 9d and 9e in which the optical waveguide portions do not have a polarization state maintaining structure.
And are connected to the optical waveguides 9a and 9c via an optical splitter 28 and an optical multiplexer 29 in the optical circuit 21, respectively. The optical waveguides 9a, 9c, the optical circuit 21a, and the connecting portion 10c, which do not have the polarization state maintaining structure, are included in the input portion 19, and are polarized.
The optical waveguide 7 having the state holding structure and its output terminal 11 are included in the output unit 20.

Also in this embodiment, an edge emitting light emitting diode is used for the light source 6b having a low degree of polarization, a PANDA type fiber is used for the optical waveguide 7 having a polarization state maintaining structure, and the polarization maintaining state is not used.
A single mode optical fiber can be used for the optical waveguide 9 which does not exist. As in the case of the first embodiment, the output terminal 11 of the optical circuit
, The polarization state is sufficiently maintained.

[0035]

[Embodiment 4] FIG. 4 is a view showing the configuration of still another embodiment of an optical circuit according to the present invention, in which a light source 6b having a low degree of polarization is polarized.
Waveguide 9a are not in a state holding structure is connected, polarized wave
Taiho lifting structure optical circuit 21b is connected to the optical waveguide 9a are not, waveguide 9c to the optical circuit 21b is not a polarization state holding structure are connected, the polarization state holding the non-polarization state holding structure waveguide 9c An optical waveguide 7 having a structure is connected. Reference numeral 11 denotes an output terminal of the optical waveguide 7 having a polarization maintaining structure, and reference numeral 10c denotes an optical waveguide 9c having no polarization maintaining structure.
An optical connector or a fusion splicer is used at a connection between the optical waveguide 7 and the optical waveguide 7 having the polarization state maintaining structure . The optical circuit 21b includes an optical waveguide 9f in which the optical waveguide portion does not have a polarization maintaining structure. One end of the optical waveguide 9f is connected to the optical waveguides 9a and 9c via the optical branching coupler 30, and the other end is reflective. Mirror 31
It is connected to the. The optical waveguides 9a, 9c, the optical circuit 21b, and the connecting portion 10c, which do not have the polarization state maintaining structure,
And the output terminal 11 of the optical waveguide 7 having the polarization maintaining structure and the output terminal 11 thereof.

Also in this embodiment, an edge emitting light emitting diode is used as the light source 6b, and a PAN is used as the optical waveguide 7 having the polarization maintaining structure.
As the DA type fiber, a single mode optical fiber can be used for the optical waveguide 9 having no polarization state maintaining structure . As in the case of the first embodiment, the polarization state is sufficiently maintained at the output terminal 11 of the optical circuit.

In the first to fourth embodiments, an example of a relatively simple optical circuit has been described. Instead of the optical circuits 21a and 21b of the third and fourth embodiments, the polarization state of light such as an analyzer is changed. Any optical circuit can be used as long as it does not include an optical component to be changed. In Examples 1 to 4, the polarization
The PANDA type fiber was used as the optical waveguide of the state holding structure . However, the optical fiber and the clad part which increased the circular deformation and provided the side pits which were off-axis symmetric in the refractive index distribution to increase the structural off-axis symmetry. Is an elliptical jacket-type fiber or the like in which the intermediate cladding portion is deformed elliptically by applying a stress to the core. Further, instead of using an optical fiber for the optical waveguide, an optical integrated circuit may be used. Any other configuration may be used without departing from the configuration of the present invention.

[0038]

Fifth Embodiment FIG. 5 shows a light source having a low degree of polarization and a polarization state maintaining structure.
1 shows an example of the configuration of an optical circuit that implements a polarization state control method for an optical circuit according to the present invention that enables polarization control in a certain region of a Poincare sphere by combining a structured optical waveguide and polarization state changing means. The configuration of the present embodiment is the polarization state maintaining structure of FIG.
The polarization state changing means 25 is inserted in the middle of the optical waveguide 9 having no . Optical waveguide 9 not having polarization maintaining structure
The polarization state changing means 25 and the connection part 10 are included in the input part 19, and the optical waveguide 7 having the polarization state holding structure and the output terminal 1
1 is included in the output unit 20. The polarization state change means 25 is polarized
It is inserted on the input section 19 side with respect to the optical waveguide 7 having the wave state holding structure .

When the optical waveguide 7 is an optical waveguide having no polarization state maintaining structure, a specific polarization state cannot be created without complicated control. However, the optical waveguide 7
Is composed of an optical waveguide having a polarization state maintaining structure, when the state of the elliptical knitted wave incident on the optical waveguide 7 changes arbitrarily, the light held in the optical waveguide 7 is transmitted through the meridian of the Poincare sphere shown in FIG. It turned out that it traced uniquely on 109.
Therefore, in this embodiment, since the optical waveguide 7 is constituted by an optical waveguide having a polarization state maintaining structure , the polarization state of the output terminal 11 can be changed by using the polarization state changing means 25 by using the Poincare sphere. Control can be performed in a fixed area on the meridian 109 and easily.

It is known that when an ordinary optical fiber receives a stress, the polarization state is changed by birefringence or the like. If this is utilized, the polarization state changing means 25 can be simply configured. For example, as shown in FIG. 19, when the loop 32 is formed by the single mode optical fiber 9 and the loop 32 is rotated as shown by the arrow, the polarization state of the light passing therethrough changes. Such a polarization state changing means is called a fiber type polarization controller. In addition, one quarter-wave plate and one half-wave plate are arranged in series, and any polarization state can be created by rotating the wave plate. May be used.

In this embodiment, an edge emitting light emitting diode is used as the light source 6b, and a PAN is used as the optical waveguide 7 having the polarization maintaining structure.
A single-mode optical fiber was used for the optical waveguide 9 which was not a polarization state maintaining structure for the DA type fiber, and it was confirmed that the polarization state could be sufficiently controlled at the output terminal 11 when the degree of polarization was 30% or less. .

[0042]

Sixth Embodiment FIG. 6 shows a light source having a low degree of polarization and a polarization state maintaining structure.
Another configuration example of an optical circuit that implements a polarization state control method for an optical circuit that enables polarization control in a certain region of a Poincare sphere by combining a structured optical waveguide and a polarization state changing unit will be described.
Connect the optical waveguide 9 in a low degree of polarization light source 6b is not a polarization state holding structure, not the polarization state holding structure waveguide 9
Through the optical demultiplexer 24 instead of the two polarization state maintaining structures.
The optical waveguides 9g and 9h are branched into optical waveguides 9g and 9h, and the polarization maintaining state is connected to the optical waveguides 9g and 9h via the connecting portions 10a and 10b, respectively.
Concrete of the optical waveguide 7a, connected to 7b, in polarization state holding structure
The polarization state changing means 25 is inserted in the middle of the optical waveguide 9 having no . Reference numerals 11a and 11b are output terminals of the optical waveguides 7a and 7b having the polarization state maintaining structure .

The optical waveguide 9 having no polarization state maintaining structure, the polarization state changing means 25, and the optical demultiplexer 24 are included in the input section 19, and the optical waveguides 9g and 9h having no polarization state maintaining structure and the connecting section 10a. , 10b and optical waveguide 7 having polarization maintaining structure
a, 7b and output terminals 11a, 11b are included in the output unit 20. This configuration is a modification of the embodiment shown in FIG. Incidentally, an optical waveguide 9 and the polarization state changing means 25 and the optical demultiplexer 24 is not a polarization state holding structure polarization state holding structure
The optical waveguides 9g and 9h and the connecting portions 10a and 10b are included in the input portion 19, and the optical waveguides 7a and
7b and the output terminals 11a and 11b may be interpreted as being included in the output unit 20. The polarization state changing means 25 maintains the polarization state.
The optical waveguides 7a and 7b having the holding structure are inserted on the input unit 19 side.

Also in this embodiment, an edge emitting light emitting diode is used as the light source 6b, and a PAN is used as the optical waveguide 7 having the polarization state maintaining structure.
A single-mode optical fiber can be used for the optical waveguide 9 which is not a polarization-maintaining structure . The polarization states at the output terminals 11a and 11b can be controlled sufficiently.

[0045]

Seventh Embodiment FIG. 7 shows a light source having a low degree of polarization and a polarization state maintaining structure.
Another configuration example of an optical circuit that implements a polarization state control method for an optical circuit that enables polarization control in a certain region of a Poincare sphere by combining a structured optical waveguide and a polarization state changing unit will be described. In the configuration of the present embodiment, instead of inserting the polarization state changing means 25 in the configuration of FIG. 6 in the middle of the optical waveguide 9 having no polarization state holding structure , two polarization state changing means 25 are used.
a and 25b are respectively inserted in the middle of the optical waveguides 9g and 9h not having the polarization state maintaining structure .

The optical waveguide 9 and the optical demultiplexer 24 not having the polarization state maintaining structure are included in the input section 19 and have the polarization state maintaining structure.
Optical waveguide 9 g, 9h and polarization state changing means 25a not,
25b, the connecting portions 10a and 10b, the optical waveguides 7a and 7b having the polarization maintaining structure , and the output terminals 11a and 11b are connected to the output portion 2.
It is included in 0. This configuration is a modification of the embodiment shown in FIG. In addition, the optical waveguide 9 not having the polarization state maintaining structure
, Optical demultiplexer 24 and optical waveguide 9 not having polarization maintaining structure
g, 9h, the polarization state changing means 25a, 25b, and the connection part 1.
0a and 10b are included in the input unit 19 and have a polarization state maintaining structure.
The optical waveguides 7a and 7b and the output terminals 11a and 11b may be interpreted as being included in the output unit 20. The polarization state changing means 25a and 25b are inserted on the input unit 19 side with respect to the optical waveguides 7a and 7b of the polarization state maintaining structure, respectively.

Also in this embodiment, an edge-emitting light emitting diode is used as the light source 6b, and a PAN is used as the optical waveguide 7 having the polarization maintaining structure.
As the DA type fiber, a single mode optical fiber can be used for the optical waveguide 9 having no polarization state maintaining structure . The polarization states at the output terminals 11a and 11b can be controlled sufficiently. Although the fifth to seventh embodiments have described examples of relatively simple optical circuits, it goes without saying that the present invention can be applied to other optical circuits without departing from the configuration of the present invention.

Although the fifth to seventh embodiments have described examples of a comparatively simple polarization state control method for an optical circuit, the present invention can be applied to other polarization state control methods for other optical circuits without departing from the configuration of the present invention. It goes without saying that the present invention can be applied.

[0049]

As described above, according to the present invention,
It is possible to provide an optical circuit having a simple configuration in which a polarization state changing unit such as a polarization controller is omitted, but having a characteristic of maintaining a sufficient polarization state. That is, the polarization state changing means can be omitted, and an optical circuit capable of maintaining the polarization state simply and inexpensively can be manufactured.

Further, by inserting the polarization state changing means in the middle of such an optical circuit, it is possible to provide a polarization state control method for an optical circuit which can easily control the polarization state of the propagation light. That is, it is possible to easily and inexpensively create a unique polarization state.

Further, by using the present invention, it is possible to easily and inexpensively configure a device requiring polarization state maintenance or polarization state control, which is advantageous for miniaturization and easy handling.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an optical circuit according to the present invention.

FIG. 2 is a diagram showing a configuration of another embodiment of the optical circuit according to the present invention.

FIG. 3 is a diagram showing a configuration of still another embodiment of the optical circuit according to the present invention.

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

FIG. 5 is a diagram showing an example of the configuration of an optical circuit that implements the optical circuit polarization state control method according to the present invention.

FIG. 6 is a diagram illustrating another example of the configuration of an optical circuit that implements the optical circuit polarization state control method according to the present invention.

FIG. 7 is a diagram showing still another example of the configuration of an optical circuit that implements the optical circuit polarization state control method according to the present invention.

FIG. 8 is a diagram illustrating an embodiment of an optical circuit according to the present invention.

FIG. 9 is a diagram for explaining an embodiment of a polarization state control method for an optical circuit according to the present invention.

FIG. 10 is a diagram for explaining another embodiment of the polarization state control method of the optical circuit according to the present invention.

FIG. 11 is a cross-sectional view of a typical PANDA type fiber as a polarization maintaining optical fiber.

FIG. 12 is a diagram illustrating a configuration of a conventional optical circuit that performs polarization control.

FIG. 13 is a diagram illustrating a light propagation state of a conventional optical circuit that performs polarization control.

FIG. 14 is a diagram showing a light propagation state of a conventional optical circuit without polarization control.

FIG. 15 is a diagram showing a configuration for observing a light propagation state of an optical circuit.

FIG. 16 is a diagram showing a polarization state of a conventional optical circuit in a Poincare sphere.

FIG. 17 is a diagram showing a light propagation state of an optical circuit according to the present invention.

FIG. 18 is a diagram showing a polarization state of an optical circuit according to the present invention in a Poincare sphere.

FIG. 19 is a diagram showing a configuration of a fiber polarization controller in the polarization state changing means.

[Explanation of symbols]

Reference Signs List 1 Cross section of PANDA fiber 2 Core 3a, 3b Stress applying part 4, 5 Direction capable of holding polarization plane 6a Light source with high degree of polarization 6b Light source with low degree of polarization 7, 7a, 7b Optical waveguide having polarization maintaining structure 8 Polarization Wave controller 9, 9a, 9b, 9c, 9d, 9e, 9f, 9g, 9
h, 9i Optical waveguide not having polarization state maintaining structure 10, 10a, 10b, 10c Connection portion 11, 11a, 11b Output terminal 12a, 12b Elliptically polarized light 13 Polarization plane of light emitted from light source 14 Linearly polarized light 15 Light Polarization plane of light output from circuit 16 Perturbation 17 Polarization plane of light output from optical circuit (after being perturbed) 18 Polarization analyzer 19 Input unit 20 Output unit 21, 21a, 21b Optical circuit 22, 22a, 22b Optical waveguide without branching 23a, 23b, 23c, 23d With polarization maintaining structure
No optical waveguide 24 Optical demultiplexer 25, 25a, 25b Polarization state changing means 26, 2 Linearly polarized light 28 Optical demultiplexer 29 Optical multiplexer 30 Optical branching coupler 31 Reflecting mirror 32 Optical fiber loop 101 Clockwise Circular polarization 102 -45 ° linear polarization 103 Vertical linear polarization 104 + 45 ° linear polarization 105 Horizontal linear polarization 106 Counterclockwise circular polarization 107 Equator of Poincare sphere 108 Irregular trajectory on Poincare sphere 109 Poincare sphere meridian

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/00-6/54

Claims (6)

(57) [Claims] 1. An optical circuit comprising a light source, an input unit, and an output unit, which does not have a polarization state changing unit, and the light source is a light source having a polarization degree of 30% or less (excluding 0%). The input unit is configured such that an optical waveguide having no polarization state maintaining structure is connected to the light source, and is constituted only by an optical waveguide having no polarization state maintaining structure, or constituted by an optical waveguide having no polarization state maintaining structure and an arbitrary optical circuit. And the optional optical circuit is singular or plural.
Singular or plural optical waveguides without polarization maintaining structure
Optical components (excluding those that actively change the polarization state)
And the output section is constituted by an optical waveguide having no branch connected to one or more of the input sections, and each of the optical waveguides having no branch is at least partially polarized.
An optical circuit comprising an optical waveguide having a holding structure . 2. The optical circuit according to claim 1, wherein said light source is an edge emitting light emitting diode. 3. A waveguide of the polarization state retention structure PAN
A DA fiber, optical circuit according to claim 1, wherein the optical <br/> waveguide not the polarization state holding structure characterized in that it is a single mode optical fiber. Against 4. The optical circuit according to claim 1, the polarization state changing means inserted in the input side to either of the optical waveguide of the polarization state holding structure, change said polarization state A polarization state control method for an optical circuit, wherein the polarization state is controlled in a fixed area of a Poincare sphere by means. Respect 5. The optical circuit according to claim 1, the polarization state changing means inserted in the input side of the optical waveguide of any of the polarization state holding structure, said polarization state changing means A polarization state control method for an optical circuit, comprising: controlling a polarization state in a fixed region of a Poincare sphere by using the method. 6. A polarization state control method for an optical circuit according to claim 4, wherein said polarization state changing means comprises a fiber type polarization controller.