JPH05303065A - Polarization state control method - Google Patents

Abstract

PURPOSE:To control a polarization state of light by a simple constitution by varying double refraction of each optical axis of polarization plane maintaining optical fiber by a double refraction control means. CONSTITUTION:It the periphery of a polarization plane maintaining optical fiber 401, a double refraction controller 402 is provided. By controlling double refraction in the direction of optical axes (x), (y) of the optical fiber 401 by this double refraction controller 402, an arbitrary phase difference is given, and a plane of polarization of an incident light 403 is varied and emitted as an emitted light 404. In this case, it is necessary that the incident light 403 is propagated so as to be equal to each of each optical axis (x), (y). Therefore, a linearly polarized light is made incident on between each optical axis (x), (y). Also, as for an elliptically polarized light, its major axis or minor axis is made incident on between each optical axis (x), (y). As for the constitution of the double refraction controller 402, there are that which applies external force of a piezoelectric element and a voice coil, etc., and that which generates a stress by giving a temperature variation by using a Peltier element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization state control method for emitting incident light as light having an arbitrary polarization state.

[0002]

2. Description of the Related Art Conventionally, in order to control the polarization state of light, there is a method using an optical phase plate such as a λ / 4 plate or a λ / 2 plate or a Babinet-Soleil compensating plate. In any of these methods, it is necessary to allow spatial light to enter. Therefore, for example, when controlling the polarization plane of light propagating in a light guide member such as a fiber, it is returned after entering spatial light. ..

Further, the obtained optical phase difference is determined by the type of the optical phase plate. Therefore, when a polarization state different from the one currently used is to be obtained, the optical phase difference is obtained each time. I changed the optics.

[0004]

In the above-described conventional control of the polarization state of light, it is necessary to make it incident as spatial light, so the light propagating through the fiber must be returned to spatial light. Although it is necessary to make the light incident, there are problems that the propagation state becomes unstable and light loss occurs due to the spatial light.

Further, in order to obtain a polarization state different from the one currently used, the optical system must be changed every time, so that the optical system becomes complicated and troublesome. There is a point.

The present invention has been made in view of the problems of the above-mentioned conventional techniques, and provides a polarization state control method capable of controlling the polarization state of light with a simple configuration. Aim to achieve.

[0007]

A polarization state control method of the present invention is a polarization-maintaining optical fiber configured such that refractive indexes of optical axes that are substantially orthogonal to each other are different from each other, and each optical element of the polarization-maintaining optical fiber. A polarization state control method for emitting incident light to a polarization-maintaining optical fiber as light of an arbitrary polarization state by using a birefringence control means for changing the birefringence of the optical axis,
The polarization plane-maintaining optical fiber is arranged so that the incident light propagates equally to each optical axis of the polarization plane-maintaining optical fiber, and then the birefringence control unit controls the optical axis of the polarization plane-maintaining optical fiber. A polarization state control method characterized by changing refraction.

[0008]

In recent years, a polarization-maintaining optical fiber formed so as to have a difference in refractive index between optical axes that are substantially orthogonal to each other has been widely used.

The polarization-maintaining optical fiber is formed so that the refractive indices of the optical axes that are substantially orthogonal to each other are different from each other, and the polarization plane of incident light is preserved. As shown in FIG. 1A, as a method of giving the refractive index difference to the axes which are substantially orthogonal to each other, two high refractive index portions 103 ₁ and 103 ₂ are sandwiched between the core 101 and a clad 102 which covers the core 101. Linearly arranged so as to be symmetrical with respect to each other, as shown in FIG. 1B, the core 104 embedded in the clad 105 has an elliptical shape, and as shown in FIG. For example, the clad 107 that covers the core 106 has an elliptical shape, and the periphery thereof is covered with a support 108.

The principle of changing the polarization state in the present invention will be explained. As shown in FIG. 2, when linearly polarized light enters at an inclination of θ ° with respect to each optical axis x, y of a polarization-maintaining optical fiber. , x, y components of the electric field vector E becomes _{E x = a x COS (ωt} -δ 1) a x = a 0 cosθ E y = a y COS (ωt-δ 2) a y = a 0 sinθ. Where a _x and a _y are amplitudes in the x and y directions, δ ₁ ,
δ ₂ is the phase. Clear the .omega.t, when the _{δ 1 -δ 2 = δ, (} E x 2 / a x) + (E y 2 / a y) -2 × (E x / a x) ×
(E _y / a _y ) × cos δ = sin δ ^2, which is an expression representing an ellipse.

Now, assuming that the tilt angle θ is 45 °, x, y
Since the amplitudes in the directions are the same, the polarization states when the phase difference δ changes are as shown in FIGS. 3 (a) to 3 (h).

Therefore, a desired polarization state can be obtained by setting the inclination angle θ at 45 ° and giving an arbitrary phase difference to each optical axis.

In the present invention, the birefringence control device changes the birefringence of each optical axis of the polarization-maintaining single-mode optical fiber, and the phase difference is controlled thereby, so that a desired polarization state can be obtained. Becomes

[0014]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 4 is a schematic diagram showing the structure of an embodiment of the present invention.

In this embodiment, a birefringence controller 402 is arranged around a polarization-maintaining optical fiber 401 having a cross-sectional shape as shown in each of FIGS. The birefringence of the optical fiber 401 in the optical axes x and y is controlled to give an arbitrary phase difference, the plane of polarization of the incident light 403 is changed, and the incident light 403 is emitted.

As the structure of the birefringence control device 402, a device for applying an external force such as a piezoelectric element or a voice coil, or a device for applying a temperature change by using a Peltier device to generate stress can be considered. Any of these can be electrically controlled, and birefringence can be easily controlled.

Incident light 4 on the polarization-maintaining optical fiber 401
The incident light of No. 03 will be described. It is necessary that the incident light propagates equally to each of the optical axes x and y. For this reason, when the linearly polarized light is incident, it must be incident on the middle of the optical axes x and y (approximately π / 4 or 3π / 4) as shown in FIG. When polarized light is incident, it is necessary that the long axis or the short axis is incident between the optical axes x and y as shown in FIG. 5B.
When circularly polarized light is incident, the direction of incident light is irrelevant as a matter of course.

Incident light 40 incident under the above conditions
The birefringence control device 402 makes the polarized light 3 have an arbitrary polarization state and emits it as outgoing light 404. At this time, the direction in which the emitted light 404 is emitted is similar to the incident condition. When the emitted light 404 is linearly polarized light, it is emitted from the middle of the optical axes x and y, and when it is elliptically polarized light, the optical axes are emitted. x, y
It is emitted with the middle of the as the long axis or the short axis.

FIG. 6A is a schematic diagram showing the configuration of the second embodiment of the present invention.

In this embodiment, a polarization source preserving optical fiber 401 and a birefringence controller 402 shown in FIG. 4 are combined with a light source 601 and a polarizer 602 to produce a light source capable of emitting light in an arbitrary polarization state. It is composed.

The light source 601, the polarizer 602, the polarization-maintaining optical fiber 401, and the birefringence control device 402 are sequentially provided in series. The light generated by the light source 601 is made into linearly polarized light by the polarizer 602 and then enters the polarization-maintaining optical fiber 401. The polarizer 602 and the polarization-maintaining optical fiber 401 are arranged so that the linearly polarized light obtained by the polarizer 602 is incident on the middle of each optical axis x and y of the polarization-maintaining optical fiber 401. The polarized light is emitted with its polarization state controlled by the birefringence control device 402.

FIG. 6B shows a fiber type polarizer 603 connected between the light source 601 and the polarization-maintaining optical fiber 401 by couplers 604 ₁ and 604 ₂ . With this configuration, the light emitted from the light source 601 has its polarization state controlled while propagating in the fiber, so that the emitted light having a stable plane of polarization can be obtained.

As described above, in the present invention, the polarization state of incident light can be freely controlled. The light whose polarization state has been changed is used for optical measurement, but it goes without saying that a measurement system having the configuration of the present invention may be incorporated. When such a measurement system is assembled, the optical elements forming the optical system can be connected by a fiber, and the stability of the measurement can be improved.

[0025]

As described above, the present invention uses the polarization-maintaining optical fiber and provides the birefringence control device for changing the birefringence of the optical axis of the polarization-maintaining optical fiber. There is an effect that it can be emitted as light having an arbitrary polarization state.

Further, since the change of the polarization state is completed in the fiber, when an optical system is constructed by using the device according to the present invention, spatial light is produced by connecting each element constituting the optical system with the fiber. It is possible to use an optical system that is not used, and there is an effect that the optical system can be made stable.

[Brief description of drawings]

1A to 1C are diagrams showing a configuration of a polarization-maintaining optical fiber.

FIG. 2 is a diagram for explaining the principle of changing the polarization state according to the present invention, and is a diagram showing the state of incidence on a polarization-maintaining optical fiber.

FIG. 3 is a diagram for explaining the principle of changing the polarization state according to the present invention, wherein each of (a) to (h) changes the polarization state due to the phase difference δ generated on the optical axes x and y. It is a figure which shows a mode that it does.

FIG. 4 is a diagram showing a configuration of an exemplary embodiment of the present invention.

5A and 5B are diagrams showing incident conditions of incident light in the embodiment shown in FIG. 1, in which FIG. 5A shows incident conditions of linearly polarized light and FIG. 5B shows incident conditions of elliptically polarized light.

6A is a diagram showing a second embodiment of the present invention, and FIG. 6B is a modification of the embodiment shown in FIG.

[Explanation of symbols]

101, 104, 106 core 102, 105, 107 clad 103 ₁ , 103 ₂ high refractive index part 108 support 401 polarization-maintaining optical fiber 402 birefringence control device 403 incident light 404 output light 601 light source 602 polarizer 603 fiber-type polarizer 604 _1, 604 ₂ coupler

Claims (1)

[Claims] 1. A polarization-maintaining single-mode optical fiber configured to have different refractive indexes in substantially orthogonal optical axes, and birefringence control means for changing the birefringence of each optical axis of the polarization-maintaining single-mode optical fiber. A polarization state control method for emitting incident light to a polarization-maintaining optical fiber as light of an arbitrary polarization state by using, A polarization state control method, wherein the birefringence of each optical axis of the polarization-maintaining optical fiber is changed by the birefringence control means after the birefringence is arranged so as to propagate equally to the axis.