JPH01237604A - Fiber type wavelength plate - Google Patents

Abstract

PURPOSE:To control the direction of exit light while maintaining the exact function of the wavelength plate by forming one end face of a polarization maintaining optical fiber to a sloped face inclusive of any of the optical axes thereof and adjusting the fiber length to a prescribed length. CONSTITUTION:The polarization maintaining optical fiber 11 has the 45 deg. sloped face 11a inclusive of any of the optical axes thereof and has the other end face 11b perpendicular to the axial direction of the fiber. A light exit face 11c is formed by plane polishing, etc., to the side face (rear face) of the face 11a. Further, the length L' from the face 11a to the end face 11b is so set that the sum of the phase difference generated between the two orthogonally polarized light rays by double refraction and the phase difference between the (p) polarized light and the (s) polarized light generated by the total reflection at the face 11a attains 2npi. The two orthogonally polarized light components in the exit light are thereby enabled to maintain the desired phase difference and, therefore, the direction of the exit light can be converted to the direction perpendicular to the fiber while the exact function of the wavelength plate is maintained.

Description

[Detailed Description of the Invention] [Summary] To enable the direction of emitted light to be controlled while maintaining the accurate function of the wave plate regarding a fiber type wave plate in which the wave plate is constructed using a polarization maintaining fiber. A fiber-type wave plate comprising a polarization-maintaining fiber formed in a length capable of producing a desired phase difference between two orthogonally polarized lights propagating in the fiber, the polarization-maintaining fiber being One end surface is made into an inclined surface including one of the optical axes, and p
The length is adjusted so as to compensate for the phase difference occurring between the polarized light and the S-polarized light.

[Industrial application field]

The present invention relates to a fiber-type wavelength plate constructed using a polarization-maintaining fiber.

In recent years, spatial beam optical systems have been replaced by systems with no adjustment points (
There is active research into waveguide optical systems, which have the characteristics of excellent stability and small size.

On the other hand, a wave plate for converting various polarization states into other polarization states is important as a component of an optical system, but it is not easy to make it into a waveguide.

Under these circumstances, fiber-type wave plates that are constructed using polarization-maintaining fibers are viewed as promising.

[Conventional technology]

FIG. 3 shows the configuration of a conventional fiber-type wave plate.

In the figure, a polarization maintaining fiber 1 having a predetermined length L
are connected to other polarization maintaining fibers 2 with their optical axes tilted by θ. In general, polarization maintaining fiber is
The phase difference Δφ1 between two orthogonal polarized lights due to birefringence is 2nπ
By setting the length L such that it satisfies the following equation (1), it is possible to have the function of an n-wave plate.

In equation (1), nl and n2 are the refractive indices for the above two orthogonal polarized lights, respectively. If the length of the fiber 1 is set to Δφ+=π/2 (that is, n=1/4), it will act as a 1/4 wavelength plate.Therefore, if such a polarization maintaining fiber 1 and another If the inclination angle θ of the optical axis with respect to the polarization maintaining fiber 2 is set to 45°,
The linearly polarized light propagated through the polarization maintaining fiber 2 is
The polarization maintaining fiber 1 serving as a /4 wavelength plate can convert the light into circularly polarized light and emit the light.

[Problem to be solved by the invention]

Changing the direction of the emitted light by processing the fiber tip is
This is important in increasing the degree of freedom in optical system design. However, in the conventional fiber wave plate shown in FIG. 3, it is very difficult to control the direction of the emitted light for the following reasons. In other words, if the end face 1a of the polarization maintaining fiber 1 is simply polished obliquely to make it a total reflection surface, and the light beam is bent through this total reflection surface, there will be a Also, a phase difference occurs due to total internal reflection. Therefore, even if the relationship of equation (1) is maintained, the polarization state of the emitted light will be disturbed due to the total reflection, and therefore, it will not be possible to obtain accurate wave plate function.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to make it possible to control the direction of emitted light while maintaining accurate wave plate function.

[Means to solve the problem]

One end face of a polarization-maintaining fiber is made into an inclined plane that includes one of its optical axes, and a desired phase difference is set between two orthogonally polarized lights (due to birefringence) that propagate in this fiber from the other end face to the above-mentioned inclined plane. It is formed to a length long enough to cause this. Moreover, at this time, in order to compensate for the phase difference between p-polarized light and s-polarized light caused by refraction and reflection on the inclined surface,
Adjust the length above.

Further, one end surface of another polarization maintaining fiber is connected to the other end surface of the polarization maintaining fiber configured in this manner with the optical axis thereof being inclined to each other.

[For production]

The linearly polarized light incident on the polarization-maintaining fiber is propagated to the inclined surface while creating a phase difference between the two orthogonal polarized components along its optical axis, where it is reflected or refracted to change its direction. It is emitted. At this time, since the inclined surface is a surface that includes the optical axis of the fiber, the p-polarized light and the 3-polarized light with respect to this surface are equal to each of the two orthogonal polarized lights. Since the fiber length is adjusted so as to compensate for the phase difference between the p-polarized light and the S-polarized light, the two orthogonal polarized components of the emitted light can maintain a desired phase difference. Therefore, the polarization state of the emitted light is not disturbed, and accurate wave plate function can be obtained.

Further, when such a polarization maintaining fiber is connected to another polarization maintaining fiber, the polarization state is converted according to the inclination angle of the mutual optical axes and the above-mentioned fiber length.

〔Example〕

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

FIG. 1 is a perspective view of one embodiment of the present invention.

In the figure, the polarization maintaining fiber 1 has a 45° inclined surface 11 including one of its optical axes (X direction in the figure).
a and the other end face 1 perpendicular to the axial direction (X direction) of the fiber
1b. The inclined surface 11a is a total reflection surface for the IM light transmitted through the polarization maintaining fiber 1, and for example, one end surface is cut at 45 degrees with a plane including the optical axis, and the cut surface is polished. It can be obtained by doing, etc. Further, on the side surface (lower surface) of the polarization maintaining fiber 1 on the side of the inclined surface 11a, a light output surface 11C is formed by flat surface polishing or the like.

Furthermore, the length L' from the inclined surface 11a to the end surface 11b is
The phase difference Δφl caused by birefringence between two orthogonal polarized lights and the phase difference Δφ2 between p-polarized light and S-polarized light caused by total reflection at the inclined surface 11a (=φ, -
φ, ) is set so that the sum is 2nπ. Here, since ΔφI is the same as the above equation (1), the relationship between them is expressed by the following equation.

Δφ1+Δφ2 = sub(rz−n2) L'+Δφ2 λ =2nπ ...(2) However,
In formula (2), nl and n2 each represent two directions.

This is the refractive index for polarized light in the X direction.

In the fiber type wave plate of this embodiment having the above configuration, the polarized light incident from the end face 11b is propagated to the inclined face 11a while producing a phase difference between the polarized light components in the X direction and the X direction, where it is totally reflected. After the traveling direction is changed by 90 degrees, the light is emitted to the outside from the light emitting surface 11c.

In this case, since the inclined surface 11a is a surface including the optical axis in the X direction, the p-polarized light and the S-polarized light with respect to this surface are equal to the polarized light in the Z direction and the X direction, respectively. Therefore, the phase difference Δφ2 caused between the p-polarized light and the S-polarized light due to total reflection is equal to the phase difference caused between the polarized light in the two directions and the X direction due to total reflection. From these facts, two directions due to birefringence and
Even if the phase difference Δφ1 between the orthogonal polarized lights in the direction is fluctuated (Δφ2) due to total reflection on the inclined surface 11a, the length L' is adjusted so as to compensate for Δφ2 based on equation (2). , the two orthogonal polarization components in the emitted light can maintain a desired phase difference (2nπ).

Therefore, the direction of the emitted light can be converted to the direction perpendicular to the fiber while maintaining accurate wave plate function.

In addition, the length L is set so that n=1/4 in equation (2).
If ' is set, it can function as a 1/4 wavelength plate.

Next, another embodiment of the present invention is shown in FIG.

In the figure, in contrast to the end face 11b of the same polarization maintaining fiber 11 shown in FIG.
With the end surfaces 12a of the optical axes tilted relative to each other by θ,
They are connected by fusion, etc. In the fiber-type wave plate having such a configuration, the polarized light propagated through the polarization-maintaining fiber 12 is different from the inclination angle θ of the mutual optical axes and the above-mentioned length L.
The polarization state of the light is converted according to the value ′, and the light is emitted from the light emitting surface 11c. For example, if θ-45° and L' are set so that n=1/4, the I
The linearly polarized light that has been polarized is converted into circularly polarized light by the polarization maintaining fiber 11 serving as a quarter-wave plate, and the traveling direction is converted by 90 degrees and then emitted.

Moreover, at this time, the polarization state of the emitted light is not disturbed as in the previous embodiment, and the accurate function of the wave plate can be maintained.

In each of the above embodiments, the function of a 1/4 wavelength plate was obtained by setting n to 1/4 in equation (2), but the function of various wavelength plates may be provided as necessary. .

For example, by setting n to 1/2, a 1/2 wavelength plate can be formed. In this case, as shown in FIG. 2, the polarization direction of the linearly polarized light can be converted according to the inclination angle θ of the optical axis.

Further, although the inclined surface 11a is a total reflection surface of 45 degrees, the direction of the emitted light may be set as appropriate by adjusting this inclination angle within a range that allows total reflection. Alternatively, the emission direction can also be controlled using refraction instead of total reflection.

〔Effect of the invention〕

As described above, according to the present invention, the direction of emitted light can be controlled while maintaining accurate wave plate function. Thereby, the degree of freedom in designing the optical system can be significantly increased.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of one embodiment of the present invention, FIG. 2 is a perspective view of another embodiment of the invention, and FIG. 3 is a perspective view of a conventional fiber type wavelength plate. 1. Polarization maintaining fiber, 11a... Inclined surface, 11b... End surface, 11c... Output surface, 12... Polarization maintaining fiber, 12a... End surface. Patent applicant Fujitsu Limited

Claims (1)

[Claims] 1) A fiber-type wavelength plate formed by forming a polarization-maintaining fiber (11) to a length that can generate a desired phase difference between two orthogonally polarized lights propagating in the fiber. One end face of the polarization-maintaining fiber (11) is formed into an inclined surface (11a) that includes one of its optical axes, and the inclined surface compensates for the phase difference that occurs between the p-polarized light and the s-polarized light. A fiber-type wave plate characterized in that the length is adjusted to . 2) One end surface (12a) of another polarization maintaining fiber (12) is connected to the other end surface (11b) of the polarization maintaining fiber (11) according to claim 1 with their optical axes tilted to each other. A fiber-type wave plate featuring: