JPS62205309A - Optical fiber type polarization plane rotating element - Google Patents

Abstract

PURPOSE:To simplify the constitution of a rotating element greatly and to reduce its size and weight by drawing a twisted part of an optical fiber linearly for looping and controlling the rotation of a plane of polarization. CONSTITUTION:A point O of the single-mode optical fiber is fixed and a point B is twisted by one turn to form one loop, so that the point B rotates by 360 deg. from the plane of polarization in the twisting direction. On the other hand, when the point O is fixed and the part between the points O and B is twisted by one turn, the plane of polarization of propagated light rotates by about 25 deg. at the point B. Consequently, when light is propagated from the point O to the point B, the fiber is looped and drawn and the point B is shifted in position properly to adjust the angle of the plane of polarization at the point B by 0-35 deg.. Consequently, the fiber part between the points O and B is usable as a polarization plane rotating element and the constitution of the element can be simplified greatly, so that the element is reduced in size and weight.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical fiber type polarization plane rotation element used in optical fiber communications, optical fiber sensors, and the like.

(Conventional technology and its drawbacks) Conventionally, optical fiber communication, optical fiber sensors, etc.
As an optical fiber type polarization plane rotation element that controls the rotation of the polarization plane of light propagating in a single mode optical fiber, for example, "ANEW POLARIZATION
C0NTR0L SCHEMEFOR0PTICAL
HETERODYNE RECEIVE”T, 0ko
Shi et al, 100C-ECOC'85 Te
chnicalDigesl 1985
Published by, Vol.11. ff) As disclosed in pages 405 to 408, it is common to apply a magnetic field parallel to the optical fiber and control the rotation of the plane of polarization using the Faraday effect. However, in the conventional method described above, an electromagnetic coil is wound around a coiled single mode optical fiber, and the electromagnetic coil applies a magnetic field in the axial direction to the optical fiber. The disadvantage is that the structure of the element is complicated and the overall weight is large. Furthermore, since a magnetic field is formed in the coiled fiber by the electromagnetic coil, there is a drawback that a large driving current is required.

(Means for Solving the Problems) The present invention has been made to eliminate the above-mentioned conventional drawbacks.
For this reason, the present invention does not utilize the rotation of the plane of polarization due to the Faraday effect as in the prior art, but instead utilizes the rotation of the plane of polarization due to twisting of the fiber and its relaxation. That is, in the present invention, a predetermined amount of twist is applied to a predetermined length of a single mode optical fiber, and both ends of the twisted portion are fixed 17 so that the twist is not relaxed, and at least one of the fixed ends is fixed. The single mode fiber propagates through the single mode fiber by moving it toward the other fixed end without rotating it, and causing the twisted part of the original fiber to slacken into a loop or stretch into a straight line. It is characterized by controlling the rotation of the plane of polarization of light.

(Principle and operation of the present invention) In a straight single mode fiber without birefringence, propagating light propagates while maintaining its polarization state, and of course, no rotation of the plane of polarization (including the weight on the principal axis of the ellipse) occurs.

Now, consider a straight single mode fiber with no distortion as shown in Figure 1 (al), and with the axial direction of the fiber as the two directions, points Q and A%B on the fiber (A is the midpoint of OB) The orthogonal coordinate system X, y, z,”, y′, z′ fixed on the fiber
Consider sr and X", y'/, z". By twisting this fiber once while keeping the 0 point completely fixed and bringing the B point closer to the 0 point, there is no twisting distortion between the OB and the A
Figure 1 (b) forms a single loop around a point.
).

At this time, if the diameter of the loop is made large enough so that the birefringence induced by bending the fiber can be ignored,
The plane of polarization of the propagating light at point B is no different from that in Figure 1 (al) when viewed from the coordinate system fixed on the fiber.

However, since point B is twisted by one rotation, as shown in FIG.
It is clear that it is rotated by 0°.

On the other hand, if we fix the fiber at point 2o in Figure 1 (α), twist it at point -1:B while keeping it straight, and add one rotation between OB, the coordinate system fixed to the fiber will be as shown in Figure 1. It will look like (c). At this time, it is known that the polarization plane of the propagating light is twisted and rotated at point B by approximately 25 degrees in the same direction as the twist due to torsional distortion.

Figure 1 (The state of cJ is as shown in Figure 1 [In the state of bl,
This can also be achieved by fixing the 0 point and pulling the B point in two directions without rotating it. The change in the shape of the fiber during this time is continuous and smooth.

From the above, if we assume that the light is now propagating in the direction from point O to point B, then the state force of Figure 1 + b] is shown in Figure 1 (
It is clear that during the transition to the cl state, the angle of the plane of polarization at point B continuously rotates about 335° in the direction opposite to the twist of the fiber, and this was also confirmed experimentally. Therefore, by moving the position of point B to an appropriate position between the position shown in Figure 1[bl and the position shown in Figure 1(C), the angle of the plane of polarization at point B can be adjusted to
It can be adjusted in the range of 0 to 8 degrees, and a fiber section between 0 and 8 degrees can be used as a polarization plane rotation element.

In addition, although the above explanation was given especially for the case where the point B is twisted by 360 degrees with respect to the 0 point, the polarization plane rotation element according to the present invention can be constructed using the same principle even when the twist of the point B is other than 360 degrees. I can do it.

(Example) Preferred embodiments of the present invention will be described below.

If a polarization plane rotation element is constructed by directly applying the above principle of the present invention, as is clear from FIG. It is also necessary to move the fiber parts other than E. Depending on the usage situation of the polarization plane rotation element, such an element can be fully used, but it is preferable to keep the fiber parts other than the fiber part constituting the element in a stationary state, and then move the element. It is desirable that the optical transmission in the other fiber portions is not affected in any way.The embodiment shown below is of such a preferable type, and uses the polarization plane rotating element shown in Fig. 1+b) and (c) above. It can be thought of as two consecutive lines in opposite directions.

That is, first, as shown in Fig. 2 (al), a straight single mode optical fiber Ff, length approximately 1oOCm, outer diameter 2
Insert it into a Teflon tube (not shown) with a loop-shaped bend with an inner diameter of 1.2 mm and a diameter of about 30 cm.
Both ends A and C of the tube and the midpoint B between 4 and 0 are fixed to the optical fiber core with adhesive, and this is stretched straight.

Next, as shown in Fig. 2 (1b) K, this fiber is fixed at both ends A%C and twisted by 360° at point B, and the fiber is twisted at B and C as shown in Fig. 2 (c). C point fully fixed -1
: Without rotating point A, bring it closer to point B to form a loop R with no twisting distortion between 4 and 3. In this state A,
By fixing point C and moving it between the position in Figure 2 (c) and the position in Figure 2 [dl] without rotating point B completely,
The plane of polarization of the light propagating between the optical fibers 4 and 0 is approximately 67o.

Rotation can be controlled.

That is, when a twist of 36° is applied at point B in Figure 2 (bl), a twist of 36° is applied between 4 and 3 and between E and C in the twisting direction and in the counter-twisting direction, respectively. The transformation between B and 8 and 0 corresponds to the transformation from Figure 1 (a) to Figure 1 [c]. The polarization planes at points B and C are twisted from points A and B, respectively. It is rotated approximately 25° in both the direction and the counter-twisting direction (Fig. 2+b
Rotation in the twisting direction at point B in 1 is shown as a plus sign, and rotation in the counter-twisting direction is shown as a minus sign).

Next, when the fiber is deformed from Fig. 2 (b) to Fig. 2 (c), the deformation between A and B corresponds to the deformation from Fig. 1 Icl vh et al. Fig. 1 + 1) l. , the polarization plane at point B is rotated approximately 335° in the twisting direction, and as a result, the polarization plane at point C with respect to point A is approximately 335° (25° + 335°).
°-25°) Rotation σ in the twisting direction.

Next, when the fiber is deformed from Fig. 2(c) to Fig. 2Fdl, the deformation between 4 and 3 and the deformation between 8 and 0 change from Fig. 1(b) to Fig. 1(c), respectively. This corresponds to the deformation of The polarization plane of point C relative to point A can be rotated approximately 335 degrees in the anti-twist direction (335 degrees - 335 degrees - 335 degrees).

Therefore, when the fiber is deformed from FIG. 2 (cl) to FIG.

(In the reverse process of deformation, it will rotate in the opposite direction by about 6
(rotated 70°). In this case, since the points A and C are fixed, there is no need to move the fiber portions other than the fiber portions A and C constituting the polarization plane rotation element.

In addition, when moving point B in the above, A other than point B
The fiber portion between -C is deformed by the elasticity of the Teflon tube to a state with the least strain. Also, the movement of point B does not necessarily have to be carried out along the straight line mA-C.
It is sufficient to move it so that the overall distortion is minimized.

(Effects of the Invention) As described above, according to the present invention, in order to control the rotation of the plane of polarization of light propagating through a single mode optical fiber, twisting is applied to the optical fiber to loosen it into a loop or to straighten it. Since the device is simply stretched into a shape, the structure of the device can be greatly simplified and the entire device can be made much smaller and lighter. In addition, if a part of an extremely lightweight fiber is moved using a means of movement that drives it in a voyeuristic manner, the drive current can be greatly reduced. can do.

[Brief explanation of drawings]

FIG. 19 is a diagram illustrating the principle and operation of the present invention, and FIG. 2 is a diagram illustrating an example of a non-inventive joke. Patent applicant: Sumitomo Electric Industries, Ltd. Figure 1 Figure 2

Claims (2)

[Claims] (1) Add a predetermined amount of twist to a predetermined length of single mode optical fiber, fix both ends of the twisted portion so that the twist does not relax, and rotate at least one of the fixed ends. By moving the twisted part of the optical fiber toward the other fixed end without twisting it, the twisted part of the optical fiber is slackened into a loop or stretched into a straight line, thereby reducing the amount of light propagating in the single mode fiber. An optical fiber type polarization plane rotation element characterized by controlling rotation of a polarization plane. (2) Twist the left and right sides of the middle part of a predetermined length of single mode optical fiber in opposite directions to each other, so that the middle part and the part on one side are not loosened. Fix the end part, and move the end part of the other side part toward the middle part while keeping the middle part fixed, so that the twist of the other side part becomes loose in a loop shape, and each end of the left and right sides. The linear twist and the loop-shaped slack on both sides of the intermediate part are made loop-like or linearly stretched by moving between the two ends without rotating the intermediate part while keeping it fixed. An optical fiber type polarization plane rotation element characterized by controlling the rotation of the polarization plane of light propagating in a mode fiber.