JPH04203928A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To manufacture an optical fiber gyro easily at low cost while reducing noises by providing a fiber coil obtained by winding an optical fiber a plurality of number of times around a cylindrical or columnar base material having a part of 2cm or smaller radius of curvature. CONSTITUTION:An optical fiber 12 is wound around the outer periphery of a base material 11. The curvature of radius at a part indicated by an arrow is 1.5cm. The propagation constant is different at this part depending on the direction of polarization of the light propagating in the fiber. Therefore, the mutual reaction of lights having different directions of polarization is restricted. In other words, the rotation in the direction of polarization of the light, incident upon the sensing coil of the optical fiber gyro is restricted, and moreover the interference between the polarized components in the rotating direction to the direction of polarization of the incident light and the polarized components of the direction of polarization of the incident light is controlled, so that the noises can be reduced. Further, the optical fiber gyro can be manufactured industrially easily at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical fiber gyro that is expected to be widely applied to control of automobile navigation systems and industrial robots.

A conventional optical fiber gyro uses an optical fiber wound multiple times around a cylindrical base material as a sensing coil. Input clockwise light and counterclockwise light into this sensing coil,
The principle of an optical fiber gyro is to measure the rotational angular velocity by observing the phase shift due to the Sagnac effect that occurs when the sensing coil rotates.

Fiber coils used as sensor coils have traditionally been wound around a cylindrical base material with a circular cross section.
Its radius is typically 2.5 cm to 5c+a.

Light incident on the sensing coil changes its polarization state while propagating through the coil. For example, among the light that propagates through the sensing coil and exits, it changes to elliptically polarized light even if it enters as linearly polarized light, and the polarization direction also rotates.
A polarization component in a direction rotated with respect to the polarization direction of the incident linearly polarized light interferes with a polarization component in the original polarization direction, causing noise.

Conventionally, as a means to suppress this, a method has been adopted in which a sensing coil is constructed using a polarization-maintaining fiber.

Problems to be Solved by the Invention Polarization maintaining fibers are much more expensive than ordinary single mode fibers. The sensing coil has
Since several hundred meters of optical fiber are used, if a polarization maintaining fiber is used for an optical fiber gyro, it will be a major cost increase factor.Also, polarization maintaining fiber is not suitable for fusion between fibers or fiber coupler. The disadvantage is that it is difficult to manufacture.

The present invention suppresses the rotation of the polarization direction of light incident on the sensing coil of an optical fiber gyro without using a polarization-maintaining fiber, and at the same time suppresses the rotation of the polarization direction of light incident on the sensing coil of an optical fiber gyro. It is an object of the present invention to provide an optical fiber gyro having a sensing coil that can not only suppress interference between polarized light components and reduce noise, but also be manufactured industrially and at low cost.

Means for Solving Problem 11 In order to solve the above problems, firstly, an optical fiber having a fiber coil in which the optical fiber is wound multiple times around a cylindrical or columnar base material having a portion with a radius of curvature of 2 cm or less. Let's call it a gyro. Second, the optical fiber gyro has a fiber coil in which an optical fiber is wound a plurality of times around a cylindrical or columnar base material having a cross-sectional shape composed of a straight line and a portion having a radius of curvature of 2C11 or less. Thirdly, the minor axis is 2c
A cylindrical or columnar base material having an elliptical cross section of +a or less,
The present invention is an optical fiber gyro having a fiber coil in which optical fiber is wound multiple times.

Operation A normal single-mode optical fiber is isotropic with respect to the polarization direction, and there is almost no difference in propagation constant with respect to the polarization direction.Therefore, light polarized in any direction can be propagated in the same way.

However, when an optical fiber is curved with a small radius of curvature, the anisotropy of the optical fiber in the diametrical direction becomes significantly large, the refractive index changes depending on the polarization direction, and the propagation constant changes accordingly. The difference δn in refractive index per unit length between light with a polarization direction parallel to the curved surface of the optical fiber and light with a polarization direction perpendicular to the curved surface of the optical fiber is normalized by the refractive index n of the fiber, and r is the core diameter of the fiber. , where R is the radius of curvature of the curved fiber and fiber a is a constant, δn/n=a (r/R)" (EIectoron, Letl, Vol, I6
778-780 (1980)).

In addition, when the cross-sectional shape of the fiber coil is a straight line except for the small curvature part, the length of the small curvature part for one round is 2πR
Multiplying by the number of turns N gives the refractive index change of the entire coil.

The wavy line curve in FIG. 4 shows the dependence of this refractive index change on the radius of curvature.

The solid curve in this figure represents an actual change in curvature, and it can be seen that the change in refractive index becomes significantly large when the radius of curvature is 2 cm or less.

Since the sensing coil of the optical fiber gyro according to the present invention has an optical fiber wound around a base material having a portion with a radius of curvature of 2 cm or less, the optical fiber in this portion is curved with a radius of curvature of 21 cm or less. Sensing coils are usually made by winding an optical fiber several hundred to several thousand times around a base material, so the difference in propagation constant of the curved part depending on the polarization direction has a very cumulative effect on the light propagating through the sensing coil. (Then, the lights whose polarization directions are orthogonal to each other are
There is almost no interaction while passing through the sensing coil. Therefore, not only rotation of the polarization direction in the sensing coil, which causes noise, is suppressed, but also interference between lights having different polarization directions is suppressed.

Various shapes can be considered as the cross-sectional shape of the base material of the sensing coil that realizes the above action, but the diameter is 2C1.
A simple cylindrical shape with a value of 1 or less has a problem in terms of sensitivity. The sensitivity of the sensing coil is determined by the product of the cross-sectional area of the base material around which the sensing coil is wound and the number of turns of the optical fiber. Therefore, in a cylindrical base material, the number of turns of optical fiber must be increased in order to ensure sensitivity, and a large amount of optical fiber is required. In order to ensure sensitivity without increasing the length of the optical fiber used in the sensing coil, it is sufficient to make only the - portion of the base material have a radius of curvature of 2C11 or less.

In particular, an elliptical cross-sectional shape with a minor axis of 2 cm or less, or a radius of 2 cm.
Processing is relatively easy if the cross section is a combination of two semicircles and a rectangle of 1 or less. Furthermore, in the latter case, the shape is convenient for mounting.

Embodiment FIG. 1 is a perspective view of a sensing coil of an optical fiber gyro according to a first embodiment of the present invention. Reference numeral 11 denotes a base material, around which an optical fiber 12 is wound.The radius of curvature of the portion indicated by the arrow in Figure 0 is 1.5C11. In this portion, the propagation constant varies depending on the polarization direction of light propagating in the fiber, and interaction between lights with different polarization directions is suppressed.

Compared to a normal optical fiber gyro that uses a sensing coil wound around a cylindrical base material, the optical fiber gyro that uses this sensing coil has dramatically reduced noise such as zero point drift.

FIG. 2 is a perspective view of a sensing coil of an optical fiber gyro according to a second embodiment of the present invention, with a radius of curvature of 1.5.
The optical fiber 2 is attached to the base material 21 which has three parts.
1 is wrapped around it. Compared to the embodiment shown in FIG. 1, the length of the optical fiber wound around the small radius of curvature is longer, so the noise reduction effect is greater.

FIG. 3 is a perspective view of a sensing coil of an optical fiber gyro according to a third embodiment of the present invention.
is wrapped around it. Since the shape of the base material of this example has a smoothly changing curvature on the outer periphery, the fiber is less likely to be cut during the fiber winding process, resulting in a high yield.

Note that FIG. 4 is a characteristic diagram showing the relationship between the amount of change in refractive index depending on the polarization direction and the radius of curvature according to each embodiment of the present invention.

Effects of the Invention As described above, the present invention suppresses the rotation of the polarization direction of light incident on the sensing coil of an optical fiber gyro, and also suppresses the polarization component in the direction rotated with respect to the incident polarization direction.
It is possible to provide an optical fiber gyro that not only suppresses interference between polarization components in the incident polarization direction and reduces noise, but also has a sensing coil that can be manufactured industrially easily and inexpensively. became.

[Brief explanation of the drawing]

1, 2, and 3 are the first and second embodiments of the present invention, respectively.
FIG. 4 is a perspective view of a sensing coil of an optical fiber gyro according to the third embodiment, and FIG. 4 is a characteristic diagram showing the relationship between the amount of change in refractive index and the radius of curvature depending on the polarization direction according to each embodiment. 11, 21.31... Sensing coil base material,
12.22゜32...Optical fiber. Name of agent: Patent attorney Akira Okaji, 2 people, 1 figure, 3 figures, 4 curved carriage (Q Ko)

Claims (3)

[Claims] (1) An optical fiber gyro having a fiber coil in which an optical fiber is wound multiple times around a cylindrical or columnar base material having a portion with a radius of curvature of 2 cm or less. (2) An optical fiber gyro having a fiber coil in which an optical fiber is wound multiple times around a cylindrical or columnar base material having a cross-sectional shape consisting of a straight line and a portion with a radius of curvature of 2 cm or less. (3) An optical fiber gyro having a fiber coil in which an optical fiber is wound multiple times around a cylindrical or columnar base material having an elliptical cross section with a minor axis of 2 cm or less.