JPH0961176A - Optical fiber coil for optical fiber gyro - Google Patents

Abstract

(57) An object of the present invention is to: (a) expand the maximum detection angular velocity Ωmax while maintaining the coil shape, or (b) maintain Ωmax without changing the total length L of the optical fiber, and thus the modulation frequency f. Allow the coil shape to be changed. SOLUTION: An optical fiber coil 5 having a total length L is wound at one end or both ends thereof by being folded back in the opposite direction by a total length L'of a part of the total length L. In this way, the maximum detected angular velocity Ωmax = cλ / 4πR (L-2L
′); C is the speed of light, λ is the light source wavelength, and R is the average radius. Therefore, by changing L ′ without changing L, the above (a) and (b) can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coil used in an optical fiber gyro.

[0002]

2. Description of the Related Art An optical fiber gyro is constructed as shown in FIG. 2, 1 is a light source in which a light emitting semiconductor and an optical fiber are coupled, 2 is an optical fiber coupler in which optical fibers are fused and connected, 3 Is a polarizer that allows only one of orthogonally polarized lights to pass into a single-mode light, 5 is an optical fiber coil, and 6 is a phase modulator including a refractive index change when a voltage is applied. Is. The optical fibers led out from these respective parts are fusion-spliced at points Pa to Pd in the figure.

The light from the light source 1 passes through the optical fiber coupler 2 and the polarizer 3 and is incident on the optical coupler 4. The light emitted from the point Pc of the optical coupler 4 enters the optical fiber coil 5 to become clockwise light La, passes through Pd, is modulated by the phase modulator 6, and then enters the optical coupler 4, and enters the optical fiber coupler 2 Returned to the side. On the other hand, the light emitted from the point Pd of the internal optical coupler 4 of the incident light is first phase-modulated by the phase modulator 6,
The light enters the optical fiber coil 5 from the point and becomes counterclockwise light Lb, enters the optical coupler 4 from the point Pc, and is returned to the optical fiber coupler 2 side. In this figure, the polarizer 3, the optical coupler 4, and the phase modulator 6 are configured as an optical integrated circuit 10.

The phase difference between the clockwise light La and the counterclockwise light Lb returned to the optical fiber coupler 2 side has a value corresponding to the input angular velocity. The interference light of these two lights is converted into an electric signal by the photodetector (photodiode) 7, processed by the signal processing unit 8, and the detection signal of the input angular velocity is output to the OUT terminal. A modulation signal is supplied from the modulator driver 9 to the phase modulator 6, and the modulator driver 9 is controlled by the signal processing unit 8.

The maximum angular velocity Ωmax that can be detected by the optical fiber gyro is expressed by Ωmax = cλ / 4πRL (1) when the optical fiber coil has a cylindrical shape. Here, c is the speed of light, λ is the wavelength of the light source 1,
R is the average radius of the coil, and L is the total length (fiber length) of the optical fiber coil.

The modulation frequency f of the phase modulator 6 is represented by f = 1 / 2τ = nL / 2c (2) τ = c / nL (3) Here, n is the refractive index of the optical fiber.
Ωmax is determined by the average radius R and the total length L, and the modulation frequency f is determined by the total length L.

[0007]

Consider a case where the following requirements are added to the optical fiber gyro described in the prior art. Maximum angular velocity Ωmax while maintaining the coil shape
When you want to expand. In this case, R cannot be changed, so Ωmax
In order to increase = cλ / 4πRL, L needs to be decreased.

When it is desired to deform the coil shape (R) due to the space factor limitation while maintaining the same performance (maximum detected angular velocity). In this case, Ω max = constant = cλ / 4π
Since it is RL, it is necessary to change L as much as R (shape) is changed. In any case, it is necessary to change the total length L, which means that the modulation frequency f in the equation (2) is changed, which means that the modulator driver 9 and the signal processing which are the sources thereof are changed. In addition to reviewing the design parameters of the section 8, redesigning and reselecting components, it is also impossible to share components with similar circuits of the existing optical fiber gyro, which causes a problem of cost increase.

An object of the present invention is to make it possible to expand Ωmax while maintaining the coil shape or change the coil shape while maintaining Ωmax without changing the total length L and therefore the modulation frequency f. is there.

[0010]

In the optical fiber coil for an optical fiber gyroscope of the present invention, an optical fiber is wound around a bobbin, and one end or both ends of the optical fiber are folded back and extended, and are wound in opposite directions. It is a thing.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, the optical fiber coil of the present invention has a coil having a total length L, which is wound at one end or both ends thereof by folding back in the opposite direction by a total length of L '. By doing so, the optical interference between the clockwise light La and the counterclockwise light Lb has the opposite polarity of the optical interference at the folded portion 5c of the length L ', and the optical fibers of the reciprocating 2L' reciprocally. Since optical interference is canceled by each other, the maximum detectable angular velocity Ωmax is changed from the conventional equation (1) to the following equation.

Ωmax = cλ / 4πR (L−2L ′) (4) On the other hand, the modulation frequency f in the equation (2) causes optical interference even if a part L ′ of the entire length L is folded back. Does not change because it is irrelevant. As described in the problem to be solved by the invention, "when it is desired to increase Ωmax while maintaining the coil shape", the folding length L'may be increased. Since the modulation frequency f does not change even if L'is increased, it is not necessary to change the modulator driver 9 and the signal processing unit 8 as in the conventional case.

Further, in the case of "when it is desired to deform the coil shape while keeping the same Ωmax" described in the problem to be solved by the invention, the average radius R is changed by the amount of L ', and (L-2L') It may be changed in the opposite direction. In that case also, the modulation frequency f does not change. Although not shown, the wound optical fiber 5b, including the folded-back portion 5c, is fixed with an adhesive at a plurality of points so as not to unwind.

Although the optical fiber coil 5 has a cylindrical shape in the above description, it is obvious that the present invention may have a loop shape other than a circle (for example, an elliptical shape).

[0015]

As described above, according to the present invention, since one end or both ends of the optical fiber coil are folded back,
The maximum detection angular velocity Ωmax or the coil shape (average radius R) can be set relatively freely by changing the folding length L ′ without changing the total fiber length L and therefore the modulation frequency f.

[Brief description of drawings]

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

FIG. 2 is a block diagram of an optical fiber gyro.

Claims (1)

[Claims] 1. An optical fiber coil for an optical fiber gyro, wherein an optical fiber is wound around a bobbin, and one end or both ends of the optical fiber are folded back and extended, and are wound in opposite directions.