Method and arrangement for determining angular velocities

Details Method and arrangement for determining angular velocities Method and arrangement for determining angular velocities

1992-08-05

1994-11-08

Willis, Davis L.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

G01C 1904

Patent

active

053631935

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a method and to an arrangement for determining angular velocities with the aid of an optical fiber ring interferometer, wherein the light waves passing through at least one optical fiber winding are sinusoidally modulated in phase and the amplitudes of several spectral lines of the interfering light waves exiting from the optical fiber are identified to yield the Sagnac phase shift which is proportional to the angular velocity.
A method and an arrangement of this type are disclosed in DE 3,140,110.A1. In the optical fiber of the ring interferometer forming an annular light path, two oppositely directed light waves propagate and interfere with one another upon exiting from the optical fiber. The interference is a function of the angular velocity with which the optical fiber, which forms at least one winding, is rotated. The angular velocity is proportional to the difference in phase between the two light waves that passed through the optical fiber in opposite directions.
This phase difference, it is called the Sagnac phase shift, can be determined, as disclosed in DE 3,140,110.A1, from the amplitudes of the spectral lines of the interference light leaving the optical fiber. The method according to DE 3,140,110.A1, according to which the Sagnac phase shift is determined from the amplitude of two spectral lines requires that the modulation index of the phase modulation occurring at the output of the light path is kept at a constant value by means of a control circuit.


SUMMARY OF THE INVENTION

It is now the object of the invention to provide a method and an arrangement of the above mentioned type with which the Sagnac phase shift, which is proportional to the angular velocity, can be determined without a control circuit for keeping the modulation index of the phase modulation constant.
This is accomplished according to the invention by a method for determining angular velocities with an optical fiber ring interferometer, comprising the steps of passing sinusoidally phase modulated light waves through at least one optical fiber winding; determining the amplitude values for a first, a second, and a third spectral line of the interfering light waves exiting from the optical fiber; forming a first quotient from the amplitude values of the first and the second spectral lines, wherein one of the amplitude values is a function of the sine of the Sagnac phase shift, and the other amplitude value is a function of the cosine of the Sagnac phase shift; forming a second quotient from the amplitude values of the first and the third spectral lines, wherein both of the amplitude values are a function of the sine or the cosine of the Sagnac phase shift, so that the second quotient is solely a ratio of the Bessel functions associated with the first and third spectral lines as a function of a phase modulation index; determining, from the curves of the Bessel functions, a corresponding ratio of the Bessel functions associated with the first quotient for each ratio of the Bessel functions associated with the second quotient as a function of the phase modulation index; forming a product from the first quotient and the corresponding ratio of the Bessel functions associated with the first quotient; determining a Sagnac phase shift value .vertline..phi..vertline. from the arc tangent of the product; and determining an angular velocity of the optical fiber winding from the Sagnac phase shift value .vertline..phi..ident.1.
The object is also accomplished according to the invention by an arrangement for determining angular velocities with the aid of an optical fiber ring interferometer which includes at least one optical fiber winding and a device for modulating the light waves propagating therein, with circuit units being provided which determine the amplitudes of several spectral lines of the interfering light waves that exit from the optical fiber to obtain therefrom the Sagnac phase shift that is proportional to the angular velocity, comprising a first divider which fo

REFERENCES:
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patent: 4765739 (1988-08-01), Koizumi et al.
patent: 4796993 (1989-01-01), Sonobe et al.
patent: 4883358 (1989-11-01), Okada
patent: 5127732 (1992-06-01), Gackler
Conference Proceedings OFS'84, 2nd Int'l. Conference on Optical Fiber Sensors, Sep. 5-7, 1984, Stuttgart, DE, VDE-Verlag GmbH (Berlin, DE); K. Bohm et al., "Fiber optical gyro . . . " pp. 251-258.

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