International Standard Electric Corporation

Standard Elektrik Lorenz Ag

Eberhard Schlemper

Wilfried Auch

Friedemann Mohr

Helmut Graf

Walter Steudle

A rotation rate measuring instrument is disclosed in which two light beams propagate through a coiled optical fiber in opposite directions. After passing through the optical fiber, the two light beams are combined and directed onto a photodetector. One of the light beams is phase-modulated in a phase-modulator before entering the optical fiber. The modulation frequency is f.sub.m. The output signal of the photodetector is fed to a variable-gain amplifier whose output signal is separated into a signal of frequency f.sub.m and a signal of frequency 2f.sub.m. The rotation rate is derived from the signal of frequency f.sub.m. The signal of frequency 2f.sub.m is applied to a detector whose output is fed to an operational amplifier. The other signal applied to the operational amplifier is a reference signal of amplitude U.sub.R. The operational amplifier controls the gain of the variable-gain amplifier in such a way that the output signal of the detector has the same amplitude as the reference signal U.sub.R.

Rotation rate measuring instrument

Two electrical-to-acoustical transducers (W1, W2) are attached to two contiguous sides of a cube (B) made of optically transparent material. The propagation directions of the two waves delivered by the transducers intersect inside the cube. The frequency of the light beam striking the device is shifted by f.sub.1 -f.sub.2, where f.sub.1 and f.sub.2 are the frequencies of the drive signals for the two transducers. The deflection of the light beam in the two propagation directions of the sound waves is proportional to the frequencies of the drive signals.

Acoustooptical modulator and/or deflector

The rotation rate measuring instrument, in which the phase difference caused by the Sagnac effect is evaluated, contains two optical waveguides (7, 17). From a light beam, two component beams (CW, CCW) are derived which traverse the first optical waveguide (7) in opposite directions. A passive beam splitter (16) connects the first optical waveguide with the second optical waveguide (17) and splits each of the component beams into two further component beams. Of these further component beams, one remains in the first optical waveguide, and the other enters the second optical waveguide, where it propagates in the opposite direction. Evaluation, for which the two component beams are combined after having traversed one or both optical waveguides, takes place on a time-division multiplex basis, such that either the traversal of only one optical waveguide (7) or the traversal of both optical waveguides (7, 17) is taken into account. By comparing the two measurements, additional nonreciprocal phase differences (.phi..sub.NR) are determined, which can be taken into account during evaluation.

In the measuring instrument, a light beam generated by a laser (1) is split into two component beams (L(CW), L(CCW)) which travel along a coiled optical waveguide (7) in opposite directions. After traversing the optical waveguide, the two component beams are superimposed on each other (5) and directed to an optical/electrical transducer (8). One of the two component beams (L(CW)) is frequency-modulated in a Bragg cell (6) before entering the optical waveguide (7), switchover being effected between two modulation frequencies (f1, f2) at a given frequency (F.sub.S). The modulation frequencies are chosen so that, after traversal of the optical waveguide (7), the phase differences (.phi..sub.B1, .phi..sub.B2) between the two component beams (if the rotation rate .OMEGA.=0) are .pi./2 and 3.pi./2 or even integral multiples thereof. In case of rotation, the phase difference (.phi..sub.S) caused by the Sagnac effect is superimposed on these phase differences. The output signal of the optical/electrcal transducer (8) is passed through a band-pass filter (10) whose midfrequency is equal to the frequency at which switching takes place between the two modulating signals. The amplitude of the band-pass output signal is directly proportional to the rotation rate (.OMEGA.). From this signal, a control signal can be derived which can be used to compensate for the phase difference (.phi..sub.S) caused by the Sagnac effect.

In the rotation rate measuring instrument, a light beam produced by a laser (1) is divided in a beam splitter (4) into two component beams (I.sub.CW, I.sub.CCW) which travel in opposite directions around an optical waveguard (9) forming a closed light path. A Bragg cell (6, 7) is inserted between the beam splitter and each end of the optical waveguide. One of the Bragg cells (6) is driven with a signal (f.sub.VCO) whose frequency is varied in accordance with the rotation rate. For the other Bragg cell, a switch (33) switches periodically between two drive signals (f.sub.MH, f.sub.ML), so that the component beam is frequency-modulated (f.sub.S). A regulating facility (12, 13, 54, 55, 56) is provided which compensates for intensity differences between the two component beams. In further embodiments, it is possible to compensate for those intensity variations of the component beam (I.sub.CW) which are caused by driving the Bragg cell (5) at different frequencies (f.sub.MH, f.sub.ML). It is also possible to design the instrument so that both the intensity differences between the two component beams and the intensity variations within one component beam can be compensated for.

Growing community of inventors

Vaihingen, Germany

Eberhard Schlemper