US 5,351,123 AGranted

Method and apparatus for stabilizing control loop scale factor and gain in a fiber optic Sagnac interferometer

AssigneeLITEF GmbH

InventorGunter Spahlinger

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Abstract

A method and apparatus for stabilizing the scale factor and the loop gain of the control loop of a fiberoptic Saganc interferometer with phase resetting. A digital evaluation circuit includes two auxiliary control loops, one for nominal gain of the scale factor control and the other for stabilization of loop gain of the primary control loop, in addition to the control loop for the readjustment of the phase modulator. The evaluation circuit can be realized as an integrated circuit. In addition to the optimization of control bandwidth, the circuit avoids substantial complexity of the circuit subassemblies for generating modulation and demodulation signals and control signals for the scale factor control loop.

Claims10

Dependent claims

In a method for rotational speed measurement by means of a fiber-optic Sagnac interferometer with phase resetting of the type in which two polarized light beams originating from a single light source and generated by beam splitting are irradiated in opposite directions into a fiber coil and subsequently reunited;

the interference pattern produced in the process is detected, and an electrical signal corresponding to the light intensity of the interference pattern is generated;
and in which the two light beams are modulated by a control signal composed of a plurality of variable components, of which a first signal component is a resetting signal which is generated via a digital control process and which compensates non-reciprocal, incremental phase shifts in the two light beams, and of which a second signal component, controlled by a first random number generator, assumes in each case for a time T.sub.o the values 0 or .pi., T.sub.o corresponding to the transit time of each of the two light beams through the fiber coil in the quiescent state, the improvement comprising the steps of:
a) adding a third signal component to the control signal (u.sub..phi.), said third signal component being controlled by a second random number generator and assuming the values .pi./2+d or .pi./2-d for the time T.sub.o where d is a predetermined small test variable;
and
b) subjecting the combined control signal to an integration process with modulo-2.pi. resetting, in which both the resetting signal and the second and the third signal components are supplied before the joint integration process.

2 more elements

Apparatus for rotational speed measurement with a phase-resetting, fiber-optic Sagnac interferometer of the type in which two light beams originating from one light source polarized by means of a polarizer and generated by a beamsplitter are irradiated in opposite directions into a fiber coil and subsequently reunited at the beamsplitter;

the interference pattern produced from beam recombination is scanned by a photodetector that supplies a signal corresponding to the light intensity of the interference pattern and is applied to a first amplifier having a downstream analog-to-digital converter whose output values are processed in a digital evaluation circuit that, on the one hand, provides a digital-to-analog converter having a downstream second amplifier with the digital phase-resetting signal generated via a primary control loop to obtain the resetting signal, which is applied to a phase modulator, and a signal proportional to the rotational speed and, on the other hand, provides via a first auxiliary control loop a first actuating signal for the gain a.sub.1 of the second amplifier, in such a way that the nominal value relationship a.sub.1 c.sub.1 =1 is fulfilled where c.sub.1 is the electrooptic coupling factor, the improvement comprising:
a) the gain a.sub.o of the first amplifier being controllable;
and
b) the evaluation circuit provides a second actuating signal for the gain a.sub.o of the first amplifier via a second auxiliary control loop, the value of said second actuating signal being a measure of the deviation of the product a.sub.o c.sub.o from 1 where c.sub.o is a constant that depends on the mean light power at the photodetector, the sensitivity thereof and the total gain in the primary control loop.

1 more element

Dependencies are inferred from the claim text.