Multi-axis fiber optic rotation rate sensor with parallel sensing coils

Abstract

A multi-axis fiber-optic rotation rate sensor arrangement of I/O opto-electronics (MCS) is based upon single-axis rotational rate sensor arrangements and includes a low-frequency transformation of the output signal at the photodetector by pulsed operation of the light source. The light path is divided into n independent closed light paths downstream of a main beam splitter and a phase modulator whose lengths are in the ratio L.sub.1 :L.sub.2 :L.sub.3 : . . . :L.sub.n =1:2:3: . . . :n. The light source is switched ON/OFF with a pulse duty factor whose ON duration corresponds to the transit time of light through the shortest fiber coil L.sub.1 and whose OFF duration is at least equal to the transit time of light through the longest of the fiber coils L.sub.n. The signals are distinguished either downstream of the photodetector by time-division multiplex or at the phase modulator, where the signal is virtually blanked by the corresponding bias phase application with .+-..pi..multidot.n, delivering minimal rotation rate information, or has applied to it a bias phase of .+-..pi.(n+1/2) to deliver maximum rotation rate information (n a positive integer). The use of common I/O opto-electronics for all the light paths results in substantial cost savings, reduced space requirements, lower power absorption and enhanced reliability.