Abstract

Fiber optic interferometers with single mode fibers provide high sensitivity for sensing e.g. temperature, sound, electric and magnetic fields. The inclusion of integrated optic components into the interferometer implements important functions such as splitting, recombining, phase compensation, polarization control in a compact way. Above all, integrated optic devices allow efficient heterodyne detection schemes with a linear conversion of the sensor phase θ and the sensor transmission H into corresponding electrical signals. Electra-optic LiNbO₃ devices are particularly attractive for these purposes. Here, we report on fiber optic Michelson and Mach-Zehnder interferometers which are built-up with polarization maintaining fibers and integrated optic LiNbO₃ devices. A digital heterodyne detection with an high dynamic range (up to 60 dB) is accomplished by a proper digital phase modulation. A basic configuration is depicted in Fig.1. Electra-optic phase modulators are driven with digital waveforms through a microcomputer that also samples the diode current. Due to the high linearity of LiNbO₃ phase modulators, a staircase phase modulation ϕ(t) of phase modulator PM 1 / 1/ in analogy to the analogue serrodyne /2/ or sawtooth /3/ modulation, proves to be efficient. A digital fourier transform (DFT) of the sampled diode current yields the sensor transmission H and the sensor phase θ.

© 1988 Optical Society of America