Sensor applications of a reflective fibre optic ring interferometer

D.Ing. (Electrical and Electronic Engineering)The subject of this research work was the reflective fibre optic ring interferometer utilizing allow coherence length source. The interferometer consists of an interrogating fibre connected to a fibre ring via an input/output splitting coupler, and a reflector. The fibre ring is formed between one input and one output leg of a fibre coupler. The reflector can be of any type, including a fibre loop mirror, Faraday rotator mirror, a silvered fibre end-face or multilayer dielectric mirror deposited on the fibre end face. A theoretical treatment was developed for the interferometer. It was shown that the interferometer had a reflectance vs nonreciprocal phase shift characteristic, similar to that of a Fabry-Perot interferometer. Upon phase modulation of the interferometer quadrature terms were obtained at harmonics of the modulation frequency. It was shown that by decreasing the finesse of the sensor a quadrature phase tracker could be employed. The dependence of the sensor's reflectance, finesse and sensitivity on various system parameters were simulated with the aid of the abovementioned theory. A high finesse interferometer was proposed. It utilizes a fibre doped amplifier which would increase the sensitivity above that of a Sagnac interferometer. Intermediate and low finesse versions of the reflective ring interferometer were applied as gyroscopes..