A common path fibre optic based interferometric displacement sensor with enhanced range

Abstract

The transfer functions of single and dual interferometric cavities were measured with 1300nm high power, tuneable fibre laser with a coherence length of 20mm. The interferrogram of the dual cavity is complex. The positions of the surfaces in the cavities were determined using Fast Fourier transforms. A feature of the dual cavity is an increase in the 'effective' coherence length of the source, illuminating a simple common path interferometer. A 4*1 optical switch was incorporated with the laser allowing near simultaneous data to be recorded from up to 4 probes. A potential application for a dual cavity probe is discussed. © 2012 SPIE.