Evaluation of White Light Sources For an Absolute Fiber Optic Sensor Readout System

摘要

This report summarizes work done in pursuit of an absolute readout system for Fabry-Perot optics sensors such as those built both by FISO and LLNL. The use of white light results in a short coherence length reducing the ambiguity of the Fabry-Perot gap measurement which is required to readout the sensor. The light source coherence length is the critical parameter in determining the ability to build a relative or an absolute system. Optical sources such as lasers and LEDs are rather narrow in optical spectral bandwidth and have long coherence length. Thus, when used in interferometric sensor measurements, one fringe looks much like another and it is difficult to make an absolute measurement. In contrast, white light sources are much broader in spectral bandwidth and have very short coherence lengths making interferometry possible only over the coherence length, which can be 1 or 2 microns.