Phase shift optical loop spectroscopy

Abstract From the Canadian patent

The invention provides a method and apparatus for measuring one or more optical properties, such as absorbance and refractive index of a test medium , such as a , gas, a liquid or solid material. The method comprises providing a passive optical , waveguide loop comprising the test medium launching in the optical loop an , intensity-modulated light at a reference phase, detecting a phase of said light along the optical waveguide loop, and comparing the detected phase of said light along the loop with the , reference phase, wherein the comparison provides information about one or more optical properties of the test medium.