Temperature-compensated optical fiber Michelson refractometer

Fiber optic interferometric refractometers usually possess large temperature sensitivities, especially those based on individual long-period gratings. This work introduces a compound-cavity Michelson interferometer that uses mode coupling in a long-period grating to establish the two optical paths in a single fiber, and therefore presents a compact sensor for in vivo refractive index measurement. Successful operation of the athermal refractometer was demonstrated experimentally by comparing its phase shift due to temperature-dependent changes of the refractive index of the analyte with refractive index readings from a temperature-controlled Abbe refractometer.