Ultrasensitive Gas Refractometer Using Capillary-Based Mach-Zehnder Interferometer.

In this paper, we report a capillary-based Mach-Zehnder (M-Z) interferometer that could be used for precise detection of variations in refractive indices of gaseous samples. The sensing mechanism is quite straightforward. Cladding and core modes of a capillary are simultaneously excited by coupling coherent laser beams to the capillary cladding and core, respectively.