Temperature insensitive fiber interferometry

We show for the first time the interference pattern of a Mach-Zehnder interferometer to be fully insensitive to temperature. This is achieved using silica glass made hollow core fiber and operating it at the temperature of -71OC, which is very close to the temperature at which the thermal expansion of silica glass crosses zero. Our results highlight for the first time an alternative to bulky and difficult-to-align, ultra-low-expansion glass-based optical cavities for metrology and sensing