Temperature Insensitive Delay-Line Fiber Interferometer Operating at Room Temperature

Environmental temperature fluctuations cause phase changes of the light propagating through optical fibers due to their thermal sensitivity. This limits stability fiber delay-line interferometers. Here, we present a thermally-insensitive Mach-Zehnder interferometer. It consists hollow core (HCF), which has low sensitivity coefficient, in one branch and standard single-mode with coefficient about 25 times larger other. By setting associated length ratio approximately 25:1, both arms by same amount temperature, making difference paths insensitive thus producing interference. As is itself slightly dependent, exactly-zero achieved at specific only. We show how this zero-sensitivity can be controlled via control relative lengths two interferometer set it room temperature. Further, that our over 100 less sensitive than fiber-based range as large 25–50 °C. When considering simple keeps within ±1 °C, demonstrated achieves 2000 lower an HCF-only based Finally, discuss such depends on source wavelength.