Temperature-Insensitive Microfiber Mach–Zehnder Interferometer for Absolute Strain Measurement

A temperature-insensitive microfiber Mach-Zehnder interferometer (MZI) for absolute strain measurement is investigated theoretically and experimentally depending on the diameter of the microfiber. The thermo-optic quantity of the microfiber MZI is effectively controlled by optimizing the diameter of the microfiber within the MZI incorporating an external coating overlay. Consequently, the positive thermal property of the microfiber MZI is successfully compensated by the negative thermo-optic factor of the microfiber resulting in suppression of the temperature sensitivity of the microfiber MZI. The transmission spectra of the microfiber MZI with variations in temperature are converted to the spatial frequency spectra by using the fast Fourier transform. When the diameter of the microfiber is ~7 μm, the temperature sensitivity of the spatial frequency of the microfiber MZI is dramatically mitigated to be 1.94 × 10
^-6
nm
^-1
· °C
^-1
. We apply the proposed microfiber MZI for absolute strain measurement and its strain sensitivity is measured to be 7.53 × 10
^-4
nm
^-1
· μϵ
^-1
in the spatial frequency domain.