Comparison of fiber-optic Sagnac and Mach-Zehnder interferometers with respect to thermal processes in the fiber

The impact of thermal noise in the fiber on the noise power and signal-to-noise ratio (SNR) of fiber-optic sensors is investigated, and sensors based on the Sagnac and the Mach-Zehnder interferometers are compared. The SNR is almost the same for the two interferometers; the Mach-Zehnder interferometer has slightly higher SNR at low frequencies, whereas the Sagnac interferometer may have a few dB higher SNR at high frequencies. It is also shown that thermal noise may dominate over shot noise for realistic system parameters, in which case a Sagnac interferometer has several advantages over a Mach-Zehnder interferometer.>