Fiber-optic in-line Mach-Zehnder modal interferometer for breathing monitoring application

A simple fiber-optic in-line Mach-Zehnder modal interferometer is fabricated and studied for monitoring human being's breathing rate, which is one of the most important vital signs. The sensing structure is simply fabricated by a couple of up-tapers manufactured in the common telecommunication single mode fiber (SMF) by a commercial splicer. Sensing performances with different distances between the dual up-tapers are addressed. The whole setup only contains one laser source, one photo-detector and one section of SMF with dual up-tapers. It can real-timely monitor people's respiration rhythm without complex signal processing and the scheme is simple and low-cost.