Low-cost refractive index sensor based on a fiber Mach-Zehnder interferometer fabricated by chemical etching method

A new refractometer based on a fiber Mach-Zehnder interferometer incorporating an H-shaped optical fiber is proposed and demonstrated, which was fabricated by splicing a section of polarization-maintaining fiber between two sections of single-mode fibers and subsequent chemical corrosion. Real-time monitoring of the corrosion process during device manufacturing ensures a superior contrast ratio of interference fringes. The spectral characteristics of interferometers of different lengths and the refractive index sensing performance of interferometers were investigated experimentally. When the refractive index of the analyte is close to that of the fiber material, the proposed interferometer is still usable and exhibits an ultra-high sensitivity of 105502.51 nm/RIU. Furthermore, the availability and cost of the proposed interferometer are favorable as the expensive and sophisticated equipment is not required in the manufacturing process, and parallel processing is allowed. Such a simple fiber device can potentially be employed in high-accuracy biochemical detection.