Highly Sensitive and Regulatable Optical Fiber Vernier Sensor Based on Two Integrated Parallel MZIs

An integrated and sensitive optical fiber vernier sensing structure is designed and demonstrated. By horizontally splicing a thin hollow fiber (THF) and a thin core fiber (TCF) between two multimode fibers (MMFs), two integrated parallel Mach-Zehnder interferometers (MZIs) are formed. By adjusting the lengths of the THF and the TCF reasonably, the vernier effect can be formed in air and water, respectively. As a validation, sensor probes that form vernier effect in air and water are used for bending and seawater salinity measurements, respectively. Experiments show that in the range of 0.085 m ^-1 to 0.19718 m ^-1 , the sensor exhibits a high bending sensitivity of 127.15 nm/ m ^-1 and a low-temperature cross-talk of 37.5 pm/℃. In the salinity range of 0‰ -9‰, the sensor exhibits a high salinity sensitivity of -17.80 nm/‰, and has good measurement repeatability and stability. The sensing structure not only behaves the merits of small size, simple preparation, and good robustness, but also behaves the advantage of ultra-high sensitivity, which demonstrates its great application potential in high-precision detection of weak signals.