Dual C-Type Microchannel Fiber Fabry-Perot Sensor With Long Sensing Cavity for Seawater Salinity

An optical fiber seawater salinity sensor based on a femtosecond laser inscribed dual C-type microchannel is demonstrated. Using femtosecond laser technology, the dual C-shaped microchannels are engraved on hollow core fiber (HCF) with a long sensing area, and microgrooves are also machined on a single-mode fiber. In addition, the structure can be coated with the gold film on two reflective surfaces to enhance the signal-to-noise ratio. The cavity length demodulation method resolves the issue that the classic wavelength demodulation method is not able to directly process the data signal in the same spectral range due to the excessive number of periods. The experimental results show that after the sensor is coated with gold film, the salinity sensitivity of using cavity length demodulation can reach 84.41 nm/‰ in the salinity measurement range of 0‰–35‰. It indicates that the sensor owns great sensing capability and high potentiality for high-precision measurement of seawater salinity.