Open Cavity Anti-Resonant Reflecting Waveguide for Simultaneous Measurement of Salinity and Temperature

An open cavity anti-resonant reflecting waveguide is proposed and experimentally demonstrated for simultaneous measurement of salinity and temperature. Femtosecond laser micromachining is used to introduce a pair of open channels on a hollow core fiber (HCF) based anti-resonant reflecting waveguide. Results indicate that the anti-resonant reflecting guiding mechanism still exists even when large rectangular channels are introduced to the cavity wall. The strength of the anti-resonant reflecting effect is influenced by the geometric size of the rectangular channels. Sea water salinity measurement is realized with such a device. The intensity at the resonant wavelength increases with increasing salinity, exhibiting a sensitivity of 2.05 dB/% within a 2%-7% saline concentration range, while the transmission Dips shift toward shorter wavelength with a sensitivity of -0.84 nm/%. The temperature sensitivity is 0.049 nm/°C across a temperature range of 30°C-80°C. By tracing the wavelength change of two transmission Dips, the salinity and temperature can be determined simultaneously. The proposed device has advantages such as simple structure and fast response, which has promising applications in marine environmental science and medical biology.