Salinity sensor based on polyimide-coated photonic crystal fiber.

We proposed and experimentally demonstrated a highly sensitive salinity sensor using a polyimide-coated Hi-Bi photonic crystal fiber Sagnac interferometer based on the coating swelling induced radial pressure. This is the first time to exploit fiber coating induced pressure effect for salinity sensing. The achieved salinity sensitivity is 0.742 nm/(mol/L), which is 45 times more sensitive than that of a polyimide-coated fiber Bragg grating. A bare fiber Bragg grating is incorporated into the fiber loop for temperature compensation.