Simultaneous Measurement of Salinity and Temperature in Gold-Coated D-Shaped Photonic Crystal Fiber Using Four-Wave Mixing Technique

We propose a novel nonlinear technique for simultaneous measurement of salinity and temperature of water in a gold coated D-shaped photonic crystal fiber (DPCF). In this novel nonlinear technique, the sensitivity is calculated numerically through a degenerate four-wave mixing scheme by tracking the wavelength shift of the Stokes and anti-Stokes lines for various concentrations of NaCl and temperatures. The optimized fiber design with lattice pitch of 4.49 
$\mu$
m, airhole diameter of 2.892 
$\mu$
m, and with a gold layer of 39.5 nm enables effective sensitivities of 1.6 nm/%(kg/kg) for salinity and of 12.31 nm/
$^{\circ }$
C for temperature when light is launched at the pumping wavelength of 1070.4 nm in 2 cm of length of a DPCF. To our knowledge, the obtained sensitivity is much higher than that of other simultaneous measurement techniques. This novel nonlinear sensor has been demonstrated with high resolution of about 8.625
$\times$

$10^{-4}$
%(kg/kg) and 9.74817
$\times$

$10^{-7}$
 
$^{\circ }$
C for salinity and temperature measurements, respectively.