Miniature photonic crystal cavity sensor for simultaneous measurement of liquid concentration and temperature

A new method for simultaneous measurement of liquid concentration and temperature is proposed by using a miniature photonic crystal sensor, where two cascaded cavities (H0 cavity and H1 cavity) are separately located adjacent to one waveguide. The standard liquid whose concentration is fixed and known will be infiltrated in defected holes of the H1 cavity, and the measured liquid whose concentration is unknown will be infiltrated in defected holes of the H0 cavity. Both the two independent resonant dips of cascaded cavities that can be simultaneously monitored at output spectrum of the waveguide will shift with the variation of liquid concentration or ambient temperature. By using finite difference time domain (FDTD) simulation, resonant properties of the two cavities are respectively optimized, and then the linear relationships between shifts of two resonant dips and liquid concentration/temperature are calculated. Finally, according to dual-wavelength matrix method, liquid concentration measurement with a resolution of 9.4322 ppm and temperature measurement with a resolution of 0.0136 K are simultaneously realized, which can not only solve the cross-sensitivity problem between liquid concentration and temperature, but also provide a solution for two-parameter measurement in a miniaturized system.