Double-layered subwavelength metallic slit array for performance-improvement of a fiber-optic silicon Fabry–Perot temperature sensor

The proof of concept of a polarization-sensitive temperature sensor composed of a silicon Fabry–Perot resonator sandwiched between double-layered subwavelength metallic slit arrays is presented at the operation wavelength of 1.55 µm. Temperature variations can be monitored by measuring the changes in reflection intensity, which is mainly induced by the thermo-optic effect and thermal expansion effect of silicon. For TM-polarized electromagnetic illumination (magnetic field parallel to the slits), the reflection properties of the proposed sensor can be adjusted by proper design of the subwavelength metallic slit arrays’ parameters, such as periodicity, metal film thickness, and slit width. Thus, a temperature sensor with an optimized temperature detection range and sensitivity can be designed according to the application demands. Some sensor designs are presented in this article and the effect of each design parameter on their performance is discussed. The transfer matrix method (TMM) is utilized for the theoretical analysis of the presented designs, the results of which are verified using a commercial FEM solver. The FEM simulation results are in good agreement with the TMM simulation results. The presented designs are compact and low-cost, operate in reflection which simplifies the measurement setup, and rely on the direct monitoring of optical power instead of a complicated spectral scanning. The maximum achieved sensitivity is 0.0225/°C which is higher than the maximum sensitivity for an equivalent silicon Fabry–Perot temperature sensor.