Mid-infrared holey and slotted photonic crystal waveguides in silicon-on-sapphire for chemical warfare simulant detection.

We provide the first experimental demonstration of the transmission characteristics of holey and slotted photonic crystal waveguides (PCWs) in silicon-on-sapphire at mid-infrared wavelength of 3.43 μm. Devices are studied as a function of lattice constant to tune the photonic stop band across the single wavelength of the source laser. In the holey PCW, propagation losses less than 20 dB/cm are observed below the light line while more than 400 dB/cm propagation losses are observed above the light line, characteristic of the waveguiding behavior of photonic crystal line defect modes. Comparison between the holey and slotted PCWs with PCWs without low-index inclusions shows the higher sensitivity to refractive index changes in chemical sensing for the holey and slotted PCWs compared to the regular PCWs. Triethylphosphate (TEP), a chemical warfare simulant, was detected down to a concentration of 10 ppm (parts per million) with a 800 μm long holey PCW in gas phase via optical absorbance signature. [ABSTRACT FROM AUTHOR]