Experimental Investigation Of Absorption Gas Sensor Based On Free-space Coupling Optical Waveguide

In an Attenuated-Total-Internal-Reflection (ATR) multi-layer structure, light reflectivity can be highly dependent on layer parameters such as the layer thickness and refractive index. A tiny change in these parameters can lead to a large change in the light reflectivity. This characteristic enables the realization of many novel type optoelectronic devices based on this structure.In this dissertation, we have investigated the attenuation mechanisms in the ATR structure. Based on this structure, the free-space coupling waveguide absorption gas sensor has been modeled. The core configuration of this sensor is a symmetric metal cladding waveguide structure. The light beam can directly couple into the wave-guided layer without any couplers. The thickness of wave-guided layer is of the order of sub-millimeter. Owing to the advent of the free-space coupling technology, the angle of incidence beam can be small, then we can use the high sensitivity of ultrahigh-order modes in a optical waveguide. Since the sample gas has its own absorption character, it is practical for us to realize testing selectively. As the free-space coupling optical waveguide has a filter function, the common semiconductor laser can be a choice of light source, which can further reduce the cost and improve the sensitivity.