Measurement of low gas concentration using photonic bandgap fiber

A high-sensitivity, compact set-up, enabling the precise measurement of a very low concentration of gas was designed. The micro-capillary gas flow phenomenon and the gas absorption inside fiber were estimated. Darcy - Weisbach equation for non-compressible flow and quasi - Panhandle equation for compressible gas flow were used for the calculation of the gas flow rate and gas velocity inside the photonic bandgap fiber. It was assumed that gas flowed mostly in the core. During the experimental part of work several types of optic fiber of various parameters were used. The core diameters ranged from 10.9 to 19.9 μm. It was possible to measure the flow rate of the nitrogen gas inside the fiber with various pressure differences on the opposite ends. Average velocity (Δp = 0.9 atm) ranged 0.17 m/s and was a little bit lower than expected.