First Demonstration of a 2- $\mu{\rm m}$ OTDR and Its Use in Photonic Bandgap ${\rm CO}_{2}$ Sensing Fiber

We report the first demonstration of an optical time domain reflectometer (OTDR) designed for the emerging wavelength band of 2 μm. A dynamic range of 30 dB with a spatial resolution of 5 m is achieved. The characterization of three different fibers using the 2-μm OTDR is described. Two solid core fibers (SMF with a cutoff at 1.7 μm and SMF 28e) have been probed to ascertain their transmission loss values, while measurements in a 19-cell hollow core photonic bandgap fiber show the presence of carbon dioxide gas in the fiber core and allow the contribution that it makes to the fiber loss to be quantified.