Understanding Optical Coupling in Collapsed Hollow-Core Optical Fiber

Abstract

Frequency references based on saturated absorption spectroscopy that are stable, portable, and accurate can be constructed using photonic bandgap (PBG) fibers filled with acetylene.[1][2][3][4][5][6] A method for sealing acetylene inside the PBG fiber with minimal contamination involves collapsing the core of the PBG fiber, which causes high loss in the final splice. We investigate the light coming out of the PBG fiber and methods for coupling it back into fiber. Results show that the light exiting the fiber does not have a Gaussian shape and can be coupled back into fiber using a two-lens set-up, with 26% being the highest coupling achieved.