Fusion splicing of a single-mode fiber with a pure-silica core and graded-index fiber-lens: toward an optimal fabrication of optical collimators

Lensed fibers consisting of a microlens introduced at the end of the SMF are important devices for coupling power from lasers to fibers, between two fibers, or from fibers to other waveguide devices, such as photodetectors, MEMS optical switches, and in other non-telecom applications. This work examines the parameters and manufacturing technology of graded-index fiber (GIF) lenses using fluorine-doped silica optical fibers, driven by the expanding applications of these fibers and the need for compact collimator lenses. The impact of fluorine diffusion during fusion splicing on the parameters of GIF lenses is examined. In addition, the effect of fusion splicing parameters on coupling efficiency and reflectance analysis of GIF lenses is theoretically analyzed and compared with experimental results. The collimator system, including an input and an identical output collimator, demonstrated a coupling loss of less than −0.6dB through a gap of up to 0.5 mm. The SMF/GIF splice losses were approximately –105–(–120) dB, while the return losses on the GIF lens surface end were approximately –18–(–23) dB.