Abstract

High coupling efficiency is obtained with a hemispherical termination of the fiber pigtail end in which the curvature radius is slightly greater than the fiber core. The microlens fabrication process takes several steps: fiber preparation including chemical etching for reducing the cladding diameter; cutting the fiber end taking a particular bare fiber length; and hemispherical microlens fabrication by heating with a microflame. It is a self-centering process which permits repeated efficient terminations. A 60% coupling efficiency is obtained from a laser diode using 50/125-μm core/cladding diam, 0.2 N.A. graded-index fiber pigtails terminated on a 60-70-μm diam hemispherical end (Fig. 1). About 3-dB improvement is obtained when using LEDs compared with a flat termination case. A maximum coupling efficiency is obtained when the emitter surface and the hemispherical fiber end are placed ~30 μm apart; thus positioning of both surfaces using hemispherical termination is simpler and less risky than using a flat end.

© 1983 Optical Society of America