Laser welding single mode alignment.

As part of a development, aimed at producing a second generation laser package for undersea systems, we have demonstrated that single mode alignments can be losslessly fixed in place by laser welding. Test vehicles consisting of a single mode fiber epoxied into a kovar ferrule were prepared. The fibers were aligned by manipulating the ferrules until light coupled from one fiber to the other was optimized. The ferrules were then butt welded together in four places using 4.5 joule pulses from a neodymium YAG laser. The tolerances, geometry, materials, and procedure closely simulate conditions in our proposed confocal package design. Negligible changes in coupling were observed during the welding sequence. The excess loss for three "splices" (discounting losses from fiber end-face reflections) was 0. 16+-.03 dB.