Optimized couplers between junction lasers and single-mode fibers

Single mode fiber output power of over 7.5 mW CW has been obtained by the use of unique adjustable coupling modules that were developed for this program and that are being delivered to NRL. These are the highest powers ever reported coupled between diode lasers and single mode fibers. Coupling efficiencies over 25% were obtained in simple butt coupling by taking advantage of the large mode size available from RCA CDH LOC lasers. We also observed peak fiber power of over 9 mW with 100 ns 50% duty cycle pulses. The miniature models provide relative transverse and lateral motion between fiber and laser with 2000A resolution, allowing fine tuning against long term drifts. The coupling, while adjustable, is still stable against moderate acceleration of module and motion of fiber pigtail. The adjustments may be adapted to servo control. Still higher coupling efficiencies might be expected with cylinder lenses bonded to the fiber. Initial experiments indicated the need for further work to achieve accurate and stable attachment of lens to fiber.