Injection Laser Waveguide Coupler.

The efficiency with which a double-heterostructure, GaAlAs laser diode can be edge-coupled to a TiLiNbO3 diffused waveguide has been studied using both theoretical and experimental approaches. Both the analytical and the numerical estimates of the coupling efficiency predict maximum efficiencies of approximately 50 for the laser diodes used in this program. Measurements of the sensitivity of the coupling efficiency to both transverse and longitudinal misalignment have been performed and these measurements show the coupling efficiency to be a slow function of the longitudinal separation and a strong function of the transverse offset. When the measured data are fit to an analytical model, the results indicate that a maximum coupling efficiency of about 50 has been achieved. Two coupler chips were fabricated and delivered to NRL. The coupler chips used a flip-chip design and were fabricated on silicon substrates. The units delivered to NRL had coupling efficiencies of 5 - 10 and thus fell short of the theoretically predicted efficiency. This result was due primarily to the stringent alignment tolerance imposed by the sensitivity of the coupling efficiency to transverse offset.