Abstract

As a result of the significant progress in Ti:LiNbO₃ waveguide device research in the last several years, these devices now show great promise for use in high data rate lightwave systems as well as for signal processing applications. Guided-wave modulators, switches and filters with impressive figures of merit have now been demonstrated in several laboratories. However, the practicality of these devices for systems applications is frequently questioned because devices reported to date have relatively high insertion loss and low fiber-waveguide coupling efficiency. Clearly, for the full potential of these devices to be realized, low waveguide loss and efficient fiber-waveguide coupling are essential. Currently, the lowest reported fiber-waveguide-fiber insertion loss for a 1 cm long straight Ti:LiNbO₃ waveguide is 2.5-3.0 dB for λ=1.15μm and λ=.6328μm², respectively.³ Much poorer results have been previously achieved for waveguide circuits, e.g., directional couplers, required for devices. By carefully selecting diffusion conditions to enhance the match between fiber and waveguide modes, we have achieved fiber-waveguide-fiber insertion loss as low as 1 dB for a 1.3 cm long straight Ti:LiNbO₃ waveguide and 1.65 dB for a 2 cm long directional coupler for λ=1.32μm.

© 1982 Optical Society of America