Coupling of polarization-maintaining optical fibers to Ti:LiNbO_3 waveguides with angled interfaces

Angled interfaces between Ti:LiNbO(3) guided-wave devices and fiber-optic pigtails have been used to suppress backreflections. The effect of angled interfaces on coupling loss between polarization-maintaining fibers and Ti:LiNbO(3) waveguides is investigated. The theory is developed and predicts very small increases in coupling loss for modest interface angles (10 deg). Experiments confirmed the theoretical coupling angles, and the added loss due to angling was measured to be 0.57 dB per interface. A Mach-Zehnder modulator was made, with optimized angled-interface geometry, which exhibited no additional insertion loss compared with that from similar devices with perpendicular interfaces.