Abstract

Coherent lightwave detection techniques offer significant system advantages including increased receiver sensitivity and flexibility for closely spaced wavelength-division multiplexing. For phase shift keyed coherent systems which offer particular sensitivity advantages, efficient low-loss broadband phase modulators will be required. Low loss is especially important, of course, to avoid sacrificing the sensitivity gained by using coherent techniques. Here we describe the design, fabrication, and characterization of very low-loss fiber-coupled Ti:LiNbO₃ waveguide phase modulators fabricated on X-cut lithium niobate. Devices operating at λ = 1.55 μm with permanently attached connectorized pigtails have been made with total insertion loss of −1.8 dB, 8.5-V π phase voltage, and modulation bandwidth of ≃5 GHz. This device has been employed in heterodyne differential phase shift keyed coherent lightwave system experiments at data rates of 0.4 and 1 Gbit/sec.¹

© 1986 Optical Society of America