Abstract

Extremely fast modulation response of optical phase delay in a waveguide modulator is required for photonic integrated circuits (PICs) to operate with mm-wave signals. Single phase modulators, paired phase modulators in a Mach-Zehnder interferometer, or more complex arrangements can be used for mm-wave modulation of light in either phase, amplitude, or frequency. Standard lumped-element devices are bandwidth limited by the RC time-constant of the structure. Distributed, or traveling-wave designs have been developed to surpass the RC limit. With distributed structures the bandwidth limit is determined by loss of phase synchronism between the optical and RF wavefronts within the length of the device. The generally different propagation constants of the optical and RF waves leads to a limiting length- bandwidth product in the modulation response. In the limit of zero velocity mismatch the modulation bandwidth is then limited by RF loss in the transmission line. Velocity matching in undoped or low-doped semiconductor optoelectronic modulators typically involves use of a slow-wave transmission line electrode structure. Several successful techniques have been developed[l-2], but undoped structures offer low electrooptic efficiency, resulting in undesirably large devices. We disclose a device using doped semiconductor structures to increase efficiency in a traveling-wave modulator. This new design is demonstrated to have a bandwidth greater than 40 GHz in a Mach-Zehnder intensity modulator operating at 1.32 μm wavelength while maintaining V_π = 10V with a phase modulator section only lmm-long.

© 1996 Optical Society of America