Velocity-matching techniques for integrated optic traveling wave switch/modulators

Abstract

We propose and analyze a new technique for achieving velocity match between the traveling wave electrical drive and guided optical signal for modulators in substrates for which there is an inherent mismatch. The traveling wave electrodes are laterally shifted periodically to reverse the direction of the applied electric field within the optical waveguide which exactly compensates for the polarity reversal caused by the microwave-optical walkoff. Consequently, the electrooptically induced phase shifts of each section add in phase and several sections can be used to reduce the required drive voltage at the design frequency. This artificial velocity-matching technique moves the mismatch-limited bandwidth to an arbitrarily high design frequency. In addition, we extend the new concept of phase reversal and the previously suggested technique of intermittent interaction by proposing electrode structures with large inactive to active aspect ratios. This generalization provides increased flexibility for manipulating the total available bandwidth to, for example, allow efficient modulation by a train of arbitrarily short electrical pulses. These techniques are ideally suited for several proposed integrated optic devices, including picosecond samplers and gates, which require strong overmodulation at a single high frequency.