Pulse amplitude modulation of CO2laser in an electro-optic thin film waveguide

A new technique has been used to obtain pulse-amplitude modulation of CO2laser radiation in a GaAs expitaxial thin film waveguide. This technique uses spatial perturbation of the guided-wave mode. The waveguide structure used in this experiment consists of a high-resistive ( ohm-cm) GaAs thin film expitaxially grown on a heavily doped ( ) substrate. A large index difference between the active thin film and the substrate allows the establishment of a number of TE and TM modes in the guide one at a time. To reduce the propagation loss only the TEomode was excited and propagated through this guide. When a negative square-top voltage pulse was applied to the guide through a Schottky barrier electrode, a light pulse was detected. The amplitude of the light pulse increases linearly with increasing applied voltage pulse and/or the length of the electrode. A study of the mode profile reveals that the electric field interacts with the propagating mode and produces a distributed perturbation in the mode profile. Preliminary results indicate that about one percent amplitude modulation (peak light pulse/maximum dc signal) at high repetition rates can be obtained by applying peak voltage pulses of ∼20 volts.