Four-Wave Interactions in Acoustoelectric Integrating Correlators

Device Structure Four-wave acoustoelectric interactions have been observed in an integrating correlator device. use of the four-wave process provides both signifi- cantly improved device performance over that achieved with three-wave interactions and makes possible a unique signal-processing function: triple-product c orrelation. These electric-field interactions involve the differential delay, mixing, and time-integration of two surface acoustic waves (SAWs) at frequencies w1 and 9 counter- propagating on a LiNb03 delay line in the presence of a uniform pump at a frequency w1 + w2 applied to a PtSi diode array. A narrow (%350-nm) air gap provides coupling of the array to the evanescent RF fields accompanying the SAWs. Nonlinearities in the silicon provide local mixing of the three input RF fields to create a quasi-static field of finite wavevector. Time-integration of this field produces a stationary wave of charge which is stored in the diode array. A similar four-wave process is used to scan this charge pattern. The two interactions have been cascaded to demonstrate the correlation of a waveform with a time-bandwidth product in excess of 10,000.