An Integrated Discrete-Time Microwave Photonic Filter Using Surface Acoustic Waves in Silicon

An integrated discrete-time microwave-photonic filter is implemented in standard silicon-on-insulator based on opto-mechanical interactions. Radio-frequency modulation of an incident optical pump is converted into slow-moving surface acoustic waves. The surface waves are delayed by up to 40 ns over 150 microns on-chip. Signals are recovered in the optical domain through photo-elastic modulation of probe light in multiple standard waveguides along the surface acoustic waves path. Devices do not require the suspension of silicon structures, piezo-electric actuation or hybrid material integration. A six-tap filter is demonstrated experimentally, with a central frequency, free spectral range and passbands width of 2.4 GHz, 125 MHz and 20 MHz, respectively. The measured transfer function is in excellent agreement with design. The results establish a new concept for integrated microwave photonics processing in standard silicon.