Electro-Opto-Mechanical Microwave-Frequency Oscillator in a Surface Acoustic Wave Silicon-Photonic Circuit

An electro-opto-mechanical microwave frequency oscillator is demonstrated through a silicon photonic circuit. An electrical signal modulates an optical pump wave input. Modulation is converted to a surface acoustic wave on the silicon circuit through absorption in a metallic grating and thermoelastic expansion. The acoustic wave is delayed and converted back to optics through photoelastic modulation of a continuous optical input probe wave in a racetrack resonator waveguide. The output probe is detected, and the obtained voltage is amplified and fed back to modulate the input optical pump wave. With sufficient feedback gain, the electro-opto-mechanical loop is driven to oscillations at 2.21 GHz frequency. The oscillator can be useful for integrated microwave photonics signal processing.