Photonics-aided MEMS: Towards High Performance RF oscillators

Chip-scale optical oscillators are suitable for frequencies upwards of 10GHz. Achieving lower frequency of operation requires GHz-range optical Free Spectral Range (FSR) which pushes the device size to mm-scale dimensions. On the other hand, μm-sized MEMS structures are highly area efficient, but are limited to low frequencies of operation, in the range of tens of MHz to few GHz. As such, either technology, be it MEMS or photonics, is not feasible for the microwave X-band (8-12GHz) if employed individually. In the first part of my talk, I’ll present a novel hybrid silicon opto-acoustic oscillator that combines the high displacement sensitivity of photonics and the high Q and small form factor of MEMS resonators to realize an oscillator operating at 2GHz, with -80dBc/Hz phase noise at 10kHz offset from carrier. Nonlinear opto-mechanical modulation provides noiseless up-conversion all the way up to 16.4GHz. The oscillator was enabled by innovation in microfabrication, and I shall focus on the post-release photolithography process that I developed. 

In the next part of my talk, I shall describe another oscillator design that I demonstrated at Cornell University, namely the radiation pressure driven opto-mechanical oscillator. This oscillator exploits parametric amplification and does not require external electrical feedback to sustain oscillations, thus doing away with a dominant noise source. The resultant device exhibited self-sustained mechanical oscillations at 41MHz with phase noise -91dBc/Hz at 1kHz offset from carrier. The integrated design results in immunity of the oscillation signal from environmental flicker noise. A combination of radiation pressure and electric feedback leads to further reduction of phase noise, as I shall highlight in the aforementioned silicon oscillator. 

My PhD thesis at Cornell University also focused on MEMS-aided photonics, where I demonstrated a silicon electro-mechanical photodetector and acousto-optic frequency modulation. Details can be found in my publications listed at https://siddharthtallur.wordpress.com/publications/

Bio: Siddharth Tallur received the B.Tech. degree in Electrical Engineering at IIT Bombay in 2008, and graduated with a Ph.D. degree in Electrical Engineering at Cornell University in 2014. His thesis research at the OxideMEMS Laboratory focused on designing low phase noise RF opto-mechanical and opto-acoustic oscillators with a novel approach towards bringing together MEMS and photonic resonators. Prior to joining Cornell University, he was serving as a Business Analyst at the global strategy consulting firm A.T. Kearney Ltd. His work on electro-mechanically induced optical frequency modulation was the recipient of the best student paper award at the IEEE Photonics Conference 2012 held in Burlingame, California, and was recognized by the U.S. Advisory Committee to the International Commission for Optics (USAC/ICO). He has also worked with the ApselLab in Cornell University and co-authored several papers on design and characterization of a low power ultra wide band (UWB) impulse radio transceiver. His thesis research on opto-mechanical oscillators and MEMS aided photonics applications has earned him the Cornell University ECE Director's Best Thesis Research Award, 2013. Dr. Tallur is currently with Analog Devices Inc. working as a MEMS Sensor Platform Development Engineer in the Advanced Development group for inertial sensor products.