CIAN Lecture Series Webinar – Rajat Sharma

Towards Understanding and Exploring Artificial Nonlinearities in Silicon/Dielectric Waveguides

Date:  Friday, October 28, 2016
Time:  1pm PST, 4pm EST

Please register by clicking on the link: Webinar   or copy and pasting to your browser:


rajatRajat Sharma
Ph.D. Candidate
University of California, San Diego

Rajat is a 4th year PhD student working with Prof. Shaya Fainman at the Department of Electrical and Computer Engineering at UCSD. The main focus of his research is engineering nonlinearities in silicon. He graduated with a B.S and M.S in Electrical Engineering, with a specialization in microelectronics and VLSI, from the Indian Institute of Technology (IIT) Madras in 2012.


Starting from our past-experience in studying the linear electro-optic properties of strained-silicon waveguides, we carry forth a detailed analysis of various mechanisms contributing towards the exhibited (apparent) nonlinearity. We show, both theoretically and experimentally, that the bulk of the linear electro-optic response exhibited by such waveguides can be accounted for by the so-called free-carrier, capacitive, plasma-dispersion effect. The nature (magnitude and sign) of this effect is then shown to be critically dependent on the fixed-charges that are induced on the interface between a semiconductor and a dielectric. As such, this study becomes relevant and must be taken into account, not just for silicon waveguides, but all semiconductor waveguides. The range of tunability of both the real and imaginary part of the refractive index is measured and reported, the knowledge of which can be used in desigining high-efficiency silicon-slot capacitive modulators as well as low-loss passive devices. Furthermore, in our investigations, we find that commonly used clads (in strained silicon waveguides) like silicon nitride (SiNx) can exhibit bulk second-order nonlinearity. This is demonstrated via both free-space and in-waveguide measurements and a coefficient as high as 2.23 pm/V is reported for the case of the as-deposted PECVD SiNx. This value, though small, serves as a starting point in our efforts towards leveraging the SiNx platform for on-chip modulation and nonlinear wavemixing. The value of the exhibited coefficient can be enhanced manifolds by either shifting to non-stoichiometric silicon rich nitride (SRN) and or using SiNx in a slot configuration  with silicon and utilizing the electric field induced second harmonic effect (EFISH).

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