UC San Diego

Silicon photonics is technologically attractive because of the possibility of monolithically integrating multi- element photonic waveguide circuits with complex electronic circuits. To reduce the footprint of the photonic components, it is possible to fabricate strongly- coupled waveguides and resonators, e.g., with sub-100 nm separation gaps. The most insightful design tool used for photonic devices, coupled mode theory (CMT), is considered suspect for high-index contrast strongly coupled waveguides. Using a numerically assisted coupled mode theory (NA-CMT) developed for arrayed waveguides, it was shown how one may modify the basis parameters within CMT to calculate more accurate modal profiles and more accurate estimates of the value and the wavelength dependency (i.e., dispersion) of coupling coefficients. Traditional CMT inaccurately predicts both the field peak locations and the exponential decay rates of the field envelopes in the cladding regions. Examples of strongly- coupled silicon photonic devices based on waveguides and couplers include giant birefringence multi-slot waveguides, and large-bandwidth coupled-resonator optical waveguides (CROWS) consisting of several hundred coupled silicon microring resonators. Numerical techniques will be reported for accurately simulating the transmission properties of strongly coupled arrayed waveguides and disordered CROWs in excellent agreement with experimental measurements on fabricated devices. Experimental methods were developed for the accurate measurement of transmitted intensity and group delay of silicon nanophotonic waveguides and multi-resonator circuits including CROWs and side-coupled integrated spaced sequence of resonators (SCISSORS). The role of external amplification in reliably measuring waveguide transmission using the method of swept wavelength interferometry was studied in detail. Also, a technique of swept-wavelength infrared imaging was developed and applied for quantitative diagnostics of multi-resonator circuits which need not have accessible drop ports on every device