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Optical dispersion and nonlinearity in integrated silicon nanophotonic devices


Increasing demands in speed, bandwidth and power efficiency in computing and communications has led to a burgeoning of the field of silicon photonics. Given their compatibility with complementary metal oxide semiconductor technology, optical systems on silicon provide a low cost, scalable solution to meet future data demands. In this dissertation, we address some of the issues necessary for optics to become a viable platform for applications such as data centers and microprocessors. First, using the concepts in coupled mode theory and finite difference time domain modeling, add drop filters are designed using coupled vertical gratings. The filter is further applied for use as a 1 by 4 wavelength division multiplexer offering bandwidths and a free spectral range unparalleled by state of the art alternatives such as ring resonators. Next, the issue of group velocity dispersion engineering in photonic lightwave circuits is addressed. By incorporating linear chirp into a single vertical grating, quadratic phase may be imparted to an incident wave. To overcome the loss limitations associated with the chirped vertical grating operating in reflection, a coupled chirped vertical grating structure is introduced for operation in transmission. The high index contrast in the silicon-on-insulator platform implies that weak coupling and equivalently small bandwidths, are difficult to achieve in channel waveguide geometries. We present the theory and experimental demonstration of a cladding- modulated Bragg grating implemented using periodic placements of cylinders along a silicon waveguide which enable a wide range of coupling strengths to be realized. Next, group velocity dispersion engineering by varying the waveguide geometry is studied in silicon nitride. Nonlinear loss mechanisms such as two photon absorption are shown experimentally to be absent in the fabricated waveguides at high optical intensities. Two-fold broadening of an incident pulse is demonstrated, showing that silicon nitride is a viable nonlinear material. Finally, we present the first demonstration of a nonlinear optical pulse compressor implemented on silicon. Incident pulses undergoing self phase modulation followed by spectral re-phasing using dispersive elements result in temporal compression. The compression factors achieved are the highest demonstrated on a chip to date

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