Abstract
Ultrafast all-optical signal processing uses nonlinear properties of the material,induced at the high input peak powers, for modulating optical signals at highspeeds. However, nonlinear losses such as two-photon absorption and freecarrierabsorption inherent in the widely used complementary metal- oxidesemiconductor(CMOS) platform, silicon, hinder the implementation of all- opticalsignal processing on compact photonic chips as they result in undesirableattenuation in optical fields and compromise the efficiency of nonlinear processes.This resulted in the research efforts to be directed towards engineeringnew material platforms such as chalcogenide glasses, Hydex glass, stoichiometricsilicon nitride, and silicon-rich nitrides. Here, we employ the compositionallyengineered, CMOS- compatible, ultra-silicon-rich nitride (USRN) platformto demonstrate nonlinear optical processes on photonic circuits.Nonlinear optics is based on light-matter interactions. Via utilizing both materialand structural properties of integrated photonic devices, it is possible totune the light-matter interactions at a greater scale, allowing the full potentialof on-chip nonlinear processes to be efficiently unlocked. USRN possess negligiblenonlinear losses with a large Kerr nonlinearity of 2.8 10 ??13 cm2/Wand a linear refractive index of 3.1, making it ideal for integrated nonlinear optics.More on-chip functionalities that are lacking in the photonics toolkit can bediscovered by combining structurally engineered waveguides with novel materialssuch as USRN. Here, we use CMOS-compatible silicon and USRN devicesto contribute to the field of nanophotonics particularly towards the aspect ofperiodic waveguide structures and their use as both passive and nonlinear integrateddevices with possible applications beyond data-communications.viOur first contribution is a cladding-modulated 1-D photonic crystal for creatingultra-large dispersion on a silicon chip. The design of this novel integratedgrating structure, fabrication, and characterization of the devices are presented.Employing on-chip gratings, we demonstrate spectral compression, for the firsttime on a chip, with a spectral compression factor of 2.3. Next, photonic crystalwaveguides (PhCWgs) on ultra- silicon- rich nitride (USRN) platform is usedto exploit the slow-light effects and boost the nonlinear effects. Enhancementof nonlinearities is accomplished, due to the periodic device structure, yieldingeffective nonlinear parameters above 104 (W m)??1. Furthermore, optical parametricgain is observed in ultra-short devices ( 100 m).Consequently, we move on to harnessing the dispersion of cladding-modulatedBragg gratings, at the photonic band edge, for observing high-order soliton dynamicson a chip. The significance of optical solitons comes from their fundamentalrole in crucial applications in ultrafast optics, communications and signalprocessing. We demonstrate soliton compression and fission using claddingmodulatedBragg gratings on the USRN platform. First time-resolved measurementsof soliton fission on a CMOS-compatible platform, along with largesoliton-effect temporal pulse compression with a factor of 5.7, are presented.Then, we build on the gained knowledge from this temporal characterization,and demonstrate a spectral width enhancement scheme for on-chip supercontinuumgeneration.