Nonlinear optical process enhancement by artificial resonant structures.

摘要

Nonlinear optical materials and devices respond to the intensity of light. This behavior is what allows light to control light, resulting in the ability to implement devices that perform switching, logic, and wavelength conversion operations, which are essential for the development of next-generation all-optical systems. The major problem with conventional nonlinear optical materials is that there is an inherent trade-off between nonlinear sensitivity and response time, so that nonresonant materials have ultrafast response but are weakly nonlinear, whereas resonant materials can have large nonlinear response but with slower response time and typically suffer from increased absorption. While the search for new natural materials with a large optical nonlinearity continues, the use of artificial materials and structures has been considered as a means of enhancing the optical nonlinearity. The practical advantage of using engineered resonance effects is in the more efficient use of the nonlinearity by maximizing the nonlinear effect within the bandwidth of interest. Multiresonator artificial systems, such as photonic crystals (PCs) with defect cavities (also referred to as coupled resonator optical waveguides (CROWs) or slow-wave structures (SWSs)), offer additional degrees of freedom over single resonators in the design for a specific nonlinear response where the nonlinear sensitivity, bandwidth, and loss can be controlled with some independence.; In this thesis, we propose a novel approach to the design of nonlinear optical devices by treating the desired nonlinear response in the weak perturbation limit as a discrete-time filter. We demonstrate its feasibility in the design of low intensity nonlinear phase shifters based on optical Kerr effect, where a prototype discrete-time filter of a flat-topped passband with steep linear in-band phase is preferred. Several approaches to synthesizing the prototype filter are presented, including an empirical approach based on bandwidth manipulation, a direct filter synthesis approach adapted from microwave filter design, and a discrete-time signal processing approach incorporating with a precompensation strategy. We further propose a self-consistent methodology to handle multivalued transmissions that can occur in optical resonant architectures with increasing incident intensity, providing a straightforward and efficient way to explore bistable behaviors in multiresonator systems. Four optical architectures are examined for the study of the nonlinear phase shift, optical bistability or multistability, two-photon absorption and optical pulse propagation, including thin-film photonic bandgap coupled-defects, direct-coupled ring resonators, cascaded ring resonators, and ring-resonator based Mach-Zehnder interferometer lattice. The scaling rule of the nonlinear sensitivity on the basis of linear filter parameters is evaluated; thus, nonlinear behavior can be estimated directly from linear filter responses.