| We have explored a new class of optical devices based upon multimode interference (MMI) and self-guiding that has wide applications in optical communications and optical signal processing. We devised a methodology for designing practical self-guiding MMI devices, developed a perturbation model to describe the transition from multimode interference to self-guiding in Kerr materials, numerically demonstrated a number of functions and applications of these devices, explored the feasibility of fabricating these devices in both Kerr and photorefractive materials, and experimentally demonstrated an MMI device comprised of a Kerr nonlinear material which initially exhibit features of self-guiding.; In a Kerr self-guiding MMI device, the multimode region is comprised of a material with a positive nonlinearity, i.e. the optical index increases with increasing intensity. Multimode interference describes a property of multimode waveguides by which images of the input are formed at multiple image planes. Self-guiding occurs when the light intensity is sufficient to induce the formation of a waveguide through a nonlinear effect. A self-guided beam may be used to override the modal interference effects. Therefore, at low intensities, the output coupling location is determined by the MMI effects. At high intensities, the output may be switched to that defined by the self-guided mode. The models developed in this work demonstrate that the self-guiding mode propagates through the MMI waveguide, experiencing only small residual effects from the modal interference.; A nonlinear threshold switch has been fabricated in 4-BCMU to assess the feasibility of self-guiding in a MMI device. The nonlinear polymer 4-BCMU was spin-coated onto a silica-on-silicon substrate and patterned by photo bleaching the non-guiding regions. At low powers, the linear MMI devices functioned as expected. At high power, self-guiding was initially observed. However, the high power levels and interference with unguided modes combined to increase the loss, which prevented self-guiding over long distances. Other materials, such as the photorefractive materials, offer a low power solution. |
