Stydy On Self-Imaging Properties And Application For Tapered Multimode Interference Couplers

The researches and applications of integrated optical devices are rapidly developing as the optical communication technique evolving. The multimode interference (MMI) couplers based on self-imaging effect have many advantages including large fabrication tolerance, low polarization dependency and large optical bandwidth. They therefore have been widely applied in integrated optical components, such as beam splitters, triplexers, Mach-Zehnder switches, and so on. However, the components based on conventional straight MMI couplers are not compact enough to fulfill the demand of rapid developing integrated optical circuit. Reducing the size of MMI region meanwhile guaranteeing imaging performance therefore becomes a growing important issue for MMI couplers. Although more concerns are aroused to the tapered MMI couplers due to their compact dimension, most publications are focused on designing novel devices based on the tapered MMI couplers. The principle of image formation and imaging properties in the tapered MMI couplers, which are more essential for their applications in integrated optical components have been rarely reported in literatures.By employing effective index method and guide-mode propagation analysis, this thesis is intended to explore general self-imaging properties and overlapping-image properties for line-tapered MMI couplers and exponential-tapered MMI couplers, respectively. In addition, the devices based on exponential-tapered MMI couplers were designed out to check the superiority of the tapered MMI couplers. The innovation of this thesis can be concluded as follow:1. By combining effective index method and guide-mode propagation analysis, general self-imaging properties and overlapping-image properties for line-tapered MMI couplers and exponential-tapered MMI couplers are analyzed in detail. And the author finds that the positions of images are directly related to the position of input field, the position number, the width of tapered MMI couplers. Analytical formulas for positions of images are derived and some characteristics are summarized.2. Finite-difference beam propagation method (FD-BPM) is used to confirm the analytical results deduced theoretically. The simulation results of line-tapered MMI couplers and exponential-tapered MMI couplers obtained by FD-BPM and theoretical results are demonstrated to be coincided with each other to great extent.3. Some integrated optical devices are designed out. Follow the principle "simple, smaller, smarter, saving energy, swifter" we mainly designed out one device. The triplexer based on general self-imaging properties of exponential-tapered MMI couplers is the most compact MMI device which has three wavelengths multiplexing function.This thesis is related to multiple research directions, including the theoretical study, numerical calculation and device excogitation. Partial works of theoretical study is still underway. We intend to expend the special principles to be general principles. In addition, device based on exponential-tapered MMI couplers are expected to fabricate and testified by experiment and application.