Study Of Muti-Mode Interferometer By Means Of Mode Matching Method

Multi-mode interference (MMI) devices, which are based on the self-imaging effect (SIE), are widely used in integrated optics for their unique features such as compact size, low insertion loss, ease of production and good fabrication tolerances.The thesis composed a program in Matlab language for mode matching method and analyzed the characteristics of MMIs and various MMI based optical devices. As the results shown, although the precisely calculated fields differ slightly from that given by approximate theory, the self imaging property appears the same and the positions for one-fold image, two-fold image, three-fold image, etc, predicted by two methods are very close.Next, the imaging characteristics of MMI under various conditions were studied in detail. The decreasing of output optical power under weak constrain was attributed to the increasing of the energy brought away by the radiation mode and the lowering of the number of guided modes supported by the waveguide. When the number of guided modes becomes small due to the small refraction index difference between the core and cladding layer, the quality of self-image becomes poor for many high frequency components were lost. The mismatch of the enlarged self-imaging sport and the narrow output waveguide led to the leakage of output optical power. The explanation clears away the fuzzy idea of traditional believes.Finally, the phase relation between the input and output waveguide in MMI were discussed. Utilizing the phase relation many MMI based devices are designed and calculated, which include 1×2, 1×3, 1×4, and 1×5 optical splitter, optical switches, and 13μm/1.55μm wavelength division demultiplexor.