Research On The Coupling Characteristics And Their Control Mechanisms Of Photonic Crystal Waveguide Modes

Photonic crystal (PC) slab waveguides exhibit novel characteristics of confining light by band gap and abnormal dispersion, which provides a new way to realize ultrasmall optical integrated circuits. Both the modes in several photonic crystal waveguides (PCWGs) and the different modes in single PCWG can couple with each other. The PCWG modes coupling is not only the work foundation of many PC devices, but also closely related to the loss mechanisms of PCWGs. Therefore it is great significant to research the coupling characteristics of PCWG modes. Being supported by the research projects of China, this dissertation is devoted to the coupling characteristics and their control mechanisms of PCWG modes theoretically and experimentally. The main achievements are as follows:A set of platform for theoretical simulating, fabricating and characteristics testing of PCs has been established. The technical problems in nano-scale ICP etching of silicon and silicon dioxide have been solved and a high quality photonic crystal directional coupler (PCDC) with air bridge structure has been successfully fabricated and tested. Based on these, the coupling characteristics and their control mechanisms of PCWG modes were researched.The directional coupling of PCWG modes and its application in PCDCs were studied. A PCDC with a bandwidth of 100nm, a length of about 7μm, and an insertion loss of about 0.5dB was proposed by optimal design of the structural parameters. Meanwhile it has been demonstrated theoretically that the air hole position misalignment perpendicular to the waveguide has a larger effect on the insertion loss of PCDCs, and reducing r/a is helpful to improving the robustness of PCDCs.The contra-directional coupling of PCWG modes and its application in both biochemical sensors and zero-dispersion slow light were studied. The designed biochemical sensor has a sensitivity of about 0.01nm and a large detective range from 1.00 to 1.38. The way to get zero dispersion at various low group velocity in PCWG was investigated theoretically too, and the band width of the slow light in the designed structure is ten times larger than that in normal PCWGs.The mode coupling control mechanism, which is realized by introducing asymmetry in single PCWG, has been proposed and demonstrated experimentally. The changing of the coupling transmission spectrum along with temperature has been observed, then the thermal switching effect with a 12dB extinction ratio was proved. Moreover, the mode coupling control mechanism, which is realized by introducing both asymmetry and long periodicity in single PCWG, has been studied theoretically, and a filter with a bandwidth of 1.4nm was designed.The loss mechanism, which is introduced by the coupling between the even and odd modes in single PCWG, has been proved both theoretically and experimentally. The method to enlarge the band width of the single even mode region and suppress this kind of loss by structure optimization has been proposed.