Research On Mode/Polarization Controlled Waveguides And Detectors For On-chip Multiplexing Systems

With the development of information society,the demand for communication data capacity is increasing day by day.The integrated chips of optoelectronics,which can simultaneously achieve high integration density,low power consumption,and large bandwidth,have received widespread attention from domestic and foreign researchers.Various multiplexing technologies,such as wavelength division multiplexing,polarization division multiplexing,and mode division multiplexing,offer the possibility of rapid expansion of channel capacity.The research and development of functional on-chip active and passive devices for various multiplexing technologies are also proceeding at a rapid pace.This thesis focuses on the research of mode/polarization controlled devices and integrated detectors.The specific research contents are summarized as follows:（1）An indium phosphide-based monolithic integrated receiver chip for 4×25 Gbit/s WDM system at 1310 nm waveband is investigated theoretically and experimentally.The monolithic integration of the array waveguide grating and high-speed waveguide detector is realized based on a single epitaxial structure,which reduces the process complexity.The wavelength demultiplexing function of the arrayed waveguide grating and the high-speed response characteristics of the waveguide photodiode are experimentally demonstrated,the responsivity and bandwidth of waveguide photodiode are respectively 0.548 A/W and29 GHz at-1 V bias.（2）Waveguide-type Schottky detectors for wavelength/polarization/mode-division multiplexing system is theoretically investigated and designed.The mode analyses of various plasmonic waveguides integrated with ultrathin metal strips reveal the mode hybridization effects between quasi-TE/TM modes and bound modes.In Au stripe with thickness of 8 nm and length of 5.2μm,the theoretical absorptance of up to 93.78%/93.25%and responsivity of 0.11/0.1094 A/W for the incident TE/TM modes at 1.55μm wavelength are achieved,with a polarization dependent deviation as low as 0.57%and dark current of 55.36 n A.For 2μm waveband,theoretical absorptance of 98.4%/90.2%and responsivity of 89/81.7 m A/W for the incident TE/TM mode are theoretically achieved.（3）Silicon based on-chip mode/polarization filtering devices for mode/polarization-division multiplexing systems are investigated theoretically.The mode hybridization phenomena between quasi-photonic modes and bound modes in various waveguide structures,including hybrid plasmonic waveguides and plasmonic photonic crystals,are revealed by mode analyses.The manipulation of absorption characteristics for arbitrary mode/polarization incidence can be realized by utilizing the transmission loss enhancement for hybridized modes induced by these phenomena.Therefore,a variety of universal design methods for high-order mode-pass filters and mode-transparent polarizers are proposed.The designed TE₃ and TM₃ mode pass filters can both achieve a theoretical bandwidth of 440 nm and a mode extinction ratio of better than 15 d B for various low-order modes（TE₀-TE₂,TM₀-TM₂）.The theoretical bandwidths of the designed mode-transparent TE₀ and TE₀/TE₁/TE₂/TE₃ mode pass polarizers can reach 940 nm and480 nm,respectively,and the polarization extinction ratio is better than 15 d B.The mode transparent TM₀ and TM₀/TM₁/TM₂ mode pass polarizers obtain theoretical operating bandwidths of 400 nm and 90 nm respectively,with a polarization extinction ratios better than 10 d B.These design strategies based on mode hybridization-enhanced absorption offer the advantages of ultra-compactness（<10μm）,ultra-wide bandwidth,and high scalability.