Reaserch On Novel Photodetectors With Flat-Top And Steep-Edge Response For WDM Systerm

Wavelength-division multiplexing (WDM) in optical communication can obtain abundant channel resources from tremendous potential bandwidth of the fiber. In addition, due to its compatibility with other communication technologies, WDM has been widely used in backbone network, metropolitan area network and access network. As a key technology, wavelength demultiplexing and receiving technology ensures WDM to be applied into communication system successfully. This thesis studies the integrated demultiplexing photodetector in WDM system. The main achievements are listed as follows:1. The important component of resonant cavity enhanced (RCE) photodetector-distributed bragg reflector (DBR) is thoroughly analyzed by transfer matrix method, including the relations between reflectivity and transmissivity of intrinsic DBR and refractive index difference and the number of dielectric layers, the relations between reflectivity and transmissivity of doped DBR and the lacation and refractive index of doped layer, the influence of refractive index and thickness gradient of dielectric layers on reflectivity and transmissivity of DBR, elementary principles of Fabry-Perot (FP) cavity and characteristics of DBR based FP cavity. The calculations show that DBR based FP cavity can ensure the spectral response peak to be close to 1, as well as the narrow linewidths, thus having good wavelength selectivity. 2. A novel RCE photodetector with flat-top and steep-edge response is presented. The response is obtained by designing P area in absorption cavity as gradual-thickness structure with 0.86°inclination angle. The quantum efficiency and high-speed response characteristic are analyzed. Simulation results show that the maximum and minimum values of the quantum efficiency in bandpass are 85.242% and 87.564% respectively, the ripple of flat top is about 3.6%; 0.5dB,3dB, and 20dB bandwidth is 0.3nm,0.4nm, and 1.2nm respectively. The mesa area is 10μm×10μm and the frequency response bandwidth is 87GHz. Compared with similar photodetectors, this photodetector has high quantum efficiency, narrow spectral response linewidth, good flat-top and steep-edge response, and ideal high-speed characteristics.3. Another RCE photodetector with flat-top and steep-edge response is designed. The response is obtained by dividing the filter cavity into ten parts with different length. The filtering characteristic, quantum efficiency and influences of key parameters on the performance of the photodetecter are analyzed. The quantum efficiency of the photodetector is more than 80% in bandpass, the ripple of the flat top is less than 2%, and 0.5dB,3dB, and 20dB bandwidth is 0.32nm, 0.46nm, and 0.92nm respectively. Compared with similar photodetectors, this photodetector has high quantum efficiency, narrow spectral response linewidth and good flat-top and steep-edge response.4. Monolithically integrated long-wavelength four-mirror-three-cavity photodetecor is designed and has been successfully realized for the first time. The FP cavity and spacer cavity structure with GaAs/AlGaAs DBRs and InP-based PIN structure have been integrated on GaAs substrate. The simulation results show that the photodetector has high quantum efficiency, narrow spectral response linewidth. The realized photodetector has quantum efficiency of 58.47% at 1550.3nm wavelength, and 3dB bandwidth of 0.78nm. The reduction of the quantum efficiency and the appearance of side peaks in actual response are analyzed as well.