Characteristic Analysis Of The Waveguide Photodetector (WGPD) For Optical Communication

Due to the growing demand for speed and capacity of telecommunication systems, optical networks will be continuously updated to cope with the high capacities needed for future data transmission systems. Photodetectors with both high speed response and high quantum efficiency become the key device in the fiber communication systems and optical networks. It’s well known that the waveguide photodetector overcomes the inherent bandwidth-efficiency trade-off as the frequency bandwidth and quantum efficiency can be both optimized simultaneously. Thus the WGPD become the focus of domestic and foreign research on photodetectors because it can achieve high speed response and high quantum efficiency simultaneously.The main content of this work is focused on the improvement of the structure and properties of the waveguide photodetectors and has the following achievements:1. The evanescently-coupled simulation model of the high speed waveguide photodetectors has been established, and a detailed analysis of the bandgap、electric field、carrier density and current density of the device have been made. From the view of carrier transport, the principle of the device and the mechanism of various features generated during the operation are deeply investigated.2. A novel vertically-tapered waveguide photodetector by utilizing a vertically tapered waveguide instead of the planar waveguide has been proposed to improve the external quantum efficiency. In this structure, the overlapping area is increased in order to increase the coupling efficiency between the input fiber and the photodetector. The simulation results showed the external quantum efficiency and high speed response of the vertically tapered waveguide achieved32%and20GHz, respectively. Compared to the planar waveguide photodetector, the external quantum efficiency and the high speed response have a7%and10GHz improvement, respectively.3. A novel graded-doped cladding layer waveguide photodetector has been studied to improve the high speed performance for the WGPD. That is, using a cladding layer graded doped from the absorber layer to the electrode in the end to reduce the equivalent resistance of the device and reduce the transit time of the photo-generated carriers so as to improve the high speed frequency response of the photodetector. The simulation results showed the high speed response of the graded doped waveguide photodetector reached40GHz. Compared to the common waveguide photodetector, the high speed performance has been improved significantly.4. The waveguide photodetectors have been studied experimentally. The method of epitaxial layer growth of the waveguide photodetector, the post-process processing steps and the device testing method have been described in detail. Some important experimental devices like MOCVD device and ICP device have been described. A WGPD with640nm absorber layer using InP/InGaAs materials has been made experimentally and its quantum efficiency property to the wavelength of the input light has been tested. The testing results showed the external quantum efficiency reached17.7%at the1550nm wavelength.