Research And Design Of Traveling-wave Optical Waveguide Photodetector

High-speed and high-power photodetector is an indispensable device of optical heterodyne technology.The bandwidth of photodetector determines the data transmission speed,and the THz millimeter wave power output by photodetector determines the wireless transmission distance.Now the bandwidth of the detector can reach hundreds of GHz.However,the millimeter wave generated by the detector is only milliwatt,which makes the transmission distance limited to a few meters,so it is difficult to be applied in the situation of high wireless transmission distance requirements,high-speed and high-power detector has become the bottleneck of heterodyne THz technology.Due to the demand of RoF system,the development of high-speed and high-power photodetectors began in the 1990 s.The traditional photodetectors are limited by RC time constant,carrier transit time,waveguide length,exponential current distribution and waveguide cross section,which are difficult to achieve high-speed and high-power performance at the same time.In this paper,a kind of twpd(traveling wave photodiodes)is introduced,which is based on the development of the structure of the optical waveguide detector.It is composed of an optical waveguide structure with uniform distribution of optical current and an impedance matching microwave waveguide structure.The traveling wave optical waveguide detector solves the limitation of other factors besides carrier transit time.In this paper,we focus on the traveling wave optical waveguide detector,and obtain the following research results:1.In this paper,we study the multilayer millimeter wave lossy dielectric waveguide.Via solving the effective permittivity of the waveguide,we study the continuity of the field distribution in the waveguide and explain its limitations.At the same time,we analyze the telegraph equation and the equivalent circuit model of the multi conductor transmission line.2.The specific structure of the detector is analysed by the simulation software beamprop,and the detector structure is roughly obtained by adjusting the structural parameters.Here,the absorption degree of the waveguide to the beam,namely the quantum efficiency problem,is mainly considered;the structure obtained by the simulation is verified by the supermode theory to measure the uniformity of the optical current distribution in the waveguide.3.In this paper,a hybrid waveguide structure of light wave and microwave is used to analyze the Traveling-wave photodetectors.Atlas simulation obtains the internal characteristics of devices such as the bandwidth limited by the carrier transit time and the carrier concentration;secondly,the waveguide doping concentration is converted into the conductivity of the microwave waveguide to study the transmission characteristics of high-frequency optical current in the microwave waveguide structure,and the equivalent circuit modeling of the microwave waveguide structure is carried out,and the conditions required for impedance matching are studied,which are applied to the traveling wave optical waveguide detector The equivalent circuit model of the hybrid coplanar waveguide detector is modified.4.This paper analyzes the limiting factors of the medium speed mismatch bandwidth of the traveling wave optical waveguide detector,and analyzes the small signal model of the traveling wave optical waveguide detector.