Design And Research Of High-speed And High-power Uni-traveling-carrier Optical Waveguide Photodetector

Photodetector is an indispensable component in optical fiber communication system, which has important impacts on performance of the whole communication system. Particularly in a ROF(Radio over Fiber) system, high-speed and high-power photodiodes are needed to drive the microwave antennas directly. Traditional PIN photodetector and waveguide detector are unable to achieve the high-speed and high-power requirements. This paper presents an uni-traveling-carrier vertical directional coupling waveguide photodetector(UTC-VDCPD), which employs an vertical directional coupler to solve the problem of nonuniform photocurrent distribution in a waveguide photodetector and a mutual restraint between responsivity and speed in surface-illuminated photodetector. The main work of this paper is to focus on the UTC-VDCPD, and has the following achievements:1. Supermode theory and numerical simulation software BeamProp are used to analyze the vertical directional coupling waveguide photodetector. The structure parameters of a specific waveguide are determined by considering the uniformity of the photocurrent distribution and the quantum efficiency.2. An UTC structure is designed by a tradeoff between output saturation current and 3dB bandwidth. Simulation of the basic working parameters for UTC-VDCPD by using ATLAS software is carried out. According to the design, a 3dB bandwidth about 13 GHz, a 260 mA output photocurrent, and a 1.04 A/W responsivity are expected.3. The distribution of electric field, band structure, carrier concentration and current density within the device are analyzed in detail at low and high injection light intensity. The AC small signal response and the transient characteristic of the device are also studied.4. The small signal model for uni-traveling-carrier photodiode(UTC-PD) was analyzed, and the analysis suggests that the introduction of the quasi-field in the absorption layer can reduce the accumulation of electron in this layer and increase the 3dB bandwidth of the device.5. The effects of the conduction band discontinuity on UTC-PD was theoretically analyzed based on the small signal model, and carried out on a concrete structure. The results show that, the conduction band discontinuity will reduce the 3dB bandwidth. While, increasing the collection layer doping concentration is the most effective way to eliminate the adverse effects of the conduction band discontinuity.