| Photodetector is a key device for ROF communication systems. Its characteristics directly affects the performance and design of ROF system. The emergence of optical fiber amplifiers has changed the performance requirements for photodetector. It has become a trend that traditional module of photodector and post-power amplifier is replaced by the module of optical fiber amplifier and photodetector. Therefore, the issues of high power with high bandwidth become urgent in photodetector research. In fact, a system made up of optical fiber amplifier and photodetector has better performance and lower cost.This dissertation reviews the history of photoelectric effect, and investigates the principle and structure of PIN-PD from the perspective of improving conversion efficiency. The reason of PIN-PD saturation is that the mobility of hole-carriers is low and hole-carriers gather in the depletion layer, which results in the space charge effect. In order to overcome this effect, UTC-PD was designed. In this dissertation, the structure of UTC-PD is studied and analyzed. The relationship between the thickness of UTC-PD absorption layer and the-3dB bandwidth of UTC-PD and response degree, the relationship between the thickness of collection layer and UTC-PD-3dB bandwidth, and the relationship between the doped concentration of collection layer and UTC-PD-3dB, are all obtained and physically analyzed. The results show that the performance of a UTC-PD depends significantly on the parameters of the absorption layer and the collection layer. Simulation shows that UTC-PD has a much higher saturation power and a much wider bandwidth compared to PIN-PD.The performance improvement of both PIN-PD and UTC-PD is implemented by changing the structure of single photodiode. There is a limit for the performance improvement for single photodiode. Therefore, the integration of several photodiodes is a promising technology to further improve both output power and working bandwidth of photodetector. Since the major issue of photodiodes integration is power combining, this dissertation mainly focuses on power combining. Three novel results are obtained: the optimum number of parallel photodiodes are obtained; the relationship between the number of cascade photodiodes and the light wavelength is revealed, which can be used to determine the maximum number of cascade photodiodes; and a new type cascade photodiode arrays power combining architecture is proposed.The output power will increase if photodiodes are connected in parallel. However, its junction capacitance will also increase, which leads to a narrower work bandwidth. Therefore, the photodiodes connected in parallel can not be used for high frequency. A detailed analysis shows that each photodiode will contribute less to output power if more than eight photodiodes are connected in parallel. In order to make the photodiodes in parallel work with a wide bandwidth, traveling-wave arrays is designed,which can increase output power with no decrease in work bandwidth.The cascade traveling-wave photodiode arrays detector can improve both output power and bandwidth. With the increasing number of cascade photodiode, the resistance increases linearly, which consumes more power and decreases the output efficiency.In this dissertation, the principle of travelling wave photodiode array and cascade photodiode array are studied, and a new architecture of cascade traveling-wave photodiode array(CTWDA) is proposed. This new architecture combines the advantages of traveling wave photodiode array power combining circuit and photodiode cascade power combining circuit. Theoretical analysis and EDA simulation show that the output power and work bandwidth of the architecture can be improved simultaneously. Further more, the number of the photodiode can be selected according to different requirements of output power and frequency bandwidth, which means that this architecture can fulfill different application requirements.
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