Design And Modeling Of Photodetectors In Optical Communication

With the development of the society,the amount of data traffic is increasing rapidly,the traditional electrical interconnection in communication system is therefore difficult to meet the increasingly stringent requirements.Due to the low cost and high integration,the optical interconnection technology has become the potential alternative scheme,and has been studied extensively.As an key component in optical fiber communication system,the photodetector(PD)mainly determined the performance of whole system,so the design of high-speed and high-sensitivity PDs has become one of the hot issues.At the same time,analyzing the frequency response and output port characteristics of PDs is beneficial to achieve the collaborative design of the optical receiver,thus developing the small-signal equivalent model of PDs has become an urgent problem.Based on the design and modeling of PDs in optical fiber communication system,this thesis carried out the following research work:1.Based on the analysis of PDs in 850 nm optical fiber communication system,a spatial modulation photodetector(SMPD)and a double photodetector(DPD)based on standard UMC 0.18?m CMOS process are optimally designed,and the effects of device structure and process parameter on the performance of PDs are emphasized.The results of fabricated devices indicated that that the SMPD with a responsivity of92 m A/W has a-3dB bandwidth of 154 MHz under the bias of-3.3V.The DPD has a responsivity of 23mA/W,and a 3dB bandwidth is 730 MHz.The fabricated devices can meet the requirements of the optical receiver.2.For the 1550 nm wavelength optical communication,the germanium waveguide(WG)PD is researched.Based on the discuss of different coupling modes,the end-coupling WGPD is simulated by commercial software Lumerical,and the simulation results shown that the WGPD has a responsivity of 0.78A/W,and a-3dB bandwidth of 5.68 GHz under a reverse bias-voltage of 1V.3.Considering the effects of photo-generated carriers transmission and RC time constant,the small-signal equivalent models of CMOS-based DPD and Ge WGPD are established.The optimization algorithms are utilized to extract the model parameters through fitting the scattering parameters of actual device.The performance of PDs designed in this thesis can meet the practical requirements,and the equivalent circuit model can accurately simulate the actual characteristics of our devices.The results can not only realize the collaborative design of amplifier and PD,but also provide a guidance for device structure optimization.