| The THz band covers the frequency range of 100 GHz-10 THz,THz wave is very suitable for spectrum analysis,imaging,detection,UWB communication,etc.The key problem of its application is the lack of compact solid-state THz sources.High-speed and high-saturation-current photodetectors are the key devices for making solid-state THz sources.Integration of broadband antennas and photodetectors can achieve a wide tuning range,which is more compact,flexible and reliable than other terahertz sources.Photodetectors can be divided into two categories: distributed traveling wave photodetectors and lumped photodetectors according to the electrode characteristics.The distributed structure makes it not limited by the RC time constant and can achieve a large bandwidth.The relative bandwidth of the UWB antenna is generally greater than 20%.The self-complementary structure can be designed to make the antenna have nonfrequency-dependent characteristics,and the impedance matching of the two can be achieved to improve the output.Therefore,in this thesis,the following studies are carried out for photodetectors and antennas with a wide tuning range and uniform current distribution:1.In order to reduce the coupling loss from the fiber to the waveguide detector,a 9?m×10 ?m passive waveguide is designed to couple with the fiber,and the back end is an active waveguide.Proposed oblique incidence optical waveguide detector,the R-Soft software is used to analyze the passive waveguide loss and active waveguide absorption efficiency under different incident field tilt angles and waveguide structures.When the inclination angle is "15.5°",the power loss of the passive waveguide is only 6.20%,and the absorption efficiency of the active waveguide is as high as 80.21%.When the inclination angle of incident light field is offset within "±2°",the absorption efficiency of the optical waveguide detector is higher than 75%.2.Through the equivalent circuit model of the traveling wave photodetector,the electrical properties of the detector were calculated in Matlab,and the calculated propagation length is used to optimize the design of optical waveguide detector.The velocity mismatch and impedance matching problems of traveling wave photodetectors are analyzed,and it is shown that the 3 d B bandwidth of the detector with open input is50% higher than the 3 d B bandwidth with a mismatch factor of 4 when the velocity is matched.The bandwidth of the impedance matching at the input is much larger than the open circuit case,but the response is lower.Using CST software,traveling wave structure was designed for the optical waveguide photodetector.The size of the electrode was adjusted to meet the impedance matching with the external load,and the output power of the detector was improved.Comparing the equivalent circuit model and CST simulation results,it is shown that the calculated characteristic impedances is consistent at high frequency.3.The influence of the structural parameters of the bow tie antenna on the electrical performance is analyzed.Bow-tie antennas with resonant frequencies of 100 GHz,200 GHz and 300 GHz are designed and optimized by CST.The results show that the antenna has a frequency independent characteristic in a wide frequency range,the bandwidth is as high as 74.22%,and the power loss caused by reflection is less than 4.06%.The input impedance of the bow-tie antenna is compared with the characteristic impedance of CPW,and two groups of the THz frequency points with approximate impedance matching are obtained. |
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