Manipulation And Detection Enhancement Of Terahertz Waves Using Artificial Microstructures

The utilization of artificial microstructures has garnered considerable interest in the field of terahertz science and technology,which has been developing rapidly in recent years.Microstructures such as surface plasmon resonant antennas and metamaterials have already played key roles in terahertz functional devices.This dissertation mainly focuses on the manipulation of terahertz waves using coding and programmable metamaterial and polysilicon resonant antenna for terahertz detection enhancement.The main context of the thesis includes three parts as below:1.The manipulation of transmission-type terahertz waves using coding metamaterials.Previous works on coding metamaterials mainly focus on the reflection-type metamaterial structures,which are easy to fabricate and can reduce radar cross section to a large extent.Yet the transmission-type structures are also commonly-used in the communication and imaging systems.Therefore,we design a novel transmission-type coding metasurface using multi-layer structures.At its working frequency,the metasurface bits operate at different resonant modes,yet have almost equal transmission coefficient and 180-degree phase delay.First we fabricate the proposed device at microwave frequency,and carry out the measurement and and obtain the predicted beam-splitting results,which agree well with the simulation results.After that,based on the multilayer polyimide substrate fabrication process,we fabricate and measure the terahertz coding metamaterial sample.The measurement are taken using the terahertz time domain spectroscopy(TDS)system and the measured results show that the proposed metasurface can achieve beam-splitting capability at 1.2 THz,which proves that we could successfully fabricate the transmission-type coding metasurface.2.Compared with coding metamaterial,programmable metamaterial can manipulate electromagnetic waves in a more flexible way,which dynamically shapes the spatial beam distribution.Based on the birefringence effect of the liquid crystal(LC)material,we optimize the fabrication recipe for the LC-based terahertz devices.First,we propose a novel type of terahertz wave amplitude modulator.At both TDS and continuous-wave(CW)systems,we measure the frequency response of the fabricated LC-based metamaterial device with and without the biased voltages.The measured results from the two systems both indicate strong amplitude modulation capability.Also,we design,fabricate and characterize a liquid crystal material and FPGA controlling circuits based programmable terahertz beam scanning array.The measurement is taken at different excitation incident wave angles and the measured results can agree the simulated results.This part of work suggests that the proposed metasurface beam scanning array can manipulate terahertz spatial beam distriibution in a dynamic way,which has been reported rarely in the terahertz fields.3.Terahertz detection enhancement using polysilicon resonant antenna.The standard CMOS technologies are already well-developed and highly-integrated,yet in the fabrication process the use of heavy metal such as gold is not encouraged.Therefore,we design a type of heavily-doped polysilicon-based antenna and optimize its structural geometrical and material features so as to achieve maximum field enhancement capability at 650 GHz.Also,we analyze the correlation between the field enhancement effect and the material doping density.The responsivity and noise equivalent power performance of the terahertz detector integrated with the proposed antenna was characterized by the CW system.The measured NEP result is about 200 pw/Hz1/2.This value is comparable to the present room-temperature terahertz detector,suggesting that the polysilicon-based antenna can be well-suited in the terahertz detector.Moreover,aided by an equivalent circuit model,analysis is carried out on the dipole antenna mode also resonant at 650 GHz to show more insights of the correlation between material properties to the antenna field enhancement capability.Finally,we simulate the performance of the polysilicon based two-element antenna array and propose a method to reduce the mutual coupling.