Research On Silicon-Based Integrated Terahertz Polarization Manipulation Devices

Terahertz frequencies,which are sandwiched between microwave frequencies at the lower end and optical frequencies at the higher end,are an unexplored spectrum resource in the electromagnetic spectrum and one of the current hot spots in scientific research.Terahertz technology,which is known as one of the top ten technologies that will change the world in the future,has a wide range of applications in the fields of wireless communication,radar,biomedicine,detection,and security.Among them,terahertz functional devices,as one of the important components of terahertz systems,play a crucial role in the research and application of terahertz systems.Meanwhile,polarization,as one of the fundamental characteristics of electromagnetic waves,has been proven to have significant research potential and disruptive applications in the microwave and optical wave bands.Therefore,to accelerate the development of terahertz polarization technology and promote the application of terahertz polarization systems,in-depth research on terahertz polarization manipulation devices is urgently needed.The thesis has carried out theoretical and experimental research on on-chip terahertz polarization manipulation devices.The representative research results are listed as follows:(1)The high-performance integrated terahertz polarization beam splitters based on directional coupler is investigated.The function of polarization beam splitting of directional couplers is verified based on a dual waveguide structure.On this basis,a high-performance polarization beam splitter with an extinction ratio of up to 19 d B at the center frequency of 456.5 GHz is successfully achieved by introducing a bridge waveguide in the coupling region to form a three-waveguide directional coupler.To further optimize the device size and operating bandwidth,a polarization beam splitter with a size of 15.5×4.5 mm~2 is designed based on a cascaded asymmetric directional couplers.At the center frequency of 453 GHz,the device has TE and TM polarization extinction ratios of 20 d B and 32 d B,respectively,and the operating bandwidth increases to 32 GHz for polarization extinction ratio>10 d B.(2)Highly efficient integrated terahertz polarization rotating devices are explored.Based-on asymmetric structure a highly efficient polarization rotator is designed.The waveguide symmetry is breaked by grooved waveguide and the polarization rotator achieves a polarization conversion efficiency over 90%in the 70 GHz operating frequencies.To improve device integration and simplify the process,a polarization splitter and rotator with a length of 37.5 mm is designed based on an adiabatic tapered waveguide and an asymmetric directional coupler to achieve a polarization extinction ratio>10 d B in the 30GHz range.To further optimize the device size,the particle swarm optimization algorithm is used to miniaturize the polarization splitter and rotator based on the mode hybridization principle.Optimizing the segmentation of the mode hybridization region and the asymmetric coupling region,a compact polarization splitter and rotator with a length 9 mm is obtained.This optimization approach provides a new perspective on device miniaturization design.(3)The terahertz polarization-frequency division multiplexer based on polarization beam splitting rotators and micro-ring resonators is studied,along with the implementation of terahertz multidimensional multiplexed communication based on this device.Terahertz polarization multiplexing and frequency multiplexing are realized by polarization beam splitting rotators and micro-ring resonators,respectively.The polarization-and frequency-division multiplexer simultaneously processes polarization multiplexing signals and frequency multiplexing signals,which can effectively enhance terahertz communication capacity.By building an optical mixing-based terahertz communication system,the communication link of the device is demonstrated.The terahertz transmission of a dual-frequency(377.87 GHz and 381.87 GHz),dual-polarization 1 Gbaud(micro-ring resonators with a bandwidth of approximately 1 GHz)QPSK signal at an aggregate rate of 8 Gbit/s is successfully demonstrated,which provides a novel approach to realize high-capacity wireless communication.