The Research On The Mechanism And Device Of One-way Transmission And Optical Modulation For Terahertz Waves

Terahertz?THz?isolators and modulators have urgent practical needs in THz applications.They are the key devices of quasi-optical application systems represented by THz wireless communication and security imaging.The THz isolator allows forward light to pass through the device efficiently,but forbids light from passing backwards,which can effectively isolate the reflected echo and scattering existing in the quasi-optical system,ensure the service life and working safety of active devices such as radiation sources and detectors and reduce the noise in system.At present,the study of THz isolator at home and abroad is in an early stage,and there is still lack of high-performance isolators that can meet the actual needs of application systems.High-speed THz modulator is one of the main restriction for the development of THz wireless communication.Its research has been widely concerned and made some important progress.However,the operating frequency band,modulation depth,sensitivity and modulation rate of existing THz modulation devices still cannot meet the requirements of the THz wireless communication system.To solve the questions above,we design,prepare,and experimentally study the terahertz isolators and optically pumped intensity modulators which come out of new materials and new physical mechanisms by analyzing the dielectric model of terahertz band materials in depth,combining the resonances of artificial electromagnetic microstructures and domain enhancement features basing on the basic theories and research advances of terahertz isolators and intensity modulators at home and abroad.The main work and achievements are as follows:1.The correspondence between the refractive index and absorption coefficient of magnetic fluid in the THz band and the concentration of Fe₃O₄ nanoparticles in the ferrofluid was experimentally studied.It was found that there are two different physical mechanisms of terahertz magneto-optical in the magnetic fluid in the transverse magnetic field,and we did analysis and modeling of the magneto-optical effect.2.Theoretical and experimental studies on the magneto-optical characteristics of the semiconductor InSb in the THz band.Two magneto-optical super-surface isolator structures based on InSb magneto-optical materials were proposed for the first time.The transmission characteristics and device structure parameters of these two devices and the influence of external magnetic field strength on isolation were simulated and analyzed.The results show that the isolation of the device is as high as 40dB at a frequency of 0.68 THz.At the same time,the response of the magneto-optical super-surface resonance peak to the external magnetic field can be used to sense the magnetic field intensity.In addition,we have also conducted in-depth research on the optical and magneto-optical properties of InSb materials in the terahertz band and compared them with previous related literature.3.A terahertz optical pump modulator based on molybdenum disulfide nanocrystals was designed,processed,and experimentally studied.With a low pump power density?0.24 W/cm2?irradiating from a 532 nm continuous laser,the modulator can achieve broadband amplitude modulation depth up to 75%for terahertz waves.By comparing with pure silicon wafers,we discovered the“catalytic”effect on photogenerated carriers in silicon-based molybdenum disulfide nanocrystals.That is,the heterostructure of molybdenum disulfide and silicon enables molybdenum disulfide to catalyze more carriers on the silicon surface.In recent years,research on THz sources and detectors has gradually become mature.The terahertz imaging system and the terahertz communication system have gradually become the focus of THz technology.