Research On Sub-wavelength Structured Tunable Devices In Terahertzregion

Terahertz radiation is an internationally recognized band with many excellent features, which located in the transition zone of macro electronics and micro photonics.Terahertz science and technology as an emerging discipline is constituted by the generation, transmission, control,detection and application of terahertz radiation.Terahertz science and technology has become one of the international academic frontiers due to the potential application for the short-range high-speed broadband communications, super-resolution-guided weapons, biological sensing, medical imaging, detection of material properties and safety inspection. In recent years, the application of terahertz radiation has been an unprecedented development with the rapid progress of terahertz generation and detection technology. However, the manipulation of terahertz radiation has become relatively backward, and the functional materials and tunable devices are very scarce in terahertz region.As a key part of the terahertz systems, the tunable function devices are closely related to the progress of terahertz technology. Therefore, development of tunable functional devices with high-speed, low-loss, wide bandwidth and large modulation depth has become a key issue in the field of terahertz scientific research.In this thesis, firstly,the development of terahertz technologyand tunable devices is reviewed.Secondly, the terahertz tunable devices are categorized by the technique which is employed to modulate the terahertz waves, and then the modulation mechanism and research results are introduced. Finally, we introduce our research results in four parts:1. Based on the electromagnetic response variable characteristics of InSb,we proposed a subwavelength B-shaped metallic hole arraysterahertz tunable filter with an embedded InSb semiconductor bar.The transmissions, working frequency andelectric energy density distributions of the filter were calculated with the finite-difference time domain method at various temperatures. The results show that the narrowband Terahertz wave with a transmittance peak more than80%can be selected in the frequency range from0.74THz to2.02THz by controlling the temperature of device. As the key geometric parameters of the terahertz filter, the thickness of the filter and the width of the InSb bar can significantly affect the filtering performance, and we defined the optimal values of these two parameters.2. A thermally terahertz modulatorwith phase transition of VO2film was designed and theoretically investigated. The transmission of the modulator and electric energy density distributions on the device were calculated with the finite-difference time domain method at various temperatures. A modulation depth of74.7%is obtained when the temperature is increased from50to80℃.3. Based on the optical phase transition of VO2film, we designed and fabricatedtwo types of terahertz modulators.The transmission spectra of modulators were measured by the terahertz time-domain spectroscopy system. By comparing the modulation characteristics of both modulators with moderate optical pumping,we found that the VO2film in metallic phase beneath the metallic hole arrays can effectively affect the transmissionproperties of golden hole arrays, and this phenomenon can increase the modulation depth of modulator.4. A thermally tunable terahertz metamaterial absorber consisting of a metal-dielectric-metal structure with embedded InSb was designed and simulated. The absorptions of the absorberwere calculated with the finite-difference time domain method at various temperatures.The simulated results show that the absorber has a strong absorption of nearly90%with a bandwidth of bellow60GHz and the absorption frequency can be dynamically tuned from0.82to1.02THz.