The Research On Characteristics Of Optical-control Two-wavelength Terahertz Modulator Based On Photonic Crystal

Nowadays, in the times of information explosion, the demand for bandwidth in data communication is growing rapidly. The radio frequency resource which covers the spectrum window below 300GHz has been exhausted, so the Terahertz range (100GHz ~ 10THz) is the last remaining frequency gap. And the trend of applying it to the future wireless communications to solve the problem of high-speed, ultra-broadband wireless access connection is inevitable. As a key element in future terahertz wireless communication systems, THz wave modulator is attracting extensive investigations among scholars domestic and abroad. Meanwhile, as a new kind of material, the photonic crystal is widely used to fabricate modulators, switches, filters and other functional devices in optical communication systems. The combination of THz technology and photonic crystal (PC) technology provides a new approach to designing the novel THz wave modulator. The study on the THz wave modulator will further promote the development of the terahertz communication technology.At present,most of the THz wave modulators based on photonic crystals only can achieve the modulation of THz wave with one wavelength,and most of these modulators use materials with slow response time,such as liquid crystal.These limit the applications of the THz wave in the high-speed communication system.To meet the need of high-speed,ultra-wideband THz wave communication system development,so that the THz wave modulator with high modulation rate,low insertion loss,and can achieve two wavelength modulation,this paper presents a new type of optical-control two-wavelength THz modulator based on nonlinear photonic crystal.It works in the teraherz band and has practical values.This paper firstly describes the mechanisms of modulating the on-off state of the THz wave by using the PC,especially discussing the realization of defect-mode-shift or defect-mode-change mechanisms by PC. Then designing and discussing the material as well as the structure of PC, finally it is found that the side-coupled structure with the combination of point defects and line defects has the better modulation performance. On the basis of the structural design, and by introducing a new kind of optical-control nonlinear material GaAs which has the rapid nonlinear response time, two kinds of THz modulator on the mechanism of defect-mode-change PCs which respectively contain a point defect and an ellipse defect were designed. Their steady field distribution,time-domain steady-response,extinction ratio,modulation rate and other properties were simulated.To meet the need of multi-channel THz communication, this paper designs a novel optical-control two-wavelength terahertz modulator.Simulation results show that a PC with a point defect and an ellipse defect can modulate two THz waves,and the distance between them on the modulator has an impact on its performance. In the end, based on the features of this THz wave modulator, its applications and prospects in future THz wireless communication systems are briefly discussed.