Study Of The Far-Infrared Filters Based On The Electromagnetically Induced Transparent Effect

Far-infrared and terahertz(THz)devices play an important role in the fields of national defense and security inspection.Based on the theory of electromagnetically induced transparency(EIT),a far-infrared filter with asymmetric triangle structures were prepared by using semiconductor technology.EIT effect in triangle structures results from the electromagnetic coupling between the excited bright mode by the side of triangle structures and dark mode by the gap/side of triangle structures.The experimental results showed the stronger of the electromagnetic coupling,the more significance of the EIT effect in structures.The distributions of electric fields and surface current density simulated by finite difference time domain further indicated that the EIT effect stemmed from the coupling between the two different excited modes.The simulation results showed a good agreement with the experiments.The main contents are listed as follow:1.The different sizes triangular structures were simulated based on the finite difference time domain method.The transmission of the terahertz wave and the origin of EIT effect in the triangular structure were studied.Especially,the influence of the asymmetry caused by the triangular gap and central axis on EIT effect was studied.The LC values were equivalent to the triangular filter structure by the Advanced Design System,which further verified the validity and accuracy of the experimental results.2.The filters with asymmetric triangular structure were fabricated based on semiconductor technology and the double-layered photoresist technology.The metal film was deposited on high resistance silicon by the high vacuum magnetron sputtering.THz transmission properties were characterized using a THz time-domain spectrometer.The influence of THz E-field direction on the THz transmittance of the device was studied.3.The THz transmission spectra displayed that the resonance frequency shifted to the low frequency with the increase of asymmetric distance ?.The EIT effect was appeared in the investigated frequency range.The distributions of E-field and current density indicated that the EIT effect was resulted from the enhanced coupling between the bright and the dark modes in the asymmetric triangle structures.The research based on experiments and theories are helpful to understand the physical modulation mechanism of terahertz devices with asymmetric structures.At the same time,a rich experimental data in the research of terahertz passive devices are accumulated in the present studies.