Subwavelength Metallic Gratings Transmission For Broadband Terahertz Waves

Terahertz wave is defined as the frequency band between 1011 Hz and 1013 Hz.Even though people have spent a lot of time on the electromagnetic waves in past years,as the limitation of the terahertz sources and detection means,the frequency band between infrared and microwave is still nearly blank for scientists.In the last two decades,people come to realize that terahertz waves have very good prospects in many regions such as biological detection,military and communication technology.So far compared with optical,infrared,microwave and other common frequency band,relevant research about materials and devices in terahertz waves are still weak,which limits the applications of terahertz technology.In recent years,the developments of metamaterials and plasmonics provide a new way to study materials and devices of terahertz waves.In this paper,we have theoretically and experimentally investigated the transmission for terahertz waves in subwavelength metal gratings,and achieve the innovative results as follow:First,we reveal the broadband transmission characteristics in subwavelength metal gratings for terahertz waves and demonstrate this phenomenon comes from nonresonant effect.Both the experiments and simulations show that when the transverse magnetic polarized terahertz waves incident with optimal angle,the subwavelength metal periodic gratings will achieve broadband high transmission stage at the wavelength larger than the first order Wood's anomalies.Then,through the analysis of electric field distribution,we demonstrate that the broadband high transmission comes from nonresonant effect.Also we design an oblique metal grating and confirm that this structure can retain broadband high transmission with perpendicular incident.Second,we show the broadband transmission in quasi-periodic and disordered subwavelength metal gratings.As the influence of Wood's anomalies,when the transverse magnetic polarized terahertz waves incident on the subwavelength periodic metal gratings with optimal angle,a large transmission valley will appear at the wavelength of the first order Wood' anomalies which block to widen the broadband transmission stage further.Our investigations show that quasi-periodic and disordered structures can effectively weaken and even eliminate Wood's anomalies,which are the diffraction-related characters of periodic gratings.Consequently,both the transparence bandwidth and transmission efficiency are significantly increased due to the structural aperiodicity.Experimental measurements reasonably agree with both analytical analysis and numerical simulations.The character of broadband transmission is not confined to plane wave,through specially designing broadband high transmission phenomenon can also exists in other non-plane light source.We demonstrate theoretically that line source could retain broadband transmission by specially designing structure.In conclusion,this paper investigates both theoretically and experimentally the transmission of subwavelength metal gratings including periodic,quasi-periodic and disordered sequence,and show the broadband transmission in these structures.We find that both the transparence bandwidth and transmission efficiency are significantly increased due to the structural aperiodicity.Through the analysis of electric field distribution,we demonstrate that the broadband high transmission comes from nonresonant effect.We expect that these results would be of potential applications in many fields such as transparent conducting panels and stealth objects.In addition,the observed phenomena may also shed new light on the development of broadband metamaterials,including sonic artificial materials.