| Metamaterials are materials that have electromagnetic properties purposefully designed.They can effectively manipulate electromagnetic waves on a subwavelength scale to break through the constraints of the diffraction limit,which open up a new path for large-scale integrated photonics devices.Electromagnetically induced transparency like(EIT-like)based on metamaterials cannot be limited by the harsh experimental conditions required for EIT-like in atomic systems,where the transparent window can be actively controlled employing optical control,temperature control,and electronic control.This paper focuses on the research of EIT-like terahertz metamaterials.Through the realization of EIT-like by bright mode and dark mode metamaterials,an adjustable EIT-like terahertz graphene metamaterial is designed,where the electromagnetic characteristics of the device and its performance in refractive index sensor,slow light,and modulator are simulated and analyzed.The main contents are as follows:(1)A tunable EIT-like constant frequency terahertz metamaterial device based on graphene carrier doping is designed,which is composed of two horizontally symmetrical single-layer graphene micro-rings and a vertical single-layer graphene micro-strip.An EIT-like window is observed in the transmission spectrum where the incident wave electric field polarized in the y direction.By changing the carrier mobility of graphene,the amplitude of the transparent window can be adjusted without changing the position of the EIT-like window.The physical mechanism of the EIT-like effect is explained by electric field distribution in the z direction and a three-level atomic system.The theoretical fitting results based on Lorentz harmonic oscillator model and Sparameter inversion method are consistent with the numerical simulation results.In addition,the sensing sensitivity and figure of merit(FOM)of the device are also analyzed.The numerical simulation shows that when the FOM exceeds 8.0,the sensitivity is 1.6 THz/RIU.Finally,with the increase of graphene carrier mobility,the group delay of the device increases,with the highest group delay of 1.49 ps and the group index of 400.(2)A constant frequency reconfigurable terahertz metamaterial based on tunable electromagnetically induced transparency is designed.The EIT-like transparent window doesn't vary with the Fermi level.This structure was composed of two singlelayer graphene resonators,namely,the left double graphene rings and the right double graphene rings.An evident EIT-like window was caused by the near-field coupling between bright modes of the two resonators in the transmission spectrum,in which amplitude over 0.8 was acquired at 1.98 THz.By separately reconfiguring the Fermi levels of the two bright mode resonators with the applied voltage,the EIT-like phenomenon,the amplitude of the transparent window,and the group delay can be actively adjusted while the transmission peak position of the EIT-like window remains unchanged.It is worth noting that the transparent window is fully modulated without changing its position,and the maximum modulation depth reaches 78%.In addition,since the total graphene area is effectively reduced in the proposed structure,the estimated modulation speed is also significantly improved to 9.2MHz.Compared with other terahertz metamaterial devices,the modulation speed of this structure can reach higher performance when the EIT-like window position remains unchanged.Furthermore,double EIT-like can be realized by placing a single graphene microstrip in the middle of the four rings.When only the fermi level of graphene microstrip is changed,the amplitude of the double transparent window can be adjusted and the modulation speed can be improved,up to 182.9MHz.This study provides an alternative method for the development of constant frequency reconfigurable modulation terahertz metamaterial devices(such as optical switches and modulators),as well as a potential way for the miniaturization of terahertz devices. |
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