| Electromagnetically induced transparency（EIT）,known as a unique quantum effect in three-level atomic systems which arises by the destructive interference of two different transition pathways,can induce a sharp transparency window within a wide absorption profile.The frequency selective characteristic and slow light property of the EIT make it show great potentials for applications in optical information storage,sensing,nonlinear effect and so on.Unfortunately,the scathing experimental requirements such as cryogenic temperature and high-intensity laser hamper its further researches and practical implementations.Metamaterials attracted intensive research interests for their feasibility to mimic EIT in a wide frequency region from radio frequency to visible regimes at room temperature.An active metamaterial is highly desirable in consideration of practical applications,thus functional devices and materials have been integrated into metamaterials to actively control the EIT effect by executing various external stimuli.Nevertheless,most those strategies not only require complex and expensive fabrication techniques,but also bring extra noise and instability due to the energy fluctuation of the external stimuli,which will definitely restrain their implementations in fully integrated design.Moreover,those approaches mainly concentrate on the tunable EIT in one incident light polarization.In this dissertation,we theoretically propose two kinds of metamaterials to actively control the EIT effect in metamaterials only by varying the incident light polarization without introducing external stimuli.We first propose a Z-shaped metal-based metamaterial which contains two horizontal Au bars and a vertical Au bar.Just by varying the incident light polarization,the bright and dark modes are able to be converted to each other,accompanied by a tunable amplitude of the PIT window.Theoretical fittings based on the coupled oscillator model elucidate the underlying physics behind the modulated amplitude of the PIT window when changing the geometrical parameters.We further propose an all-dielectric Si metamaterial,the metamaterial unit cell contains two orthogonal silicon bars and a silicon tetragonal ring.Owing to the extremely low non-radiation and absorption loss of the Si material,a narrowband transparency window with the high transmittance of 99.7% is observed,besides,the Qfactor and the group delay can reach up to 25000 and 36.22 ps separately.Simple by varying the incident light polarization,the different levels of interference effect of two EIT channels account for the polarization modulated EIT with constant Q-factor.Theoretical fittings based on the coupled oscillator model elucidate the underlying physics behind the modulated Q-factor of the EIT window when changing the geometrical parameter.The structure of two metamaterials designed in this dissertation are simple,which is convenient to fabricate.Moreover,our designed metamaterials will provide great potential for designing compact and chip-scale devices like optical switching,slow light devices and sensitive bio-sensing with polarization-enabled controllability. |
