Research On Broadband Light Field Polarization Control Based On Chiral Metamaterial

Metamaterials are sub-wavelength artificial materials with special electromagnetic properties.The electromagnetic properties of metamaterials can be controlled by precise design of metamaterial unit structure,and the response of metamaterials can be controlled by structure size.Due to the limited variety of natural materials,the full-band coverage of birefringence and circular dichroism can’t be realized,which greatly limits the research and development of application of polarization control devices.Therefore,polarization control metamaterials have attracted wide attention.In this paper,the polarization control of broadband light field based on chiral metamaterials is studied.Multifunctional broadband polarization conversion metamaterials and broadband polarization selective absorption metamaterials are designed respectively,and the physical mechanism of polarization control and broadband effect is revealed.The main contents of this paper include the following two aspects:Firstly,we propose a multifunctional broadband terahertz polarization conversion metamaterial based on VO₂-graphene chiral composite structure.The function of the metamaterial can be switched between transmission line-to-line polarization conversion and reflection line-to-circular polarization conversion by controlling temperature and applying voltage.At 298K,the metamaterial can realize linear-linear polarization conversion from y-polarization wave to x-polarization wave in 0.39-1.22 THz band.At the same time,by changing the Fermi energy of graphene,the linear polarization conversion angle can be changed from 90°to 45°.When the temperature rises to 358K,the incident linearly polarized wave is reflected into circularly polarized wave.Under this condition,by changing the Fermi energy of graphene,metamaterials can realize the line-to-left circular polarization conversion in the 1.57-2.74 THz band and the line-to-right circular polarization conversion in the 1.13-1.59 THz band.This switchable multifunctional broadband polarization conversion metamaterial can be applied to terahertz polarization integrated devices.Secondly,we propose a broadband selective circularly polarized absorption metamaterial based on chiral structure in mid-infrared band,which can selectively absorb right-hand circularly polarized light and reflect left-hand circularly polarized light.In the wide band range from 3640nm to 4320nm,the metamaterial can achieve an absorptivity of more than 80%,an absorptivity of more than 90%and a relative bandwidth of 17%.Further studies show that this selective absorption effect is due to the interference difference of different polarized light in multiple reflections.The selective circularly polarized absorption metamaterials proposed by us has good broadband effect and circular dichroism,which can be applied to optical filters,nonlinear optical thermal emitters and hot electron collectorsBased on the above research,we have designed multi-functional broadband polarization conversion metamaterials and broadband selective circular polarization absorption metamaterials,respectively,to realize broadband polarization control in terahertz and mid-infrared bands.The physical mechanism of broadband polarization control in different structures has potential applications in optoelectronic integrated devices such as polarization converters,detectors and filters.