基于亚波长光栅的负折射光子晶体成像研究

Imaging of photonic crystal with negative refraction based on subwavelength grating

理论上折射率为-1的平板超透镜可以实现完美成像,但等效折射率为-1的光子晶体结构,不满足介电常数ε=-1和磁导率μ=-1的条件,光子晶体与自由空间阻抗不匹配,某些角度的入射光与光子晶体内布洛赫波不能耦合,致使该空间频率光信息丢失,限制了光子晶体成像分辨率。为了提高成像分辨率,在光子晶体表面设置亚波长光栅结构,利用光栅的增透减反和波矢匹配作用,提高光子晶体对入射光的耦合效率。通过调整光栅周期,使更多高空间频率分量参与成像,同时抑制低频分量的传输。设置亚波长光栅结构后,光子晶体成像分辨率由597 lp/mm提高到了850 lp/mm,突破了衍射极限。

The super lens with refractive index of-1 can achieve perfect imaging theoretically, but the photonic crystal with equivalent refractive index of-1 does not meet the conditions of permittivity ε=-1 and permeability μ=-1. The impedance of the photonic crystal does not match the free space, and the incident light at some angles cannot be coupled with the Bloch wave in the photonic crystal, resulting in the loss of these light information. It limits the imaging resolution. In order to improve the imaging resolution, a subwavelength grating is set on the surfaces of the photonic crystal and the coupling efficiency of the incident light to photonic crystal is improved. By adjusting the grating period, high spatial frequency components are involved in the imaging and the transmission of low frequency components is suppressed. With the subwavelength grating set on the surfaces, the imaging resolution of photonic crystal increases from 597 lp/mm to 850 lp/mm,which breaks through the diffraction limit.