Some Studies On Properties And Applications Of Negative Refractive Media

On entering another medium from one medium, light usually refracts with a positive angle. However, negative refractive media (NRM) may produce negative refraction, i.e. light refracts with a negative angle. Except double negative (DNG) media, it is well known that photonic crystals (PCs) can also support negative refraction. And recently it has been suggested that chiral media could also support negative refraction under certain conditions. NRM open new avenues for achieving extraordinary physical properties and functionality unattainable with usual media. Subwavelength imaging beating the diffraction limit is the most famous application of NRM.The work of this paper on the properties and applications of various NRM (including DNG media, chiral media of negative refraction, and PCs of negative refraction) is list as:The generalized Lorenz-Mie theory and multiple-scattering method are combinded to investigate the local fields of one or two neighboring homogeneous spheres of DNG medium illuminated by a Gaussian beam. The local fields of spheres of DNG medium have their unique characteristics whenever at nonresonance or resonance.Media of negative refractive index can be used to make a one-dimensional (1D) subwavelength resonator and a two-dimensional (2D) open resonator, which result from a simple ray analysis that due to the negative refractive index, the optical path in the medium of negative refractive index may cancel the optical path in the medium of positive refractive index (ray conjecture). In this paper, it is shown that the straightforward ray analysis can not provide the complete picture for the resonance and the wave field theory should be used. The ID subwavelength resonator meets the ray conjecture only when the impedances of the layer of DNG medium and the layer of usual medium in the resonator are matched, and the resonator is rather unstable. A wavelength-sized 2D open resonator is constructed with two squares of DNG medium positioned diagonally, and the resonance is calculated with the finite-difference time-domain method.Study is given for the focusing of a slab of chiral medium supporting negative refraction for the first time. It is shown that under certain conditions, the slab can be used as a perfect lens for left or right circularly polarized waves (depending on the material). And imperfectly focusing is also studied numerically.Study is given for the surface polaritons related to a chiral medium which supports negative refraction for the first time. The conditions for the existence of surface polariton modes on the surface of a half-space or slab of such a chiral medium are studied. Numerical results for surface polariton modes are given for three typical chiral slabs. The net energy flux of the guided waves related to these surface polaritons may be forward, backward or even be stopped. Surface polaritons of such a chiral slab can be used to slow down the light effectively.An open wedge resonator (between two perfectly conducting metal plates) is suggested, half of which is filled up with some PC of negative refractive index. The resonance mechanism of the open wedge resonator is explained. Two typical modes are studied with the finite element method. Electromagnetic field in a resonator with a smaller wedge angle can be more tightly confined, and thus we may obatin a quality factor much higher than that of an open wedge resonator with a bigger wedge angle. A potential application of this novel resonator as a gas sensor is also studied.Complex triangular lattices with two or three dielectric cylinders in air per unit cell can be used to get PCs with an isotropic effective refractive index equal to -1. It is studied for the subwavelength imaging of a slab made of the PC with two dielectric cylinders in air per unit cell. And an open resonator is designed with the same PC, which may have a quality factor higher than 3000. With the plane-wave-based transfer-matrix method, investigation is given for the influence of the radius of the cylinders on the interface of a semi-infinite PC on the transmittance. The obtained result is used to decide an interface with low reflection for the slab lens and open cavity.