Steering The Temporal And Spatial Characteristics Of Electromagnetic Wave Via Artificial Microstructure Materials And Its Application

Artificial microstructure materials are artificially materials with exotic material properties that may not be found in nature,and its electromagnetic properties can be tuned at will.The realization of artificial microstructure materials not only expands the traditional electromagnetic field,but it led to a novel technology and method to steer the electromagnetic wave.Surrounding this international hot spot in the electromagnetic fields,the thesis focuses on steering the temporal and spatial characteristics of electromagnetic wave via artificial microstructure materials and its potential applications in the future.Main contents of the thesis are summarized as follows:1.Based on the effective medium theory,we firstly presented the thickness condition under which the corresponding effective electromagnetic parameters of the artificial microstructure materials will be converged.Generally,artificial microstructure materials are often characterized by the effective electromagnetic parameters(EMC).Usually,the EMC can be obtained by utilizing the S-parameter retrieval method;however,the configuration used in the traditional retrieved method mimics the infinite periodic nanostructures irrespective of the number of unit cells.However,most of the fabricated samples at optical wavelengths are only a few layers.This phenomenon led to a widespread controversy,the topic of the controversy is artificial microstructure materials can be described by the effective electromagnetic parameters or not.In order to clarify this controversy,we improved the traditional S-parameters retrieval method.By utilizing the improved method,we will extract the more accurate effective electromagnetic parameters.Furthermore,based on this method,we presented that one wavelength of the propagating wave in the microstructure is the minimum thickness requirement for effectively characterizing a finite thickness microstructure.2.We investigate the effective parameters of the two-dimensional photonic crystal,and we find that photonic crystals in a certain frequency region can indeed mimic not only double-negative but also single-negative metamaterials.Firstly,at the frequency region with negative refractive index,both the effective permeability(εeff)and permittivity(μeff)are negative indeed.Although effective refractive index neff＝-1 can be realized at a certain frequency the εeff and μeff are not equal.This result can be applied to explain the phenomena that the low transmission of the flat-slab images based on the photonic crystal,and this will be useful for us to match the impedance between the flat lens and its background.Secondly,for the photonic crystal within the first band gap,negative effective εeff or negative μeff has been found.And the real part of the εeff(Re(eeff))and μeff(Re(μeff))are split into two parts in the bandgap center,the Re(εeff)is monotonously increasing from negative to positive value,on the contrary,the Re(μeff)is monotonously decreasing from positive to negative value.Utilizing the finite-difference time-domain method,a flat slab imaging for TE waves in the near field has been demonstrated for the photonic crystal with effective negative permittivity that is similar to silver superlens for TM waves.3.We propose a scheme to controllably convert the wave front of an arbitrary incident beam into a helical one by compact transformation slabs,thus enabling the output beam to carry a desirable orbital angular momentum(OAM).First,based on transformation optics,a three-dimensional(3D)phase transformation between any two wave fronts by flat transformation media is established and then used to mold the wave front of a Gaussian beam into a helical one.Second,3D finite-difference time-domain simulations are performed to confirm the spiraling evolutions of the resultant field and phase,clearly demonstrating the OAM generated.Further theoretical analyses show that the refractive index exhibiting a helical distribution leads to the oppositely spiral phase front and that it is feasible to produce a desirable OAM by generators of the unit OAM.The results not only provide an additional way to manipulate the phase and photo OAM but also reciprocally shed further light on the phase structure of helical beams,which leads to a new means of transformation by a surface.4.We carry out theoretical analysis and experimental study of microstructure’s spatial dispersion to realize flat plug-and-play near-filed low-pass spatial filter.It is predicted theoretically that a one-dimensional photonic crystal with a defect layer has an incident-angle dependent transmittance.Growing a multilayer of the photonic crystal structure on a BK7 glass substrate by means of thermal vacuum evaporation,we have experimentally measured its transmittance at the near infrared wavelength.The measured transmittance would be in good agreement with the theoretical prediction if the influence of random errors in layer thickness resulted from the deposition process is exclude.This method is useful for us to design and fabricate the artificial microstructure materials-based devices.5.We investigate the temporal dispersion characteristics of artificial micro-structure materials.The dispersion-based device can be divided into transmissive-based or reflective-based type.We found that the transmission-type dispersion devices can provide large dispersion,but the losses are greater;the reflection-type dispersion devices have small dispersion,but its loss is almost zero,however,we can make up its small single reflected dispersion by multiple reflections.Furthermore,the compression of chirped pulse by the reflection-based dispersion device is also analyzed,and this method is useful for us to design a new type of compression device.