Characteristics Of Modes For Chiral Photonic Crystal Fiber

Since single-mode single-core silica-based fibers have approached its physical limit,the novel kinds of fibers on the basic of new materials,new structures and new mechanism become inevitable candidates to further increase the transmission capacity of information through a single fiber.As a type of fiber with new structure,photonic crystal fibers(PCFs)possess some characteristics such as the flexibility for design,controllable birefringence,dispersion and nonlinearity,which have been found important applications in optical communication,optical sensoring,laser and optical integration and so on.As a kind of electromagnetic coupled material,chiral material has different responses to the left-/right-handed circularly polarized light(LCPL/RCPL),demonstrating the optical activity(OA),correspondingly the circular birefringence(CB)and circular dichroism(CD)may occur in it.Currently,there are some researches on theory and experiment for dielectrically chiral fiber and photonic crystal(Ph C),while rare on chiral PCF,especially the PCF with multicore.So it is very important in theory and practice to study the chiral PCF.The main contents are as follows:A modified chiral 2D PWE method is developed,which is suited to investigation of dielectrically chiral 2D PhC and PCF.In this method,the longitudinal field is reasonably ignored,the electromagnetic fields and all the periodic material parameters are expanded in the reciprocal space,and then a set of eigen-equations with chiral terms are built up.Compared to simulated results for 2D Ph C structure by the chiral 3D full-vector PWE method,the achiral PWE method and the achiral finite elements method(FEM),it is proved that this method is a more universal one than conventional 2D PWE method.Under the condition of keeping the same calculation precision,this method have advantage of reducing the computation time and saving the memory.The influences of the propagation constants,structural parameters,chirality strength,and even structural squeeze on the band structures of chiral Ph C in triangular lattice are analyzed.Aimed at a kind of chiral PBG PCFs with elliptically air-core,the influences of the chirality strength and the ellipticity of core are studied on guided mode intensity,polarization and the effective mode index(EMI).It is found a cooperative effect in birefringence and a competitive effect in polarization between the asymmetry of structure and chirality of medium.The effects of lattice constant,radius of holes,chirality,and even structural squeeze on the effective index of refraction for chiral Ph C are examined.For a type of index-guided chiral PCF with the wholely squeezed solid core,the distributions of mode intensity and the polarization,the effective mode index,birefringence and polarization are explored.The interactions between the structural anisotropy and chirality and the wavelength range in which the chirality plays role are investigated.It is revealed that the effect of chirality in the short-wave region is stronger than that in the long-wave region and the effect of asymmetric structure in the long-wave region is stronger than that in the short-wave region.Through the research on the cut-off problem,a design scheme is proposed for chiral PCF possessing super-wide single-circular-polarized single-mode range.The multicore fiber with chiral Ph C structure is presented.The influences of chirality strength,concentrated rate of cores and local structural parameters near the cores are analyzed on the distribution of mode intensity and polarization,the polarization states,the mode effective index of refraction and mode areas for the first 6 modes in chiral PCF with 7 cores.The role of chirality for intensity homogenization and polarization of different cores is mainly examined and the regulation of structural parameters is beneficial to the distribution of light in different cores of guided mode.It is found that the chirality can adjust the intensity distribution and homogenize the intensity among cores with equivalent location.These modes that have the above characteristics become circularly polarized ones,while the other modes with identical intensity in equivalent location cores for achiral case become ordinary elliptically polarized ones.With increase of the effect of chirality,the modes with elliptical polarization states trend to circular polarization.All of these characteristics are helpful for development of novel type of fiber with circular polarization division multiplex(CPDM)and space division multiplex(SDM).