Research On Spectral Dispersion Devices Based On Two-Dimensional Photonic Crystals

Photonic crystal is an artificial dielectric material having a periodic arrangement structure,and has a lattice structure such as a triangle,a square,and an oblique square depending on the arrangement.The periodic structure of the photonic crystal and the resulting change in refractive index law have a forbidden effect on photons of a specific wavelength or band,thereby forming a photonic band gap,which makes the photonic crystal have special dispersion characteristics and transmission characteristics.Such as superprism effect,self-collimation phenomenon.Based on these characteristics,one can use photonic crystals to better control the transmission and scattering of light at a microscopic scale.Therefore,in the development history of just over 30 years,photonic crystal as a new material technology has always been a research hot spot in integrated optics,and has important application value in promoting the miniaturization and integration of integrated photonic circuits.The dispersion characteristics of photonic crystals have attracted researchers to apply to spectroscopic device design,but in the applications,there are two main problems:how to reduce the unnecessary divergence of the beam propagating in the photonic crystal and how to maximize the dispersion angle of photonic crystal.In order to solve these problems,we have studied photonic crystals from the following aspects.First,the dispersion characteristics and transmission characteristics of two-dimensional photonic crystals are studied.We use the plane wave expansion method to calculate the energy band frequency of the photonic crystal structure.and use the equal frequency curve to examine the transmission characteristics of the photonic crystal,and further study the influence of lattice constant.lattice structure and incident condition on the dispersion effect by means of the dispersion performance parameter.The inverted region vector brillouin region selects the appropriate region to achieve the design goal of high-collimation and strong dispersion.Through theoretical calculation and simulation analysis of beam dispersion in different lattice structures,it is found that photonic crystals with two-dimensional oblique lattice structure have strong dispersion characteristics,and can separate beams with different wavelength at the same incident angle.So in this paper,we choose two-dimensional oblique lattice structure to achieve spectral function.Secondly,the focusing characteristics of the Luneburg lens are studied.The Luneburg lens is a medium sphere with a gradual distribution of refractive index.When a plane wave is incident on the Luneburg lens.the beam is refracted and focused on the surface of the lens.The beam incident at different ansles is different at the focal point of the surface of the lens.Based on the focusing characteristics of the structure,a two-dimensional planar Luneburg lens structure is realized by two-dimensional gradient photonic crystal structure,and applied to the spectroscopic structure design.The Luneburg lens combines with a two-dimensional rhombic lattice to achieve different wavelength splitting in the rhombic lattice,re-converses the diverging beams in the lens structure.reducing unnecessary diversence during beam propasation,and achieving size optimization.We use the finite difference time domain method to analyze the efficiency of the designed structure and optimize the structure by several methods.In this paper,a two-dimensional photonic crystal structure-based WDM device is designed in combination with a uniform and gradual two-dimensional photonic crystal structure.The angular dispersion and focus of the beam are achieved,and the wavelength selection function is completed.The structure is simple.The advantages of small size,easy integration,etc.,have good application prospects in intetgrated photonic devices and optical communication.