| Photonic crystal is a kind of artificial material with periodic permittivity distribution,which can effectively control the motion of photons.Compared with electronic devices,photonic devices have the advantages of high integration,fast response speed,wide bandwidth and strong anti-interference ability.In modern information systems that require large capacity and high efficiency,photonic devices will gradually replace traditional electronic devices,and then transition to all-optical integration.Photonic crystals are considered one of the most promising schemes to realize all-optical integration,and research on photonic crystals also become a hot spot in the field of integrated photonics and optical communication.With the increasing integration of optical circuits,the interference between adjacent modules or devices in the all-optical integrated chip is becoming more and more serious,even destroying the function of the entire system.An integrated optical system requires a device that can effectively isolate inter-module interference.Circulators are a kind of non-reciprocal multi-port passive devices.In circulators,electromagnetic waves sequentially circulate in the forward direction but prevented in the reverse direction.Circulators can isolate reflected light between adjacent modules or devices,thus reducing interference and improving the stability of large scale integrated optical circuits.According to its unique properties,we can form a complex optical system flexibly with a circulator.Therefore,circulators are also widely used in high-resolution radar,radio astronomy,high-speed data communication systems.5G millimeter wave communication network is coming,while the performance of traditional high-frequency devices can hardly meet the higher requirements.We seek to design high-performance devices through photonic crystals.Here we designed the photonic crystal circulator at the millimeter-wave band of 24~28 GHz.Firstly,based on the theory of electromagnetic theory,the Plane Wave Expansion Method is introduced to calculate the band structure,defect structure and mode field distribution of photonic crystal,as well as the Finite Element Method and the Finite Difference Time Domain method commonly used to simulate electromagnetic filed in devices.Then,we propose a kind of gradient photonic crystal waveguide that can improve the performance of photonic crystal waveguide,and design a circulator based on the gradient photonic crystal waveguide.Considering that photonic crystal waveguides are the basis for designing photonic crystal circuits and devices,we first studied the design of photonic crystal waveguides.The effect of the size of the photonic crystal waveguide on its transmission efficiency is analyzed in a three-dimensional model,and a low-loss photonic crystal waveguide operating in the millimeter-wave band is finally obtained.Based on the designed photonic crystal waveguide,we designed Y-type and double Y-type photonic crystal circulators.The Y-type circulator has a design frequency range of 24~28 GHz and the isolation is better than 20 d B.The double Y-type photonic crystal circulator is in the frequency range of 24.21~28.18 GHz where the isolation better than 20 d B.Finally,we use high precision,low-cost ferrite balls fabricated by compressed air blowing to design photonic crystal circulators.Photonic crystal circulator with a ferrite sphere was developed in the millimeter-wave band.Experiments have measured that the isolation exceeds 15 d B and the insertion loss is less than 1.5 d B in the frequency range of 24-28 GHz.The performance of designed photonic crystal circulator with a ferrite sphere can meet the requirements of actual communication systems.Compared with the traditional grinding ferrite,the processing accuracy of the small-sized ferrite sphere is easy to guarantee,which is more conducive to the application research in the high-frequency band. |
PDF Full Text Request