Research And Application Of Long-period Grating Couplers

All-optical buffer can be used in packet buffer in the optical domain, and has become the important supporting device in the evolution of next generation intelligent optical networks. As a key component in wavelength division multiplexing, grating coupler have a major impact on the performance of the whole all-optical packet switching network.Supporting by the National Natural Science Foundation "Novel all-optical light control dynamic buffer shaper", the article researches the coupling characteristics of a single long period grating and the filter characteristics of two paralleled long period grating coupling systematically. An innovative complex modulation of long-period grating coupler theory is proposed, the filter characteristics of the coupler is analyzed, and the new all-optical buffer based on complex modulation of a long-period grating is designed. The buffer with the advantages of simple structure and low cost can achieve the storage, duplication and extract of light, and can be used for memory cell and pulse retiming. The main content of this paper includes:the progress of long-period gratings, coupling characteristics of LPGs, researches on two paralleled LPG coupler and LPGs coupler guided by assisted complex modulation.The main jobs of this article are as follows:(1) Based on Coupled-mode theory, the detailed coupling characteristics between coring mode and single cladding mode of long-period grating is analyzed via three layer-fiber grating model, focusing on analysis of the number of cycles and the coupling grating depth on the impact of the transmission spectrum.(2) The solution method of parameters when mode-coupling between fundamental mode and cladding mode of LPG happens is proposed, such as effective refractive index of core and cladding mode, coupling constants, and propagation constant of cladding mode. The transmission spectrum of LPG from core fundamental mode to odd cladding mode of first-order is simulated. The effects of parameters including the external environment, the radius of cladding and the grating length on the filter characteristics of a single LPG are simulated and analyzed.(3) The conditions in two parallel LPGs for achieving a100%coupling efficiency with different offset distance is analyzed, and the characteristics of coupling is simulated. (4) A theory of complex modulation of long-period grating coupler is proposed, and the coupled mode equations under complex modulation situation is derived, the spectrum with different modulation ratio and input signal is simulated and discussed. The feature of the coupler that can realize the storage, duplication and extract of light is simulated, and the application in memory cell and pulse retiming is researched.(5) A novel all-optical buffer based on complex modulation of a long-period grating is proposed, and its working mechanism is analyzed. The buffer may have important theoretical significance in the solution to the current network congestion and costs reduction of network construction.