Mode multiplexing and de-multiplexing using few-mode tilted fiber Bragg grating for SDM-WDM transmission system

A novel approach based on few-mode tilted fiber Bragg grating (FM-TFBG) to realize mode conversion, mode multiplexing, mode de-multiplexing and space-division multiplexing (SDM)-wavelength division multiplexing (WDM) simultaneously is proposed and studied theoretically in this paper. In FM-TFBG, forward-propagating core guided modes can be converted to radiated modes when the phase matching condition of fiber waveguide is satisfied. The radiation angles of radiated modes scattered from the fringe plane of FM-TFBG will change with the variation of wavelength and core mode respectively. As launching the incident light onto the cladding of FM-TFBG through the refractive index matching liquid at an optimized angle, radiation-mode can also be coupled to core mode whose properties will also change with variation of wavelength and the angle of the incident light. According to coupled mode theory and our theoretical analysis, we can realize the mode conversion, mode multiplexing, mode de-multiplexing and SDM-WDM based on FM-TFBG which can be used in few-mode multiplexing transmission systems.