Wavelength insensitive mode selective coupler based on ultra-wideband resonant effect

We report on an ultra-wideband resonance effect between LP01 mode and LP21 mode in a fused-biconical taper mode selective coupler. The dispersion characteristics of the LP01 and LP21 modes are changed by tapered fibers, and achieved resonance over a large range of over 1000 nm. Based on this effect, we designed and manufactured a super wide-band fused biconical LP21 mode selective coupler, which covers the S+C+L band with an insertion loss flatness of better than 0.17 dB and a minimum insertion loss of 0.16 dB. A broadband and flat mode converter facilitates cost-effective integration of wavelength division multiplexing systems and space division multiplexing systems.