Three-dimensional ultra-broadband integrated tapered mode multiplexers

The demonstration of a three-dimensional tapered mode-selective coupler in a photonic chip is reported. This waveguide-based, ultra-broadband mode multiplexer was fabricated using the femtosecond laser direct-write technique in a boro-aluminosilicate glass chip. A three-core coupler has been shown to enable the multiplexing of the LP01, LP and LP spatial modes of a multimode waveguide, across an extremely wide bandwidth exceeding 400 nm, with low loss, high mode extinction ratios and negligible mode crosstalk. Linear cascades of such devices on a single photonic chip have the potential to become a definitive technology in the realization of broadband mode-division multiplexing for increasing optical fiber capacity.