Tapered multi-mode interference couplers for high order mode power extraction

Abstract

Tapered 1 × 1 multi-mode interference (MMI) devices are proposed for high order to fundamental modeconversion. Like adiabatic tapers, the device provides a down-tapered image of theinput fundamental mode, while acting as a short taper for higher even-orderedmodes. This is the first tapering scheme capable of near 100% transmission ofthe input fundamental mode, as well as mode conversion for the input higherorder modes. When directly excited by diode lasers, the tapered MMI couplerpresented can convert the fundamental and second-order transverse modes ofdifferent wavelengths into the fundamental mode signals of a single-mode outputwaveguide.