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

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