Three-dimensional mode multiplexer based on adiabatic-tapered waveguides forming vertical directional couplers over C + L band and beyond

Abstract

We present a mode multiplexer based on vertical directional couplers that are formed by adiabatic-tapered waveguides. We design and fabricate the device via the micro-fabrication processing to (de)multiplex the E11, E21, and E12 modes from the few-mode bus waveguide. Our experimental device shows a coupling ratio higher than 98.6% and 97.0% for the E21 and E12 modes, respectively, over the C + L band and beyond. The modal cross talk of this device can be lower than –17.1 dB, –18.4 dB, and –15.1 dB caused by the unintended E11, E21, and E12 modes, respectively. This mode multiplexer can work over a broader wavelength range with weak polarization sensitivity, which could be used in the mode-division-multiplexing systems where mode (de)multiplexing is required in the expanded communication wavelength window other than the C-band.