  Employing counterdiabatic shortcut to adiabaticity (STA), we design shorter
and robust achromatic two- and three- waveguide couplers. We assume that the
phase mismatch between the waveguides has a sign flip at maximum coupling,
while the coupling between the waveguides has a smooth spatial shape. We show
that the presented coupler operates as a complete achromatic optical switch for
two coupled waveguides and as an equal superposition beam splitter for three
coupled waveguides. An important feature of our devices is that they do not
require larger coupling strength as compared to previous designs, which make
them easier to realize in an experimental setting. Additionally, we show that
the presented waveguide couplers operate at a shorter device length and are
robust against variations in the coupling strength and the phase mismatch.
