An adiabatic elliptical optical coupler device is provided comprising: a substrate having an edge; a first waveguide on the substrate, the first waveguide comprising a constant-width region and a tapered region terminating at the edge of the substrate, the tapered region having a smaller width at the edge than at the constant-width region; and, a pair of second waveguides on the substrate, and located on either side of the tapered region, each of the pair of the second waveguides terminating at the edge at a first end and extending to a second end adjacent the constant-width region, and distal the first end; at least a portion of each of the pair of second waveguides being tapered, and optically coupled to the first waveguide to transition a mode of an optical signal in the first waveguide from an elliptical mode at the edge towards a confined mode.