Methods and apparatus for optical coupler

An optical coupler having at most two optical waveguides, the optical coupler comprising:

• a substrate;
• a cladding layer supported above the substrate, the cladding layer and the substrate defining a facet;
• a first optical waveguide arranged within the cladding layer, the first optical waveguide configured with a first tapering angle;
• and
• a second optical waveguide arranged substantially parallel to the first optical waveguide and spaced apart from the first optical waveguide by a transverse distance at the facet, the second optical waveguide comprising a first tapered portion with an increasing tapering angle, the increasing angle is less than the first tapering angle, and a second tapered portion with a decreasing tapering angle, thereby defining a first operating region and a second operating region,
• wherein a coupled mode formed between the first optical waveguide and the second optical waveguide from an incoming optical signal is transmitted along the first and the second optical waveguides, the confinement of the coupled mode increases in the first operating region, and the coupled mode is transformed onto the first optical waveguide, and gradually decoupled from the second optical waveguide over the second operating region.