An apparatus includes a plasmonic transducer with first and second oppositely disposed outer edges. A waveguide is configured to receive light from a light source, the waveguide have first and second portions that deliver first and second portions of the light to the first and second edges of the plasmonic transducer. The first and second portions are different by at least one of a geometry and a construction to cause a relative phase shift between the first and second portions of the light.