An apparatus includes a core waveguide for directing electromagnetic radiation to a focal point, the core waveguide having a first interface on a first side of a longitudinal axis for directing a first plurality of rays of the electromagnetic radiation to a focal point and a second interface on a second side of the longitudinal axis for directing a second plurality of rays of the electromagnetic radiation to the focal point, wherein the first and second interfaces are shaped such that at the focal point, the second plurality of rays are about 180.degree. out of phase with respect to the first plurality of rays.