An apparatus comprising a first portion and a second portion wherein the first portion includes sides shaped to direct a guided electromagnetic planar waveguide mode to a focal region outside of the first portion. The second portion is adjacent the first portion and contains at least a part of the focal region. The first portion and the second portion are structured and arranged to provide a depth of focus adjacent to the focal region. The depth of focus may be in the range of about 300 nm to about 2000 nm.