| abstract |
Apparatus and methods can include an optical waveguide coupled to a photonic crystal comprising a dielectric material, the photonic crystal located on an exterior surface of the optical waveguide and comprising a first surface including a first array of periodic features on or within the dielectric material, the array extending in at least two dimensions and including an effective dielectric permittivity different from the surrounding dielectric material. In an example, the periodic features include a specified lattice constant, the periodic features configured to extract a portion of propagating optical energy from the waveguide through the photonic crystal, the portion determined at least in part by the specified lattice constant. |