A method of forming an optical structure includes forming a circular
grating resonator (CGR) on a substrate, the CGR including a center disc
and a plurality of concentric rings spaced from one another; forming an
input planar waveguide and an output planar waveguide on the substrate,
the input planar waveguide and the output planar waveguide optically
coupled to the CGR; and forming an electrode pair on the substrate,
coplanar with the input and output planar waveguides, the electrode pair
comprising an electrically conductive material in contact with opposing
ends of the center disc of the CGR so as to render the CGR capable of
electro-optical control.