an integrated planar waveguide system including at least two primary waveguides for light propagation and coupling , and two or more mirror - imaged symmetrization structures in close proximity to the primary waveguides in order to provide micro - process - equalization during etch , growth , annealing and reflow processes . the primary waveguides are designed to carry light signals . the symmetrization waveguide structures are designed so that all the trenches between primary waveguides are identical to the desired degree . at the same time , the symmetrization structures are designed to have minimal detrimental impact on the optical performance of the coupler .