Patent ID: 6947653

Claim:
A planar lightwave circuit comprising: a) a substrate; b) at least one optical waveguide core; c) an undercladding formed over the substrate and under the core; d) at least one feature proximate the core having at least one stress-engineered property to balance stress and therefore minimize birefringence affecting the core, wherein the one feature comprises an overcladding layer formed over the core, and doped to balance stress affecting the core wherein the overcladding is doped to have a coefficient of thermal expansion approximately matched to that of the substrate to thereby symmetrically distribute stress in the undercladding between the overcladding and the substrate, and therefore away from the core; and e) a protective passivation layer comprising silicon nitride formed over the core and the feature, the passivation layer having a coefficient of thermal expansion approximately matched to that of the overcladding such that it is substantially non-interfering with the balanced stress affecting the core provided by the overcladding.