Method to produce stress-free optical waveguides to reduce stress-induced birefringence in planar lightwave circuit (PLC) devices

A method of forming a waveguide comprising the following steps. A structure is provided. An underclad layer is formed over the structure and a core layer is formed over the underclad layer. Patterning: the core layer to form the waveguide; and partially into the underclad layer, forming an overetched underclad layer having a projection underneath the waveguide. The waveguide having stress gradients and the overetched underclad layer having stress gradients.