Patent ID: 7099548

Claim:
A planar optical waveguide for guiding optical signals comprising: a substrate; a lower cladding layer supported on the substrate; a waveguide core supported on the lower cladding material having four side surfaces, the core having a refractive index (RI core) and a coefficient of thermal expansion (CTE core); an upper cladding layer having a refractive index (RI clad) unequal to RI core and a birefringence B; and a CTE matching material disposed between the waveguide core and the upper cladding layer contacting at least one surface of the waveguide core where an overlap integral between a mode profile transmitted therethrough and the cladding birefringence B is largest, the CTE matching material having a refractive index (RI material) substantially equal to RI clad and a coefficient of thermal expansion (CTE material) substantially equal to CTE core.