A photonic waveguide structure includes a first photonic waveguide layer located over a substrate. A sidewall cladding layer is located cladding a sidewall, but not covering a top, of the first photonic waveguide layer. A second photonic waveguide layer may be located upon the top of the sidewall cladding layer while contacting, but not straddling, the first photonic waveguide layer. The sidewall cladding layer protects the first photonic waveguide layer from environmental exposure, thus providing enhanced performance of a photonic waveguide structure. A planarizing sidewall cladding layer allows the fabrication of optical chips with multiple layers of lithographically defined devices.