Reducing polarization dependent loss caused by polarization dependent wavelength shift using core over-etch for planar lightwave circuit fabrication

Abstract

A method of making a polarization insensitive optical waveguide structure. An optical core layer is formed on a substrate, wherein the optical core layer has a higher refractive index than the substrate. A mask is formed over the optical core layer. The unmasked areas of the optical core layer are then over-etched to define the core, wherein the over-etching removes the unmasked area of the optical core layer and a portion of the substrate disposed beneath the unmasked area, and defines the optical core. The mask is subsequently removed from the optical core. A cladding layer is then formed over the optical core and the substrate, the cladding layer having a lower refractive index than the optical core, to form a polarization insensitive optical waveguide structure. The amount of over-etching can be controlled to control an amount of substrate disposed beneath the unmasked area of the optical core layer that is removed. The amount of substrate removed, in turn, controls the polarization sensitivity of the optical waveguide structure. The amount of the portion of the substrate removed during the over-etching can be determined to minimize the polarization dependent wavelength shift and the polarization dependent loss of the optical waveguide structure. The amount of the portion of the substrate removed during the over-etching can be determined in accordance with a blanket stress of the cladding layer. The over-etching can be within a range between 7.5 percent and 30 percent.