Patent attributes
An improved method is provided for fabricating a polarisation rotator in a rib waveguide having a propagation axis and opposite side walls. The method includes etching a pit in the substrate surface to form a recess in one of the side walls of the waveguide, during formation of the waveguide on the substrate surface, so as to provide an asymmetric waveguide section for imparting polarisation rotation to radiation propagated along the propagation axis. Preferably the pit is formed by a wet etching step forming an upper side surface within the recess that is inclined relative the waveguide side walls, and the waveguide side walls are formed by a dry etching step to extend perpendicularly to the substrate surface. In addition the dry etching step forms a lower side surface adjoining the upper side surface within the recess and tilted relative to the upper side surface. Such a method is significantly simplified as compared with prior art production methods, as well as providing greater yield and more predictable device performance since mask alignment errors no longer affect the design parameters of the rotator.
