Waveguides that include a top cladding layer made of a material having an index of refraction n4; a core bilayer structure, the core bilayer structure including a lower index core layer having an index of refraction n3; and a higher index core layer having an index of refraction n1, wherein the higher index core layer includes TiO2 and one or more than one of Nb2O5, CeO2, Ta2O5, ZrO2, HfO2, Y2O3, Sc2O3, MgO, Al2O3 and SiO2, wherein the lower index core layer is adjacent the higher index core layer; a bottom cladding layer made of a material having an index of refraction n2, wherein the waveguide is configured with the higher index core layer of the core bilayer structure adjacent the top cladding layer and the lower index core layer of the core bilayer structure adjacent the bottom cladding layer, and wherein n4 is less than n3 and n1, and n2 is less than n3 and n1.