A thermo-optical device may use a heater to tune an optical device such as an optical switch, a Mach-Zehnder interferometer, or a variable optical attenuator, to mention a few examples. In some embodiments, polarization-dependent losses caused by the heating and power efficiency may be improved by defining a clad core including an optical core and cladding material on a substrate and covering the clad core on three sides with a heater.