Use of mesa structures for supporting heaters on an integrated circuit

An optical switch comprising a planar light circuit (PLC), an integrated circuit (IC) and a mesa structure, the PLC comprising a waveguide and being joined to the IC, the mesa structure being interposed between the PLC and a top surface of the IC, a trench being formed in the underside of the PLC and filled with a liquid, the trench intersecting the waveguide at a cross-point disposed above the mesa structure, the mesa structure being disposed above the IC and separated therefrom by a passivation layer, at least top and bottom resistive layers being formed atop the mesa structure and operably connected to metal leads corresponding thereto, the top and bottom resistive layers being separated by an insulating layer disposed therebetween, a first portion of bottom resistive layer not covered by the metal leads having an area larger than a second portion of the top resistive layer not covered by metal leads, the top and bottom resistive layers being configured to heat the liquid in the trench and thereby effect a change in an index of refraction of the liquid in response to electrical current passing through the top and bottom resistive layers, at least portions of the mesa structure projecting upwardly above the passivation layer and the top surface of the IC, wherein at least a portion of the bottom resistive layer is conformably disposed above the projecting portion of the mesa and thereby placed within close proximity to the liquid in the trench to effect efficient heating of the liquid.