Apparatus including a waveguide segment having a cladding that surrounds
an optically-transmissive core extending along a path; a heater in
thermal communication with the waveguide segment along at least a part of
the path; a thermally-conductive substrate; a thermally-conductive base
in fixed alignment with the waveguide segment and the
thermally-conductive substrate, the thermally-conductive base being
discontinuously on the waveguide segment along the path; and a rib in
fixed alignment with the waveguide segment and the thermally-conductive
substrate, the rib transversely extending in a direction away from the
waveguide segment at a point along the path. Process utilizing apparatus
for generating a phase shift in light.