  We describe a method that enables free-standing whispering-gallery-mode
microresonators, and report spectral tuning of photonic molecules formed by
coupled free and on-chip resonators with different geometries and materials. We
study direct coupling via evanescent fields of free silica microtoroids and
microspheres with on-chip polymer coated silica microtoroids. We demonstrate
thermal tuning of resonance modes to achieve maximal spectral overlap, mode
splitting induced by direct coupling, and the effects of distance between the
resonators on the splitting spectra.
