  This work takes inspiration from chemistry where the spectral characteristics
of the molecules are determined by hybridization of electronic states evolving
from the individual atomic orbitals. Based on analogy between quantum mechanics
and the classical electrodynamics, we sorted dielectric microspheres with
almost identical positions of their whispering gallery mode (WGM) resonances.
Using these microspheres as classical photonic atoms, we assembled them in a
wide range of structures including linear chains and planar photonic molecules.
We studied WGM hybridization effects in such structures using side coupling by
tapered microfibers as well as finite difference time domain modeling. We
demonstrated that the patterns of WGM spectral splitting are representative of
the symmetry, number of constituting atoms and topology of the photonic
molecules which in principle can be viewed as "spectral signatures" of various
molecules. We also show new ways of controlling WGM coupling constants in such
molecules. Excellent agreement was found between measured transmission spectra
and spectral signatures of photonic molecules predicted by simulation.
