Track changing by use of the phase response of microspheres and resonators

A microsphere or resonator that is side coupled to an incident optical beam induces a phase response in the beam. In the so-called overcoupled regime, the amplitude of the incident beam remains unmodulated, whereas the phase goes through a shift of p at resonance. This shift is insensitive to the details of the coupling geometry or the resonant mode. In conjunction with an interferometer, the phase response can be used to switch the beam between two well-defined outputs, thus offering a robust means of deploying microspheres and other microresonators in practical photonic devices.