Large Phase-by-Phase Modulations in Atomic Interfaces

Phase-resonant closed-loop optical transitions can be engineered to achieve broadly tunable light phase shifts. Such a novel phase-by-phase control mechanism does not require a cavity and is illustrated here for an atomic interface where a classical light pulse undergoes radian level phase modulations all-optically controllable over a few micron scale. It works even at low intensities and hence may be relevant to new applications of all-optical weak-light signal processing.