Disorder induced rotational-symmetry breaking to control directionality of whispering gallery modes in circularly symmetric nanowire assembly.

Effect of disorder on the emission directionality of a whispering gallery mode resonator comprising of circularly symmetric nanowire array is investigated using finite-difference time-domain analysis technique. In spite of rotational symmetry breaking, whispering gallery mode-like isotropic emission characteristics are retained by the nanowire array up to a certain degree of spatial disorder. For higher degrees of randomness, Anderson localized resonant modes are obtained with unidirectional emission characteristics, though the beam direction remains unpredictable because of the underlying random-scattering process. This shortcoming is overcome by designing a system of correlated disorder where nanowire spacing is varied gradually along the preferred axis of unidirectionality. This system, in spite of its high degree of disorder, can effectively support high-Q whispering gallery modes with tunable unidirectional emission characteristics.