  We investigate the lasing action in coupled multi-row nanopillar waveguides
of periodic or fractal structure using the finite difference time domain (FDTD)
method, coupled to the laser rate equations. Such devices exhibit band
splitting with distinct and controllable supermode formation. We demonstrate
that selective lasing into each of the supermodes is possible. The structure
acts as a microlaser with selectable wavelength. Lasing mode selection is
achieved by means of coaxial injection seeding with a Gaussian signal of
appropriate transverse amplitude and phase profiles. Based on this we propose
the concept of switchable lasing as an alternative to conventional laser tuning
by means of external cavity control.
