Photonic flat-band laser.

Flat-band photonic lattices, i.e., arrays of waveguides or resonators displaying a flat Bloch band, offer new routes for light trapping and distortion-free imaging. Here it is shown that flat-band lattices can show stable and cooperative laser emission when optical gain is supplied to the system, despite the large degree of degeneracy of flat-band supermodes. By considering a quasi one-dimensional rhombic lattice of coupled semiconductor microrings, selective pumping of the outer sublattices can induce cooperative lasing in a supermode of the flat band.