Square-lattice photonic band-gap single-cell laser operating in the lowest-order whispering gallery mode

Square-lattice photonic band-gap lasers are realized at room temperature from single-cell photonic crystal slab microcavities fabricated in InGaAsP quantum-well materials emitting at 1.5 μm. This single-cell photonic band-gap laser operates in a class of two-dimensional mode to be classified as the smallest possible whispering gallery mode with genuine energy null at the center. The low-loss nondegenerate mode with modal volume of 0.1 (λ/2)³ demonstrates a spectrometer-limited below-threshold quality factor >2000 and a theoretical quality factor >10000. The other class of photonic crystal lasers is also observed outside the photonic band gap of the square lattice, operating in the dipole mode.