Multidirectionally distributed feedback photonic crystal lasers

The lasing mode of a two-dimensional (2D) photonic crystal laser with in-plane multidirectionally distributed feedback effect is analyzed theoretically and experimentally. From an investigation of the Bragg diffraction conditions at several points in the photonic band diagram where lasing is expected, we identify a particular Gamma point at which lasing occurs due to the coupling of lightwaves propagating in six equivalent Gamma-X directions and diffraction normal to the substrate surface. In order to investigate the lasing mode in detail, the distribution of the electromagnetic field at the band edges at the Gamma point is calculated, and each band edge is found to have a different field pattern. The lasing characteristics of the 2D photonic crystal laser at the lasing wavelength corresponding to the Gamma point are measured. Single-mode lasing over a broad circular area is observed by microelectroluminescence measurements under pulsed conditions at room temperature. We also demonstrate the correspondence between the measured lasing wavelengths and calculated band edges by comparing the polarization characteristics with the calculated distribution of the electromagnetic field. The results indicate that 2D coherent lasing oscillation does, in fact, occur due to the multidirectional coupling effect in the 2D photonic crystal. From the theoretical calculation, we show that the polarization patterns of the lasers can be controlled by introducing artificial lattice defects.