Theoretical analysis of feedback mechanisms of two-dimensional finite-sized photonic-crystal lasers

Abstract

Theoretical investigations are carried out for close-to-lasing two-dimensional finite-sized photonic crystals with active (gain) lattice points. First, laser oscillations with lower thresholds are found to occur near the photonic band edges where optical gain is enormously intensified. For several modes isolated around the band edge, the field-intensity spectra in reciprocal space and the Poynting-vector distributions in real space are investigated in detail in close-to-lasing photonic crystals. By comparing the phenomena that occur in photonic crystals with a symmetric or an asymmetric outward form, this paper clarifies the differences in the feedback mechanisms of these crystals. In a symmetric photonic crystal, laser oscillation occurs through the waves propagating along the straight passages. This feedback is basically the same as that of ordinary one-dimensional lasers, although it exhibits a complicated behavior that light waves propagating in a variety of directions interfere with each other. In an asymmetric photonic crystal, laser oscillation occurs through the waves circulating within the crystal, which could be called recurrent-photon feedback. This feedback, however, can be construed as an extension of the feedback in ordinary one-dimensional distributed-feedback lasers.