Directional lasing oscillation of two-dimensional organic photonic crystal lasers at several photonic band gaps

We fabricated a series of two-dimensional (2D) hexagonal organic photonic-crystal lasers whose lattice constant varies from 0.18 to 0.44 μm, and observed clear lasing oscillation at the four lowest band gap frequencies (M1, K2, M2, and Γ1). We used in-plane beam propagation analysis to clarify the 2D feedback mechanism at each gap frequency, which differs for different gaps. The observed K1 lasing oscillation is due to coupling of three nonparallel diffracted waves, which has a purely 2D character. This shows that photonic crystal lasers can operate with various feedback essentially different from that of conventional 1D distributed feedback lasers.