Distributed feedback-like laser emission in photonic crystal waveguides on InP substrate

Lasing of triangular and square lattice photonic crystal, waveguides on InP substrate is investigated around the 1.5-μm wavelength by optical pumping. The lattice period of the fabricated structures is varied over a very large scale, thereby allowing a detailed exploration of the laser behaviors in the cases of micrometer width waveguides. A genuine distributed feedback (DFB) laser emission is observed in the gap for W2-3 waveguides in the ΓM direction of a triangular lattice. A different behavior is obtained for W3 waveguides in the ΓK direction of the same lattice as well as for W1 and W3 waveguides in the ΓX direction of a square lattice. The laser emission is found to occur at the Γ point of the Brillouin zone (wavevector k=0) when the emission frequency is outside the gap. The DFB-like laser emission is intrinsically single mode in this case. Plane wave calculations show that the field distributions of the two DFB components are radically different. The emitting mode is well localized in the guide core while the non-lasing mode spreads over the whole crystal.