Defect Mode Passband Lasing in Self-Assembled Photonic Crystal

Up to now colloidal photonic crystal (CPC) lasers essentially relied on photonic band gap <i>edge</i> effects, as a consequence of the poor passband quality achieved by previously reported engineering methods. In this paper, we demonstrate lasing oscillation in CPCs based on the defect mode <i>passband</i> effect. As defect mode, we introduce a high-quality monolayer of silica spheres internally functionalized with laser dyes in a sandwiched CPC structure. This defect layer contains the gain medium for lasing action and at the same time breaks the translational symmetry of the crystal, resulting in a pronounced passband within the photonic band gap. The CPC acts as an optical resonator, effectively ensuring the feedback mechanism. The spectroscopic measurements and theoretical simulations match well and reveal that the relatively low-threshold lasing exhibited by the structure can uniquely be attributed to the efficient coupling of the spontaneous emission of the dye to the defect mode of the CPC. Our work provides a new promising strategy toward applications of functionalized self-assembled CPCs with a planar defect in all-optical switching, optoelectronics, and energy-harvesting, and even in the future generation of electro-optical devices, such as lab-on-a-chip with all-integrated optical spectroscopy techniques