: Hyunho Jung, Myungjae Lee, Changhyun Han, Yeonsang Park, Kyungsang Cho, and Heonsu Jeon

: Opt. Express 25(26), 32919-32930 (2017)

High-density photonic integrated circuits (PICs) are expected to replace their current electronic counterparts in the future. The most crucial prerequisite for realizing successful PICs is to develop a low-loss coupling technique between active and passive photonic components based on various nanoscale materials and devices. Here we propose and demonstrate an on-chip integration technique in which a high-refractive-index layer constitutes the coplanar structural backbone across the entire PIC chip. To prove the concept, patterns of a two-dimensional photonic crystal (PhC) band-edge laser and grating couplers are engraved into the backbone layer, and colloidal quantum dots (CQDs) for optical gain are selectively deposited in the PhC area by a conventional lift-off process. Using optical excitation, we observe that the CQD-PhC structure emits coherent single-mode laser light, which is subsequently coupled to and propagates through an adjacent free-space waveguide section in the well-defined directions corresponding to the selected band-edge point, finally emerging through the grating coupler. Our study demonstrates a simple but highly suggestive PIC platform that automatically guarantees high coupling efficiencies between the micro- and nanophotonic devices to be integrated (through high degrees of modal match in the vertical direction) and will therefore advance the development of high-density PIC technologies.