Detailing their research in a paper titled "Printed Nanolaser on Silicon" published in the ACS Photonics letter, the authors first designed an asymmetric one-dimensional InGaAsP photonic crystal (PhC) nanobeam laser 580nm wide, 8μm long and 280nm thick.
The laser was fabricated as a standalone, freestanding nanobeam structure (InGaAsP over an InP sacrificial layer) containing three active quantum wells in the middle, with thin short tether structures at both ends to allow easy separation from the substrate during the transferring step.
The target laser device was then selectively picked up from its InGaAsP/InP wafer with the help of a micro polydimethylsiloxane (PDMS) stamp (only 15×15×40μm in size), breaking the thin tethers before lifting up the nanobeam structure and transferring it to the prepared SOI waveguide. High-resolution optical imaging allowed the researchers to align the laser on top of the SOI waveguide only 20nm wider than the nanobeam and designed to operate in a single transverse electric (TE) propagation mode.
It is noteworthy that the structure of the III−V nanolaser is based on an asymmetric one-dimensional photonic crystal cavity, which allows light propagation with high efficiency in one direction only (−x direction). The researchers were able to experiment various coupling strengths by simply adjusting the number of air holes between the cavity and the waveguide. While positioned onto its waveguide, the photonic crystal nanobeam laser was bridging a 7μm-long air gap so it would maintain its original high quality factor (Q-factor) and its resonant wavelength.