Recent Progress in on-Demand Transfer-Enabled Integration of Wavelength-Scale Light Sources.

The growing demand for massive and high-speed data processing within compact photonic circuits has highlighted a critical challenge: the efficient integration of high-quality ultrasmall light sources and emitters onto next-generation integration platforms. Despite notable advancements achieved through conventional and cutting-edge strategies, integration technologies utilizing the micro-transfer-printing technique-employing microstructured polymeric stamps, such as polydimethylsiloxane (PDMS)-have garnered considerable attention. This innovative approach facilitates heterogeneous integration by enabling the deterministic placement of micro- and nanoscale optical structures and materials with sub-micrometer alignment onto diverse photonic integration platforms. This review paper presents recent developments in the micro-transfer-enabled integration of light sources across four representative categories of devices and materials: microdisk and microring cavity lasers, photonic crystal nanobeam lasers, semiconductor nanowire lasers and LEDs, and quantum light sources based on semiconductor quantum dots and localized emitters in two-dimensional materials. For each category of light source integration, we analyze the application of micro-transfer-printing in relation to the overall integration configuration, the desired optical properties, device performance optimization, and resolution of challenges and limitations encountered in previous methodologies. Collectively, these demonstrations position PDMS-assisted micro-transfer-printing not merely as a fabrication technique but as an innovative integration paradigm that connects diverse material systems and device architectures.