Silicon photonics constitutes the cornerstone technology of on-chip optical interconnects. However, silicon cannot generate or amplify light, and the seamless integration of gain elements with passive waveguides on silicon substrates remains a critical challenge. In this work, we propose a strategy to effectively address the waveguide coupling bottleneck between III/V gain regions and silicon photonic circuits to establish a scalable, monolithic, and CMOScompatible linked platform. Our approach exploits silicon nitride waveguides deposited at low temperature and coupled through anti-reflective layers to epitaxially grown InAs/GaAs quantum dot gain regions on a silicon wafer. The fabricated junctions exhibited coupling losses below 1.5 dB and back-reflections close to -15 dB for a normal interface. Continuous-wave lasers with distributed Bragg reflectors were experimentally demonstrated with threshold currents below 215 mA at room temperature and a maximum single-port output power exceeding 2 mW. To the best of our knowledge, the first waveguide-coupled monolithically integrated electrically pumped optical amplifiers on silicon substrate are also demonstrated, with net gains greater than 5 dB and a 3 dB optical bandwidth of 46 nm. This advance enables the cost-effective co-integration of positive net gain amplifiers and broadband passive components on silicon, paving the way for next-generation data center interconnects.
Photothermal mid-infrared spectroscopic imaging (MIRSI) enables label-free visualization of the chemical composition and microstructure of complex materials, such as biological tissues and polymers. However, existing MIRSI platforms are confined to bulky benchtop instrumentation, restricting their use to controlled laboratory environments and precluding clinical or field deployment. Here, we introduce a compact, handheld MIRSI platform that translates this powerful analytical modality into a portable form factor, enabling its use beyond the laboratory for the first time, to our knowledge. The architecture integrates a flexible fiber-optic imaging scanner with configurable scanning modes, enabling adaptable operation across diverse operational contexts. We validate performance across a range of specimens, including human ovarian, cervical, and bone marrow cancers, kidney tissue, and representative polymers, demonstrating high-fidelity molecular contrast and structural resolution. This work establishes portable MIRSI as a versatile tool for label-free molecular imaging and lays the foundation for point-of-care diagnostics and in situ chemical analysis beyond the laboratory environment. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
