Heterogeneously integrated evanescently coupled lasers emitting in the submicrometre wavelength range

Abstract

Owing to its broad transparency window, ultra-low propagation losses, and compatibility with complementary metal–oxide–semiconductor (CMOS) fabrication processes, silicon nitride (SiN) has emerged as a highly attractive platform for extending integrated photonics into the visible and near-infrared spectrum. By incorporating active components such as modulators, light sources, and detectors, complex photonic systems with unprecedented functionality and performance become possible. These systems enable a wide range of applications, including biosensing, on-chip spectroscopy, imaging, and quantum computing. However, the low refractive index of SiN relative to III–V gain materials poses a major challenge for implementing evanescently coupled lasers, the dominant coupling scheme in silicon photonics at the telecommunication wavelengths. Although a silicon intermediate layer is often used to alleviate this mismatch, its strong absorption at shorter wavelengths precludes its use. Here, we present an integration strategy that overcomes this limitation by employing a CMOS-compatible a-Si:H layer with two etch depths, which was engineered to achieve the required optical properties at shorter wavelengths. This intermediate structure enables efficient vertical coupling between the SiN photonic circuit and a micro-transfer-printed GaAs-based semiconductor optical amplifier. Using this scheme, we demonstrate on-chip amplification with a gain of more than 13 dB as well as lasing in the submicrometre wavelength range. Finally, we showcase the versatility of this process by integrating a second amplifier stage following the laser, achieving on-chip output powers exceeding 4 mW. These results highlight the potential of this method for developing fully integrated evanescently coupled laser systems operating in the near-infrared band.