  Integrated photonics has profoundly impacted a wide range of technologies
underpinning modern society. The ability to fabricate a complete optical system
on a chip offers unrivalled scalability, weight, cost and power efficiency.
Over the last decade, the progression from pure III-V materials platforms to
silicon photonics has significantly broadened the scope of integrated photonics
by combining integrated lasers with the high-volume, advanced fabrication
capabilities of the commercial electronics industry. Yet, despite remarkable
manufacturing advantages, reliance on silicon-based waveguides currently limits
the spectral window available to photonic integrated circuits (PICs). Here, we
present a new generation of integrated photonics by directly uniting III-V
materials with silicon nitride (SiN) waveguides on Si wafers. Using this
technology, we present the first fully integrated PICs at wavelengths shorter
than silicon's bandgap, demonstrating essential photonic building blocks
including lasers, photodetectors, modulators and passives, all operating at
sub-um wavelengths. Using this platform, we achieve unprecedented coherence and
tunability in an integrated laser at short wavelength. Furthermore, by making
use of this higher photon energy, we demonstrate superb high temperature
performance and, for the first time, kHz-level fundamental linewidths at
elevated temperatures. Given the many potential applications at short
wavelengths, the success of this integration strategy unlocks a broad range of
new integrated photonics applications.
