High-coherence hybrid-integrated 780  nm source by self-injection-locked second-harmonic generation in a high-Q silicon-nitride resonator

Visible, high-coherence optical sources are important to a wide range of applications spanning spectroscopy to precision timing. Integration of these sources on a semiconductor chip is a necessary step if the systems that use these devices are to be made compact, portable, and low power. Here, by self-injection-locking a 1560 nm distributed feedback semiconductor laser to a high-Q silicon-nitride resonator, a high-coherence 780 nm second-harmonic signal is generated via the photogalvanic-induced second-order nonlinearity. A record-low frequency noise floor of 4Hz 2 /Hz is achieved for the 780 nm emission. The approach can potentially generate signals over a wide range of visible and near-visible bands, and thereby help transition many table-top systems into a fieldable form.