First demonstration of a hybrid integrated InP-Si3N4diode laser for broadband optical frequency comb generation

We demonstrate the first on-chip laser frequency comb based on hybrid integration with low-loss Si3N4 waveguide circuits. The laser comprises an InP diode amplifier of which a small fraction is reverse biased for passive locking, while a Si3N4 feedback waveguide extends the optical cavity to a roundtrip length of 15 cm. The generated comb densely covers a 25 nm broad spectrum, at a 3 dB level, with more than 1600 comb-lines at 2 GHz spacing. With such properties, hybrid integrated diode lasers show great promise for widespread use in applications such as integrated microwave photonics or metrology