290 Hz intrinsic linewidth from an integrated optical chip-based widely tunable InP-Si 3 N 4 hybrid laser

Widely tunable, narrow linewidth diode lasers have found a wide range of important applications, from terrestrial ones, such as fiber-optic communications [1] or optical sensing [2], to applications in space, for instance in atomic clocks [3]. Monolithic diode lasers for such tasks, i.e., distributed feedback (DFB) lasers and distributed Bragg reflector (DBR) lasers, approach their limits since they typically show either a small tuning range [4] or large spectral linewidths at the MHz level [5]. In contrast, these limitations are not present in hybrid lasers. In such lasers, the gain from a semiconductor optical amplifier chip is receiving spectrally filtered feedback from a second chip fabricated from dielectric material. The second chip carries an integrated-optical waveguide circuit with which highly selective filtering and a long photon lifetime can be realized.