Integrated closed-loop cavity of a tunable laser

In this paper, a closed-loop cavity of a tunable laser integrated onto a silicon chip is demonstrated. The closed-loop cavity consists of a semiconductor optical amplifier chip, two separated micro-ring resonators, and a U-shaped waveguide sub-loop, enabling dominating lasing in the counterclockwise direction. The lasing wavelength is tuned by varying the effective refractive index of the thermal ring-resonators. It has achieved wide tuning range (55.4 nm), high spectral purity (50-dB side mode suppression ratio), ∼1-mW output power, and 36-dB counter-propagation power suppression ratio. The integrated tunable laser has high potential in applications such as optical network, optical sensing, and integrated optoelectronic systems.