Ultra-broadband Flat-top Quantum Dot Comb Lasers

A quantum dot(QD)mode-locked laser as an active comb generator takes advantage of its small footprint,low power consumption,large optical bandwidth,and high-temperature stability,which is an ideal multi-wavelength source for applications such as datacom,optical interconnects,and LIDAR.In this work,we report a fourth-order colliding pulse mode-locked laser(CPML)based on InAs/GaAs QD gain structure,which can generate ultra-stable optical frequency combs in the O-band with 100 GHz spacing at operation temperature up to 100℃.A record-high flat-top optical comb is achieved with 3 dB optical bandwidth of 11.5 nm(20 comb lines)at 25℃.The average optical linewidth of comb lines is measured as 440 kHz.Single-channel non-return-to-zero modulation rates of 70 Gbit/s and four-level pulse amplitude modulation of 40 GBaud/s are also demon-strated.To further extend the comb bandwidth,an array of QD-CPMLs driven at separate temperatures is proposed to achieve 36 nm optical bandwidth(containing 60 comb lines with 100 GHz mode spacing),capable of a total transmission capacity of 4.8 Tbit/s.The demonstrated results show the feasibility of using the QD-CPML as a desirable broadband comb source to build future large-bandwidth and power-efficient optical interconnects.