Quantum-dot lasers for 35 Gbit/s pulse-amplitude modulation and 160 Gbit/s differential quadrature phase-shift keying

TLDR: In this article, a GaAs-based edge-emitter structure incorporating a standard p-doped active region with ten quantum-dot layers enables 15 Gbit/s data transmission at 70 °C upon direct modulation.

Abstract: We report on the dynamic properties of 1.31 μm InAs/GaAs and 1.55 μm InAs/InP quantum-dot Fabry-Perot lasers with the main focus on the increase of their large-signal modulation capabilities. A GaAs-based edge-emitter structure incorporating a standard p-doped active region with ten quantum-dot layers enables 15 Gbit/s data transmission at 70 °C upon direct modulation. The large number of layers and wide barriers cause significant carrier transport limitations. Since the carrier distribution across the stack is not uniform, a graded p-doping profile is implemented leading to an increased data rate of 20 Gbit/s, but at the expense of somewhat lower temperature stability. GaAs-based lasers operating exclusively from the first excited state demonstrate a further data rate increase to presently 25 Gbit/s, due to the larger degeneracy of the higher quantum-dot energy levels. 25 Gbit/s data transmission at 70 °C is also achieved with InAs/InP quantum-dot devices emitting in the C-band. Four- and eight-level pulse-amplitude modulation formats are utilized to increase the data rate at a given bandwidth compared to a standard on-off keying scheme. Data rates up to 35 Gbit/s are presented for both wavelength bands. Monolithically integrated two-section mode-locked lasers based on the graded pdoping structure provide low-jitter optical pulse trains and are utilized as optical sources for non-return-to-zero transmitters. 80 Gbit/s on-off keying and 80 GBd (160 Gbit/s) differential quadrature phase-shift keying data transmission based on optical time-division multiplexing are demonstrated using a packaged 40 GHz module.