Photonics Research, Vol. 8, Issue 12, 12001937 (2020)
Quantum dot mode-locked frequency comb with ultra-stable 25.5 GHz spacing between 20°C and 120°C 
Shujie Pan1,†, Jianou Huang2,†, Zichuan Zhou1, Zhixin Liu1, Lalitha Ponnampalam1, Zizhuo Liu1, Mingchu Tang1, Mu-Chieh Lo1, Zizheng Cao2,5, Kenichi Nishi3, Keizo Takemasa3, Mitsuru Sugawara3, Richard Penty4, Ian White4, Alwyn Seeds1, Huiyun Liu1, and Siming Chen1,*

Author Affiliations

- 1Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, United Kingdom
- 2Institute of Photonic Integration, Eindhoven University of Technology, Eindhoven 5600 MB, The Netherlands
- 3QD Laser, Inc., Kawasaki 210-0855, Japan
- 4Centre for Photonics Systems, Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom
- 5e-mail: z.cao@tue.nl
Abstract
Semiconductor mode-locked lasers (MLLs) are promising frequency comb sources for dense wavelength-division-multiplexing (DWDM) data communications. Practical data communication requires a frequency-stable comb source in a temperature-varying environment and a minimum tone spacing of 25 GHz to support high-speed DWDM transmissions. To the best of our knowledge, however, to date, there have been no demonstrations of comb sources that simultaneously offer a high repetition rate and stable mode spacing over an ultrawide temperature range. Here, we report a frequency comb source based on a quantum dot (QD) MLL that generates a frequency comb with stable mode spacing over an ultrabroad temperature range of 20–120°C. The two-section passively mode-locked InAs QD MLL comb source produces an ultra-stable fundamental repetition rate of 25.5 GHz (corresponding to a 25.5 GHz spacing between adjacent tones in the frequency domain) with a variation of 0.07 GHz in the tone spacing over the tested temperature range. By keeping the saturable absorber reversely biased at
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