Universal frequency-comb platform for datacenter communications

Project Information

UNICO

Grant agreement ID: 101136762

DOI

10.3030/101136762

EC signature date 2 October 2023

Start date 1 November 2023

End date 31 January 2027

Funded under

• The European Innovation Council (EIC)

Total cost

€ 2 499 998,75

EU contribution

€ 2 499 998,75

Coordinated by

INNOLUME GMBH
Germany

Periodic Reporting for period 1 - UNICO (Universal frequency-comb platform for datacenter communications)

Reporting period: 2023-11-01 to 2024-10-31

Summary of the context and overall objectives of the project

By 2028, it is expected that overall datacom capacity will reach 100,000 Petabit/s, corresponding to 1 billion 100-Gbps equivalent SerDes shipments, and several hundred million O-band CW laser wavelength lines (25/50/100 Gbaud PAM4/PAM8). Comb lasers are an ideal technology platform for compact WDM solutions with the high throughput required by growing needs of the datacom industry. Currently, two compact comb-laser technologies stand out as promising platforms for datacom light sources: InAs/GaAs quantum-dot based comb lasers and micro resonator-based Kerr combs. The project, facilitated by the fundamental complementarity of both technologies, will strive towards their unification in one versatile chip-scale comb platform, covering full range of WDM spacings (ultra-dense to coarse) and addressing key challenges of the datacentre market - power efficiency, harsh operating environment (85°C) and scalability. The competitive advantage is based on current world-leading technologies of QD comb lasers and microcombs being commercialized by the partners, the results of the originating H2020 CALADAN and PHOENICS projects, as well as the novel features, such as chirped-DBR comb laser, comb SOA and evanescent coupling to SiP. The goals of the project: (i) to develop a novel design and technological process of CW comb laser PIC fabrication with enhanced mode stability and ultra-low noise; (ii) to develop 2 prototypes of GaAs/SiNon- SiP comb PIC, including 1.3-μm comb laser, evanescent coupling to SiP substrate, and comb-SOA: (1) QD chirped DBR comb for UDWDM/DWDM, and (2) microcomb for DWDM/CWDM. The consortium consists of Innolume (world market leader in InAs/GaAs QD), Dublin City University (high-speed communications), and Enlightra (associated partner, start-up established in 2021, world’s first commercial optical comb with large frequency spacing 100-1000 GHz). This consortium combines scientific expertise with experience in translating ideas into products and scaling them.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Innolume has been developing distributed Bragg reflector (DBR) comb lasers, testing multiple epitaxy structures for optimal quantum dot density and photoluminescence (PL) intensity. DBR gratings were fabricated using electron-beam lithography and evaluated for bandwidth, reflection coefficient, and wavelength performance. A high-gain recipe was selected for 50 GHz and 100 GHz DBR comb lasers, though final processing is ongoing. Collaboration with X-Celeprint focuses on preparing source wafers for micro-transfer printing, including encapsulation, release etching, and stress compensation techniques. In addition, Innolume has also developed low-noise comb SOAs, with findings published in the IEEE Journal of Lightwave Technology.

Enlightra has advanced high-efficiency microcombs for DWDM/CWDM in the O-band with frequency spacings of 200, 400, and 800 GHz, achieving up to 75-80% optical-to-optical conversion efficiency and ~2 dB power uniformity.
Enlightra and Innolume are jointly developing Comb-chiplet designs and III-V to SiN/Si integration for WDM transceivers. Efforts include refining microring resonators, edge-coupling, and optimizing SiN components. First-generation designs have been submitted to the foundry, but mask delays have postponed production until January 2025.

DCU has established a testbench to characterize SOAs, including ASE spectrum, gain, noise figure, and nonlinear effects. Their system evaluation can assess bit error rates for up to 8 channels at 100 Gbaud using OOK and PAM4 modulation.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Two early open-access publications on data transmission using SOAs have made a notable scientific impact. These contributions are expected to enhance the scientific and industrial community's confidence in the objectives of the UNICO project.
• “2×53 Gbit/s PAM-4 Transmission Using 1.3 μm DML with High Power Budget Enabled by Quantum-Dot SOA” in IEEE Photonics Technology Letters DOI 10.1109/LPT.2024.3504841 which demonstrates high-capacity, energy-efficient optical data transmission using directly modulated lasers and quantum dot SOAs, reducing loss and energy per bit while enabling long-distance links;
• “Bit Error Rate in WDM Data Transmission Links with Semiconductor Optical Amplifier” in JOURNAL OF LIGHTWAVE TECHNOLOGY DOI 10.1109/JLT.2024.3475885 which marks a milestone in understanding the possibilities and limitations of semiconductor optical amplifiers (SOAs) in data transmission.