At Pilot Photonics, we are committed to tackling one of the most advanced challenges in datacentre scaling, impacting millions of lives every day with faster, more responsive, and highly efficient optical communications to support the AI-driven digital world.
Backed by €2.5M in funding from the European Innovation Council’s HORIZON-EIC-2023-TRANSITION CHALLENGES programme, our COCOPOP project is developing the world’s first coherent-capable External Laser Source (ELS) based on a chip-scale frequency comb. This isn’t just about more bandwidth — it’s about future-proofing the backbone of the digital world. Whether through pluggables or co-packaged optics (CPO/OIO), our innovation unlocks a new scaling dimension and paves the way for coherent communication inside the datacentre. In our view, the question isn’t if the datacentre goes coherent, it’s when. And COCOPOP is what makes that possible.
The Challenge: Scaling Optical Interconnects in AI and Cloud Data Centres
The rapid growth of AI/ML, cloud computing, and data-intensive applications is pushing datacentres to their limits. Meeting these demands requires new levels of optical interconnect scalability. Today’s optical links inside datacentres typically rely on 1, 4, or 8 wavelengths, often using the CWDM4 grid. However, CWDM4, with its wider channel spacing and susceptibility to dispersion, doesn’t scale efficiently.
To address the limitations of faceplate density, power consumption, and signal integrity, the industry is transitioning toward Co-Packaged Optics (CPO) and Optical I/O (OIO), architectures that place optics closer to the switch ASIC. This brings performance gains, but also introduces a new challenge: the laser sources at the heart of these systems must now meet stricter requirements for power, wavelength accuracy, and scalability.
Laser arrays, commonly used in these systems, provide high per-channel power but struggle with wavelength accuracy and thermal drift, which becomes critical as the number of wavelengths per fibre is scaled. Moreover, the industry is nearing the physical limits of scaling through fibre count. There’s no clear path forward, unless there is a shift in the paradigm towards using the remaining scaling axis: data rate per wavelength.
Today’s systems rely on IM/DD (Intensity Modulation / Direct Detection). To go further, the industry must shift to multi-level modulation and, down the line, to coherent transmission. However, coherent optics demand ultra-stable, narrow-linewidth, phase-coherent light sources where existing commercial laser arrays will struggle. That’s the bottleneck COCOPOP is working to eliminate.
By delivering a coherent-capable external laser source based on chip-scale comb technology, COCOPOP addresses the critical need for scalable, stable, and high-performance light sources for today’s systems and also unlocks the next generation of datacentre capacity.
The COCOPOP Solution
COCOPOP is developing the world’s first comb-based External Laser Source (ExCELS) – a novel light source that delivers multi-wavelength precision, high optical power per-channel, and coherent-capable performance.
Rather than relying on multiple free-running lasers, which suffer from wavelength drift and noise, Pilot Photonics, drawing on over a decade of experience in integrated comb laser technology, has engineered a 'best of both worlds' approach. COCOPOP combines a chip-scale optical frequency comb to synchronise, lock and stabilise an integrated laser array. This architecture achieves the phase coherence and wavelength precision of a comb, while retaining the high power per wavelength characteristic of a laser array.
Figure 1 – (Left) ExCELS Architecture comprising an optical frequency comb that injection-locks a laser array (Right) Competitive positioning of the ExCELS against other technologies.
This hybrid architecture allows ExCELS to overcome the major limitations of traditional laser arrays, providing high power, stable and accurate wavelengths with excellent linewidth and relative intensity noise (RIN), capable of high data-rate IM/DD while unlocking a third scaling dimension: data rate per wavelength, enabling coherent transmission inside the datacentre.
The result? More wavelengths, tighter spacing (aligned with the CW-WDM MSA grid), higher stability and accuracy, lower noise and dramatically improved data throughput — all in a chip-scale and pluggable solution.
COCOPOP aims to bring this ExCELS solution from Technology Readiness Level (TRL) 4 to TRL 7, culminating in a market-ready ELS compatible with today’s co-packaged and optical I/O systems but designed to future-proof the datacentres of tomorrow for the inevitable transition to coherent optics.
Figure 2 – COCOPOP objectives, focused on advancing the ExCELS from a TRL4 to a TRL7.
First Year Project Highlights
The first year of COCOPOP has been marked by substantial technical progress and commercial momentum — laying the foundation for the successful delivery of the ExCELS architecture.
Comb-ELS Lab Demonstration
3x Throughput and 15 dB RIN Reduction
We successfully demonstrated the ExCELS comb-laser array architecture, achieving a TRL4 and the first major milestone of the project. By injection-locking the laser array to individual comb lines we validated the core concept of ExCELS and unlocked the full potential of the comb, providing over 15 dB improvement in RIN and enabling a 3x increase in data throughput – achieving 160 Gbit/s PAM4 on a single wavelength, compared to 50 Gbit/s with passive filtering.
This result confirms the performance advantage of the COCOPOP’s ExCELS architecture and highlights its potential to support the next generation of high-density, scalable optical interconnects for datacentres.
Figure 3 – Relative intensity noise measured on comb lines using a passive filter (blue)
Optical frequency comb using a SiN ring structure, and the Bragg-grating comb.
Scalable Comb Sources in O-band
SiN Rings and Bragg-grating combs
COCOPOP has demonstrated optical frequency comb generation with two integrated photonic structures: a Silicon Nitride (SiN) micro-ring resonator and a Bragg grating-based comb. The SiN micro-ring achieved comb generation in a breadboard module, validating its role as the core of a scalable ELS. In parallel, the Bragg comb offers a promising lower-power alternative, able to produce a sculpted multi-wavelength spectrum with only the desired number of wavelengths and without the need for high-power pumping.
Figure 4 – Optical frequency comb using a SiN ring structure, and the Bragg-grating comb.
CW-WDM 16-Channel Laser Array
Pilot Photonics has developed a 16-channel photonic integrated circuit, aligned to the CW-WDM MSA O-band grid with 200 GHz spacing. Originally designed as the injection-locked demultiplexer for the COCOPOP comb-based ELS, ExCELS, this PIC can also function as a standalone ELS for today’s IM/DD systems.
Now part of Pilot Photonics' commercial product portfolio, this PIC reinforces Pilot Photonics’ strategic role in shaping the CW-WDM ecosystem, further supported by the company’s recent membership in the CW-WDM MSA.
Figure 5 – Laser array PIC and overlapped spectra of the 16 channels.
ExCELS ELSFP - A Comb-based ELS
Designed for pluggable form factors, ExCELS enables coherent-capable transmission inside data centres, aligning with the CW-WDM MSA and future-proofing AI and cloud-scale networks.
A final architecture for the pluggable ExCELS was selected and two photonic integrated circuit (PIC) fabrication runs were completed: one in Silicon Nitride (SiN) for comb generation and one in Indium Phosphide (InP) for the demux laser array.
An ELSFP-compliant housing has been sourced, and early closed-loop control techniques for long-term locking stability have been validated.
A flyer summarising ExCELS capabilities and specifications is now available for early adopters.
Figure 6 – ELSFP pluggable, and flyers for ExCELS
What’s Next?
As COCOPOP enters its second year, the focus shifts from demonstrations to integration and market-ready form factors.
Having proven the performance of its core components, the project is now targeting the packaging in a pluggable ELSFP form factor. Key activities in Year 2 include:
- Closed-loop feedback implementation for long-term stability
- System-level integration of comb and demultiplexer PICs
- Packaging of hybrid PICs (SiN/InP)
- Pluggable module design and assembly
These efforts are all aimed at achieving TRL7 by the end of the project, delivering a market-ready External Laser Source that supports coherent transmission and aligns with the CW-WDM MSA and next-generation datacentre requirements.
Year 2 is execution-focused: from prototype to product, from lab to customer trials.
COCOPOP is just getting started, and the most exciting breakthroughs are yet to come. Stay tuned as we bring ExCELS to market and reshape the future of datacenter optics.
Further information is available here:
Optical Parallelism - Comb Lasers or Laser Arrays for Next-Generation Interconnects
Gazettabyte - Home - A coherent roadmap for co-packaged optics
