For this episode, Antonin Léonard sat down with Alexis Jonville, CEO and co-founder of Lumisync.

Lumisync is a French deep-tech spinout from the C2N (Centre for Nanoscience and Nanotechnology, CNRS / Paris-Saclay), founded in December 2024 by Alexis Jonville, Giuseppe Bravo Modica (CTO), and Rémi Braive (CSO). The company is building the first on-chip photonic oscillator designed to replace electronic quartz synchronization inside AI data centers — eliminating a hidden bottleneck that wastes GPU capacity at every clock cycle.

The analogy Alexis uses to explain it: imagine driving at 250 km/h on a motorway, but hitting a toll booth every two kilometres. Improving GPU power is the 250 km/h. Lumisync removes the toll booths.

Networking represents 15–20% of a data center's energy consumption, and synchronization sits at its core. By replacing electronic oscillators with a photonic network connected via optical fibre, Lumisync estimates it can cut the number of synchronization components by a factor of 10 to 100, reduce CapEx by tens of millions per HPC data center, and shave 2–3% off total energy consumption — at scale, millions of dollars and tonnes of CO₂ per data center per year.

The technology traces back to a PhD thesis started at C2N in 2017, supported by CNRS Innovation pre-maturation funding from 2022 and SATT Paris-Saclay, with IP transferred in early 2025. Three patent families protect the oscillator design, manufacturing protocol, and synchronization network architecture.

In this conversation, we explore:

→ Why networking is the overlooked bottleneck — and why fixing the GPU alone doesn't fix the data center

→ The photonics transition already underway: from optical fibre on long distances to on-chip oscillators

→ Why startups — not Nvidia — are building the photonics layer, and what a decade of academic head start means competitively

→ The 90/10 rule: how a founder with no PhD shares decisions with a world-class researcher-turned-CTO

→ What it means to sell a €106k POC before your product is finished — and why your early adopters are also your R&D partners

→ The pari that has to be won: earning the trust of Nvidia, Google and Microsoft when you're an 8-person company

To learn more:
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