Tiny Photonic Chip Slices Light to Push Direct-Detection Links Past 200 GBaud

A team of European researchers has unveiled a photonic integrated receiver that dramatically extends the reach and speed of the simplest and cheapest form of optical communication, demonstrating data transmission at up to 200 gigabaud over tens of kilometres of standard fibre without the costly coherent detection hardware that such speeds normally demand. The work, published in Communications Engineering, addresses one of the most stubborn bottlenecks in the rollout of next-generation passive optical networks and data centre interconnects: chromatic dispersion.

Intensity modulation with direct detection, or IM/DD, has long been the workhorse of cost-sensitive optical links. A laser is switched or modulated in brightness, and a simple photodiode at the far end converts the light back into an electrical signal. It is compact, energy-efficient and inexpensive, which is precisely why it dominates short-reach systems. The trouble begins as symbol rates climb. At 200 gigabaud, the spectral width of the signal becomes so large that chromatic dispersion, the tendency of optical fibre to smear different wavelengths of light at slightly different speeds, wreaks havoc. The signal develops frequency-dependent power fading, deep notches in its spectrum that can obliterate information before it ever reaches the receiver.

Conventional fixes are unattractive at this scale. Digital dispersion compensation demands enormous signal-processing power and bandwidth-hungry analogue-to-digital converters. Coherent detection, which measures both the amplitude and phase of light, solves the problem elegantly but at a price in complexity, power consumption and cost that is hard to justify for the short links that connect data centres or serve homes through passive optical networks. The research consortium, spanning the University of Southampton, the University of West Attica, the Technical University of Denmark, CEA-Leti and Ghent University working with imec, took a different route: fix the problem in the optical domain before the signal is ever detected.

The team’s solution is an architecture they call recurrent optical spectrum slicing, or ROSS, implemented as a photonic integrated circuit. The concept is a form of optical preprocessing that provides frequency-diversity detection. Instead of letting a single photodiode see the whole, dispersion-distorted spectrum, the ROSS receiver splits the incoming signal into multiple spectral slices and recombines them in a recurrent configuration, generating several complementary intensity-domain observations of the same data stream. Because the power-fading notches induced by dispersion fall at different points in each sliced observation, information lost in one slice survives in another, allowing the original data to be reconstructed.

The elegance of the approach lies in what it removes from the receiver’s electronic burden. By performing the heavy lifting optically, the ROSS receiver allows the system to use low-bandwidth electro-optic components, which are cheaper, more readily available and consume less power than the ultra-wideband devices that a 200-gigabaud signal would otherwise require. Recovery of the data then relies on simple feed-forward equalization, a lightweight digital technique, rather than the computationally intensive compensation schemes that would be needed to undo dispersion after detection.

The experimental results are striking. The researchers demonstrated intensity-modulated, direct-detected transmission of 4-level pulse-amplitude modulation, or PAM-4, at 160 gigabaud over 50 kilometres of uncompensated standard single-mode fibre, and at 175 gigabaud over 25 kilometres. Pushing further, they transmitted 200-gigabaud on-off keying, the simplest modulation format of all, over 75 kilometres of the same uncompensated fibre. These figures translate into a measured dispersion tolerance of up to 2.4 times 10 to the power of 5 gigabaud-picoseconds per nanometre, a metric that quantifies how much dispersion a signal of a given symbol rate can endure.

To put those numbers in perspective, uncompensated standard single-mode fibre accumulates roughly 17 picoseconds per nanometre per kilometre of dispersion at telecommunication wavelengths. A 200-gigabaud signal over 75 kilometres therefore accumulates a dispersion-length product that would ordinarily produce catastrophic power fading in a conventional direct-detection receiver. That the ROSS architecture handles this with simple components and modest equalization suggests a practical path to scaling short-reach links without migrating to coherent technology.

The implications reach well beyond the laboratory. Passive optical networks, the fibre-to-the-home infrastructure serving hundreds of millions of subscribers, are under pressure to deliver ever higher bit rates while keeping per-user costs and power consumption low. Data centre operators face a similar squeeze, as artificial intelligence workloads drive explosive growth in the traffic flowing between servers and switches over links of a few hundred metres to a few tens of kilometres. A receiver that keeps the cost and simplicity of direct detection while tolerating dispersion at 200 gigabaud could reshape the economics of both markets, reducing the energy footprint of the optical layer at exactly the moment when its power draw has become a strategic concern.

The photonic integration aspect is equally significant. By fabricating the spectrum-slicing receiver as an integrated chip, the team moves the concept from a bench-top arrangement of discrete components toward a manufacturable device that could be mass-produced using established foundry processes. Integration shrinks size, improves stability against environmental drift, and lowers packaging cost, all prerequisites for adoption in the high-volume, cost-sensitive segments where IM/DD reigns. The work was supported by the European Union’s Horizon Europe PROMETHEUS project, the H2020 NEoteRIC project, the Villum Foundations OPTIC-AI project, and the UK’s EPSRC HASC Telecommunications Hub and DSIT REASON programmes, with experiments conducted at the University of Southampton’s X-band laboratories.

Challenges remain before such receivers appear in commercial transceivers, including refining the equalization algorithms and demonstrating performance across the temperature and manufacturing variations of real deployments. But the demonstration marks a clear milestone: a photonic chip that lets the humblest optical modulation format carry some of the highest symbol rates yet achieved over dispersive fibre, using detection hardware that a network operator could actually afford. As data demand continues its relentless climb, solutions that trade silicon-area optical ingenuity for expensive electronics are likely to become increasingly central to the internet’s physical backbone.

Subject of Research: Photonic integrated recurrent optical spectrum slicing receivers for dispersion-tolerant high-speed direct-detection optical communications

Article Title: Photonic integrated recurrent spectrum slicer enabling low complexity direct detection over 200 GBaud dispersive links

Article References: Liu, H., Sozos, K., Teofilovic, I., Wantee, S., Bottrill, K. R. H., Malhouitre, S., Garcia, S., Sarantoglou, G., Bienstman, P., Charbonnier, B., Mesaritakis, C., Vigliar, C., Da Ros, F., Bogris, A., & Petropoulos, P. (2026). Photonic integrated recurrent spectrum slicer enabling low complexity direct detection over 200 GBaud dispersive links. Communications Engineering. https://doi.org/10.1038/s44172-026-00801-6

Image Credits: AI Generated

DOI: 10.1038/s44172-026-00801-6

Keywords: photonic integration, optical communications, direct detection, chromatic dispersion, spectrum slicing, PAM-4, on-off keying, passive optical networks, data centre interconnects, feed-forward equalization, IM/DD, fibre optics