Hollow-Core Fiber (HCF) has carried the label “someday technology” for years. Loss records were broken annually, and lab demonstrations piled up. But the mood at OFC 2026’s Th1J and W1F sessions is different. Microsoft, Nokia Bell Labs, and Sumitomo Electric are each answering the same question from different angles. What must be solved to deploy HCF in real networks?

For context, as of early 2026 Microsoft has deployed over 1,280 km of live Azure HCF with zero field failures [5][6]. AWS has also begun production HCF deployment across roughly 10 data centers [7]. The loss number race is over. YOFC has reached 0.04 dB/km [9], and Microsoft reported 0.091 dB/km operational loss (over 1,200 km of production fiber) in Nature Photonics [8]. However, the real significance of that paper may lie not in the loss record itself, but in securing a physical platform for WDM (Wavelength Division Multiplexing) scale-up through the combination of nonlinearity removal, ultra-low dispersion, and low latency [10]. The remaining hurdles are CO₂ gas absorption, inter-modal interference (IMI), manufacturing yield, and cost. The four papers reviewed here are the cards each organization has played against these four challenges.

Four Papers at a Glance

HCF vs SMF: System Design Comparison

Note on measurement conditions: Distances and capacities are not directly comparable due to differing experimental methods (straight-line vs recirculating loop) and fiber types. All values are as reported by the respective authors.

From here, I examine what each paper actually demonstrated and what these results mean for HCF commercialization.

1. Microsoft Azure Fiber: Beating GLA over 442 km

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Two Fronts

Datacenter optical interconnects are pushing density on two fronts simultaneously. One is scaling IM-DD (Intensity Modulation / Direct Detection) lane rates from 200 Gb/s to 400 Gb/s. The other is scaling coherent pluggables from 800 Gb/s to 1.6 Tb/s. The two fronts look independent, but they are deeply entangled. Once 400G/lane IM-DD becomes prevalent, routing systems will shorten the electrical traces between the switch ASIC and the optics, accelerating CPO/NPO adoption. At that point, coherent line optics get pushed out of the router chassis and back into standalone transport platforms.

Six papers from OFC 2026 map the current technical coordinates of these two fronts. The thesis: 400G/lane IM-DD and 1.6T coherent pluggables are each approaching their physical limits, and the tradeoff structures for pushing past those limits are fundamentally different. Not a single one of the six papers showed a measured link demonstration.

Six Papers at a Glance

IM-DD vs Coherent: Technology Positioning

From here I break down each paper’s technical substance, cross-compare across papers, and extract structural insights for the value chain.

1. Broadcom: Pushing the Physical Ceiling of 400G/Lane with DD EML

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Introduction

The AI infrastructure race has moved beyond chip design into packaging.

No matter how fast GPU and switch ASIC performance scales, the optical interconnect that moves data off-chip becomes the bottleneck if packaging cannot keep pace. Co-Packaged Optics (CPO) attacks this bottleneck head-on by pulling the optical engine inside the switch package, minimizing electrical interconnect length, and improving both bandwidth and power efficiency simultaneously.

The question is “on what substrate, and how do you attach the chips?” The answer to this question determines the path to CPO commercialization.

This installment analyzes technologies that answer this question in different ways, drawing on four papers presented at OFC 2026 and one foundational journal paper. Corning demonstrated its “glass platform” through two OFC papers, with a 2023 JSTQE paper providing the underlying technology base. UC Davis / Lawrence Berkeley National Lab presented the world’s first 3D hybrid-bonded EPIC demonstration with solder completely eliminated. Sumitomo / PETRA introduced a compact InP-on-Si PIC that resolves the L-band coherent receiver trade-off through heterogeneous integration.

All five papers share a single core message: packaging technology determines system performance.

Five Papers at a Glance

CPO Packaging Technology Comparison

From here, I analyze each paper individually, examining where each technology sits in the CPO packaging stack, its limitations, and structural insights across the full value chain.

1. Corning: Redesigning CPO on Glass

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AI clusters are doubling in scale every year. Meta’s current ORv3 rack connects 72 GPU nodes over a copper backplane. The ORW rack, soon to be deployed, scales to 144 nodes. The next generation exceeds 256 nodes, pushing single-rack power past 1 MW [1]. At this scale, copper-based electrical interconnects hit walls simultaneously across power, bandwidth density, and routing complexity.

CPO (Co-Packaged Optics) as an alternative is not a new story. What is new is that Meta drew a public baseline at OFC 2026: “For optical technology to be compelling, it must be reliable and performant while offering comparable cost and power efficiency to electrical solutions.” All three conditions must be met, or it does not get used. This single framing defines the entire CPO session at OFC 2026.

In Part 2, we examine five papers from OFC 2026 that cover four segments of the CPO value chain: external laser sources (Furukawa), link margin compensation (Lightmatter QD-SOA), transceiver systems (Lightmatter BiDi), field reliability (Meta/Broadcom), and photodetectors (Marvell/McGill). Each addresses a different layer, but they share one underlying question.

“CPO has entered the stage where it must prove operational viability, not just performance. And there are still significant gaps in that proof.”

Five Papers at a Glance

Cross-Comparison

From here, we analyze each paper individually, examining where each technology sits in the CPO value chain, its limitations, and structural insights across the full chain.

1. Meta/Broadcom: What 36 Million Hours Tell Us, and What They Don’t

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Two Ways to Read a Conference Paper

Every conference paper has two layers. There are the numbers the authors put front and center, and there are the quieter signals buried in the body text. Read the seven papers that Samsung, GlobalFoundries, and NVIDIA presented at OFC 2026 side by side, and you begin to see that the gap between those two layers varies considerably across institutions.

The silicon photonics foundry race toward 200G/λ is no longer primarily a device performance competition. It is a contest of system integration completeness and ecosystem maturity. And in that contest, where the three players actually stand looks somewhat different from what their press releases suggest.

Seven Papers at a Glance

Samsung vs. GlobalFoundries Platform Comparison

(Note: MRM BW comparisons are sensitive to bias voltage and detuning conditions — direct comparison requires care)

From here, I break down what each institution’s papers actually show, what they do not show, and where the gap between official announcements and paper content lies.

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