OFC 2026 takeaways: pluggables, multi-rail, HCF and AI

OFC 2026 was held in Los Angeles, with the technical conference running March 15-19 and the exhibition running in parallel from March 17-19. Here are my key takeaways from attending all five days of the technical conference, multiple exhibition hall presentations and panels, and from visiting exhibitor booths.

1600ZR/ZR+ progress

OFC 2026 was a good opportunity to catch up on progress with 1600G coherent pluggables. 1600ZR leverages OFEC and 236 GBaud, with targeted power consumption in the ~32–35 W range. The digital baseline, required for DSP development, was approved in the third quarter of 2025 and the implementation agreement (IA) is due in the second quarter of 2026.

1600ZR+ uses OFEC, PCS, dual subcarriers and 252 GBaud, with targeted power consumption in the 38–40 W range. The 1600ZR+ digital baseline was approved in the fourth quarter of 2025 and the IA is scheduled for the third quarter of 2026.

Multiple vendors, including Nokia, announced new 1600ZR and ZR+ products. However, some vendors are prioritizing 1600ZR time to market with a DSP that does not support the 1600ZR+ standard, while others are prioritizing a single DSP for both 1600ZR and 1600ZR+. According to Cignal AI, 800G and 1600G pluggables together are forecast to account for approximately 60 percent of coherent revenues by 2030.

Coherent lite and “coherent extra lite”

In addition to 1600ZR and ZR+, the OIF is also defining a 1600CL standard, where CL is an abbreviation for coherent lite. 1600CL was kicked off in the fourth quarter of 2024 and is behind 1600ZR and ZR+ in terms of standardization, with ongoing work to balance power consumption, performance and latency. Forward error correction (FEC) and baud rate are still under discussion. Targets were ~30 W power consumption, 300 ns latency and ~20-40 km maximum reach.

Looking one step ahead, Nokia announced a 3.2T-capable coherent lite solution.

A related topic, which I refer to as “coherent extra lite,” focuses on reducing the power, latency and cost of coherent even further for use inside the data center by using optical techniques to reduce the amount of electronic digital signal processing required. These include self-homodyne techniques, optical ADCs and DACs and coherent approaches that use lower-power PAM4 DSPs instead of high-power coherent DSPs.

New pluggable form factors and MSAs

Another key trend was the emergence of new pluggable form factors and multi-source agreements (MSAs), including extra-dense pluggable optics (XPO), co-packaged interconnect (CPX) and the Optical Compute Interconnect (OCI) MSA.

XPO is a new MSA defining a liquid-cooled pluggable with 12.8 Tb/s capacity, corresponding to 64 lanes at 200 Gb/s per lane. While XPOs are physically larger than today’s 1.6 Tb/s OSFP and QSFP-DD modules, their much higher capacity still enables significantly higher faceplate density. XPOs were displayed in multiple booths on the exhibition floor.

Open CPX is another new MSA targeting co-packaged optics (CPO)-type applications, with a new pluggable form factor and the term “socketed CPO” used as a descriptor. CPO was itself a prominent topic at OFC 2026,

The OCI-MSA targets optical interconnects for AI scale-up, connecting GPUs within a rack. The OIF also has a high-density connector project looking at potential pluggable form factors with a focus on 400 Gb/s per lane.

Multi-rail ILAs

Another hot topic was multi-rail technology, in particular multi-rail in-line amplifiers (ILAs). These ILAs typically support bidirectional amplification for multiple fiber pairs on a single ~1RU card, sharing components such as optical time-domain reflectometry (OTDR), optical channel monitoring (OCM) and digital gain equalization (DGE), while also using low-power uncooled and/or multi-chip pump lasers.

Nokia announced a multi-rail ILA solution enabling up to 160 C+L ILAs per rack. In terms of fiber pair requirements, Meta presented that while regional data center interconnectivity typically requires 16 to 48 fiber pairs or more, AI-driven regional data center interconnectivity requires 128 or more fiber pairs.

Full-spectrum transponders and media converters

Another related topic that appeared in multiple presentations was the full-spectrum transponder (FST). With large AI and cloud providers deploying capacity in full fiber-pair increments, FSTs provide the ability to light an entire band, such as the C-band, or a full fiber pair with a single card, for example one supporting 32 x 300 GHz 1.6T interfaces.

These transponders may also use media converters that integrate IM-DD client optics with coherent line optics in a single pluggable or package inside the full-spectrum transponder. Media converters provide an attractive solution for integrating co-packaged optics switches with coherent transmission for scale-across. An interesting question raised during the conference was whether FSTs will ultimately rely on pluggable coherent technology or whether there is a role for multi-wavelength embedded technologies such as comb lasers, highly integrated multi-wavelength photonic integrated circuits (PICs) and multi-wavelength DSPs.

Hollow-core fiber

As at ECOC 2025, hollow-core fiber (HCF) was again a hot topic at OFC 2026. State-of-the-art loss is now down to 0.04 dB/km. 

One characteristic of HCF is very low backscattering, which has both advantages and challenges. On the positive side, it enables bidirectional transmission with transmit and receive operating at the same frequency with minimal penalties. This was the subject of presentations on bidirectional HCF testing results from both Microsoft and Nokia Bell Labs. On the challenging side, low backscattering makes OTDR more difficult, with mitigation requiring much higher OTDR power along with bidirectional OTDR to account for changes in gas pressure along the fiber.

Additional challenges related to gas line absorption (GLA) and inter-mode interference (IMI) were discussed, with potential solutions including per-wavelength power optimization for GLA and digital subcarriers for IMI. Another notable observation was the move toward different HCF designs optimized for different applications, such as prioritizing low SMF-to-HCF connector loss for intra-data-center connectivity versus minimizing loss per kilometer for long-haul applications.

Probabilistic constellation shaping

I attended a session marking the tenth anniversary of probabilistic constellation shaping (PCS), a modulation scheme pioneered by Nokia with the PSE-3s in 2018 that has since become a standard feature in both embedded coherent engine and the latest 800ZR+ pluggables. 

Since then, PCS has evolved in terms of interoperability, including Open ROADM modes, as well as lower complexity, latency and power consumption (for pluggables). Additional improvement vectors include taking PCS gain closer to the Shannon limit, reducing nonlinear penalties due to higher symbol power variation and optimizing the use of overhead between PCS and FEC.

And of course, lots of AI

As expected, AI was an overarching theme throughout the conference. Topics included the maximum distance for scale-across architectures, with differing views of approximately 50 km for inference, ~100 km for synchronous training and more than 5,000 km for asynchronous training.

Nokia Bell Labs presented work on using AI to model optical impairments such as stimulated Raman scattering (SRS) and polarization-dependent loss (PDL) for real-time planning and control. I also heard about a pretrained optics-specific AI agent that outperforms much larger general-purpose models and human graduate students in optics exams, with applications including OSNR estimation and fault location and recovery.

What OFC 2026 means for AI-ready optical networks

OFC 2026 highlighted an industry rapidly evolving to meet the demands of the AI era. Taken together, these trends point toward optical networks that are more scalable, more power-efficient and more tightly coupled to compute infrastructure. For Nokia, this reinforces the importance of delivering end-to-end innovation across components, pluggables, photonics, systems and software.