ECOC 2025 Tech Focus: Coherent's Latest Progress in Optical Components, Modules and Co-Packaged Optics

Introduction

At the 2025 European Conference on Optical Communication (ECOC 2025), Coherent CTO Julie Yang shared the company's latest progress in optical components and subsystems for data centers and data center interconnect (DCI). The talk covered pluggable optical modules, co-packaged optics (CPO), optical switching, long-haul interconnect, and emerging quantum key distribution (QKD).

In today's AI-driven data center architectures, demand for scale-up (high-speed XPU-to-XPU interconnect) and scale-out (cross-node expansion) is rising sharply, and the role of optical interconnect is becoming ever more critical. Coherent's R&D strategy reflects optics expanding from traditional datacom into full-spectrum applications across AI factories and hyperscale computing.

Content

1. Data Center Network Architecture: The Scale-Up and Scale-Out Challenge

• Scale-Out (cross-node): Optical interconnect is already widely used, spanning 10 meters to 10 kilometers. It must interoperate with diverse equipment and stay highly flexible, so pluggable optical modules remain mainstream.

• Scale-Up (XPU-to-XPU within a system): Traditionally dominated by copper, but as rates rise to 200G, 400G and beyond, copper's reach and power become the bottleneck. This domain prioritizes density, power and cost, which is why embedded optics such as CPO, NPO and CIO are emerging.

2. Roadmap for Pluggable Optical Modules

Coherent stressed that pluggable modules still have a long runway ahead:

• Higher per-lane rates: 200G VCSEL, SiPh and InP solutions have been demonstrated, with progress toward 400G.

• More lanes: OIF is driving high-density interfaces supporting 16/32/64 lanes at 400G per lane, mapping to 3.2T, 6.4T and even 25.6T.

• Advantages: a standardized multi-vendor ecosystem, deferred architecture decisions, and easy maintenance.

3. Two Technology Paths for Co-Packaged Optics (CPO)

• VCSEL-based CPO:

  • Low cost, with power as low as 1 pJ/bit.

  • Suited to short-reach applications; Coherent has demonstrated it together with IBM and ARPA-E.

  • The downside is the reliability challenge in high-temperature environments.

• Silicon Photonics-based CPO:

  • Paired with an InP external laser source (ELS), offering high reliability and medium-to-long reach (>500m).

  • Compatible with single-mode 1.3µm optical switching, making it a fit for future optical circuit switching architectures.

  • The downside is the challenge of 400G lane rates, which may require InP or thin-film lithium niobate modulators.

4. New Applications for Optical Circuit Switching (OCS)

• Advantages: flexibility, network reconfigurability, and fault tolerance.

• Technology: Coherent uses liquid-crystal technology with no mechanical moving parts and has demonstrated configurations from 64×64 to 320×320.

• Market forecast: US$2 billion by 2030.

5. Data Center Interconnect (DCI) and Transport Networks

• Demand drivers: AI workloads must be distributed across data centers, driving 400G, 800G and 1.6T ZR/ZR+ optical modules.

• Technology strategy:

  • InP: high output power (e.g., 0 dBm in L-band without an EDFA), suited to demanding optical and electrical specs.

  • SiPh: cost advantage and high integration, suited to applications where it meets the spec.

• Multi-fiber-pair (multi-rail) challenges:

  • ILA hut space and power are constrained, while capacity must grow by 10x or more.

  • Coherent optimizes through high-efficiency pump lasers, stacked packaging, and integrated dynamic gain equalizers, among other approaches.

6. A New Push into Quantum Key Distribution (QKD)

• Conventional encryption is expected to be breakable by quantum computers around 2030.

• Together with Qubit, HPE, Juniper and Liberty Global, Coherent demonstrated a pluggable QSFP-QKD, shrinking QKD into a module-slot form factor for the first time and enabling transmission in parallel with data traffic.

Summary

Coherent's ECOC 2025 talk revealed optical interconnect advancing on multiple fronts at once:

• Pluggable modules remain the market mainstream and will keep advancing toward 400G/lane and multi-lane designs.

• CPO is gradually landing in scale-up scenarios, with VCSEL and SiPh progressing in parallel.

• Optical circuit switching shows AI data centers' need for dynamic network structures, with the market growing rapidly.

• DCI and multi-fiber challenges reflect the new pressure from AI workloads spanning multiple data centers.

• QKD is a forward deployment, preparing for future network security.

Overall, AI-driven traffic growth is accelerating optical interconnect innovation, from short reach to long haul and from modules to switches, and Coherent's R&D strategy shows a comprehensive, multi-generation footprint.