The optical communications industry is undergoing a profound transformation. As bandwidth demands surge — driven by AI workloads, cloud-scale data centers and global satellite connectivity — coherent optics has emerged as the foundational technology enabling this next wave of innovation. From long-haul networks to metro, access, data center and even space-based links, coherent optics is redefining how we transmit data optically.
CableLabs has been instrumental in shaping this revolution, pioneering advancements in point-to-point and point-to-multipoint coherent architectures that enable greater efficiency and scalability in the optical access networks.
About a decade and a half ago, long-haul optical networks relied on Intensity Modulation and Direct Detection (IM-DD), effectively constrained to 10 Gbps, or 10G, per wavelength. Dispersion and polarization effects required complex compensation, and scaling was difficult.
The first real-world deployments of coherent optics around 2010 changed everything. By leveraging amplitude, phase and polarization — alongside powerful coherent detection and digital signal processing (DSP) — coherent systems unlocked 100G, 400G, 800G and now 1.6 Tbps transmission rates per carrier, with dramatically improved reach, spectral efficiency and capacity.
Coherent optics delivers transformative advantages across multiple dimensions:
- Spectral efficiency: Maximizes data throughput over a given spectrum, increasing overall network capacity.
- Power efficiency: Reduces energy consumption per bit transmitted, making networks more sustainable.
- Architectural efficiency: Supports flexible and scalable network designs, accommodating diverse deployment scenarios.
- Operational efficiency: Simplifies network management and provisioning, enabling easier scaling and maintenance.
The Building Blocks of Coherent Optics
What began as bulky 100G embedded modules consuming 80 watts have evolved into thumb-sized quad small form-factor pluggable (QSFP) transceivers consuming as little as 5 watts for 100G coherent in access applications. This miniaturization enables direct integration into routers and switches, transforming deployment models across network segments.
Modern coherent optical transceivers achieve unprecedented performance and efficiency through deep integration of electronics and photonics. The key building blocks are included in the diagram below.
At the core, complementary metal-oxide semiconductor (CMOS)-based Application-Specific Integrated Circuits (ASICs) and DSP enable high-speed signal processing and advanced modulation formats. These are paired with high-speed analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) — now sampling at rates exceeding 300 gigasamples per second (GS/s) — to support ultra-high-capacity links such as 1.6T ZR.
Optical and electronic components are increasingly co-packaged, combining modulators, photodiodes (PD), drivers and transimpedance amplifiers (TIAs) into compact assemblies that reduce footprint and power consumption. Stable and tunable laser sources in the C- and O-bands provide multi-channel transmission capability, while advanced packaging techniques — such as wafer-level integration and liquid cooling — preserve signal integrity and thermal stability.
This holistic approach to integration not only minimizes size and cost but also enables scalable architectures for next-generation optical networks.
Technology Trends Shaping the Future
Several trends are accelerating coherent optics innovation:
- Baud and data rates: The industry surpassed 1 Tbps per carrier in 2022, with multi-carrier architectures pushing toward 3.2 Tbps.
- CMOS Moore’s Law: Continued CMOS scaling drives higher integration and lower power, with 3 nanometer (nm) nodes today and 2 nm on the horizon.
- DSP advancements: Techniques like probabilistic constellation shaping (PCS), equalization-enhanced phase noise (EEPN) equalization, digital subcarriers and advanced forward error correction (FEC) bring performance closer to Shannon’s limit (i.e., the maximum theoretical capacity at which data can be transmitted).
- Optical materials: Thin-film lithium niobate (TFLN), polymers, silicon-organic and plasmonic-organic hybrids (SOH/POH), and barium titanate (BTO) are enabling next-generation modulators for higher bandwidth and lower power consumption with compact integration compatibility.
- Laser innovation: Recent advances in laser technology are driving a shift toward low-phase-noise, high-output and cost-effective tunable and fixed lasers.
Expanding Applications: From Core to Edge — and Beyond
Coherent optics was first deployed in long-haul networks because it solved critical challenges that IM-DD could not. Today, it’s everywhere due to technology maturation, bandwidth demand and the whole ecosystem support:
- Regional and metro networks: Supporting regional connectivity with high capacity and flexibility.
- Data center interconnect (DCI): AI-driven workloads demand massive bandwidth; pluggable modules like 400ZR and 800ZR are now standard.
- Access networks: Coherent optics is now deployed at the edge, with interoperable 100G and 200G P2P transceivers reducing cost, power and complexity in fiber access environments.
- Free space optics: Coherent transceivers now enable high-speed laser links between low-earth orbit (LEO) satellites, supporting global broadband coverage.
What’s Next?
Innovation isn’t slowing down. Coherent optics is poised to move deeper into the network:
- Coherent Lite: Low-power, short-reach solutions are ideal for campus and urban deployments (up to 20 km).
- Inside the data center: As speeds climb, coherent optics may be co-packaged with switch silicon to overcome optical loss and scale bandwidth.
- Next-gen passive optical networking (PON): Coherent optics is redefining passive optical networks with higher speeds, longer reach and new architectures that support both P2MP and legacy coexistence.
CableLabs Is Leading the Coherent Frontier
While coherent optics continues to expand across the network, CableLabs is leading the charge to define what’s next. Our specifications for P2P coherent optics have enabled interoperable 100G and 200G transceivers optimized for access networks — already deployed by major operators to extend fiber reach and reduce cost, power and complexity.
We also introduced the industry’s first architecture and technologies for coherent passive optical networks (CPON), supporting 100G per wavelength with up to 512-way splits or 80 km reach. CPON enables seamless coexistence with legacy PON and P2P coherent systems, unlocking new possibilities for residential, enterprise and wireless transport.
As coherent optics moves deeper into the network, we invite the industry to collaborate with CableLabs on specifications, interoperability and deployment strategies that will shape the next decade of optical innovation.