1.6T DCI: Next-Generation Optical Technologies for Data Center Interconnects

1. What Is 1.6T DCI?

1.6T DCI refers to optical networking solutions designed to transport up to 1.6 terabits per second of data between separate data center locations. These connections support AI training infrastructure, distributed storage, cloud service replication, large-scale Ethernet networks and geographically distributed computing environments.

Compared with earlier 400G and 800G DCI deployments, 1.6T architectures provide greater capacity per interface. This can help network operators increase aggregate bandwidth while managing rack space, fiber utilization, equipment density and network expansion.

The most suitable architecture depends on the physical distance between sites, the available fiber infrastructure, optical line-system capabilities and the required interoperability with routers, switches and transport equipment.

2. Why 1.6T DCI Is Becoming Important

AI workloads are increasing the amount of data exchanged between computing facilities. Training clusters, inference platforms and distributed storage systems may operate across multiple buildings or separate data center campuses. Their traffic creates growing demand for high-capacity inter-site connectivity.

AI Scale-Across Networks

Large AI systems increasingly distribute computing resources across multiple facilities. Moving model data, checkpoints and training information between locations requires high-throughput network connections. Higher-capacity DCI links help accommodate this traffic without relying exclusively on large numbers of lower-rate interfaces.

Cloud and Storage Replication

Cloud platforms use inter-site networks for data replication, backup, workload migration and service continuity. A 1.6T interface can provide additional capacity for these operations as storage systems and distributed applications expand.

Fiber and Port Density

Increasing bandwidth per port can help reduce the number of physical interfaces needed for a given aggregate capacity. This is valuable in high-density router and switch platforms where front-panel space, fiber routing and cooling capacity are limited.

3. Main 1.6T Optical Transmission Technologies

Several optical architectures can support 1.6T connectivity, but they serve different distances and network environments. Direct-detection PAM4 and coherent transmission should be evaluated separately.

DR8, 2×FR4 and FR8 are direct-detection PAM4 approaches. 1600ZR is a coherent optical interface designed for a different transmission environment. The choice between them depends on the required reach, fiber topology and network equipment.

4. 1.6T PAM4 Transceivers for Data Center Connectivity

1.6T PAM4 optical modules use high-speed electrical and optical lanes to achieve an aggregate data rate of 1.6 terabits per second. A common architecture uses eight lanes operating at 200 Gbps per lane.

PAM4 encodes two bits per symbol using four signal levels. Compared with NRZ, it carries more information per symbol and supports higher data rates within a given signaling bandwidth. However, the smaller separation between signal levels increases sensitivity to noise, distortion and channel impairments.

1.6T DR8

A 1.6T DR8 module typically uses eight parallel optical lanes over single-mode fiber. It is suitable for short-reach connections where the required optical distance and fiber infrastructure match the module specification.

1.6T 2×FR4

A 1.6T 2×FR4 architecture combines two 800G FR4 optical groups within one module. It can provide two 800G optical connections or a single aggregate 1.6T connection, depending on the host interface and supported operating mode.

1.6T FR8

FR8 implementations use wavelength-multiplexed optical channels to deliver high aggregate bandwidth over single-mode fiber. The exact wavelength grid, lane rate and optical reach depend on the implementation.

5. 1600ZR: Single-Wavelength Coherent 1.6T DCI

Coherent optics are central to the development of high-capacity DCI because they support advanced optical signal processing and transmission over amplified fiber routes. The 1600ZR interface represents an important step toward carrying a complete 1.6T Ethernet client over one coherent optical wavelength.

In September 2026, the Optical Internetworking Forum published its 1600ZR Coherent Interface Implementation Agreement. The specification defines an interoperable coherent line interface and frame format for single-span, amplified, point-to-point DWDM links up to 120 km.

This development extends the ZR technology progression from 400ZR and 800ZR to 1.6T. It provides a common technical framework for client mapping, framing, FEC, modulation and optical characteristics.

Single-Span DCI

1600ZR is intended for point-to-point amplified optical routes. Its target application is a connection between two sites using a DWDM line system, with the optical performance designed around the specified reach and operating conditions.

Interoperability

An implementation agreement establishes common interface requirements so equipment from different vendors can work toward interoperable operation. Actual deployment still requires validation of module support, host electrical interfaces, optical line-system characteristics and system-level performance.

Reach and Optical Conditions

The 120 km target is associated with the specified amplified single-span application. It should not be interpreted as a guaranteed distance over every fiber route. Fiber attenuation, amplifier noise, OSNR, connector loss and optical power conditions remain important.

6. 1.6T Coherent Transmission Beyond Single-Span DCI

Not every 1.6T inter-site network uses the same coherent operating mode. Some deployments require longer metro or regional routes, multiple optical spans or more demanding optical performance than a single-span DCI connection.

Extended-reach coherent solutions may use different modulation formats, baud rates, FEC configurations and optical power levels to balance spectral efficiency and transmission distance.

The term ZR+ is often used for vendor-specific or extended-reach coherent operating options. It should not be treated as a single universal 1.6T specification with one fixed reach. The supported modes and distances must be confirmed from the relevant equipment documentation.

7. How a 1.6T Coherent DCI Link Works

A coherent DCI system converts client traffic into a modulated optical signal, transports it through a fiber and DWDM line system, and reconstructs the original data at the destination.

Coherent detection uses a local oscillator and phase-sensitive signal recovery. This allows the receiver to recover information encoded in both the amplitude and phase of the optical field, supporting advanced compensation of transmission impairments.

8. DWDM and Fiber Infrastructure for 1.6T DCI

DWDM is an important part of high-capacity DCI because it allows multiple optical wavelengths to share the same fiber infrastructure. Each wavelength carries a separate optical channel, increasing the total capacity available over a fiber pair.

Wavelength Allocation

Coherent channels must operate within the supported wavelength range and channel plan of the optical line system. The selected channel spacing must accommodate the signal's spectral characteristics and the system's filtering requirements.

Optical Amplifiers

EDFAs compensate for fiber attenuation in amplified DCI links. Their gain, noise figure, output power and channel loading influence the OSNR available to the receiving transceiver.

ROADM-Based Networks

ROADMs allow optical wavelengths to be routed through multi-site transport networks. Their insertion loss, filtering characteristics and passband must be considered when deploying high-baud-rate coherent channels.

Fiber Quality

Fiber attenuation, chromatic dispersion, polarization-mode dispersion and nonlinear effects influence the achievable transmission performance. Existing fiber routes should be characterized before selecting a coherent operating mode.

9. Optical Link Budget and OSNR Requirements

A 1.6T DCI design requires a complete evaluation of optical power and signal quality. The distance between sites alone is not enough to determine whether a particular transceiver can operate reliably.

For direct-detection PAM4 links, engineers typically evaluate transmitter output power, receiver sensitivity, insertion loss and the supported optical budget. For coherent DWDM links, OSNR and the performance of the complete optical line system are equally important.

10. 1.6T DCI Power Consumption and Thermal Design

Higher data rates increase the demands placed on transceiver electronics, optical components and host platforms. A 1.6T module may integrate high-speed DSP functions, multiple optical lanes, laser sources and advanced thermal-management structures.

The actual power consumption depends on the module architecture. A parallel PAM4 module and a coherent DCI transceiver may have different processing requirements, optical components and cooling characteristics. Their power ratings should not be treated as interchangeable.

• DSP architecture: Higher processing throughput and advanced signal recovery affect electrical power consumption.

• Optical components: Laser sources, drivers and receiver circuits contribute to the total module power.

• Host power support: The switch or router must support the module's specified power class.

• Cooling capability: Airflow, heat sinks and chassis thermal design must accommodate high-power modules.

• Port density: Fully populated 1.6T interfaces can create concentrated thermal loads.

OSFP and OSFP-RHS mechanical designs are relevant to high-density optical platforms, but the form factor alone does not establish a module's power consumption or cooling capability. The exact product datasheet and host platform requirements must be checked.

11. 800G DCI vs. 1.6T DCI

Moving from 800G to 1.6T increases the capacity available per client interface. However, the transition involves more than doubling the nominal data rate. Electrical lane speed, optical modulation, DSP architecture and line-system performance all influence the deployment.

The 1600ZR interface is particularly significant because it enables a 1.6T Ethernet client to be transported over one coherent wavelength in the specified single-span amplified application. This differs from simply combining two independent 800G client links.

12. C-LIGHT 1.6T Optical Connectivity Solutions

C-LIGHT offers high-speed optical connectivity solutions for next-generation data center and AI networking environments. Its 1.6T OSFP-RHS product family is relevant to high-density 1.6T optical connectivity, while the appropriate application depends on the exact optical configuration and supported interface.

For DCI projects, the product selection process should include a review of optical reach, wavelength configuration, host electrical interface, module power, connector type, FEC behavior and DWDM compatibility. A 1.6T PAM4 client module should not be assumed to support 1600ZR coherent line transmission unless its specifications explicitly state that capability.

13. Key Considerations When Selecting a 1.6T DCI Solution

A successful 1.6T DCI deployment requires matching the optical technology to the actual network environment. The following factors should be evaluated before selecting transceivers and transport equipment.

14. Conclusion