DCO QSFP-DD and CFP2 ZR+

With the explosive growth of AI training clusters, 5G network evolution, and data center traffic, traditional optical modules can no longer meet the demands of metro and backbone networks for ultra-high bandwidth, ultra-long distance, and low-cost operation and maintenance. C-LIGHT’s 400G DCO coherent optical module series, available in two mainstream form factors — QSFP-DD and CFP2 — brings coherent optical technology from traditional transmission equipment down to pluggable ports, offering a cost‑effective “colored‑light direct‑connect” solution for data center interconnect (DCI) and carrier‑grade optical networks.

1. DCO Technology Enables 400G Ultra‑Long‑Haul Transmission

The biggest difference between 400G DCO modules and traditional non‑coherent modules is that they integrate a digital signal processor (DSP) and a tunable laser (ITLA) within a compact pluggable package. Using advanced modulation and digital signal processing, the transmission distance is dramatically extended from less than 10km to 120km or even hundreds of kilometers.

C‑LIGHT’s 400G DCO product line covers both QSFP-DD and CFP2 form factors, supporting multi‑rate adaptation (100G/200G/400G) to meet diverse requirements ranging from inter‑data‑center connectivity to long‑haul backbone transmission.

2. Form Factors and Key Parameters

2.1 QSFP-DD ZR+: The Premier Choice for High‑Density Deployment

QSFP‑DD (Quad Small Form Factor Pluggable – Double Density) is the most widely deployed 400G package standard, offering high density and backward compatibility. Key parameters of the C‑LIGHT QSFP‑DD ZR+ module are as follows:

• CL400GQDDZR+-HP (high‑power version, supports amplified links)

• CL400GQDDZR-120 (120 km ZR version)

• CL400GQDDZR+-300 (300 km ZR+ version)

2.2 CFP2 DCO: Long‑Haul Transmission and Carrier‑Grade Applications

The CFP2 package is slightly larger than QSFP‑DD but offers better heat dissipation and richer functional integration, making it suitable for telecom scenarios with higher demands on transmission distance and reliability. Key parameters of the C‑LIGHT CFP2 DCO module:

The CFP2 DCO version also supports an integrated extended C+L‑band design, covering wavelengths from 1524 nm to 1627 nm, achieving continuous tuning over more than 100 nm – a foundation for doubling per‑fiber capacity from 96 Tbps to 192 Tbps.

3. Core Technology Highlights

3.1 Integrated DSP and Advanced Modulation to Break Distance Barriers
C‑LIGHT’s 400G DCO modules use a 7nm process coherent DSP that supports multiple modulation formats (DP‑16QAM/8QAM/QPSK). Digital signal processing compensates in real time for fiber dispersion, polarization mode dispersion, and other impairments, enabling signals that traditionally traveled only 2‑10 km to be stably transmitted over 80‑500 km or more, greatly reducing the need for intermediate optical amplification and regeneration.

3.2 Full C‑Band Tunability for Simplified Wavelength Management
The modules incorporate a nano‑ITLA (narrow‑linewidth tunable laser) supporting on‑demand configuration of all 96 C‑band DWDM channels. Operators no longer need to stock multiple module types for different wavelengths – wavelength scheduling is done via software, dramatically reducing operational complexity.

3.3 High Transmit Optical Power Design for ROADM Compatibility
Compared to standard ZR modules (typically around ‑10 dBm transmit power), C‑LIGHT’s ZR+ high‑power version raises transmit power to 0 dBm or even +4 dBm, allowing direct connection to ROADM (Reconfigurable Optical Add‑Drop Multiplexer) line systems. This avoids signal attenuation caused by insufficient power and truly enables interoperability with carrier‑grade WDM systems.

3.4 Integrated EDFA and Tunable Optical Filter for All‑in‑One Amplified Links
The high‑power version integrates an EDFA and a tunable optical filter (TOF) that pre‑amplifies the output signal, achieving transmission over 80 km even without external amplifiers – further reducing system integration complexity.

3.5 Multi‑Standard Compliance for Interoperability
The modules comply with multiple standards including Open ZR+ MSA 2.0, OIF 400ZR, IEEE 802.3cw, and Open ROADM, supporting both OFEC and SFEC error correction configurations. They can interoperate with 400G DCO modules from other vendors, meeting operators’ needs for multi‑vendor procurement.

4. Typical Application Scenarios

4.1 Data Center Interconnect (DCI) – Core Scenario
For data centers located in different parts of a city or even across cities, C‑LIGHT 400G DCO modules can be plugged directly into QSFP‑DD ports of data center switches to achieve “colored light direct from the switch”, enabling interconnection over tens to hundreds of kilometers without expensive dedicated transport equipment. This significantly reduces equipment procurement costs, rack space occupancy, and overall power consumption.

Taking the QSFP‑DD ZR+ high‑power version as an example, with an optical amplifier (EDFA) the single‑hop transmission distance reaches 450 km, while in 200G/100G modes it reaches 600 km and 1000 km respectively – perfectly covering metro DCI and regional data center interconnection needs.

4.2 AI/HPC Cluster Synchronization Across Data Centers
Distributed AI training requires low‑latency, high‑bandwidth data synchronization among geographically dispersed data centers. C‑LIGHT 400G DCO modules, using coherent optical technology, deliver up to 400 Gbps per fiber while maintaining very low round‑trip time (RTT) over hundreds of kilometers, effectively supporting unified training tasks for cross‑region GPU clusters.

4.3 5G Transport Network: Midhaul/Backhaul and Core Layer
In the 5G era, base station density and service traffic surge. C‑LIGHT 400G DCO modules can be deployed in the midhaul and backhaul layers of 5G transport networks, directly connecting aggregation nodes to the core network via DWDM colored light, meeting the rigid bandwidth requirements of 5G eMBB scenarios at very low cost per bit.

4.4 Metro WDM and Long‑Haul Backbone Capacity Expansion
The CFP2 DCO version, with its capability to transmit 400G over 1000 km and 100G over 5000 km, is ideal for capacity upgrades of carrier metro core networks and national backbone lines. Combined with extended C+L‑band technology, a single fiber can achieve nearly 200 Tb/s of transmission capacity, significantly improving spectral efficiency.

5. Product Selection Guide

6. Service and Support

C‑LIGHT provides the following for its 400G DCO coherent optical module series:

• 3‑year warranty, lifetime technical support

• Compatibility verification – interoperability tested with mainstream switches, routers, and transport equipment

• Customization services – firmware modifications, alarm thresholds, custom labeling, and specific FEC configurations

• Fast delivery – standard models ship within 3‑5 working days

From traditional non‑coherent optical modules to 400G DCO coherent modules, C‑LIGHT – in both QSFP‑DD and CFP2 form factors – brings the benefits of digital coherent optical technology to every corner of data center and telecom networks. Whether it is the QSFP‑DD ZR+ for high‑density DCI or the CFP2 DCO for long‑haul backbone applications, C‑Light leverages its self‑developed core components and full‑industry‑chain advantages to deliver highly reliable, cost‑effective solutions for IP‑over‑DWDM networks in the 400G era.