1. Project Background: Real DCI Network Deployment Requirements

In a metropolitan Data Center Interconnect (DCI) project, the customer deployed the C-LIGHT 100G QSFP28 ZR4 FEC-Free optical modules to connect two core data center sites.

Deployment conditions:

• Fiber distance: 68 km

• Estimated total link loss: ~24 dB @1310 nm

• Switch platform: Huawei 6700 series 100G Ethernet switches

• FEC status: Disabled by default on ports

Key project requirements:

• Ultra-low latency transmission

• Simplified switch configuration (FEC OFF default mode)

• Stable 100G traffic for storage replication and data synchronization

Validation focus:

Whether the C-LIGHT 100G QSFP28 ZR4 FEC-Free module can operate stably without FEC assistance under real DCI conditions.

2. C-LIGHT 100G QSFP28 ZR4 FEC-Free Product Overview

The C-LIGHT 100G QSFP28 ZR4 FEC-Free optical module is designed for 50–80 km medium-to-long distance optical interconnect applications without requiring FEC support.

It integrates advanced optical and electrical technologies, including:

• MACOM driver ICs

• EML LAN-WDM transmitter

• SOA-based receiver architecture

• Multi-generation optimized control circuitry

This product fills the market gap for high-performance long-distance 100G optics that can operate without system-level FEC configuration, reducing complexity and power consumption in real deployments.

2.1 Core Specifications

• Form factor: QSFP28

• Data rate: 100Gbps (4×25.78G NRZ)

• Wavelength: LAN-WDM 1295–1309 nm

• Interface: LC duplex

• Maximum tested reach: 80 km (single-mode fiber)

• Optical components: EML laser + SOA receiver

• Power consumption: 4.5–5.5 W

2.2 Design Features (C-LIGHT Optimization)

• High link budget design: up to 27 dB @ BER 1E-12

• Supports stable operation with FEC OFF under high-loss conditions

• Optimized for long-distance metro and DCI applications

• Low power design (~5 W typical)

3. Engineering Validation Results: FEC-Free Operation Performance

3.1 Test Environment Setup

• Fiber type: G.652D single-mode fiber

• Link distance: 68 km

• Total insertion loss: ~24 dB

• Switch configuration: 100G QSFP28 ports (FEC OFF)

• Traffic load: IP data + continuous storage replication

3.2 Test Results (FEC OFF Mode)

Under full FEC disabled operation:

• ✔ Stable link uptime (>72 hours continuous operation)

• ✔ Bit Error Rate (BER) maintained below 1E-12

• ✔ Throughput stability at 99.99% line rate

• ✔ Link margin still maintained at ~2–3 dB safety buffer

3.3 Key Conclusion

Even with FEC completely disabled, the C-LIGHT 100G QSFP28 ZR4 module maintained stable 100G transmission over a 68 km DCI link.

4. Why C-LIGHT ZR4 Can Operate Without FEC

The stability is not accidental but based on three engineering factors:

4.1 Link Distance Below Design Limit

The module is designed for:

• Up to 80 km reach without FEC

• 27 dB link budget capability at 1E-12 BER

Actual deployment:

• 68 km distance

• ~24 dB loss (≈85% of design capacity)

4.2 Sufficient Optical Power Margin

Measured optical performance:

• Transmit power: > +4 dBm

• Receiver sensitivity: ~ -24 dBm @ BER 1E-12

• Actual received power: ~ -20 dBm

This provides:

• 2–3 dB remaining margin

• Stable BER performance without error correction

4.3 Optimized Receiver Design (C-LIGHT Engineering)

The module incorporates:

• Enhanced transmitter stability

• SOA receiver temperature optimization

• Reduced noise figure (NF)

• Improved weak-signal detection capability

This ensures strong raw signal recovery even without FEC.

5. Engineering Value of FEC-Free Operation

Disabling FEC is not only feasible but also beneficial in real networks.

5.1 Lower Latency

FEC processing introduces:

• ~100 ns to 2 µs latency in 100G systems

By disabling FEC:

• End-to-end latency is significantly reduced

• Ideal for real-time applications (AI, storage sync, financial trading)

5.2 Reduced System Load

• Eliminates FEC encoding/decoding overhead

• Reduces power consumption by 3–4 W per port

• Improves switch port efficiency

5.3 Improved Multi-Vendor Compatibility

In heterogeneous networks:

• Some devices operate with FEC OFF by default

• ZR4 modules must support “bare-link operation”

• C-LIGHT ZR4 ensures seamless interoperability

6. When Can ZR4 Operate Without FEC? (Engineering Guidelines)

Based on field experience, FEC-free operation is suitable under the following conditions:

✔ Recommended Conditions:

• Distance: 40–80 km

• Link loss: < 27 dB

• High-quality fiber: G.652D / G.657A

• Limited connector count (≤5–10 connectors)

7. Product Value Summary

This real-world deployment demonstrates that:

The C-LIGHT 100G QSFP28 ZR4 FEC-Free module not only meets standard ZR4 specifications but also delivers:

• Strong link budget headroom

• Optimized receiver sensitivity

• Stable performance without FEC dependency

• Excellent compatibility for metro and DCI hybrid networks

8. Conclusion

The field deployment confirms that:

• ✔ “No FEC” does not mean instability

• ✔ Properly designed ZR4 modules can operate reliably without FEC

• ✔ FEC-Free operation is ideal for low-latency, high-efficiency networks

The C-LIGHT 100G QSFP28 ZR4 FEC-Free solution provides a practical and high-performance option for modern DCI and metro interconnect architectures.