English
In today's digital era, data centers are experiencing unprecedented demand for high-speed, high-bandwidth, and low-latency network solutions. For 400G single-mode fiber applications exceeding 100 meters in transmission distance, 400G DR4 and 400G FR4 optical modules have emerged as the two dominant and critical technical solutions.
This blog delves into the technical specifications, core differences, and typical connection methods of 400G DR4 and 400G FR4 optical modules. By thoroughly analyzing their working principles and application scenarios, AICPLIGHT aims to help you better understand their roles and value in modern data center interconnect architectures.
I.What is a 400G DR4 Optical Module?
The 400G DR4 optical module is a transceiver that achieves 400G transmission using Parallel Single-Mode Fiber (PSM) technology. It employs four independent 100G PAM4 signal channels, each operating at the same 1310nm wavelength. At the transmitter end, an integrated laser array drives the four optical signals, which are then transmitted via an MPO-12 APC multi-fiber connector.
This module supports two typical transmission distances: 500 meters and 2 kilometers. AICPLIGHT offers IEEE-compliant 400GBASE-DR4 (500m) and the extended-reach version 400GBASE-XDR4 (2km).
400G QSFP-DD DR4 Schematic
400G OSFP DR4 Schematic
II.What is a 400G FR4 Optical Module?
The 400G FR4 optical module utilizes Wavelength Division Multiplexing (WDM) technology. Its core mechanism combines four distinct wavelengths (1271nm, 1291nm, 1311nm, and 1331nm) into a single composite optical signal via a multiplexer (MUX).
At the receiving end, a demultiplexer (DEMUX) separates the composite signal back into the original four channels. Unlike DR4, FR4 utilizes a duplex LC UPC interface, requiring only two single-mode fibers (one transmit, one receive), significantly conserving fiber resources.
400G QSFP-DD FR4 Schematic
400G OSFP FR4 Schematic
III.400G DR4/XDR4 vs 400G FR4
| Parameter | 400G DR4/XDR4 | 400G FR4 |
|---|---|---|
| Technology | Parallel optics (4×100G PAM4) | WDM (4 wavelengths combined) |
| Fiber Count | 8 fibers (MPO-12) | 2 fibers (LC duplex) |
| Connector | MPO-12 APC | LC UPC |
| Wavelengths | 4×1310nm (identical channels) | 1271nm/1291nm/1311nm/1331nm |
| Distance | 500m (DR4), 2km (XDR4) | 2km |
| Use Cases | • 400G point-to-point • 4×100G breakout | 400G point-to-point (fiber-efficient) |
IV.Connection Solutions
4.1 400G Direct Connection Solution
Both 400G DR4/XDR4 and 400G FR4 support 400G-to-400G links. However, their differing optical interfaces require specific fiber cables:
- 400G DR4/XDR4: Uses MPO-12 trunk cables.
- 400G FR4: Uses duplex LC patch cables.
Cost Note: At the same transmission distance, MPO-12 cables are more expensive than LC duplex cables.
4.2 400G Breakout Solution
A key advantage of 400G DR4/XDR4 lies in its interoperability with 100G single-wavelength optical modules. This enables compatibility with equipment scenarios requiring high-density connections, achieving 1-to-4 branch connections.
V.Conclusion
The 400G DR4/XDR4 and 400G FR4 modules embody two foundational technologies:
- DR4/XDR4: Parallel optics for flexible breakout and short-to-mid-reach scalability
- FR4: WDM for fiber efficiency and 2km reach
They have become core components for constructing efficient, scalable interconnect architectures in today's hyperscale data centers.
