400G Optical Transceiver: Technology, Variants, and Applications in Modern Data Centers

Introduction

The rapid expansion of cloud services, artificial intelligence (AI), high-performance computing (HPC), and 5G networks has created unprecedented demand for high-capacity interconnect solutions. Among these, the 400G optical transceiver has become a cornerstone technology. With its ability to deliver high bandwidth, low latency, and scalable deployment, it has been adopted widely by hyperscale data centers and large enterprises.

Several form factors and standards exist within the 400G ecosystem, such as 400G OSFP SR4, OSFP-400G-DR4, OSFP-400G-SR8, OSFP-400G-FR4, and 400G-ZR. Each option has been designed for specific reach, cost, and application scenarios. This article provides a comprehensive overview of the 400G optical transceiver market, exploring its key variants, applications, vendor-specific deployments, and future prospects.

Understanding the 400G Optical Transceiver

A 400G optical transceiver is a high-speed pluggable device used to connect networking equipment such as switches, routers, and servers. It converts electrical signals into optical signals and vice versa, enabling data transmission over optical fibers.

The demand for 400G optics has been fueled by the limitations of earlier 100G and 200G solutions, which are no longer sufficient to meet the explosive traffic requirements. The 400G OSFP (Octal Small Form-factor Pluggable) standard has emerged as one of the most prominent, due to its thermal design, high-density support, and forward compatibility with 800G.

400G OSFP SR4: The Most Common Variant

What Is 400G OSFP SR4?

The 400G OSFP SR4 module is designed for short-reach connections within data centers. It typically uses multimode fiber (MMF) with an 850 nm wavelength, supporting transmission distances up to 100 meters using OM4 fiber or 50 meters, which we call 400g osfp vr4.

Manufacturers like Juniper Networks and Arista have already deployed 400G OSFP SR4 modules in their next-generation switches. Queries such as “400G OSFP SR4 Juniper” and “OSFP 400G SR8 Arista” reflect real-world demand for vendor-specific compatibility in enterprise environments.

Key Features of 400G OSFP SR4

Reach: Up to 100 meters over OM4 MMF

Fiber type: Multimode

Lane count: 4 lanes × 100G PAM4

Applications: Data center interconnects, TOR (Top-of-Rack) to spine connections

Comparing 400G OSFP SR4 with Other Variants

OSFP-400G-DR4

OSFP-400G-DR4 module is designed for single-mode fiber (SMF) transmission up to 500 meters. It uses four parallel 100G PAM4 channels and is often used in point-to-point connections between data center switches.

Reach: 500 meters

Fiber: SMF

Application: Leaf-to-spine interconnect

OSFP-400G-SR8

The 400G SR8 or OSFP 400G SR8 transceiver uses eight parallel 50G or 100G lanes. It is designed for very short-reach data center connections, often supporting breakout modes (e.g., 8 × 50G or 2 × 200G).

Reach: 70m–100m on OM3/OM4 MMF

Applications: High-density intra-rack or TOR connections

Vendor adoption: OSFP 400G SR8 Arista products are widely used

OSFP-400G-FR4

The OSFP-400G-FR4 supports longer reaches, typically up to 2 km, by using four lanes of 100G PAM4 over SMF. It is a cost-effective choice for mid-range interconnects between buildings or across campuses.

400G-ZR

The 400G-ZR module is built for long-haul transmission, reaching up to 80 km using coherent optical technology. It is designed for metro and regional networks where long-distance transmission with minimal regeneration is required.

OSFP-400G-XDR4-S

This is an extended-reach variant supporting distances up to 2 km–10 km, bridging the gap between DR4 and ZR modules. It has gained popularity in hyperscale networks that require flexible deployment.

400G DR4 vs. 400G FR4: Which to Choose?

A common comparison in the industry is 400G DR4 vs FR4.

400G DR4 Transceiver:

Reach: Up to 500m over SMF

Cost: Lower due to simpler design

Best for short-distance leaf-spine links

400G FR4 Transceiver:

Reach: Up to 2 km over SMF

Cost: Higher but eliminates expensive repeaters

Best for inter-building or campus connections

The choice between DR4 and FR4 depends on distance requirements and budget.

400G OSFP VR4 and VR4 MM850

Another variant is the 400G OSFP VR4, optimized for very short-reach multimode applications. When paired with MM850 fiber, it provides highly cost-effective intra-data center links, typically under 100 meters. The 400G OSFP VR4 MM850 is often used in high-density environments where power efficiency and cost per bit are critical.

Vendor-Specific Deployments: Juniper and Arista

400G OSFP SR4 Juniper:
Juniper’s 400G-capable switches rely heavily on SR4 and DR4 optics for intra-data center connectivity. Their solutions focus on seamless scalability and interoperability.

OSFP 400G SR8 Arista:
Arista Networks has integrated SR8 modules in its modular switches, providing high-density, low-latency links ideal for AI workloads.

These deployments highlight the ecosystem of 400G optical transceiver vendors, where interoperability and standardization play key roles.

Applications of 400G Optical Transceivers

Data Center Interconnects

400G OSFP SR4 for TOR-spine connections

OSFP-400G-DR4 for longer leaf-spine connections

Metro and Regional Networks

400G-ZR for long-haul applications up to 80 km

High-Performance Computing (HPC)

OSFP 400G SR8 for dense, high-bandwidth intra-rack connections

Enterprise and Campus Networks

OSFP-400G-FR4 for medium-range connectivity

Future of 400G and Migration to 800G

The 400G OSFP ecosystem has established itself as a robust solution. However, migration to 800G OSFP is already underway, with backward compatibility in design. Many 400G SR4 and DR4 modules will continue to serve as building blocks while networks transition to 800G.

Conclusion

The 400G optical transceiver family offers a wide range of solutions tailored for different distances, fiber types, and application needs. From 400G OSFP SR4 for short-reach data center interconnects to OSFP-400G-ZR for long-haul transmission, the technology provides flexibility and scalability.

Enterprises evaluating options such as 400G DR4 vs FR4 or considering vendor-specific deployments like Juniper and Arista should carefully assess cost, distance, and compatibility. As demand continues to grow, the 400G ecosystem will remain a key stepping stone toward the 800G era.

FAQ

1. What is a 400G OSFP SR4 optical transceiver?

A 400G OSFP SR4 optical transceiver is a short-reach module that uses multimode fiber (MMF) at 850 nm to support up to 100 meters over OM4 fiber. It is widely used in data centers for TOR-to-spine connections. Vendors like Juniper have deployed 400G OSFP SR4 Juniper modules in their next-generation switches.

2. What is the difference between 400G DR4 vs FR4?

The 400G DR4 transceiver is designed for single-mode fiber up to 500 meters, making it cost-effective for leaf-to-spine links. The OSFP-400G-FR4 supports distances up to 2 km and is ideal for inter-building or campus connections. Choosing 400G DR4 vs FR4 depends on budget and transmission distance requirements.

3. When should I use a 400G OSFP SR8 module?

The 400G OSFP SR8 or OSFP-400G-SR8 module is optimized for very short-reach connections in data centers, typically up to 100 meters over OM3/OM4 fiber. It supports breakout modes such as 8 × 50G or 2 × 200G. OSFP 400G SR8 Arista switches often use SR8 modules to support AI and HPC workloads.

4. What is OSFP-400G-ZR used for?

The OSFP-400G-ZR module is designed for long-haul transmission up to 80 km using coherent optics. It is commonly used in metro and regional networks where 400G optics are required for high-capacity, long-distance interconnects without regeneration.

5. What are the applications of 400G OSFP VR4 and VR4 MM850?

The 400G OSFP VR4 and 400G OSFP VR4 MM850 are optimized for very short-reach multimode connections within data centers, typically under 100 meters. They provide a cost-effective solution for high-density environments where power efficiency and cost per bit are critical.