Picking up where we left off about 400G optical modules: In this section, we’ll dive into the key 400G transmission standards—VR4, SR4, SR4.2,SR8, DR4, FR4, LR4, LR8, ER4,ZR4.These are likely the very standards that leave you scratching your head when shopping for 400G modules. Don’t worry, though! By the end, we’ll break it all down and provide you with a comprehensive purchasing guide to make your decision-making process much smoother.

First, let’s clarify what VR, SR, DR, FR, LR, ER and ZR stand for, so that we can understand and identify them:

• VR (Very Short Range): Transmission distance usually 0~100 meters,using multimode fiber for short data center connections.
• SR (Short Range): Up to 300 meters, using multimode fiber for short data center connections.
• DR (Distance Range): Up to 500 meters, using single-mode fiber for inter-data center links.
• FR (Long Range): Up to 2 kilometers, using single-mode fiber for longer network connections.
• LR (Long Range): Up to 10 kilometers, using single-mode fiber for wide-area and long-distance links.
• ER (Extended Range): Up to 40 kilometers, using single-mode fiber for applications needing longer reach.
• ZR (Zero-Dispersion Range): Up to 80 km -120 km,using single-mode fiber for ultra-long distance, high bandwidth transmission, mainly used for interconnection between data centers, long-distance metropolitan area network connection, etc.

These standards guide users in selecting the right optical module for their network’s specific distance and performance needs.

400G Optical Modules’ Transmission Standards

Signal Modulation:

PAM4 (4-Level Pulse Amplitude Modulation): This is the predominant modulation technique used in 400G modules. PAM4 allows each symbol to represent two bits of information, effectively doubling the data rate compared to traditional NRZ (Non-Return-to-Zero) modulation 1.

Transmission Distance:

• Multi-Mode Fiber (MMF): Typically supports shorter distances, around 100 meters.
• Single-Mode Fiber (SMF): Can extend to tens of kilometers, making it suitable for long-distance applications

Transmission Type of 400G Optical Modules

400GBASE-VR4

• Transmission Distance: Up to 50 meters on OM4 multimode fiber, up to 30 meters on OM3 multimode fiber
• Fiber Type: Multimode fiber (MMF)
• Central Wavelength: 850 nm.
• Connector: MPO/MTO
• Channel Count: 4 channels, each supporting a 100G data rate, totaling 400G of transmission bandwidth.
• Transmission Method：Uses PAM4 (4-level pulse amplitude modulation) technology to achieve parallel transmission of data through 4 pairs of fibers.

Application Scenarios:

• 400G VR4 modules ideal for intra-data center connections where high-bandwidth, short-range links are necessary .

400G SR4

Features:

• Transmission Distance: With a maximum transmission distance of 100 meters (on OM4 fiber). For OM3 fiber, the maximum transmission distance is generally around 70 meters.
• Fiber Type : Multimode fiber (MMF). This is the standard configuration for SR4 modules, which supports high-speed transmission through four pairs of fiber channels.
• Central Wavelength: 850nm
• Connector: MPO-12/ MTP-12
• Number of Channels : 4 channels for parallel transmission (each channel at 100G), with a total bandwidth of 400G throuth PAM4 technology.
• Transmission Method : Parallel transmission, meaning that data is transmitted simultaneously through multiple independent fiber channels, typically with 100G per channel. It is usually based on the SR (Short Range) standard, which offers shorter transmission distances but is suitable for high-density connections and high-speed data transmission.

Application Scenarios : The 400G SR4 optical module is suitable for environments requiring high-speed, short-distance transmission, especially for data centers, cloud service providers, and large enterprise network interconnects.

The 400G SR4.2

400G SR4.2 module is an updated version of the traditional 400G SR4 module, optimized for higher performance and longer transmission distances.

The main difference between the 400G SR4 and 400G SR4.2 optical modules lies in their wavelength division multiplexing functionality. Each pair of fibers uses two wavelengths, 850nm and 910nm, effectively doubling the capacity.

Below are the main features of the 400G SR4.2 optical module:

• Transmission Distance : Typically reaching up to 150 meters (on OM4 fiber). On OM3 fiber, the maximum distance is 100 meters. This improvement, compared to the SR4’s 100 meters and 70 meters, expands its application in large data centers or high-density connections.
• Fiber Type : Multimode fiber (MMF), but with enhanced performance and longer transmission distance, making it suitable for providing longer-distance connections within data centers.
• Central Wavelength: 850nm and 910nm （Wavelength Division Multiplexing）
• Connector: MPO-12/ MTP-12
• Number of Channels: The 400G SR4.2 module uses 8 channels,each with a bandwidth of 50G, for a total bandwidth of 400G through PAM4 Technology.
• Transmission Method : The SR4.2 module uses parallel transmission, with each channel transmitting data through a separate fiber. The SR4.2 supports higher bandwidth and longer transmission distances, making it suitable for applications that require higher transmission quality.

Application Scenarios :The 400G SR4.2 optical module is primarily used for high-density, high-performance short-to-medium distance transmission， making it ideal for data center interconnects, large-scale cloud computing, high-performance computing, and enterprise network applications.

400GBASE-SR8

Features:

• Transmission Distance: the transmission distance can reach 70m on OM3 multimode fiber and 100m on OM4 multimode fiber, ideal for short-range transmission.
• Fiber Type: Multimode fiber (OM3/OM4/OM5).
• Central Wavelength: 850nm.
• Connector: MTP/MPO-16
• Channel Count: 8 channels, 50G per channel, totaling 400G.
• Transmission Method: Parallel optical transmission using 8 pairs of fibers for data transfer.
• Cost-Effective: SR8 standard offers lower deployment costs due to the lower cost and easier maintenance of multimode fibers.

Application: Intra-data center connections, particularly suitable for high-density interconnects in short-range, rack-to-rack setups.

400GBASE-DR4

Features:

• Transmission Distance: Up to 500 meters
• Fiber Type: Single-mode fiber.
• Central Wavelength: 1310nm
• Connector: MPO-12/ MTP-12
• Channel Count: 4 channels, 100G per channel, totaling 400G through PAM4 technology.
• Transmission Method: Uses 4 parallel optical fiber pairs (1 pair for transmission/receiving each) to transfer data, with each fiber carrying 100G.

Application: Ideal for medium-range backbone networks and inter-data center connections, such as fiber links between buildings.

400GBASE-FR4

Features:

• Transmission Distance: 2 kilometers.
• Fiber Type: Single-mode fiber.
• Central Wavelength: 1270nm, 1290nm, 1310nm, 1330nm
• Connector: Duplex LC Connector
• Channel Count: 4 wavelength-multiplexed optical channels, each 100G, totaling 400G.
• Transmission Method: Uses wavelength division multiplexing (CWDM) to transmit 4 x 100G signals over a single single-mode fiber.

Application: Suitable for short-range Metropolitan Area Networks (MAN) and inter-data center connections.

400GBASE-LR4

• Features:
  • Transmission Distance: 10 kilometers.
  • Fiber Type: Single-mode fiber.
  • Central Wavelength: 1270nm、1290nm、1310nm、1330nm
  • Connector: Duplex LC
  • Channel Count: 4 wavelength-multiplexed optical channels, each 100G, totaling 400G.
  • Transmission Method: Similar to FR4, uses CWDM technology to transmit data over a single fiber, but supports longer transmission distances.
• Application: Ideal for medium to long-range connections between Metropolitan Area Networks (MAN) and data centers, particularly for links up to 10 kilometers.

400GBASE-LR8

• Features:
  • Transmission Distance: 10 kilometers.
  • Fiber Type: Single-mode fiber.
  • Central Wavelength: 1273 nm, 1277 nm, 1282 nm, 1286 nm, 1295 nm, 1300 nm, 1304 nm, and 1309 nm
  • Connector: Duplex LC
  • Channel Count: 8 wavelength-multiplexed optical channels, each 50G, totaling 400G.
  • Transmission Method: Uses 8 different WDM channels to achieve 400G transmission, suitable for long-distance applications.
• Application: Similar to LR4 but with 8 channels, each 50G, ideal for high-speed data transmission over distances up to 10 kilometers.

400GBASE-ER4

• Features:
  • Transmission Distance: 40 kilometers.
  • Fiber Type: Single-mode fiber.
  • Central Wavelength: 1310nm or 1550nm
  • Connector: Duplex LC
  • Channel Count: 4 wavelength-multiplexed optical channels, each 100G, totaling 400G.
  • Transmission Method: Uses WDM technology to transmit data over a single-mode fiber, supporting long-distance transmission of up to 40 kilometers.
• Application: Ideal for ultra-long-distance backbone and telecom network applications, commonly used for long-range interconnections in MANs and WANs.

400GBASE-ZR4

• Features:
  • Transmission Distance: 80-120 kilometers.
  • Fiber Type: Single-mode fiber.
  • Central Wavelength: 1528.77~1567.13 nm
  • Connector: Duplex  LC
  • Channel Count: 4 wavelength-multiplexed optical channels, each 100G, totaling 400G.
  • Transmission technology: It employs a combination of dense wavelength division multiplexing (DWDM) and high-order modulation to facilitate the transmission of 400G over data centre interconnect (DCI) links up to 120 kilometres in length. It employs coherent optical techniques, which typically entail the utilisation of higher-order modulation methodologies, such as 16-QAM (Quadrature Amplitude Modulation)

Application:

• Data Center Interconnect (DCI): 400G ZR4 is a powerhouse for connecting data centers, delivering high bandwidth over long distances. It seamlessly links data centers across cities and regions, fueling large-scale cloud computing and big data processing.
• Carrier Networks: Ideal for telecom operators’ backbone networks, 400G ZR4 efficiently connects data centers and network nodes across diverse regions, meeting the surging bandwidth demands.
• High-Speed Network Backbone: This standard is perfect for large-scale enterprise and operator networks, especially for backbone facilities that span longer distances, providing efficient data transmission solutions between and within cities.
• Long-Distance Transmission: Unlike short-distance standards like 400G SR4, ZR4 shines in long-distance applications, making it perfect for geographically distributed enterprise networks and remote data storage.

Choosing the Right 400G Optical Modules: A Quick Guide

When it comes to selecting the perfect 400G transmission standard for your network, understanding your specific needs is key. Here’s a concise breakdown to help you make an informed choice!

Transmission Distance

• Short Distances (up to 100 meters): For intra-data center connections,VR4, SR4,SR8 is your go-to option. It’s optimized for short-range transmission over multimode fiber.
• Medium Distances (500 meters to 2 kilometers): If you need to connect data centers or buildings, DR4 or FR4 are ideal choices, providing reliable performance over single-mode fiber.
• Medium to Long Distances (up to 10 kilometers): For connections that require a bit more reach, LR4 or LR8 are excellent options, ensuring robust transmission over single-mode fiber.
• Ultra-Long Distances (up to 40-120 kilometers): When your needs extend beyond the typical range, ER4 and ZR4 is the best choice, perfect for long-distance applications.

Fiber Type

• Multimode Fiber: Generally more cost-effective, this fiber type works best with VR4,SR4,SR8 for short-range applications.
• Single-Mode Fiber: Ideal for longer distances, it supports standards like DR4, FR4, LR4, LR8, and ER4, ZR4 making it versatile for various applications.

Application Scenarios

• Intra-Data Center Interconnects: Use VR4,SR4, SR4.2and SR8 for seamless connections within the same data center.
• Inter-Data Center or Building-to-Building Connections: Opt for DR4 or FR4 to ensure reliable data transfer between locations.
• Metropolitan Area Networks and Medium to Long-Range Connections (up to 10 kilometers): LR4 or LR8 are perfect for these scenarios, providing the necessary bandwidth and distance.
• Wide-Area Networks or Long-Distance Connections (up to 40 kilometers): For extensive reach, ER4 and ZR4 is your best bet.

Today, we have provided a definitive overview of the transmission standards for 400G optical modules. We are confident that this article will assist you in selecting the optimal standard. In the next article, we will address frequently asked questions and answers related to compatibility, packaging selection, and other pertinent topics. Stay tuned！400G Optical Modules: The Most In-Depth Q&A You’ll Ever Need!

Q&A about 400G Modules:

Q1: Does Asterfusion offer 400G switches?

A1: Absolutely! Asterfusion offers a cutting-edge 400G switch, specifically our self-developed 12.8T switch, which is powered by our enterprise version of SONiC NOS—AsterNOS. This switch is engineered to meet the demanding requirements of various applications, including AI, machine learning, data centers, high-performance computing (HPC), and distributed storage. Curious to learn more? Check out Asterfusion’s product page for all the details!

Q2: Can an OSFP optical module be used on one end of a 400G link while a QSFP-DD module is on the other end?

A: Absolutely! As long as both modules adhere to the same protocol standard, OSFP and QSFP-DD optical modules can work together seamlessly. The key is that they follow compatible protocols, despite their different physical dimensions.

Q3: Can a 400G OSFP optical module be used in a QSFP-DD port?

A: Not quite. Due to the differences in physical size and incompatible connector protocols, a 400G OSFP optical module cannot be inserted into a QSFP-DD port. Each module has been designed for specific applications, so it’s essential to match them correctly!

Q4: Can an OSFP optical module be inserted into a QSFP-DD port?

A: Nope! These two formats are incompatible due to their differing sizes. If your equipment is designed for OSFP, it’s best to stick with OSFP optical modules, Direct Attach Copper (DAC) cables, or Active Optical Cables (AOCs) to ensure optimal performance.

Q5: Can a 100G QSFP28 optical module be inserted into an OSFP port?

A: Unfortunately, no. A 100G QSFP28 module cannot be directly plugged into an OSFP port. However, if you really need to bridge that gap, a converter module can be used to adapt it—just keep in mind that the link will still operate at 100G speeds.

Reference:

400GBASE-ER8, 200GBASE-ER4, 50GBASE-ER1 Specifications Proposal

https://www.opencompute.org/documents/meta-400g-fr4-optical-transceiver-specification-for-ocp-rev0-1-1-pdf#:~:text=Sep%2013%2C%202021%20%2D,this%20specification%20is%20focused