LR4 in the optical module

LR4 stands for "Long Reach 4," indicating an optical module designed for long-distance transmission using four separate channels.

Definition and Meaning

LR4 is a designation used in optical transceivers to indicate long-reach transmission over single-mode fiber (SMF) using four optical channels. The "LR" stands for Long Reach, and the "4" denotes the four-channel architecture that splits the total data rate across multiple wavelengths or lanes to achieve high-speed transmission efficiently .

How LR4 Works

• Channel Structure: LR4 modules divide the total data rate into four separate channels. For example, a 100G LR4 module uses four 25G channels, while a 400G LR4 module uses four 100G channels or eight 50G channels depending on the design .
• Fiber Type: LR4 modules use single-mode fiber (SMF), which supports long-distance transmission with minimal signal loss .
• Modulation: 100G LR4 typically uses NRZ (Non-Return-to-Zero) modulation, while 400G LR4 modules use PAM4 (4-Level Pulse Amplitude Modulation) combined with wavelength division multiplexing (CWDM4 or LWDM) to achieve higher data rates over long distances .
• Transmission Distance: LR4 modules are designed for long-reach applications, typically supporting distances up to 10 km for 100G and 400G modules, making them suitable for inter-campus or data center interconnects .

Applications

LR4 modules are commonly used in scenarios where high bandwidth and extended reach are required:

• Data Center Interconnect (DCI): Connecting multiple data centers over several kilometers.
• Campus Networks: Linking buildings or facilities within a campus.
• Backbone Links: High-speed connections in metropolitan or regional networks .

Comparison with Other Modules

• SR4 (Short Reach 4): Uses multimode fiber for short distances (up to 100m), ideal for intra-data center connections.
• DR4 (Medium Reach 4): Single-mode fiber for medium distances (up to 500m).
• FR4 (Intermediate Reach 4): Uses CWDM for distances up to 2 km.
• LR4 (Long Reach 4): Single-mode fiber for distances up to 10 km, optimized for long-distance, high-bandwidth links .

Key Takeaways

• The "4" in LR4 indicates four parallel channels, which improves signal-to-noise ratio and reliability compared to single-channel long-reach modules.
• LR4 modules are essential for long-distance, high-speed optical networks, balancing performance, cost, and error resilience.
• They are widely used in 100G and 400G networks, with 400G LR4 modules leveraging advanced PAM4 modulation and wavelength multiplexing to achieve 400Gbps over single-mode fiber .