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Common transmission distances of optical modules

ODN and passive infrastructure knowledge brief Published 20 Jun 2025

Prepared for preliminary research by the GESTIONVAL ODN knowledge desk. Confirm network topology, split ratio, box or cabinet capacity, joint closure rating and loss budget against current standards and product documentation.

Optical modules are classified by transmission distance into short-range (up to 300m), medium-range (up to 10km), and long-range (over 30km), with variations depending on fiber type, wavelength, and module design.Short-Distance Modules (SR)

Short-range (SR) optical modules are optimized for high-speed connections within data centers or racks, typically using multimode fiber (MMF). Their transmission distances usually range from 100 meters to 300 meters, depending on the fiber grade (OM3, OM4, or OM5) and data rate. SR modules commonly operate at 850nm using VCSEL lasers, which are cost-effective but more susceptible to modal dispersion, limiting their reach .

Medium-Distance Modules (LR)

Longer-range modules, often labeled as LR (Long Reach), are designed for single-mode fiber (SMF) and can transmit data over up to 10km or 20km. They typically use 1310nm DFB lasers, which reduce attenuation and chromatic dispersion, allowing stable transmission over campus networks, data center interconnects, or metro networks. Some extended LR variants can reach 40km or 80km, depending on the module specification and optical power budget .

Long-Distance Modules (ER/ZR)

Long-distance modules, sometimes called ER (Extended Reach) or ZR (Ultra-Long Reach), are used for telecom or metro networks requiring distances over 30km, with some modules capable of 80km or more. These modules often employ DFB or EML lasers and may include optical amplifiers or advanced modulation techniques to maintain signal integrity over long distances. Single-mode fiber is standard for these modules, and careful consideration of link loss, dispersion, and optical power is essential to achieve maximum reach .

Factors Affecting Transmission Distance
  • Fiber Type: MMF limits short-range distances; SMF supports longer distances.
  • Wavelength: 850nm for SR, 1310nm for LR, 1550nm for ultra-long distances.
  • Laser Type: FP lasers for short distances, DFB/EML for long distances.
  • Data Rate: Higher speeds reduce maximum achievable distance due to dispersion.
  • Link Loss and Dispersion: Attenuation (dB/km) and chromatic/modal dispersion affect signal quality .
Summary

Optical modules are selected based on distance requirements, fiber type, and network design. Short-range modules are ideal for intra-rack or intra-data center links, medium-range modules suit campus or metro connections, and long-range modules are necessary for inter-city or telecom networks. Matching the module type to the actual link distance ensures cost efficiency and reliable performance .

Common transmission distances of optical modules - GESTIONVAL ODN INFRASTRUCTURE S.L. [PDF]

Common transmission distances of optical modules

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Technical note

This reference is intended for preliminary ODN and passive infrastructure research. Topology, split ratio, box or cabinet capacity, closure rating, cable type, test limits and applicable standards must be verified for the specific project.

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