Longest Distance Optical Module

Ultra-long-haul coherent optical modules, such as ZR/ZR+ and Cisco 400G QSFP-DD ULH, can transmit data over distances exceeding 2,500 kilometers.Short- and Long-Range ModulesOptical modules vary widely in transmission distance depending on design, wavelength, and fiber type. Short-range (SR) modules typically operate at 850 nm over multimode fiber and reach up to 300 meters. Long-range (LR) modules, such as QSFP28 LR4, operate at 1310 nm over single-mode fiber and can transmit up to 10 km, making them suitable for data center interconnects . Extended range (ER) and ZR modules are designed for backbone and metro networks, with distances from 80 km to over 2,500 km .Coherent Optical Modules for Ultra-Long-HaulCoherent optical modules use advanced digital signal processing (DSP) to maintain signal integrity over very long distances. For example:100G ZR/ZR+ modules can transmit approximately 80 km, with field demonstrations showing interoperability at 520 km .400G QSFP-DD Ultra Long-Haul (ULH) modules support dense wavelength division multiplexing (DWDM) networks and can extend regional and ultra-long-haul links previously handled by high-power transponders .800G coherent modules with probabilistic shaping technology (PCS) have been tested to transmit over 1,000 km at 800 Gbps and up to 2,500 km at 400 Gbps . These modules operate primarily over single-mode fiber and use wavelengths in the C-band or L-band (1550–1595 nm) to minimize attenuation and dispersion. Coherent detection and DSP allow them to approach the Shannon limit, maximizing spectral efficiency and distance .Factors Affecting Maximum DistanceThe achievable distance depends on several factors:Fiber type: Single-mode fiber supports longer distances than multimode fiber.Wavelength: Longer wavelengths (1310–1550 nm) reduce attenuation.Optical power and link budget: Proper planning ensures the receiver can detect the signal without overload or loss.Environmental conditions: Connector cleanliness, splices, and fiber quality impact real-world performance .SummaryFor ultra-long-haul applications, ZR/ZR+ and 400G QSFP-DD ULH coherent modules represent the current state-of-the-art, capable of transmitting data over hundreds to thousands of kilometers. For shorter distances, LR4 modules provide reliable 10 km links, while SR modules are limited to hundreds of meters. Selecting the right module requires matching the optical design to the fiber type, link budget, and deployment environment to ensure stable and efficient transmission .