100G optical module loss typically ranges from 1.5 dB to 15.8 dB depending on module type, fiber type, and link distance.

Typical Loss Budgets

Multimode Fiber (MMF) Modules:

• Cisco QSFP-100G-SR4-S modules support 70 meters over OM3 and 100 meters over OM4 multimode fiber, with link loss budgets including connector losses of 1–1.5 dB .
• Short-link modules like QSFP-100G-SL4 support 20–30 meters, with similar connector loss considerations . Single-Mode Fiber (SMF) Modules:
• 100G CWDM Single Lambda modules for 10 km and 40 km links have optical budgets of 6.3 dB and 15.8 dB, respectively. After accounting for MUX/DEMUX insertion losses (~2.4 dB total), the remaining budget is available for fiber span and connectors: ~3.9 dB for 10 km and ~13.4 dB for 40 km .
• Cisco QSFP-100G-PSM4-S modules support up to 500 meters over SMF with MPO connectors, with loss budgets designed to accommodate fiber and connector attenuation .

Components of Optical Loss

1. Fiber Attenuation:
   • Multimode fiber (OM3/OM4) typically has 0.5–3 dB/km, depending on wavelength and fiber quality.
   • Single-mode fiber (G.652) has ~0.4 dB/km at 1310 nm, which is used conservatively in planning .
2. Connector Loss:
   • Each connector contributes ~0.5–1.5 dB, depending on type and quality. Cisco modules often include 1–1.5 dB for connectors in their link budget .
3. Splice Loss:
   • Fusion splices typically add 0.1–0.3 dB per splice, which must be included in the total link budget.
4. Module-Specific Margins:
   • Some modules include incremental margins (e.g., 0.7 dB for QSFP-40/100-SRBD) to account for additional connector or fiber losses while maintaining a target BER .

Practical Considerations

• Link Distance vs. Loss: Longer fiber spans reduce the available loss budget for connectors and splices.
• FEC and Modulation: Modern 100G modules use PAM4 modulation and FEC, which can tolerate higher loss than non-FEC systems .
• DWDM/CWDM Systems: Dense wavelength multiplexing systems require careful budgeting for MUX/DEMUX insertion loss and OSNR, which directly affects the allowable module loss .

Summary

For 100G optical modules, loss budgets vary widely: short-reach multimode modules may have 1.5–2 dB, while long-reach single-mode modules can exceed 15 dB. The total loss includes fiber attenuation, connector and splice losses, and any system-specific margins. Proper planning ensures the optical link operates within the module's specified budget, maintaining signal integrity and low bit error rates.