Attenuation Mechanism
Localized optical power loss mechanisms in single-mode and multimode optical fibers result from high-frequency microscopic axis perturbations along the fiber length. Micro-bending optical attenuation occurs when random mechanical lateral pressure forces core light to couple into unguided cladding modes.
Mode Coupling
Periodic spatial distortions with spatial frequencies matching the difference between guided mode propagation constants trigger light transfer from core modes into cladding radiation modes. Micro-bending optical attenuation increases significantly when spatial perturbation wavelengths match the critical mode-coupling conditions of the fiber geometry. Higher order optical modes leak into the cladding layer, dissipating optical power as thermal energy or radiated light.
Single-mode fibers with low mode-field diameters exhibit higher resistance to micro-bending loss.
Coating Defense
Dual-layer acrylate buffer coatings protect optical fibers by absorbing high-frequency mechanical contact forces. Soft primary coatings redistribute transverse loads over longer longitudinal distances, dampening micro-scale axis distortions.
Measurement Protocol
Fiber sensitivity to micro-bending forces is evaluated using expandable wire mesh drum tests or basketweave spooling procedures in accordance with IEC 60793-1-47. Standardized test setups apply controlled lateral pressure across fiber spools while monitoring real-time optical power transmission. Sourcing acceptance thresholds limit permitted attenuation increases to less than zero point zero five decibels per kilometer at operating wavelengths.
Fibers exceeding attenuation thresholds during qualification testing are rejected for long-distance sensing applications.
