Optical Attenuation
Microscopic deviations in the axis of an optical fiber cause light to leak from the core into the cladding. This micro bending loss occurs when small scale lateral displacements force the light to exceed the critical angle for internal reflection. Random bends with periods of a few millimeters are the primary source of this power reduction.
Mechanical Influence
Structural pressure from protective coatings or irregular spool surfaces induces these small scale deformations. When a fiber is wound too tightly or subjected to freezing temperatures, the surrounding materials contract and press against the glass. These localized stresses create high frequency ripples in the fiber path.
Specialized buffers and loose tube cable designs mitigate these effects by decoupling the glass from external mechanical forces.
Testing Method
Specialized laboratory setups measure the sensitivity of a fiber by wrapping it around a drum covered in sandpaper. Increasing the tension on the fiber provides a repeatable way to characterize how much power is lost per unit of lateral pressure. High resolution power meters detect changes as small as 0.01 decibels during these qualification tests.
System Impact
Long distance transmission links suffer from reduced signal to noise ratios when these losses accumulate over several kilometers. Engineers must budget for these losses when designing optical budgets for harsh environments. Signal degradation is more pronounced at longer wavelengths such as 1550 nanometers.
