microbending

Microbending is the small-scale bending or curvature of a slender structure, such as an optical fiber, caused by localized stress, deformation, or defects. In fiber optics, microbending refers to localized bends along the length of a fiber that produce optical power loss beyond intrinsic material absorption or scattering. These bends can arise from packaging, routing, pressure from protective jackets, thermal expansion mismatches, or flaws in coatings. Microbending losses add to macrobending losses and can dominate at certain wavelengths or bend radii, especially in single-mode fibers.

Mechanism and effects

Light guided in the core can couple into cladding modes or radiate away when the fiber is perturbed by micro bends. The effect is more pronounced when the bend radius is small relative to the fiber geometry and the perturbations occur along the length of the fiber. Microbends can cause broadband attenuation, alter polarization properties, and contribute to increased noise or reduced system margin in fiber-optic links. The phenomenon can be exacerbated by mechanical stress, temperature cycling, and packaging tensions.

Measurement and mitigation

Mitigation focuses on reducing induced stress and preventing sharp, localized deformations. This includes using bend-insensitive or trench-assisted fiber designs, improving coating and jacketing, ensuring proper strain relief, and avoiding tight or repeated bending during installation. Maintaining appropriate bend radii and ensuring gentle routing during handling minimize microbend sensitivity. Optical time-domain reflectometry (OTDR) and spectral measurements help identify microbend-related losses and guide corrective action.

Other contexts

While most commonly discussed in telecommunications, microbending can also refer to localized curvature effects in other slender structures, where small curvature variations lead to localized stress or energy loss, though the term is chiefly used in fiber optics.