The effects of polymeric coatings on the low-temperature microbending losses in initially curved double-coated optical fibers

Abstract

The thermally induced microbending losses in initially curved double-coated optical fibers at low temperature are investigated. The deflections in an initially curved fiber increase gradually with an increase in the thermally induced compressive axial force. The increase of deflection in an optical fiber results in an increase of microbending loss. In order to minimize such a microbending loss, the Young’s modulus and Poisson’s ratio of the primary coating should be increased. This means that a best selection of the Poisson’s ratio of the primary coating is 0.5. On the other hand, the effective thermal expansion coefficient of the primary coating, and the thickness, Young’s modulus, and effective thermal expansion coefficient of the secondary coating should be decreased. However, there exists an optimum value for the thickness of the primary coating. The thermally induced lateral pressure on the glass fiber can also produce microbending loss. Both effects of the axial force and lateral pressure on the microbending losses must be considered, so there exist optimum values for the Young’s moduli and effective thermal expansion coefficients of the primary coatings. An easy rule for the selection of the polymeric materials and their thicknesses to minimize the low-temperature microbending losses are also proposed.