By a theoretical analysis, it was indicated that multiple losses of optical fiber transmission were suitable to superposition
principle, i.e. the total loss of optical fiber transmission equaled the linear superposition of losses caused by various factors. On
the basis of the superposition principle and the regression analysis of experimental data, a bend-torsion dual loss model of
spiral bend optical fiber was proposed that the spiral bend loss of optical fiber was the superposition of pure bend loss and
torsion loss.