Empirical Study of Helical Bend Loss in Optical Fibers

Abstract

We propose a method to estimate helical bend loss in optical fibers and extend the method to predict the loss in a different fiber. In our approach, we consider the in-plane bend loss as the reference and approximate the loss curve as an exponential function decaying with bend diameter. For in-plane bends, we compute loss over the bend diameter range of 9.5−19.5 mm at 1550 nm wavelength. For helical bends, we perform experiments for the same range of bend diameters and pitch values of 2,4,5,7 and 10 mm. We extend the exponential function approximation to the experimental measurements of helically wound fibers and obtain an empirical formula to estimate the helical bend loss. We find that for a given bend diameter, the bend loss increases initially with the pitch, attains a maximum value and then decreases below the corresponding in-plane bend loss. We extend the empirical formula developed for a single fiber with a specific refractive index to evaluate the helical bend loss in another fiber. We conduct the in-plane bend loss experiments for the new fiber and repeat the exponential fit and obtain fit coefficients. We calculate the fit coefficients for different pitch values using empirical formula and predict the helical bend loss. We compare the predicted loss with corresponding experimental measurements, which are in good agreement.