Applied stress on coated multimode optical fibres: a different point of view to bending losses

Abstract

The power losses introduced by bending multimode optical fibres have been studied since the last forty years, when the efficient transmission of those fibres was regarded as very useful for devices that require the transmission of spatially incoherent light (white light), e.g. Integral Field Units (IFU) for Astrophysics. In the literature, the influence of the fibre coating on transmission properties is rarely taken in account, i.e. the fibres under test are frequently stripped, however, in practical applications the fibres are used with their coating. We present the results of an experimental study of attenuation due to bending stress on several large-core multimode coated optical fibres. In this experiment the attenuation is studied as a function of applied stress in kilo pounds squared inches [kpsi]. The fibres under test are similar to the type of optical fibre used in astronomy for fibre based spectroscopic applications, or used as probes for chemical sensing applications. We investigate a range of different core diameters for both all-silica and hard cladding step-index fibres. Optical-fibres manufacturers are offering a variety of coating materials and, the tested fibres are coated with the following: silicone, polyimide, two types of fluorine doped acrylate, and acrylate. We show that for a given coating material, applying the same bending stress on fibers introduces the same amount of attenuation, regardless of the fibre bending radius or fibre core diameter. We also show differences in attenuation due to the use of different coating material.