Attenuation of Unwanted Cladding Modes

This paper contains design criteria for the suppression of cladding modes in optical fibers by means of a lossy jacket. The calculations are actually based on the slab waveguide model. However, it is believed that the results are representative, at least to order of magnitude, for the round optical fiber. It is found that the cladding modes are absorbed most effectively if the real part of the refractive index of the lossy jacket equals the refractive index of the cladding material. However, slight deviations from this optimum design are not critical. The loss of the cladding modes depends on many parameters so that general statements as to the order of magnitude of the expected loss are hard to make. However, a loss of 1 dB/m should be easily obtainable.