The bandwidth of a multimode fiber chain

We propose a new method for evaluating the baseband transmission in a multimode fiber chain. Carnevale and Paek (Bell Syst. Tech. J., vol. 62, pp. 1415-1431, 1983) stated that errors in the fiber manufacturing process will randomly distort a desired index profile, presumably of power-law type. We extend their discussion to the bandwidths of concatenated fibers, by considering Gaussian approximations to actual transfer functions. The bandwidth can thus be separated into two parts, one of which is due to the over- and undercompensation of individual, idealized power-law profiles and the other of which refers to random profile distortions as well as possible mode coupling within mode groups. The former part should normally dominate the length dependence of longer chains. The latter part may be replaced by an expectation value, typical for the actual manufacturing process. A remarkably good agreement is achieved between experimental and predicted bandwidths for various chain configurations.