Derivation of impulse response and transfer function of an optical fiber under chromatic dispersion and application to a linear fiber-optic communication system

Treating the frequency-dependent time delay caused by the presence of chromatic dispersion in a fiber-optical channel of length L as a random variable, it is possible to obtain a simple expression for the impulse response of the channel. This idea is used to derive the impulse response in terms of parameters such as the zero-dispersion wavelength, the second derivative of the refractive index, and the linewidth of the source. The result indicates an asymmetrical impulse response, and the corresponding transfer function has a low-pass characteristic with a first-order pole which may be readily determined from the fiber parameters. The derived impulse response is applied to the case of a simple fiber-optic communication system configured as a phase diversity receiver, to illustrate how a linear systems approach, under certain approximations, may be used to predict and analyze the behavior of such a system. The analysis includes calculations involving the field amplitudes in (n*n) hybrid couplers, and how such couplers must be connected in order to obtain the desired optical components in the phase diversity scheme is described.<
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