Optimization of the dispersion characteristics of a fiber waveguide and of the parameters of an optical source

The wave approach is used to solve the problem of design of a fiber-optic line consisting of a high-coherence source emitting a linearly polarized spherical wave, a fiber waveguide, and a threshold photodetector. The intensity of the radiation emitted by the source is modulated by a simple binary code. The optimization criteria are the requirement of minimum distortion of the signal waveform at the exit from the fiber and the maximum stability of the communication process. Allowance is made for all types of dispersion (material, waveguide, and mode), and also for the coupling between the modes because of slight irregularities of the fiber resulting in distortion of the pulse shape. The dependences of the duration of the input pulses and of the photodetector threshold on the wavelength of the radiation emitted by the source are given and analyzed, together with the dependence of the reliability of reception of the transmitted signal on the fiber waveguide length.