A vector wave analysis is presented of a multimode optical fiber with an α-power law index profile that includes an additional fourth-order term. By optimizing a and the coefficient of the fourth-order term, the ultimate limit of the width of the impulse response is derived. The effect of the second-order material dispersion of the refractive index is completely compensated by the fourth-order term in the index distribution. As a result, the rms width of the impulse response is reduced to 20 ps/km, one-fifth of the value achievable with the ordinary a-power distribution, even if all modes carry equal power and there is no mode coupling. For a fiber whose normalized frequency is less than 40, the ultimate width of the impulse response is determined by the term with the gradient of the square of the index or ∇n 2 in the wave equation.
© 1978 Optical Society of AmericaFull Article | PDF Article
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