Design method for triple–clad silica core optical fibers with zero total dispersion at wavelengths of 1.3 and 1.55 μm

Abstract

AbstractThis paper describes the design method for triple‐clad silica core optical fibers with zero total dispersion at wavelengths of 1.3 and 1.55 μm; (ac, Sc) is the point where the total dispersion (= S) at wavelengths of 1.3 μm becomes equal to that at 1.55 μm when the core radius (= a) is varied. We denote the relative index difference between the core and the mth clad at 1.55 μm by Δm+1 (> 0, m × 1, 2, 3), the thickness of the mth clad by tm (m × 1, 2, 3), the cut‐off wave length for the second mode by λc and the equivalent bending radius (= radius where the bending loss is 0.01 dB/km as R. The following conclusions have been obtained: (1) even if the conditions for the zero dispersion are satisfied in an ideal triple clad (TC type), the zero dispersion condition cannot be satisfied when fluctuations and round shoulders happen to exist in the clad layers (nonideal TC type); (2) to fabricate fibers of TC type and nonideal TC type with |Sc| < 0.1 ps/km/nm, λc ≤ 1.15 μm and R < 5 cm. The following conditions should be satisfied: Δ2 = 2Δ4, Δ3 ≤ Δ4, Δ4 ≥ 0.7% and t1/ac ≤ 1.04 for t2/t1 × 0.5; (3) if the item (2) is satisfied, the sensitivities of Sc to ac, Δ2, and Δ3 for wavelength of 1.3 μm are constant when t1/ac ≤ 2.0. However, at wavelength of 1.55 μm, they decrease as t1/ac decreases; and (4) R for wavelength of 1.55 μm is about 10 times larger than R for wavelength of 1.3 μm.In this paper, the total dispersion is computed by the differentiation formula for determinant. Therefore the significant digits of the total dispersion in our results are more than four.