Fiber Refractive Index Profile Research Articles

Dispersion in optical fibres with stairlike refractive-index profiles

In multimode circularly symmetric fibres whose index distribution is a stairlike approximation of an optimum profile, the modal dispersion increases as the number of steps decreases. For a fibre with Δn/n=0.02 and a core radius of 40 μm, numerical calculations based on wave optics show that the r.m.s. impulse response width at λ=1 μm increases from 0.075 ns/km for the smooth optimum profile to 0.23 ns/km for 40 steps of equal areas. Thus an important conclusion of the analysis is that one should avoid introducing steps in the refractive-index profile of fibres for optimum results.

Optical Fibers with Coupled Dispersive Modes

Marcuse's coupled-power theory incorporates the effect of different modal group velocities as the only mechanism responsible for pulse broadening in multimode, imperfect, optical fibers. In this paper the earlier theory is generalized to include the bandwidth-dependent effects: material dispersion and the waveguide dispersion that occurs within each mode. It is predicted that the latter two effects may partially cancel one another, the degree of cancellation depending on the shape of the fiber's refractive-index profile. Whether this effect causes a significant reduction in the calculated pulsewidth is shown to depend on the amount of mode coupling.