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We propose a set of transformed two-dimensional (2-D) rate equations, which allow the computation of dynamic gain competition resulting from inhomogeneous field and carrier spatial distributions inside a vertical cavity surface-emitting laser cavity. Any explicit spatial dependency has been removed from the modified equations, reducing the computational time by several orders of magnitude. Resulting 2-D dynamic intensity profiles allow investigating effects related to improper fiber coupling due to transverse misalignment between laser beam and fiber. Although the expected increased relative intensity noise (RIN) levels associated with mode partition noise are observed, other effects might have larger contributions to the total noise under specific conditions. We show that the minimum RIN level is not necessarily reached for zero misalignment, but at positions where modes with broad far-field profiles and low power experience important filtering.

In analog RF fiber-optic (FO) links with directly modulated multimode laser diodes (LD's), nonlinear distortions of the received modulation signal occur due to fiber dispersion. Using a simple analytical two mode model, we show that the mutual compensation of strong nonlinearities between particular modes breaks down at high-modulation frequencies. The effect can be observed even in 1300-nm links with single-mode (SM) standard fibers. Simulations as well as measurements of intermodulation (IM) illustrate this argument.