ON THE JOINT EFFECTS OF FIBER PARAMETRIC GAIN AND BIREFRINGENCE AND THEIR INFLUENCE ON ASE NOISE

Parametric gain (PG) in optical fibers may substantially enhance ampli fied spontaneous emission (ASE) noise, especially in long-haul amplifi ed links. We present new results that permit to accurately characteriz e the effects of PG on ASE noise, as well as the interplay of PG and A SE noise,vith fiber dispersion in both the anomalous and normal disper sion regions. In a recent letter [1], we introduced the concept of a P G transfer matrix, that allows the easy evaluation of ASE noise enhanc ement over chains of amplified fiber spans. In the same letter we show ed that the transfer matrix can be expressed in analytical closed-form when a scalar (single polarization) fiber is assumed. In this paper w e extend the analysis to a more realistic two-polarization fiber model that accounts for both linear and nonlinear polarization coupling eff ects. We show that the new transfer matrix does not have an analytical expression, but can be easily evaluated using standard numerical algo rithms. ASE noise enhancement due to PG turns out to be slightly lower in a realistic birefringent two-polarization fiber than a single-pola rization fiber. An interesting result is that the single polarization model yields a convenient approximation to ASE noise enhancement, that can be evaluated analytically.