Thermo-optic instabilities in asymmetric dual-core amplifiers

Dynamical thermo-optic instabilities in asymmetric dual-core fiber amplifiers are investigated by numerical simulations. A coupled-mode model capable of describing the asymmetric dual-core structure is derived, and structures with various levels of refractive-index asymmetry from $ {{10}^{ - 6}} $10−6 to $ {{10}^{ - 4}} $10−4 are studied. The most viable route to avoid thermally induced power signal field fluctuations is found to be core decoupling via large separation and strong refractive-index asymmetry. A design criterion for this strategy to be effective is suggested based on the numerical results.