PT symmetry in nonlinear twisted multicore fibers

We address propagation of light in nonlinear twisted multicore fibers with alternating amplifying and absorbing cores that are arranged into the parity-time (PT)-symmetric structure. In this structure, the coupling strength between neighboring cores and global energy transport can be controlled not only by the nonlinearity, but also by gain and losses and by the fiber twisting rate. The threshold level of gain/losses, at which PT-symmetry breaking occurs, is a non-monotonic function of the fiber twisting rate, and it can be reduced nearly to zero or, instead, notably increased just by changing this rate. Nonlinearity usually leads to the monotonic reduction of the symmetry-breaking threshold in such fibers.