In this work, we propose a concept of a coupled fiber laser exhibiting PT-symmetry properties. We consider a system operated via Raman gain. The scheme comprises two identical fiber loops (ring cavities) connected by means of two fiber couplers with variable phase shift between them. We show that by changing the phase shift one can switch between generation regimes, realizing either PT-symmetric or PT-broken solution. Furthermore, the paper investigates some peculiarities of the system such as power oscillations and the role of nonlinear phase shift in fiber rings.
We reveal a number of fundamentally important effects which underpin the key aspects of light propagation in
photonic structures composed of coupled waveguides with loss and gain regions, which are designed as optical
analogues of complex parity-time (or PT) symmetric potentials. We identify a generic nature of time-reversals
in PT-symmetric optical couplers, which enables flexible control of all-optical switching and a realization of
logic operations. We also show that light propagation in PT-symmetric structures can exhibit strongly nonlocal
sensitivity to topology of a photonic structure. These results suggest new possibilities for shaping optical beams
and pulses compared to conservative structures.