Pulse shortening in an actively mode-locked laser with parity-time symmetry

We consider an actively mode-locked laser system with parity-time symmetry. The system consists of two ring cavities, each incorporating an amplitude modulator operating at the same modulation frequency, but with the modulation phases differing by pi. We show that spontaneous parity-time symmetry breaking can be used to shorten the temporal width of the pulse generated through active mode locking in this system. Our work highlights the importance of applying the concept of parity-time symmetry in pulsed laser systems. (C) 2018 Author(s).