Energy quantization of twin-pulse solitons in a passively mode-locked fiber ring laser

A novel twin-pulse form of solitary wave was recently revealed in a passively mode-locked fiber ring laser. In this paper we report on the energy quantization feature of the twin-pulse solitons in the laser. We show that, as in the case of single-pulse solitons, multiple twin-pulse solitons can coexist in the laser cavity, and, in particular, that all of them have exactly the same pulse energy and twin-pulse separation. The pump-power hysteresis effect previously reported for the single-pulse soliton operation is also observed for the twin-pulse soliton operation of the laser.