Ultrafast gain recovery in a QW-SOA and its application for 40 Gb/s regenerative format conversion from NRZ-DPSK to RZ-OOK

We propose a scheme to realize gain recovery of the order of a few picoseconds in a typical quantum well semiconductor optical amplifier (QW-SOA) using a pump signal with amplitude dips. In the scheme, the gain recovery is determined by the fast carrier density depletion and carrier temperature heating processes. The ultra-fast gain recovery is numerically verified by a completed model combining the QW band structure calculation with rate equations in the QW-SOA. In practice, a pump signal with amplitude dips can be partly characterized by a non-return-to-zero differential phase-shift keying (NRZ-DPSK) signal generated by a Mach-Zehnder modulator. Therefore, we experimentally demonstrate 40 Gb/s wavelength-converting and regenerative format conversion from NRZ-DPSK to return-to-zero on-off keying (RZ-OOK), which may be a key function to connect different kinds of modulation formats at gateway nodes between long-haul backbone networks and metro area networks. (C) 2016 Optical Society of America