A Novel Thresholder Based on XGM Effect in a DFB Laser Combined With External Optical Filtering

A novel thresholder based on cross-gain modulation (XGM) effect in a distributed-feedback (DFB) semiconductor laser combined with offset optical filtering is proposed and demonstrated. To the best of our knowledge, this is the first XGM effect-based thresholder that is operated by optical injection of a DFB laser. In this scheme, a DFB laser without an isolator is the key component, which costs less than the nonlinear devices required in other schemes. The spectrum output from the DFB laser can be broadened after the pulses injected to the laser cavity, which is induced by the XGM effect. Only the correct codes that have enough peak power will be able to broaden the spectrum of the DFB laser, while the low-power noise cannot. By offset filtering the broadened parts of the optical spectrum, the correct optical pulse is acquired, while the undesired noise is diminished. In this scheme, an injection power of 7 dBm is enough to generate the XGM effect, which is much lower than most of the existing schemes. In addition, as the DFB laser is used as the pump laser as well as the nonlinear medium, this scheme is more compact and low cost compared with the schemes proposed before.