Accurate Prediction of Photon–Photon Resonance Frequency in Passive Feedback DFB Laser

Delay-coupled schemes enhance modulation bandwidth in passive feedback DFB (PF-DFB) lasers via photon-photon resonance (PPR) effect. Accurate prediction of PPR frequency is essential for achieving a flat small-signal modulation response and an extended 3-dB modulation bandwidth, though hindered by unmeasurable feedback phase in PF-DFB lasers. Current models estimate feedback phase solely using injection current-induced carrier dispersion, neglecting thermal effects that critically influence phase dynamics. We propose a thermal-coupled model integrating both carrier dispersion and thermal effects for accurate phase prediction. Experiments confirm a root mean squared error (RMSE) of 0.97 GHz between predicted and measured PPR frequencies, achieving a 12.3-fold accuracy improvement over conventional models. This advancement enables more reliable design and optimization of PF-DFB lasers for high-speed optical communication systems.