Pulse-Generation Maps in External-Cavity Semiconductor Lasers with Short-Delay Optical Feedback

We investigate pulse generation in external-cavity semiconductor lasers subject to short-delay optical self-feedback using a deterministic quadrature-based delay-differential model. High-resolution pulse-generation maps are constructed in the (lg(C),ϕf) parameter space, where lg(C)≡log10(C), for pump ratios μ=4, 6, 8, and 10, where μ=J/Jth. For each pump level, the feedback delay is normalized to the solitary-laser relaxation-oscillation period and set to τf/TR=0.5 and 1, providing a physically consistent basis for comparing pulsing regimes across operating conditions. Post-transient intensity traces are classified in the time domain using complementary measures of pulse separation, temporal regularity, pulse width, duty factor, valley-to-peak ratio, peak prominence, baseline occupancy, and autocorrelation, thereby reducing the misclassification of strongly distorted periodic oscillations as regular pulse trains. The resulting maps characterize the existence, repetition rate, mean pulse width, and duty factor of the detected pulses. The results reveal that pulse generation is governed by the combined effects of feedback strength, feedback phase, pump ratio, and normalized delay. Notably, increasing the pump ratio systematically shifts the pulsing regimes toward higher repetition rates, with representative values increasing from approximately 2 GHz at μ=4 to above 7 GHz at μ=10, demonstrating clear pump-controlled tuning of the generated pulse trains. The considered short delays correspond to millimeter- to centimeter-scale optical feedback paths for representative photonic platforms. These results provide a reproducible framework for identifying feedback-induced regular pulsing regimes and may support the design of compact semiconductor-laser sources for sensing, ranging, and integrated photonic applications.