Design-oriented modulation waveform engineering and design maps for flat OFC generation in GS-OIL lasers

Optical frequency comb (OFC) generation using gain-switched (GS) semiconductor lasers combined with optical injection locking (OIL) provides a compact multiwavelength source for photonic systems. In GS-OIL operation, however, OFC flatness is strongly governed by modulation-driven carrier depletion and recovery dynamics in the injection-locked GS laser, which shape the spectral envelope through waveform-dependent time-domain gating. This paper presents a design-oriented numerical study of modulation waveform engineering in GS-OIL lasers, formulating the modulation waveform as a continuous temporal design space and establishing a direct linkage between the depletion–recovery window in the time domain and achievable flatness regions in the frequency domain. Using rate-equation time-domain simulations under fixed OIL conditions, Gaussian and square-wave modulations are employed as representative cases within this design space, and a modulation design map is constructed parameterized by the peak total drive current and an effective duration (duty-cycle-equivalent temporal support). The map identifies practical operating regions that maximize the number of consecutive OFC lines within a 3-dB power window while retaining the spectral-stability benefits of OIL. The resulting framework provides generalized, design-map-based guidelines that extend beyond specific waveform shapes for flat-comb optimization.