Lasers designed to emit at multiple and controllable modes, or multi-wavelength lasers, have the potential to become key building blocks for future microwave photonic technologies. While many interesting schemes relying on optical injection have been proposed, the nonlinear mode coupling between different modes of a multi-wavelength laser and their dynamical behavior under optical injection remains vastly unexplored. Here, we experimentally and numerically study the effect of optical injection around the suppressed mode of a dualwavelength laser and the resulting interactions with the dominant mode. We highlight a wavelength shift of the dominant mode triggered by injection locking of the suppressed mode and report a strong impact of the mode suppression ratio on the locking range. Finally, we show numerically that the cross-coupling parameter between the two modes might have a key role in this effect.

On-chip frequency comb sources have emerged as a revolutionary technology that enables broadband frequency combs with unprecedented compactness, energy efficiency, and cost-effectiveness. This technology has found widespread applications ranging from spectroscopy and lidar to telecommunications. However, on-chip comb sources face a fundamental trade-off between controllability and bandwidth: Broadband combs, generated in microresonators, lack free-spectral range or spectral envelope control, while combs generated with electro-optic modulators can be carefully tailored but are limited in bandwidth. Here, we present a novel approach to overcome this trade-off by enabling agile spectral multiplication of a narrowband comb. We demonstrate that by exploiting the nonlinear dynamics of a multi-wavelength semiconductor laser under modulated optical injection, we can achieve spectral multiplication of an injected narrowband comb at frequency offsets of 26 GHz, 54 GHz, and up to 1.3 THz. Our approach incorporates on-chip optical feedback control that allows for high suppression ratio and nanosecond-scale tuning of the offset frequency. We show that this approach is scalable and can cover a range of several THz with a suitable laser design, compatible with generic foundry platforms. Our system, when combined with THz photomixers, would enable low-cost, compact, and power-efficient sources for agile THz comb generation, paving the way towards a new generation of THz applications.

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