Agile THz-range spectral multiplication of frequency combs using a multi-wavelength laser

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.