https://doi.org/10.1140/epjs/s11734-025-01699-5
Regular Article
Harmonic mode-locking at Farey fractions induced by delayed self-feedback
1
Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623, Berlin, Germany
2
Institut für Physik, Technische Universität Ilmenau, Weimarer Str. 25, 98693, Ilmenau, Germany
Received:
11
March
2025
Accepted:
19
May
2025
Published online:
27
May
2025
Semiconductor quantum-well mode-locked lasers with time-delayed optical feedback are versatile dynamical systems for applications but also paramount examples to explore the universal properties of non-linear systems with two competing frequencies. For rational ratios between the feedback delay-time and the laser-round-trip time, second harmonic, third harmonic, and fourth harmonic combs occur. With this contribution, we explore the parameter dependence of different dynamic regimes which range from frequency-locking at Farey fractions to complex quasi-periodic pulse trains with a focus on the impact of feedback phase, strength, and delay length. We characterize the emission in the temporal, spectral, and radio-frequency domain. Our numerical approach is based on traveling-wave equations and is able to explain experimental data over a large parameter range. We show that the predictive power of the model allows for on demand sub-THz harmonic comb generation. We achieve a fine-tuning range of 450 MHz around the fundamental beat note of 13.6 GHz and a continuous pulse-width tuning from 7 to 26 ps solely by delay-time control.
© The Author(s) 2025
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