Laser Cavity-Soliton Micro-Combs (1902.09930v2)

Abstract: The field of micro-cavity based frequency combs, or 'micro-combs'[1,2], has recently witnessed many fundamental breakthroughs[3-19] enabled by the discovery of temporal cavity-solitons, self-localised waves sustained by a background of radiation usually containing 95% of the total power[20]. Simple methods for their efficient generation and control are currently researched to finally establish micro-combs as out-of-the-lab widespread tools[21]. Here we demonstrate micro-comb laser cavity-solitons, an intrinsically highly-efficient, background free class of solitary waves. Laser cavity-solitons have underpinned key breakthroughs in semiconductor lasers[22,23] and photonic memories[24-26]. By merging their properties with the physics of both micro-resonators[1,2] and multi-mode systems[27], we provide a new paradigm for the generation and control of self-localised pulses in micro-cavities. We demonstrate 50 nm wide soliton combs induced with average powers one order of magnitude lower than those typically required by state-of-the-art approaches[26]. Furthermore, we can tune the repetition-rate to well over a megahertz with no-active feedback.

• The paper introduces a laser cavity-soliton micro-comb architecture that embeds a Kerr micro-resonator in a fiber loop with gain to generate background-free soliton pulses.
• It achieves energy-efficient operation with soliton combs spanning 50 nm at power levels one order lower than traditional methods and supports tunable repetition rates exceeding 1 MHz.
• The study validates its approach through numerical simulations and experiments using a silicon oxynitride resonator, highlighting promising applications in metrology, quantum communication, and optical networks.

Insights into Laser Cavity-Soliton Micro-Combs

This paper presents a comprehensive paper on the application of laser cavity-solitons within the field of optical micro-combs, introducing a paradigm shift in micro-cavity technology. The research rigorously demonstrates the generation and efficient control of temporal laser cavity-solitons in micro-cavities, effectively merging the principles of laser solitons with micro-comb physics.

Key Contributions

The primary contribution of this research lies in the development of a laser cavity-soliton micro-comb architecture. By embedding a Kerr micro-resonator within a fibre loop with gain, the authors exploit the properties of laser cavity-solitons to produce highly efficient, background-free pulses. The pulses exhibit soliton combs over 50 nm bandwidth and operate at powers significantly lower—one order of magnitude less—than conventional methods. This innovation in energy efficiency marks a salient departure from the traditional Lugiato-Lefever solitons driven by continuous-wave backgrounds.

Furthermore, the authors have devised mechanisms to fine-tune the soliton repetition-rate without active feedback. By adjusting parameters such as cavity length, this method facilitates repetition-rate alterations exceeding a megahertz. This characteristic makes the proposed system remarkably agile and adaptable, a significant advancement over existing micro-comb technologies.

Numerical and Experimental Validation

Through a combination of theoretical analysis and experimental validation, the researchers scrutinize the behavior of solitary states. They employ a mean-field model to approximate the dynamics of laser cavity-soliton interactions. Both stability and numerical propagation of localised solitons are meticulously examined, leading to a robust characterization of soliton dynamics as a function of critical parameters such as frequency detuning and fiber gain.

The experimental intricate setup employs a sophisticated silicon oxynitride resonator with a Q factor of approximately 1.3 million, integrated within a Ytterbium-Erbium fibre-cavity. The researchers use intra-cavity laser-scanning spectroscopy to discern the soliton comb lines, confirming the theoretical predictions with high precision. These detailed examinations provide a compelling juxtaposition of theory and practice, underpinning the laser cavity-soliton propositions.

Implications and Future Directions

The research evidences significant implications for advancements in various fields, including metrology, quantum communication, and frequency synthesis. The established framework for laser cavity-solitons unlocks new opportunities for precision applications while offering an energy-efficient alternative to Lugiato-Lefever solitons.

The architectural approach also suggests a pathway for genetic algorithms that enhance passive mode-locking systems through adaptive soliton control—paving the way for self-starting operations, a crucial parameter in practical applications.

In future work, exploring the integration of these solitons in photonic networks could revolutionize the processing capabilities in optical signal environments. Furthermore, leveraging the coherence and broader bandwidth potentials could yield advances in optical communication and spectroscopy.

Conclusion

This paper rigorously delineates a transformative method for generating laser cavity-solitons within micro-combs, marked by their unprecedented energy efficiency and tunable repetition rates. The fusion of theoretical rigor with experimental veracity presents a robust case for the viability and utility of laser cavity-solitons in advancing micro-comb technology, setting the stage for a suite of innovations in optical systems and applications.