Nonlinear topological photonics (1912.01784v1)

Abstract: Rapidly growing demands for fast information processing have launched a race for creating compact and highly efficient optical devices that can reliably transmit signals without losses. Recently discovered topological phases of light provide a novel ground for photonic devices robust against scattering losses and disorder. Combining these topological photonic structures with nonlinear effects will unlock advanced functionalities such as nonreciprocity and active tunability. Here we introduce the emerging field of nonlinear topological photonics and highlight recent developments in bridging the physics of topological phases with nonlinear optics. This includes a design of novel photonic platforms which combine topological phases of light with appreciable nonlinear response, self-interaction effects leading to edge solitons in topological photonic lattices, nonlinear topological circuits, active photonic structures exhibiting lasing from topologically-protected modes, and harmonic generation from edge states in topological arrays and metasurfaces. We also chart future research directions discussing device applications such as mode stabilization in lasers, parametric amplifiers protected against feedback, and ultrafast optical switches employing topological waveguides.

• The paper demonstrates that integrating nonlinearity with topological photonics enables the formation of robust edge solitons at interfaces.
• It explains how nonlinear interactions induce dynamic phase transitions in photonic circuits for on-demand reconfiguration.
• It shows that topological protection in laser cavities and harmonic generation processes enhances resilience against imperfections.

Nonlinear Topological Photonics

The paper of nonlinear topological photonics represents an ambitious attempt to merge the robust properties of topological phases with the inherent complexities of nonlinear optics. This intersection offers unique opportunities to explore new functionalities in photonic devices, particularly those that leverage the topological robustness of edge states to disorder and scattering losses.

Core Contributions

The paper outlines several key areas where the integration of nonlinearity into topological photonics could revolutionize device performance and capabilities. These include:

1. Edge Solitons: The paper describes how nonlinearity can facilitate the formation of edge solitons, localized states that exist at the interface of topologically distinct regions. Solitons, stabilized by a balance of dispersion and nonlinearity, could leverage the topological protection typically afforded to edge states, resulting in highly robust, localized modes.
2. Nonlinear Topological Circuits: Photonic circuits with nonlinear components offer a pathway to dynamic reconfiguration. The presence of nonlinearity can induce phase transitions, allowing circuits to switch between different topological phases. This behavior opens the door to on-demand tunability and control of photonic states.
3. Topological Lasers: By integrating topological protection into laser cavities, the authors highlight the potential for designing lasers with enhanced resilience to fabrication imperfections and environmental perturbations. This concept extends to frequency stabilization and differential path protection in lasing dynamics that could improve the efficacy of novel laser sources.
4. Harmonic Generation: The paper identifies the prospects for exploiting nonlinear topological photonics in harmonic generation processes. These processes can potentially enhance the efficiency of frequency conversion due to the phase-matching conditions facilitated by topologically protected states.

Theoretical and Practical Implications

Theoretical progress in this field entails a deeper understanding of how nonlinear effects modify band topology, usually defined in linear regimes. One promising direction is the exploration of non-linear Dirac models adapted from high-energy physics and their application in photonics to describe the interaction of light fields at topological boundaries.

Practically, the integration of nonlinear dynamics with topological protections could significantly improve the robustness and efficiency of photonic devices. For example, incorporating nonlinearity into photonic crystal designs might yield components with dynamic functionalities like ultrafast switches, modulators, and logic gates that are highly resilient to defects and variances in operational conditions.

Future Directions

The merging of nonlinear dynamics with topological phase engineering remains a fertile area for research with broad implications for the future of optical technologies. Progress will likely revolve around:

• Experimental Realization: Advancing fabrication techniques to accurately implement the complex designs required for nonlinear topological photonic structures.
• Nonlinear Material Systems: Developing new materials with tailored nonlinear properties compatible with the constraints of topological photonics.
• Integration with Quantum Photonics: Understanding how these concepts can be extended to the quantum regime, where topologically robust states could facilitate robust quantum information processing and transmission.

Conclusion

This paper delineates a detailed landscape of nonlinear topological photonics, addressing possible implementations and the transformative implications they could have on photonic technology. By further exploring the complex interplay of nonlinearity and topological protection, researchers can pave the way toward a new class of photonic devices that not only perform with unprecedented efficiency and robustness but also open new directions in nonlinear and quantum optics.