Programmable on-chip nonlinear photonics (2503.19861v1)

Abstract: Nonlinear photonics uses coherent interactions between optical waves to engineer functionality that is not possible with purely linear optics. Traditionally, the function of a nonlinear-optical device is determined during design and fixed during fabrication. In this paper, we present a photonic device with highly programmable nonlinear functionality: an optical slab waveguide with an arbitrarily reconfigurable two-dimensional distribution of $\chi^{(2)}$ nonlinearity. The nonlinearity is realized using electric-field-induced $\chi^{(2)}$ in a $\chi^{(3)}$ material. The programmability is engineered by massively parallel control of the electric-field distribution within the device using a photoconductive layer and optical programming with a spatial light pattern. To showcase the versatility of our device, we demonstrated spectral, spatial, and spatio-spectral engineering of second-harmonic generation by tailoring arbitrary quasi-phase-matching (QPM) grating structures in two dimensions. Second-harmonic light was generated with programmable spectra, enabled by real-time in situ inverse design of QPM gratings. Flexible spatial control was also achieved, including the generation of complex waveforms such as Airy beams and the simultaneous engineering of spectral and spatial features. This allowed us to create distinct spatial light profiles across multiple wavelengths. The programmability also allowed us to demonstrate in situ, real-time compensation of fluctuations in pump laser wavelength. Our work shows that we can transcend the conventional one-device--one-function paradigm, expanding the potential applications of nonlinear optics in situations where fast device reconfigurability is not merely practically convenient but essential -- such as in programmable optical quantum gates and quantum light sources, all-optical signal processing, optical computation, and structured light for sensing.

Overview of Programmable On-Chip Nonlinear Photonics

Programmable nonlinear photonics represents a promising avenue for overcoming the inherent limitations of traditional nonlinear optical devices. In the paper "Programmable On-chip Nonlinear Photonics," the authors present a groundbreaking photonic device that enables highly flexible and programmable control over nonlinear-optical processes, specifically focusing on second-harmonic generation (SHG). This innovative device employs an optical slab waveguide with a reconfigurable two-dimensional distribution of $\chi^{(2)}$ nonlinearity, realized using electric-field-induced $\chi^{(2)}$ in a $\chi^{(3)}$ material. The authors showcase the versatility of their device through spectral, spatial, and spatio-spectral engineering of SHG.

Key Results and Contributions

The central contribution of the paper is the demonstration of a photonic device capable of programmable nonlinear functionality. The device is characterized by an optical slab waveguide with a reconfigurable $\chi^{(2)}$ nonlinearity pattern. This pattern can be dynamically changed by controlling the electric-field distribution with a photoconductive layer and optical programming using a spatial light pattern. Notable results include:

• Spectral Engineering: The authors demonstrate spectral control by engineering quasi-phase-matching (QPM) grating structures with varying periods that can be programmatically altered. This tunability enables real-time compensation for environmental fluctuations, making nonlinear processes robust against variations such as pump wavelength drifts.
• Spatial Engineering: Through controlled variations in the transverse structure of $\chi^{(2)}$, the authors achieve spatial control of SHG, producing complex wavefronts such as Airy beams. This capability is pivotal for applications requiring structured light, with potential implications for sensing and imaging technologies.
• Spatio-Spectral Engineering: By leveraging the full two-dimensional programmability, the device produces distinct spatial light profiles across multiple wavelengths simultaneously. This profound versatility could play a crucial role in next-generation optical communication systems and adaptive imaging methodologies.

Implications and Future Directions

The programmable nonlinear waveguide developed in this paper transcends the conventional one-device-one-function paradigm, setting a precedent for multifunctional photonic devices. With this, the paper opens new possibilities in several fields:

• Quantum Optics and Computing: Programmable $\chi^{(2)}$ nonlinearity can enable the realization of programmable optical quantum gates and sources of quantum light. This flexibility is particularly advantageous for developing adaptive, multifunctional quantum computing platforms.
• All-Optical Signal Processing: The ability to dynamically tailor nonlinear optical processes offers enhanced capabilities in optical computing and signal processing, potentially leading to faster and more efficient information processing technologies.
• Adaptive Sensing and Imaging: Structured light, which can be dynamically programmed, offers significant benefits in adaptive sensing technologies, especially in environments where rapid changes necessitate real-time adaptability.

Conclusion

The research outlined in this paper represents a significant step forward in nonlinear photonics. The implications for practical applications are substantial, especially in fields requiring adaptive and multifaceted photonic solutions. Future work may focus on improving the nonlinearity prominence to rival traditional materials and developing methods for integrated microelectronics to further miniaturize programmable devices. As the technology matures, the programmable nonlinear waveguide could become a cornerstone in the growing field of adaptive, multifunctional photonics.