Nonlinear nanophotonic control of light

Summary

Nonlinear optics enables transformation of optical fields through light-matter interactions. These transformations strictly conserve energy and phase-matching determines the efficiency of the process. The use of integrated photonics for nonlinear processes provides small mode areas and geometrically reconfigurable phase-matching, providing unparalleled nonlinearity that is broadly tunable. However, controlling light with nonlinear processes through geometric phase-matching alone is restrictive. We explore the use of networks of nonlinear photonic elements and the incorporation of nanoscale patterns or nanophotonic structures for novel control of integrated nonlinear processes.

Description

Light-matter interactions with nonlinear materials provide a powerful tool for converting optical fields from one state to another. For example, nonlinear wavelength conversion leverages efficient scattering of photons of a single frequency to another, enabling generation of coherent sources across vast spectral regimes. Such nonlinear optical processes conserve energy and their efficiency is determined by the momenta of the involved fields, called phase-matching. These well-known constraints offer deterministic control of light but impose strict limitations in nonlinear optical systems. Our project explores novel ways to manipulate optical fields using novel nonlinear integrated photonic systems to attain scalable control of light with otherwise impossible functionality.

Novel nanophotonic control of light. a) Nonlinear network for optical synthesis by spectral translation. (b) Photonic-crystal ring resonator with multiple frequency-shifting modulation periods. (c) Orthogonal nanophotonic resonator. The horizontal (vertical) cavity guides Einstein (Debye) modes, which can independently be dispersion engineered for four-wave-mixing.

The use of integrated photonics for nonlinear optical processes has demonstrated powerful control of optical fields at low optical powers due to tight optical mode confinement on a scalable, chip-scale platform. Moreover, integrated photonic devices offer broadly reconfigurable phase-matching by controlling device geometry. Nonetheless, these devices suffer frequency and phase-matching constraints just as in bulk nonlinear optical systems. By leveraging networks of nonlinear elements, we can overcome the existing limitations imposed by nonlinear processes. Indeed, we benchmark a nonlinear network by generating an optical frequency synthesizer with unprecedented operational bandwidth. Two nonlinear integrated photonic microresonators comprise the network where one creates an optical frequency comb and the other enables four-wave-mixing spectral translation to deterministically convert light to a target frequency. Figure panel a shows images of the two microresonators in the network and the bottom trace is the measured synthesizer error measured over 10 minutes, demonstrating sub-Hz accuracy. 

Common approaches to frequency and phase-matching in integrated photonics are highly dispersion dependent and exceptionally challenging for certain device geometries, especially at visible wavelengths. The addition of a nano-scale modulation to the inner ring wall of a microresonator, a so-called photonic crystal microresonator (PhCR), enables single-mode frequency shifting for very fine dispersion tuning. Such PhCRs enable access to universal phase-matching for nonlinear optical processes even in devices which otherwise would not support such dynamics. Indeed, PhCRs with multiple nanostructures are possible for multiple-mode frequency splitting for arbitrary, mode-by-mode dispersion design. Figure panel b shows a PhCR with multiple modulation periods imparted on a single device as seen in the zoom-in on the right. Moreover, incorporating other nanostructures into the PhCR architecture enable decreased threshold power for nonlinear processes and enhanced performance through optimal conversion of light from one state to another. We also explore novel linear-cavity designs, without a microresonator structure. These nanostructured linear cavities enable a compact footprint and broadly tunable dispersion to support nonlinear processes. Lastly, we are interested in novel cavity designs like that seen in Figure panel c. This device incorporates two orthogonal nanopatterned linear optical cavities which support different types of optical guiding. By utilizing two cavities with common modal overlap, we can independently control the dispersion in both cavities for a novel approach to phase-matching.

Publications

[1] Black, Jennifer A., et al. "Nonlinear Networks for Arbitrary Optical Synthesis." Accepted PRX, 04/27/2023: https://journals.aps.org/prx/accepted/9c070KafI0c15d0db7664867aeeff10db…

[2] Black, Jennifer A., et al. "Optical-parametric oscillation in photonic-crystal ring resonators." Optica 9.10 (2022): 1183-1189. 

[3] Lucas, Erwan, et al. "Tailoring microcombs with inverse-designed, meta-dispersion microresonators." arXiv preprint arXiv:2209.10294 (2022).

[4] Zang, Jizhao, et al. "Near unit efficiency in microresonator combs." CLEO: Science and Innovations. Optica Publishing Group, 2022.

[5] Yu, Su-Peng, et al. "Photonic-crystal-reflector nanoresonators for Kerr-frequency combs." ACS Photonics 6.8 (2019): 2083-2089.

[6] Yu, S-P., et al. "Geometric Four-Wave Mixing Phase-Matching in Photonic Nanoresonators." CLEO: Science and Innovations. Optica Publishing Group, 2022.

Major Accomplishments

1. Demonstrated nonlinear networks for unique functionalities, including broadband optical synthesizer.
2. Innovated photonic-crystal resonators for arbitrary, mode-by-mode group-velocity dispersion engineering.
3. Innovated two-dimensional nanophotonic cavities for novel phase matching.