26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Optimization of Degenerate Four-Wave Mixing in Epsilon-Near-Zero Plasmonic Slot Waveguides

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral ANZOS | Photonics and Optics (ANZCOP)

Description

Metal–dielectric–metal (MDM) plasmonic slot waveguides combine strong field confinement with slow-light effects, enabling enhanced light–matter interactions over short propagation lengths [1]. This makes MDM waveguides ideal platforms for exploiting materials with large Kerr nonlinearities but also high losses, such as epsilon-near-zero (ENZ) materials [2,3]. However, harnessing the nonlinear response of these materials remains challenging, owing to their counterintuitive optical properties and modal behaviour in such structures. Here, we investigate the relationship between the nonlinear effectiveness (EFF), which quantifies how efficiently a guided mode exploits the material nonlinearity, and the degenerate four-wave mixing conversion efficiency ($\eta_{\mathrm{DFWM}}$), which quantifies the efficiency of nonlinear photon generation [4]. Our results show that, unlike in conventional nonlinear materials, the maxima of $\eta_{\mathrm{DFWM}}$ and EFF in ENZ-MDM waveguides do not coincide with the wavelength at which the nonlinear coefficient and slow-light enhancement peak. At this wavelength, the reduced field uniformity and the lower weighted electric-energy overlap limit the EFF, while high propagation losses outweigh the benefit of the enhanced ENZ nonlinearity. As a result, the highest values of $\eta_{\mathrm{DFWM}}$ and EFF are reached where the modal confinement remains effective and material losses are minimized. Nevertheless, ENZ-MDM waveguides still outperform conventional MDM structures in terms of $\eta_{\mathrm{DFWM}}$ across the explored spectral range, even under low pump-power conditions. These results establish ENZ materials as the preferred nonlinear medium for ultra-compact frequency-conversion devices in which conversion efficiency is prioritized over modal homogeneity.

References
[1] A. Tuniz, O. Bickerton, F. J. Diaz, et al., Nat. Commun. 11, 2413 (2020).
[2] O. Reshef, I. De Leon, M. Z. Alam, et al., Nat. Rev. Mater. 4, 535–551 (2019).
[3] M. Z. Alam, I. De Leon, R. W. Boyd, Science 352, 795–797 (2016).
[4] L. Rojas Yanez, H. Hu, C. Ciracì, S. Palomba, Front. Nanotechnol. 7, 1536462 (2025).