Polarization-selected nonlinearity transition in gold dolmens coupled to an epsilon-near-zero material

Abstract

Nonlinear optical materials are cornerstones of modern optics including ultrafast lasers, optical computing, and harmonic generation. The nonlinear coefficients of optical materials suffer from limitations in strength and bandwidth. Also, the nonlinear performance is typically monotonous without polarization selectivity, and to date, no natural material has been found to possess nonlinear coefficients with positive or negative signs simultaneously at a specific wavelength, all of which impede practical applications in the specific scenario. Here, we realize broadband large optical nonlinearity accompanied with ultrafast dynamics in a coupled system composed of gold dolmens and an epsilon-near-zero material for dual orthogonal polarizations simultaneously. The system also shows the polarization-selected nonlinearity transition properties, where the sign of the optical nonlinear refractive indexes can be converted via polarization switching. This guarantees active transitions from self-focusing to self-defocusing by polarization rotation without tuning wavelength in practical utilizations. The measured nonlinear refractive index and susceptibility demonstrate more than three orders of magnitude enhancement over a 400-nm-bandwidth compared with the constituents, while maintaining the sub-1 ps time response. The realized enhanced, ultrafast response, and the polarization tunability ensure the designed system a promising platform for the development of integrated ultrafast laser sources, all-optical circuits and quantum chips.

Integrated Terahertz Generator-Manipulators Using Epsilon-near-Zero-Hybrid Nonlinear Metasurfaces

“…Hybridizing metasurfaces with ENZ films could further boost the nonlinearity by leveraging the strong near-field distribution of the resonant meta-atoms at desired frequencies [39][40][41] .…”

Polarization-Independent Large Third-Order-Nonlinearity of Orthogonal Nanoantennas Coupled to an Epsilon-Near-Zero Material

“…Figure 9 shows the function of the fundamental wave and the THG signal in the flat and rough interfaces. In the flat interface, the THG signal is the largest at a wavelength of 1390 nm, and the maximum enhancement factor compared with the bare AZO film is 210,000, which is 9.1 times larger than that in the literature [19]. In the rough interface, the THG signal is the largest at a wavelength of 1440 nm and is redshifted compared to the flat interface, the maximum enhancement factor is similar to the flat interface.…”

“…The absolute maximum value of the nonlinear refractive index of the two polarization states is 7.65 cm 2 •GW −1 at I = 150 MW•cm −2 , which is 4 orders of magnitude higher than that of the bare AZO thin film [7] and 3 orders of magnitude larger than that of the highly nonlinear metamaterial and the bare ITO film [6,22]. The effective third-order nonlinear susceptibility also provides a greater than 210000-fold enhancement with polarization insensitivity, which is 9.1 times larger than the literature [19].…”

“…Strong nonlinearity occurs only when the polarization direction of the incident light is parallel to the long axis of the antenna. Niu et al [19] proposed a polarization-selected nonlinearity transition in gold dolmens coupled to an epsilonnear-zero material and realized the change of the sign of nonlinear coefficients through polarization conversion. In addition to studying metal nanoantennas, dielectric nanoantennas have also gained increasing interest due to lower loss.…”

Near-zero-index ultra-fast pulse characterization

“…Among the most noticeable proof-of-concept applications, which make use of TCOs’ enhanced nonlinearities, are tuneable nanocavities 21 , three-state logic 22 , ultra-fast signal routing 23 , 24 , polarisation selectors 25 , and nano modulators 26 – 28 . However, despite all these remarkable experimental demonstrations, the integrated photonics community is still seeking the perfect “killer” application that could take full advantage of TCOs’ unique optical properties.…”