Ultra-fast transient plasmonics using transparent conductive oxides

Abstract

During the last decade, plasmonic-and metamaterial-based applications have revolutionized the field of integrated photonics by allowing for deep subwavelength confinement and full control over the effective permittivity and permeability of the optical environment. However, despite the numerous remarkable proofs of principle that have been experimentally demonstrated, few key issues remain preventing a widespread of nanophotonic technologies. Among these fundamental limitations, we remind the large ohmic losses, incompatibility with semiconductor industry standards, and largely reduced dynamic tunability of the optical properties. In this article, in the larger context of the new emerging field of all-dielectric nanophotonics, we present our recent progresses towards the study of large optical nonlinearities in transparent conducting oxides (TCOs) also giving a general overview of the most relevant and recent experimental attainments using TCO-based technology. However, it is important to underline that the present article does not represent a review paper but rather an original work with a broad introduction. Our work lays in a sort of 'hybrid' zone in the middle between high index contrast systems, whose behaviour is well described by applying Mie scattering theory, and standard plasmonic elements where optical modes originate from the electromagnetic coupling with the electronic plasma at the metal-todielectric interface. Beside remaining in the context of plasmonic technologies and retaining all the fundamental peculiarities that promoted the success of plasmonics in the first place, our strategy has the additional advantage to allow for large and ultra-fast tunability of the effective complex refractive index by accessing the index-near-zero regime in bulk materials at telecom wavelength.

Broadband frequency translation through time refraction in an epsilon-near-zero material

“…An ENZ material is defined as a medium that has a near-zero linear permittivity, and consequently low linear refractive index. The near-zero permittivity in such a medium leads to highly nonintuitive linear effects [41][42][43] and strong nonlinear light-matter interactions 9,[44][45][46][47] . In order to implement a temporal boundary with a large index change, we make use of the large and ultrafast optically induced change in refractive index of a 620 nm thick ITO film in its near-zero-permittivity spectral range.…”

Photonics of Time-Varying Media

“…Time-refraction in pump probe experiments has been shown in bulk ITO and AZO thin-films, [207][208][209][210][211] with frequency shifts as strong as 58 THz 209 when the probe field and the modulation overlap [see diagram in Fig. 14(b)].…”

Optical Metasurfaces: Evolving from Passive to Adaptive

“…Based on this method, metasurfaces exhibiting phenomena such as Doppler shifts, time refraction or the violation of Lorentz reciprocity have been proposed . In this context, pump‐probe experiments on AZO films have enabled a first demonstration of temporal gradient effect by inducing ultrafast changes in refractive index of the film resulting in a wavelength shift in the probe pulse . Employing transparent conductive oxide films with a structured metasurface could further enhance these effects.…”

“…[222,223] In this context, pump-probe experiments on AZO films have enabled a first demonstration of temporal gradient effect by inducing ultrafast changes in refractive index of the film resulting in a wavelength shift in the probe pulse. [224][225][226] Employing transparent conductive oxide films with a structured metasurface could further enhance these effects. Such ultrafast modulation enabled by time-gradient metasurfaces may find applications in nonmagnetic optical isolators, optical signal routing and wavelength division multiplexing.…”