Ultrafast all-optical tuning of direct-gap semiconductor metasurfaces

Abstract

Optical metasurfaces are regular quasi-planar nanopatterns that can apply diverse spatial and spectral transformations to light waves. However, metasurfaces are no longer adjustable after fabrication, and a critical challenge is to realise a technique of tuning their optical properties that is both fast and efficient. We experimentally realise an ultrafast tunable metasurface consisting of subwavelength gallium arsenide nanoparticles supporting Mie-type resonances in the near infrared. Using transient reflectance spectroscopy, we demonstrate a picosecond-scale absolute reflectance modulation of up to 0.35 at the magnetic dipole resonance of the metasurfaces and a spectral shift of the resonance by 30 nm, both achieved at unprecedentedly low pump fluences of less than 400 μJ cm–2. Our findings thereby enable a versatile tool for ultrafast and efficient control of light using light.

Broadband, High‐Speed, and Large‐Amplitude Dynamic Optical Switching with Yttrium‐Doped Cadmium Oxide

“…With pump‐probe experiments, we demonstrate broadband optically induced switching of unpatterned films in the transmission mode and the reflection mode, with a maximum reflectance change of 135% in the MIR region with a relaxation time of 45.6 ps for a pump fluence of 1.3 mJ cm −2 . This change in the reflectance with respect to pump power is significantly higher than previous demonstrations of optical modulation in switching platforms such as ENZ AZO films (40% for 4 mJ cm −2 ), ITO nanocrystals (150% at 18.16 mJ cm −2 ), and even patterned metasurfaces (35% for 0.40 mJ cm −2 ) . We identify the possible carrier relaxation mechanisms for photoexcited carriers in CdO and show that the relaxation time decreases with increasing doping levels.…”

“…All‐optical switching, with its large bandwidth and ultrafast response times, can enable the next generation of switchable devices for communication systems. Previous demonstrations of all‐optical switching have involved complex metasurfaces, ENZ films, high‐Q resonant cavities, and other processes mostly employing a single wavelength probe. Here, we demonstrate simultaneous broadband responses in the NIR and the MIR frequencies by employing interband pumping.…”

“…A change of up to 4% was observed in the transmission mode was observed at NIR frequencies (Figure c), using a pump fluence of 0.90 mJ cm −2 per pulse, with relaxation times as low as 22 ps. The modulation can be enhanced by the design of dielectric or hybrid metasurfaces for optical switching at telecom wavelengths.…”

Photocarrier‐Induced Active Control of Second‐Order Optical Nonlinearity in Monolayer MoS2

“…Therefore, the excited states of such dielectrics enable optical switching, even within their transparency window. The span of active media for optical switching covers a wide range of metals, [1,[11][12][13][14][15] conductive oxides, [1,[16][17][18][19] dielectrics, [1,[20][21][22][23][24] and organic materials, [25,26] utilized either in bulk formats or tailored as miniaturized device platforms. The formation of excited charge carriers induces a transient change in material properties, namely linear and nonlinear indices of refraction, activating a category of ultrafast optical processes that are unlikely to happen through the interaction of light with the static form of matter.…”

Ultra-fast transient plasmonics using transparent conductive oxides

“…Other important works exploit the large nonlinearities achievable from all-dielectric systems. In this direction, it is worth mentioning the results by Shcherbakov et al where ultrafast reflectance modulation of about 45% is attained by means of low intensity pumping using a gallium arsenide (GaAs) metasurface [18]. A similar GaAs-based structure is also used by Liu et al to develop an optical metamixer where, by exploiting numerous nonlinear processes, frequency generation is demonstrated for eleven new spectral lines ranging from ultraviolet to near infrared [19].…”