Ultrafast and Broadband Tuning of Resonant Optical Nanostructures Using Phase‐Change Materials

Abstract

The functionalities of a wide range of optical and opto-electronic devices are based on resonance effects and active tuning of the amplitude and wavelength response is often essential. Plasmonic nano-structures are an efficient way to create optical resonances, a prominent example is the extraordinary optical transmission (EOT) through arrays of nano-holes patterned in a metallic film. Tuning of resonances by heating, applying electrical or optical signals has proven to be more elusive, due to the lack of materials that can induce modulation over a broad spectral range and/or at high speeds. Here we show that nano-patterned metals combined with phase change materials (PCMs) can overcome this limitation due to the large change in optical constants which can be induced thermally or on an ultrafast timescale. We demonstrate resonance wavelength shifts as large as 385 nm --an order of magnitude higher than previously reported--by combining properly designed Au EOT nanostructures with Ge2Sb2Te5 (GST). Moreover, we show, through pump-probe measurements, repeatable and reversible, large-amplitude modulations in the resonances, especially at telecommunication wavelengths, over ps time scales and at powers far below those needed to produce a permanent phase transition. Our findings open a pathway to the design of hybrid metal-PCM nanostructures with ultrafast and widely tuneable resonance responses, which hold potential impact on active nanophotonic devices such as tuneable optical filters, smart windows, bio-sensors and reconfigurable memories.* These authors made equal contribution †valerio.pruneri@icfo.eu 2 Nanophotonic devices incorporating metallic elements can support plasmons, which are collective oscillations of conduction band electrons driven by an external electromagnetic field 1 . Plasmons can confine and guide light well below the diffraction limit, and when supported by suitably engineered nanostructures, they enable the design of disruptive devices for a wide range of applications, including perfect lenses . Plasmons also play an important role in the phenomenon of extraordinary optical transmission (EOT) of visible and infrared light through periodic arrays of subwavelength nanoholes drilled in metallic films. The observation of transmission resonances in these arrays is attributed to the resonant interaction between holes mediated by surface plasmons propagating on the film surfaces 7 . More precisely, transmission peaks emerge close to the Wood anomalies 8 and are well explained in terms of geometrical resonances in the periodic lattice 9,10,11 . An important challenge in the design of plasmonic nanostructures is the precise control of their optical responses in order to meet the requirements of specific device applications. This can be accomplished by casting nanostructures with appropriate materials and geometries. However, such an approach is static and limited by material inhomogeneity and fabrication tolerances. More critically, many applications (e.g., optical switching and modulation) ...

Ultrafast optical response of the amorphous and crystalline states of the phase change materialGe2Sb2Te5

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Vanadium Oxide as a Key Constituent in Reconfigurable Metamaterials

“…This functionality is the result of phase transitions from crystalline to amorphous states and is typically triggered by a thermal, electrical or optical stimulation. Nanoscale electro-optical metamaterial switch using chalcogenide materials has also been demonstrated [2][3][4][5][6].…”

Dynamic Thermal Emission Control Based on Ultrathin Plasmonic Metamaterials Including Phase‐Changing Material GST

“…The ultrathin feature is achieved by adopting the MIM plasmonic metamateirals, in which the emission wavelength can be controlled by the geometric size of top metallic particles without sacrificing the total device thickness. The dynamic low‐power‐consumption control is implemented by incorporating zero‐static‐power phase‐changing material Ge2Sb2Te5 (GST), which has been applied in various energy‐efficient switchable photonic devices . The whole structure shows a total thickness of 550 nm (∼0.023λ), which is well below the subwavelength scale.…”