Reconfigurable multilevel control of hybrid all-dielectric phase-change metasurfaces

Abstract

All-dielectric metasurfaces comprising arrays of nanostructured high-refractive-index materials are re-imagining what is achievable in terms of the manipulation of light. However, the functionality of conventional dielectric-based metasurfaces is fixed by design; thus, their optical response is locked in at the fabrication stage. A far wider range of applications could be addressed if dynamic and reconfigurable control were possible. We demonstrate this here via the novel concept of hybrid metasurfaces, in which reconfigurability is achieved by embedding sub-wavelength inclusions of chalcogenide phase-change materials within the body of silicon nanoresonators. By strategic placement of an ultra-thin G e 2 S b 2 T e 5 layer and reversible switching of its phase-state, we show individual, multilevel, and dynamic control of metasurface resonances. We showcase our concept via the design, fabrication, and characterization of metadevices capable of dynamically filtering and modulating light in the near infrared (O and C telecom bands), with modulation depths as high as 70% and multilevel tunability. Finally, we show numerically how the same approach can be re-scaled to shorter wavelengths via appropriate material selection, paving the way to additional applications, such as high-efficiency vivid structural color generators in the visible spectrum. We believe that the concept of hybrid all-dielectric/phase-change metasurfaces presented in this work could pave the way for a wide range of design possibilities in terms of multilevel, reconfigurable, and high-efficiency light manipulation.

Multistate Switching of Photonic Angular Momentum Coupling in Phase‐Change Metadevices

“…[ 22–26 ] However, the tunability of PSOIs has been demonstrated with only “ON” and “OFF” states, although a couple of demonstrations of multilevel (even up to 11 states) and fully reversible tuning of metasurfaces have been reported. [ 27–31 ] Since the information can be coded in merely “ON” state, it is unavoidable to employ interleaved subarrays to achieve multiple functions with each one contributing to only a single function, resulting in the fundamental limitations of pixel loss, information infidelity, and low energy efficiency. [ 17 ] Additionally, interlacing different subarrays also increase the period of unit cells, resulting in a dramatic loss of light to spurious diffraction orders, which may further deteriorate the information fidelity and energy efficiency.…”

Design for quality: reconfigurable flat optics based on active metasurfaces

“…Compared to VO 2 , chalcogenide O-PCMs exemplified by GST offer even larger optical contrast in the near-IR and UV spectral regimes with an index change up to 2.8 [172][173][174][175][176]. In addition to tuning response of identical metaatom arrays [177][178][179][180][181][182][183][184][185][186][187][188][189], advanced active control of metasurface devices, including varifocal metalenses [190][191][192][193], metasurface color display [194], spatial light modulators [188], spectral filters [180,187,189], beam-steering metadevice [195], reconfigurable holograms [196], tunable thermal absorbers [197] and emitters [198][199][200][201], switches [202], free-form rewritable metasurfaces [203,204], and topologically optimized metadevices [205], have also been experimentally demonstrated leveraging phase-change behavior of GST alloys.…”

Enhanced Performance and Diffusion Robustness of Phase-Change Metasurfaces via a Hybrid Dielectric/Plasmonic Approach

“…While crystallization requires moderately elevated temperatures (around 180 to 400 °C for GST, depending on heating rate [ 8 ]), reamorphization requires the PCM to be heated above its melting temperature (630 °C for GST [ 8 ]), followed by a quick cooling rate to retain the less energetically favorable amorphous phase. In the case of traditional PCMs such as GST, reamorphization can be achieved via the use of short electrical or optical pulses (e.g., tens to hundreds of nanoseconds in PCM-based memories) [ 4 , 8 ] over small PCM volumes surrounded by good thermal conductors to avoid thermal insulation (and thus slow cooling rates) [ 9 , 10 ]. Access to intermediate or fractionally crystallized PCM states can also be achieved by appropriate excitation (heat stimulus), and can allow for both increased degrees of freedom (multilevel states) and more precise control over the PCM’s optical properties [ 9 , 11 , 12 , 13 ].…”

“…Another recently proposed active metasurface approach relied on the combination of all-dielectric silicon metasurfaces with deeply subwavelength-sized PCM inclusions, which provided a promising way of manipulating the amplitude and phase of light with high efficiency via the excitation of Mie-like resonances, free from plasmonic losses [ 9 ]. However, despite providing superior optical efficiencies, the in situ reversible switching of the phase-change layer was, in this case, complicated by the lack of metal layers to provide heating elements (as shown in Figure 1 a).…”