Abstract
AbstractA very large dynamic optical reflection modulation from a simple unpatterned layered stack of phase‐change material ultra‐thin films is experimentally demonstrated. Specifically, this work demonstrates that properly designed systems comprising deeply subwavelength GeSbTe (GST) films, a dielectric spacer, and a metallic mirror produce a dynamic modulation of light in the near‐infrared from very strong reflection (up to ) to perfect absorption () by simply controlling the crystalline state of the phase‐change material. While the amplitude of modulation experimentally reaches an optical contrast higher than 104, intermediate levels of reflection in between extreme values can also be actively encoded, corresponding to partial crystallization of the GST layer. Several layered system designs are further explored and guidelines are provided to tailor the efficient wavelength range, the angle of operation, and the degree of crystallization leading to perfect absorption.
Highlights
Adjusting the absorption, reflection and transmission properties of systems is the basis of most photonic devices engineering, from mirrors to dispersion gratings as well as photodetectors and solar cells
This class of materials enables a very large optical modulation at the nanoscale via a fast change of phase in their crystalline structure. This large optical modulation of phase-change materials (PCM) has been used in designed nanostructures to enable active beam-steerers [5], dynamic modulation of light emission [6], light absorption [7] or light transmission [8]
We show how we can fully exploit the design space offered by this platform to tailor many features of the modulation, such as the wavelength of operation and the crystallization fraction at which occur the perfect absorption
Summary
Reflection and transmission properties of systems is the basis of most photonic devices engineering, from mirrors to dispersion gratings as well as photodetectors and solar cells. We design and demonstrate actively reconfigurable lithography-free flat optics whose optical properties can be continuously tuned from a strong reflection (up to R>80%) to a perfect absorption (A=(1-R)∼99.99%) i.e an extinction of -68 dB that is actively controlled by adjusting the crystalline fraction of a standard GST thin-film (see Figure 1a) for an illustration of the concept). Such a modulation depth surpass most of free-space optical modulators reported so far [8, 19, 20, 21] with the additional advantage of not requiring any complex nanopatterning processes. We further propose practical implementations of this concept in multilayered configurations designed for electrical modulation that conserves all achieved properties
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