Abstract
In recent years there has been much interest concerning the development of modulators in the mid- to long-wave infrared, based on emerging materials such as graphene. These have been frequently pursued for optical communications, though also for other specialized applications such as infrared scene projectors. Here we investigate a new application for graphene modulators in the mid- to long-wave infrared. We demonstrate, for the first time, computational spectroscopy in the mid- to long-wave infrared using a graphene-based metasurface modulator. Furthermore, our metasurface device operates at low gate voltage. To demonstrate computational spectroscopy, we provide our algorithm with the measured reflection spectra of the modulator at different gate voltages. We also provide it with the measured reflected light power as a function of the gate voltage. The algorithm then estimates the input spectrum. We show that the reconstructed spectrum is in good agreement with that measured directly by a Fourier transform infrared spectrometer, with a normalized mean-absolute-error (NMAE) of 0.021.
Highlights
In recent years there has been much interest concerning the development of modulators in the midto long-wave infrared, based on emerging materials such as graphene
This motivates an investigation into performing MWIR-LWIR spectroscopy using another type of modulator, i.e. a graphene-based metasurface, that is considerably smaller than the interferometers used in Fourier transform infrared spectrometer (FTIR) systems
We experimentally demonstrate graphene metasurface modulators, each composed of metallic nanostructures and a dielectric cavity integrated with graphene, whose MWIR-LWIR reflection spectra can be tuned via a voltage (VG) applied to its back gate
Summary
A schematic diagram of our metasurface modulator is shown as Fig. 1a. It comprises a periodic array of cross-shaped nanoantennas formed over a single layer of graphene which in turn sits on a stack containing alumina (Al2O3), titanium dioxide (TiO2), and gold (Au) layers on a silicon substrate. We check the robustness of this method by re-doing the reconstruction with a delay of several months between the characterization of the metasurface stored in vacuum desiccator (i.e. determination of RVG(λ)) and the measurement of the signal vs gate voltage (i.e. collection of data when metasurface is illuminated by unknown spectrum) These results are obtained with the P = 2250 nm device over the spectral range λ = 7501.75 nm to 10003 nm. It can be seen that both reconstructions (Fig. S7a,b) are in reasonable agreement with the spectrum measured directly by our FTIR system
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