Currently, there are no cheap and compact sources in the mid-infrared range that can be modulated at high frequencies. Incandescent sources such as hot membranes and globars are widely used for mid-infrared spectroscopic applications, but for detection or communication applications where fast temperature modulation are desirable, thermal inertia quickly becomes a limiting factor. Besides, such incandescent sources are typically unpolarized, isotropic, broadband and have a low efficiency. However, these properties are not imposed by fundamental limitations stemming from physics laws, except for the low brightness dictated by Bose-Einstein distribution. Here, we introduce a metasurface that combines nanoscale heaters to ensure fast thermal response and nanophotonic resonances to provide large spectrally selective and polarized emissivity. We report a peak emissivity of 0.8 and an operation up to 20 MHz, six orders of magnitude faster than commercially available hot membranes.
In the last decades, designs of most incandescent sources have been realized by heating the whole device. Here we propose a novel approach consisting in taking advantage of hot nanoemitters that can be cooled in a few tens of nanoseconds. It offers a new opportunity for high speed modulation and for enhanced agility in the active control of polarization, direction and wavelength of emission. To compensate the weak thermal emission of isolated nanoemitters, we propose to insert them in some complex environments, such as e.g. the gap of cold nanoantenna, which allow a significant thermal emission enhancement of the hot nanovolume. In order to optimize this kind of device, a fully vectorial upper bound for the thermal emission of a hot nanoparticle in a cold environment is derived. This criterion is very general since it is equivalent to an absorption cross-section upper bound for the nanoparticle. Moreover, it is an intrinsic characteristic of the environment regardless of the nanoparticle, so it allows to decouple the design of the environment from the one of the hot nanovolume. It thus provides a good figure of merit to compare the ability of different systems to enhance thermal emission of hot nanoemitters.
Currently, there are no cheap and compact sources in the mid-infrared range that can be modulated at high frequencies. While hot membranes are common IR sources, their thermal inertia limit the modulation rates to a few tens of Hertz. Moreover, available thermal sources are unpolarized, isotropic, broadband and have a low efficiency. However, there is no fundamental limit that imposes these properties. It turns out that they can be strongly modified by using appropriate nanostructures. In this presentation, we report the design, fabrication and characterization of infrared incandescent sources, modulated faster than 10 MHz with a controlled spectrum and polarization.
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