Microstructured photonic polymer membranes for modulation of the reflectivity in the mid infrared

Recently, photonic crystals (PC) have attracted much attention in several fields of applications like in photovoltaic or optomechanic, and various implementations have been tested using either silicon or polysilicon. Our goal... [ view full abstract ]

Recently, photonic crystals (PC) have attracted much attention in several fields of applications like in photovoltaic or optomechanic, and various implementations have been tested using either silicon or polysilicon. Our goal is to develop a polymer based photonic membrane to control heat losses through radiative exchange in the mid infrared (MIR) range for applications such as wearable textiles, building insulation or food packaging.

We first studied numerically and experimentally silicon based PC, constituted of either ridges or holes, with dimensions of the lattice parameter about tens microns. These structures have been simulated with numerical models (finite differences and finite elements methods) and characterized in the 5-15 µm range. Various geometries have been studied to understand the effects of the geometry on the reflective spectrum of the silicon membrane. An experimental comparison of the spectra has been done with a good agreement.

We then investigate the case of a microstructured polymer membrane of benzocyclobutene (BCB) in the MIR. Numerical simulations have been undergone in order to study the influence of the geometry on the reflectivity. These membranes show narrow Fano’s type bands presenting high reflectivity together with Fabry-Perot oscillations. The efficiency of the various designs is compared by integrating the reflected energy on 5-15 µm spectrum divided by the energy produces by a black body in the same spectrum. The following figure represents the evolution of the efficiency as a function of the diameters of the air holes in the membrane and for different periods of the photonic lattice. One can clearly see that the variation of the diameter induces a modulation of the efficiency.

This work permits to quantify the efficiency of the polymer membranes and paves the way for the design of a smart responsive membrane which modifies its reflectance in response to external stimuli like temperature or the embedded medium.