Fig. 2: Structure and angular-resolved spectral emissivity of a pixelated directional micro-emitter.
From: Directional thermal emission and display using pixelated non-imaging micro-optics
a 2D schematic of the pixelated directional micro-emitter (PDME) structure. Through conservation of etendue, the angular distribution of thermal radiation is compressed by enlarging the areal spread from \({A}_{0}\) to \({A}_{1}\). The control of thermal radiation is broadband and polarisation-independent. \({\theta }_{a}\) represents the acceptance angle of the PDME. b A 3D hexagonal pixel structure composed of three pairs of oppositely-facing parabolic reflectors is used to tessellate over a horizontal plane and minimise azimuthal anisotropy. Unpolarised thermal radiation exits the top aperture within a small angular range. Ex and Ey stand for electric field vectors, namely polarisations, along x and y directions. c Simulated angular-resolved spectral emissivity of a PDME with a 15° acceptance angle (15°-PDME), where an abrupt drop in emissivity is apparent above 15°. d An SEM image of a 15°-PDME, scale bar: 500 μm. The inset shows a close-up image of its 3D hexagonal pixels, scale bar: 50 μm. e Measured spectral emissivity of 15°-PDME showing strong directional selectivity over an ultrawide wavelength range from 5 μm to 20 μm.
