Periodic guided-mode resonance structures which provide perfect reflection across sizeable spectral bandwidths have been known for decades and are now often referred to as metasurfaces and metamaterials. Although the underlying physics for these devices is explained by evanescent-wave excitation of leaky Bloch modes, a growing body of literature contends that local particle resonance is causative in perfect reflection. Here, we address differentiation of Mie resonance and guided-mode resonance in mediating resonant reflection by periodic particle assemblies. We treat a classic 2D periodic array consisting of silicon spheres. To disable Mie resonance, we apply an optimal antireflection (AR) coating to the spheres. Reflectance maps for coated and uncoated spheres demonstrate that perfect reflection persists in both cases. It is shown that the Mie scattering efficiency of an AR-coated sphere is greatly diminished. The reflectance properties of AR-coated spherical arrays have not appeared in the literature previously. From this viewpoint, these results illustrate high-efficiency resonance reflection in Mie-resonance-quenched particle arrays and may help dispel misconceptions of the basic operational physics.
Whereas various technologies including thin film optics and liquid crystals [4,5] potentially realize tunable filters, guidedmode resonant (GMR) periodic lattices are superb candidates for fashioning compact and efficient notch filters with lossless dielectric media. [6] In particular, conventional multilayer thin-film technology is impractical in the LWIR band as quarterwave films are much thicker than those for the visible region thwarting successful deposition. Hence, the present singlelayer tunable elements are advantageous. Previously, we demonstrated tunability of 1D GMR notch filters by employing chirped gratings and by angular rotation. [7,8] In contrast, the tuning properties of 2D lattices remain largely untreated. Here, we ameliorate that situation and formulate the properties underlying the tunability of 2D structures in detail. An advantage of the 2D case relative to 1D filters is that by simple polarization rotation, an entirely new tunable spectral range becomes available.
This study reports design, fabrication, and characterization of high-performance guided-mode resonance (GMR) infrared filters based on germanium (Ge) operating in the 7 to 15 µm spectral region. The GMR filters exhibit deep transmittance nulls and high sideband efficiency functioning as band-stop filters. There is reasonable agreement between experimental and theoretical spectral results. By modifying design parameters and incorporating an anti-reflection (AR) layer on the substrate backside, the functionality of the filter is significantly enhanced. The measured low transmittance value of the fabricated filters is found to be as low as 0.021% corresponding to an optical density of OD = 3.68. The one-dimensional (1D) GMR filters produced exhibit agile wavelength tunability when the angle of incidence is varied. The results highlight the potential of GMR technology operating at long infrared wavelengths with creating high performance filters with tunable spectral characteristics. Anticipated application domains include the fields of sensing, imaging, and spectroscopy.
This study reports design, fabrication, and characterization of high-performance guided-mode resonance (GMR) infrared filters based on germanium (Ge) operating in the 7 to 15 µm spectral region. The GMR filters exhibit deep transmittance nulls and high sideband efficiency functioning as band-stop filters. There is reasonable agreement between experimental and theoretical spectral results. By modifying design parameters and incorporating an anti-reflection (AR) layer on the substrate backside, the functionality of the filter is significantly enhanced. The measured low transmittance value of the fabricated filters is found to be as low as 0.021% corresponding to an optical density of OD = 3.68. The one-dimensional (1D) GMR filters produced exhibit agile wavelength tunability when the angle of incidence is varied. The results highlight the potential of GMR technology operating at long infrared wavelengths with creating high performance filters with tunable spectral characteristics. Anticipated application domains include the fields of sensing, imaging, and spectroscopy.
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