effects, [ 25,26 ] fi lm stacks-based Fabry-Pérot (FP) cavity absorber, [ 27,28 ] shallow grating, [29][30][31][32] metallic convex groove plasmonic absorber with adiabatic nanofocusing, [ 33,34 ] metallic surfaces with grooves, [ 35,36 ] etc. For spatial optical sensing and signal processing, the spatially and spectrally resolved narrowband absorbers (whose absorption strongly depends on the incident angle) are highly desirable. Of all the aforementioned absorbers, fi lm stacks-based FP cavity absorber demonstrates a good spatially and spectrally resolved narrowband characteristic; however, its cavity length is limited to quarter-wavelength since it is dependent on multipass transmission phase shifts. The metallic shallow grating-based optical absorber, which utilizes surface plasmon polaritons (SPPs) at metal-dielectric interface, [ 37,38 ] shows the ability of confi ning light beyond the diffraction limit and thereby signifi cantly reduces the device thickness. This absorber has shown spatially and spectrally narrow-band absorption with a 1D metallic shallow grating confi guration [ 29,39 ] or a 2D ring-based grating confi guration [ 30 ] at normal incidence. However, its spatially-resolved characteristic is still to be explored. Considering its potential applications in spatial optical measurement and signal processing, it is of vital importance to study its spatially-resolved characteristic.In this paper, two kinds of spatially and spectrally resolved narrowband absorber based on 2D grating nanostructures on metallic fi lms are presented: a PMMA nanohole array and an Au nanodisk array on metallic fi lms. Both spatially and spectrally resolved narrowband absorption under both TE and TM polarizations is experimentally demonstrated. For the TE polarization, the absorption corresponds to a localized mode. For the TM polarization, both a localized mode and a lattice mode can be obtained. For angle measurement utilizing the TM lattice mode, it could show a large measurement range (between −30° and 30°) and a relatively low resolution (10 −3 degree) by resolving the peak resonant wavelength. A small measurement range (within 0.75°) and an extremely high resolution (10 −7 degree) can also be obtained by resolving the resonant absorbance. Therefore, these spatially and spectrally resolved narrowband absorbers have a potential application for spatial optical measurement and signal processing.Two spatially and spectrally resolved narrowband absorbers based on 2D grating nanostructures (polymethylmethacrylate (PMMA) grating and gold grating) on metallic fi lms are designed, fabricated, and characterized. For PMMA grating on a metallic fi lm, the measured absorption bandwidth is 12 nm with a nearly 80% absorption at normal incidence. The transverse electric (TE) localized mode shows a calculated 3.5° angular width. The transverse magnetic (TM) resonant mode supports both a localized mode and a lattice mode. The TM lattice mode shows a calculated angular width of 0.75° and exhibits a large wavelength-angle sensitivity of ...

An ultra-narrow band absorber consisting of continuous silver and alumina films is investigated. Owing to Fabry–Pérot resonance and silver's inherent loss, an ultra-narrow spectral range of light can be entirely trapped in the structure. By varying thicknesses of metallic and dielectric films, absorption peak shifts in visible and near-infrared regions. When two such metal-insulator-metal stacks are cascaded, experimental results show that an ultra-narrow absorption bandwidth of 7 nm is achieved, though theoretical results give that of 2 nm. Features of high-efficiency and ultra-narrow band absorption have huge potential in optical filtering, thermal emitter design, etc.

In this Letter, plasmonic sectoral horn nanoantennas working at near-infrared wavelength (1550 nm) have been investigated. We demonstrate that, although there are certain differences between the plasmonic and classical radiofrequency (RF) sectoral horn antennas, the plasmonic horns still possess a number of attractive features, like their RF counterparts, such as tunable high directivities, simplicity in fabrication, and ease of coupling to waveguides. As a specific application, we further show how to exploit these findings to optimize an optical wireless nanolink using the proposed horn nanoantennas, and obtain a 60-fold increase in the received power compared with the situation of matched dipole nanoantennas.

Turning the surfaces of noble metals (metasurfaces) into black (highly absorptive) surfaces can be potentially applied in thermophotovoltaics, sensing, tailoring thermal emissivity, etc. Here we demonstrate an extremely broadband absorber for the 900-1600 nm wavelength range with robust high absorption efficiency. The inexpensive droplet evaporation method is implemented to create patterns of nanoparticles dispersed on a gold film spaced by a thin dielectric layer. The diversity of the complicated random stacking of the chemically synthesized gold nanorods is the major factor for the broad absorption band. Such a metamaterial absorber may pave the way for cost-effective manufacture of large-area black metasurfaces.

Au nanoparticles show large third-order nonlinear effect and ultra-fast response. Here a high nonlinear aggregate film based on self-assembled gold nanoparticles is reported and its third-order nonlinear refractive index coefficient is measured by Z-scan experiment. The third-order nonlinear refractive index coefficient of the Au nanoparticle aggregate film (γ1 = 9.2 × 10−9 cm2/W) is found to be larger than that of an 8-nm-thick sputtered Au film (γ2 = 6.5 × 10−9 cm2/W). This large nonlinear effect can be attributed to the strong field enhancement due to localized plasmon resonances between Au nanoparticles. The result shows that the self-assembled Au nanoparticle aggregate film could be a promising candidate as a third-order nonlinear optical material.