Spatially and Spectrally Resolved Narrowband Optical Absorber Based on 2D Grating Nanostructures on Metallic Films

Abstract

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 ...

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