Beam-Size Invariant Spectropolarimeters Using Gap-Plasmon Metasurfaces

Metasurfaces enable exceptional control over the light with surface-confined planar components, offering the fascinating possibility of very dense integration and miniaturization in photonics. Here, we design, fabricate and experimentally demonstrate chip-size plasmonic spectropolarimeters for simultaneous polarization state and wavelength determination. Spectropolarimeters, consisting of three gap-plasmon phase-gradient metasurfaces that occupy 120{\deg} circular sectors each, diffract normally incident light to six predesigned directions, whose azimuthal angles are proportional to the light wavelength, while contrasts in the corresponding diffraction intensities provide a direct measure of the incident polarization state through retrieval of the associated Stokes parameters. The proof-of-concept 96-{\mu}m-diameter spectropolarimeter operating in the wavelength range of 750-950nm exhibits the expected polarization selectivity and high angular dispersion. Moreover, we show that, due to the circular-sector design, polarization analysis can be conducted for optical beams of different diameters without prior calibration, demonstrating thereby the beam-size invariant functionality. The proposed spectropolarimeters are compact, cost-effective, robust, and promise high-performance real-time polarization and spectral measurements

Do Demographic Characteristics Make Differences? Demographic Characteristics as Moderators in the Associations between Only Child Status and Cognitive/Non-cognitive Outcomes in China

Different family compositions and sizes may affect child development through the different modes of interaction between family members. Previous studies have compared only children with non-only children in cognitive/non-cognitive outcomes. However, relatively little research has systematically investigated the potential moderators among them. Using a large and representative sample of Chinese students (Grades 7–8; N = 5,752), this study examines the roles of demographic characteristics, such as gender, region, parental educational level, parental expectations, family socio-economic status and family structure, in the associations between only child status and cognitive/non-cognitive outcomes. For the cognitive outcomes, only child status exerts an influence on the students' academic performance in Chinese and mathematics in the sample of three districts' students. The examined associations between only child status and cognitive outcomes are different in region, parental education, parental expectations and family structure, while gender and family socio-economic status did not. For the non-cognitive outcomes, only child status exerts an influence on the students' school well-being, academic self-efficacy, academic self-concept, and internal academic motivation in the full sample of students, but not on external academic motivation. Further, the examined associations between only child status and non-cognitive outcomes are different in region, parental education, family socio-economic status and family structure, while gender and parental expectations did not. These findings suggest that the associations between only child status and cognitive/non-cognitive outcomes are heterogeneous in terms of some of the demographic characteristics. Possible explanations are proposed in some concepts of region and family environment in China

Random-phase metasurfaces at optical wavelengths

Random-phase metasurfaces, in which the constituents scatter light with random phases, have the property that an incident plane wave will diffusely scatter, hereby leading to a complex far-field response that is most suitably described by statistical means. In this work, we present and exemplify the statistical description of the far-field response, particularly highlighting how the response for polarised and unpolarised light might be alike or different depending on the correlation of scattering phases for two orthogonal polarisations. By utilizing gap plasmon-based metasurfaces, consisting of an optically thick gold film overlaid by a subwavelength thin glass spacer and an array of gold nanobricks, we design and realize random-phase metasurfaces at a wavelength of 800 nm. Optical characterisation of the fabricated samples convincingly demonstrates the diffuse scattering of reflected light, with statistics obeying the theoretical predictions. We foresee the use of random-phase metasurfaces for camouflage applications and as high-quality reference structures in dark-field microscopy, while the control of the statistics for polarised and unpolarised light might find usage in security applications. Finally, by incorporating a certain correlation between scattering by neighbouring metasurface constituents new types of functionalities can be realised, such as a Lambertian reflector

Laser writing of bright colours on near-percolation plasmonic reflector arrays

Colouration by surface nanostructuring has attracted a great deal of attention by the virtue of making use of environment-friendly recyclable materials and generating non-bleaching colours [1-8]. Recently, it was found possible to delegate the task of colour printing to laser post-processing that modifies carefully designed and fabricated nanostructures [9,10]. Here we take the next crucial step in the development of structural colour printing by dispensing with preformed nanostructures and using instead near-percolation metal films atop dielectric-metal sandwiches, i.e., near-percolation plasmonic reflector arrays. Scanning rapidly (~ 20 {\mu}m/s) across 4-nm-thin island-like gold films supported by 30-nm-thin silica layers atop 100-nm-thick gold layers with a strongly focused Ti-sapphire laser beam, while adjusting the average laser power from 1 to 10 mW, we produce bright colours varying from green to red by laser-heating-induced merging and reshaping of gold islands. Selection of strongly heated islands and their reshaping, both originating from the excitation of plasmonic resonances, are strongly influenced by the polarization direction of laser illumination, so that the colours produced are well pronounced only when viewed with the same polarization. Conversely, the laser colour writing with circular polarizations results in bright polarization-independent colour images. The fabrication procedure for near-percolation reflector arrays is exceedingly simple and scalable to mass production, while the laser-induced modification occurs inherently with the subwavelength resolution. This unique combination of remarkable features makes the approach developed for laser colour writing readily amenable for practical implementation and use in diverse applications ranging from nanoscale patterning for security marking to large-scale colour printing for decoration.Comment: 29 pages, 17 figure

Efficient interfacing photonic and long-range dielectric-loaded plasmonic waveguides

Long-range dielectric-loaded surface plasmon-polariton waveguides (LR-DLSPPWs) operating at telecom wavelengths are efficiently (end-fire) interfaced with photonic waveguides by taking advantage of very similar lateral mode field profiles in these waveguide configurations. The LR-DLSPPWs are formed by 1-μm-high and 1-μm-wide polymer ridges fabricated atop 15-nm-thin and 500-nm-wide gold stripes supported by a 289-nm-thick ormoclear polymer deposited on a low-index (1.34) layer of cytop, whereas gold stripes are absent in the photonic waveguide configuration that is identical to the plasmonic one in all other respects. The coupling efficiency between LR-DLSPPWs and photonic waveguides is numerically estimated to be 97%, decreasing by only a few percents for non-centered gold stripes (as long as a gold stripe is kept inside the polymer ridge). The fabricated LR-DLSPPWs coupled to photonic waveguides are first characterized using amplitude- and phase-resolved near-field imaging of propagating radiation that reveals very similar mode field distributions in these waveguides as well as their efficient interfacing. The coupling efficiency is then experimentally characterized using the cutback approach resulting in an average level of 75% per interface, while the LR-DLSPPW mode propagation length is estimated to be on average 0.3 mm. Possible reasons for differences between experimental and simulation results are discussed, indicating that a 3-nm-thin titanium layer (used for improving adhesion between gold and ormoclear) introduces substantial mode absorption. The results obtained open new perspectives for realization of hybrid photonic-plasmonic components and circuits