We report on numerical simulations and fabrication of an optical fiber plasmonic lens for near-field focusing applications. The plasmonic lens consists of an Archimedean spiral structure etched through a 100 nm-thick Au layer on the tip of a single-mode SM600 optical fiber operating at a wavelength of 632:8 nm. Three-dimensional finite-difference time-domain computations show that the relative electric field intensity of the focused spot increases 2:1 times when the number of turns increases from 2 to 12. Furthermore, a reduction of the intensity is observed when the initial inner radius is increased. The optimized plasmonic lens focuses light into a spot with a full-width at half-maximum of 182 nm, beyond the diffraction limit. The lens was fabricated by focused ion beam milling, with a 200nm slit width.
Surface texturing in thin-film solar cells provides a promising way of addressing the loss components due to reflection and poor light absorption inside the cells. In this work, we study the reflection suppression performance of different submicron-scale periodic surface texturing morphologies through two dimensional (2D) finite-difference time-domain (FDTD) computations. The broadband reflection response is investigated at two interfaces, air/glass and glass/TCO (transparent conductive oxide), for a spectral range of 300-2500 nm. A Drude-Lorentz model is used to account for material dispersion and absorption within the wavelengths of interest. In order to optimize the light trapping performance, numerical simulations of various surface texture structures are compared with those of flat interfaces. Numerical results show a reduction in reflection at the air/glass interface to values below 0.2% for some of the triangular gratings, compared to up to 4% for the non-textured interface. For the glass/TCO interface, reflection decreases to less than half when compared to the non-textured interface, also for triangular gratings. Further structures that replicate perfect multi-layer anti-reflection coatings are also studied. These structures are tuned to cancel specific wavelengths and can create an arbitrary effective index, overcoming the constraint of the limited number of refractive index values available. The best structures obtained for the air/glass and glass/TCO interfaces are combined in one stack, achieving reflectance values at least one order of magnitude below the non-textured air/glass/TCO stack.