We numerically and experimentally demonstrate that metasurfaces can be used to control the light emission from light emitting diodes (LED). This control provides a desired wavefront and functionality of the light emission in addition to enhancing light extraction efficiency. Simply placing the metasurface on top of the LED does not work as conventional metasurface designs require plane wave excitation, which LEDs cannot provide. To overcome this challenge we implement a novel concept using internal and external resonant cavities combined with the LED. Guided by our numerical simulations, we experimentally demonstrate this concept by fabricating Si and TiO2 metasurfaces on top of the resonant cavity LED structures. The integration of these metasurfaces with commercially available GaN and GaP LED devices show full wavefront control, beam deflection and beam collimation. Both the cavity and the metasurface enhance the LED radiation. Moreover, following the proposed principle, any random light emitting sources including fluorescent molecules and quantum dots can be integrated into a similar optical device to achieve focusing, beam deflecting, vortex beam generation and other capabilities.
Laser beam shaping is a widely used technique in many application areas, such as material processing, lithography, optical data storage, and medical procedures. In most cases a laser beam shaping system consists of conventional lenses with curved surfaces. However these lenses are bulky and their fabrication precisions are limited. In this work, we design and fabricate a lens for laser beam shaping using nanostructures. The lens is designed with traditional geometrical optical methods, using energy conservation and optical coordinate transformation algorithms. But instead of using curved surfaces to implement the lens design, we realize the designs with dielectric nanostructures. The lens is then fabricated using electron beam lithography to achieve a high precision. The fabricated lens has very low profile and is capable of fine tuning laser beams. The lens is then experimentally tested. In the experimental setup a laser beam is directed into a multimode fiber and the irradiance of the output beam irradiance profile is measured. Then the lens is placed in front of the multimode fiber and the outcome beam irradiance profile is measured again to test the effects of our laser beam shaping lens.
High power fiber lasers are proposed to be a better candidate than conventional solid-state lasers for industries such
as precision engineering since they are more compact and easier to operate. However, the beam quality generally
degrades when one scales up the output power of the fiber laser.
One can improve the output beam quality by altering the phase of the laser beam at the exit surface, and a promising
method to do so is by integrating specially designed nano-structures at the laser facets. In fact, this method was recently
demonstrated – by integrating gold concentric ring grating structures to the facet of a quantum cascade laser, one
observes significant improvement in the beam quality. Nevertheless, to improve the beam quality of high power fiber
lasers using the method mentioned above, the material of the nano-structures must be able to withstand high laser fluence
in the range of J/cm2.
In this work, we investigated the laser-induced damage threshold (LIDT) values of a suitable material for high
intensity fiber laser applications. Consequently, we demonstrated that the shortlisted material and the fabricated nanostructures
can withstand laser fluence exceeding 1.0 J/cm2.
We have studied the ability of a lamellar near-field superlens to transfer an enhanced electromagnetic field to the far side
of the lens. In this work, we have experimentally and numerically investigated superlensing in the visible range. By
using the resonant hot-spot field enhancements from optical nanoantennas as sources, we investigated the translation of
these sources to the far side of a layered silver-silica superlens operating in the canalization regime. Using near-field
scanning optical microscopy (NSOM), we have observed evidence of superlens-enabled enhanced-field translation at a
wavelength of about 680 nm. Specifically, we discuss our recent experimental and simulation results on the translation of
hot spots using a silver-silica layered superlens design. We compare the experimental results with our numerical
simulations and discuss the perspectives and limitations of our approach.