The recent new development of Meta Resonant Waveguide-Gratings (RWG) allows adapting the unique optical properties of Resonant Waveguide-Grating away from the specular reflection and direct transmission, in which they were confined in the last 35 years. Exploiting Wood's second type of anomalies, the so-called resonance anomalies in meta-devices based-on horizontal guided-mode resonances (GMR) create excellent transparency out of the resonance condition. Meta RWG can be engineered to exhibit highly selective and tunable optical properties to realize as examples monochromatic diffraction gratings, monochromatic metalenses and meta-couplers, while their nanostructures are made very compact and with flat aspect-ratio.
Examples of new optical combiners implementation for augmented and mixed reality will be presented. A roadmap for future developments will be sketched as well as their advantages and limitations, for which they will be compared to surface relief grating, volume holograms and visible-light metasurfaces.
The author will focus on the implementation of Meta-RWG in augmented and mixed reality systems addressing the many challenges of such see-through near-eye display system, such as large field of view, large eye-box with a sufficient eye-relief distance, high transparency, high compactness and low-weight, high pixel angular resolution as well as a mitigated vergence accommodation conflict or a non single/fix focal plane architecture.
Resonant waveguide gratings (RWGs) are thin-film structures, where coupled modes interfere with the diffracted incoming wave and produce strong angular and spectral filtering. The combination of two finite-length and impedance matched RWGs allows the creation of a passive beam steering element, which is compatible with up-scalable fabrication processes. Here, we propose a design method to create large patterns of such elements able to filter, steer, and focus the light from one point source to another. The method is based on ellipsoidal mirrors to choose a system of confocal prolate spheroids where the two focal points are the source point and observation point, respectively. It allows finding the proper orientation and position of each RWG element of the pattern, such that the phase is constructively preserved at the observation point. The design techniques presented here could be implemented in a variety of systems, where large-scale patterns are needed, such as optical security, multifocal or monochromatic lenses, biosensors, and see-through optical combiners for near-eye displays.
A novel thin-film single-layer structure based on resonant waveguide gratings (RWGs) allows to engineer selective color filtering and steering of white light. The unit cell of the structure consists of two adjacent finite-length and cross-talking RWGs, where the former acts as in-coupler and the latter acts as out-coupler. The structure is made by only one nano-imprint lithography replication and one thin film layer deposition, making it fully compatible with up-scalable fabrication processes. We characterize a fabricated optical security element designed to work with the flash and the camera of a smartphone in off-axis light steering configuration, where the pattern is revealed only by placing the smartphone in the proper position. Widespread applications are foreseen in a variety of fields, such as multifocal or monochromatic lenses, solar cells, biosensors, security devices and seethrough optical combiners for near-eye displays.
Plasmonics involves the interaction of light with metallic structures at the nanoscale, which enables in particular the generation of strong reflection and absorption effects in the visible and near infrared range. The fabrication of plasmonic nanostructures using ultra-violet (UV) imprint and thin metallic coatings is reported. Wafer-scale fabrication and process compatibility with cost-efficient roll-to-roll production are demonstrated, which paves the road towards an industrial implementation. The color, phase, polarization and direction of the transmitted light are controlled by tuning the process parameters and the symmetry of the nanostructures. A family of devices is presented, for which the potential for sensing, filtering, anticounterfeiting and optical security is evaluated.
We present an innovative disposable endoscope based on extra flat flexible polymer slabs used as multimode
waveguides. The waveguides are compatible with low-cost roll-to-roll production technologies and can be easily
customized by patterning, coating and printing techniques according to the specifications of the target application. In
order to couple the light (i.e. the illumination beam and the imaging beam) in and out of the waveguide, diffractive
subwavelength gratings are used. These nano-scale optical structures enable an efficient and controlled light trapping by
total internal reflection, thus minimizing the distortion effects generated by the rough edges. Nano-patterning is obtained
using established techniques (i.e. hot embossing and/or UV casting) that are compatible with industrial roll-to-roll
production lines or plastic injection molding.
Unique features of these innovative endoscopes are i) the achievable very thin form that can be reduced to thicknesses
below 200 μm, ii) the ability to record lateral images with respect to the endoscope direction, iii) the ability to image
samples (e.g. tissues, tiny objects) in direct contact with the polymer slab, with a minimum imaging distance equal to
zero, and iv) the access to high volume fabrication techniques that can enable the production of low-cost disposable
A possible device implementation is demonstrated and tested, which consists of a flat line-scanning endoscope enabling
the acquisition of 1D images in monochromatic illumination and the reconstruction of 2D images by scanning. Images
taken with such a disposable endoscope are discussed and the related technological constraints such as manufacturing
tolerances, image distortion, scattered light and signal to noise ratio are further described. Finally, advantages and
disadvantages with respect to other endoscopic techniques will be discussed, thus demonstrating the potential of this
innovative approach for endoscopic applications in very confined volumes.
Metallic nanostructures interact strongly with light through surface plasmon modes and many application fields
have been proposed during the past decade, including light harvesting, sensing and structural colors. However,
their implementation for the industry requires the development of up scalable and cost effective manufacturing
processes. The fabrication at wafer scale of plasmonic nanostructures and metamaterials using nano imprint
lithography is reported. After structuring, the evaporation of various plasmonic materials are performed with a
tilt angle with respect to the substrate, which increases the light interactions with the different metallic layers as
well as enlarges the design possibilities. A step and repeat process is used to increase further the area of nanostructured
surface. The measured optical properties of the fabricated structures show a very good agreement
compared to numerical calculations using the rigorous coupled wave analysis. These numerical calculations together
which structural characterization, increase the process control and enable the design of the nanostructures
for specific applications. In particular, nanostructures with a shape similar to split ring resonators and which
support high order plasmonic modes showing Fano resonances are shown to be promising for sensing applications.
The structures were designed in such a way to have a strong spectral response in the blue/green region of the
visible spectrum. Examples of refractive index sensors and stretch sensors were finally discussed.
The fabrication by nanoimprint lithography of large-area plasmonic and photonic sensing platforms is reported. The plasmonic nanostructures have the shape of split–ring resonators and support both electric dipole and quadrupole modes. They carry the spectral signature of Fano resonances. Their near-field and far-field optical properties are investigated with an analytical model together with numerical calculations. Fano-resonant systems combine strong nanoscale light confinement with a narrow spectral line width, which makes them very promising for biochemical sensing and immunoassays. On the other hand, chemical sensors based on resonant gratings are obtained by patterning a sol-gel material, evaporating a high refractive index semiconductor and coating with a chemically sensitive dye layer. By exposition to a liquid or an invisible gas such as ammonium, the change in absorption is detected optically. An analytical model is introduced to explain the enhancement of the signal by the resonant grating, which can be detected with the naked eye from a color change of the reflected light.