A volume hologram recorded with a lens array is proposed as a color transflective screen for Head Worn Display (HWD) systems. Design, fabrication as well as proof of concept are reported. Light from a single MEMS-based projector is efficiently diffracted towards the eye with an angular spread given by the numerical aperture of the lenses forming the lens array. Using a dual-focus contact lens, full color high-resolution images are added to the HWD user's normal vision. A full color system with a 55 degrees lateral field of view is demonstrated. This screen offers the possibility for small footprint and large field of view HWD's.

A volume hologram recorded with a lens array is proposed as a transflective screen for Head Worn Display (HWD) systems. Design, fabrication as well as proof of concept are reported. Light from a projection system, with similar properties to one mounted on the side of an eyewear, is efficiently diffracted towards the eye with an angular spread given by the numerical aperture of the lenses forming the lens array. Using a dual-focus contact lens, high-resolution images can be added to the HWD user's normal vision, as light from the surrounding environment is transmitted through the screen with low aberrations. This screen offers the possibility for small footprint and large field of view HWD's.

An analytical model based on a modal expansion method is developed to investigate the optical transmission through metal gratings. This model gives analytical expressions for the transmission as well as for the dispersion relations of the modes responsible for high transmission. These expressions are accurate even for real metals used in the visible - near-infrared wavelength range, where surface plasmon polaritons (SPP's) are excited. The dispersion relations allow the nature of the modes to be assessed. We find that the transmission modes are hybrid between Fabry-Pérot like modes and SPP's. It is also shown that it is important to consider different refractive indices above and below the gratings in order to determine the nature of the hybrid modes. These findings are important as they clarify the nature of the modes responsible for high transmission. It can also be useful as a design tool for metal gratings for various applications.

Gold membranes with large arrays of sub-μm holes were fabricated and optically characterized. The fabrication is a combination of a bottom-up, self-assembly based patterning technique, Nanosphere Lithography (NSL), and standard microfabrication. This was achieved by 1) up-scaling of the deposition of close-packed bead monolayers to 4" wafer substrates, 2) controlled bead size reduction, 3) etching of high aspect-ratio Si pillar arrays, 4) using the pillar arrays as a lift-off template, and 5) releasing the membranes by dry-etching. In this way, millimeter-size, 200 nm thick gold membranes with dense, short-range ordered hole arrays were fabricated. The array periodicity was either 428 nm or 535 nm, depending on the initial bead size. The hole diameter was tuned in the range of 150 nm to 250 nm. Optical transmission spectroscopy showed surface plasmon mediated extraordinary optical transmission (EOT) with an enhancement factor greater than two.

In this paper, a fast and inexpensive wafer-scale process for the fabrication of arrays of nanoscale holes in thin gold films for plasmonics is shown. The process combines nanosphere lithography using spin-coated polystyrene beads with a sputter-etching process. This allows the batch fabrication of several 1000 µm2 large hole arrays in 200 nm thick gold films without the use of an adhesion layer for the gold film. The hole size and lattice period can be tuned independently with this method. This allows tuning of the optical properties of the hole arrays for the desired application. An example application, refractive index sensing, is demonstrated.

Enhanced optical transmission (EOT) through a single aperture is usually achieved by exciting surface plasmon polaritons with periodic grooves. Surface plasmon polaritons are only excited by p-polarized incident light, i.e. with the electric field perpendicular to the direction of the grooves. The present study experimentally investigates EOT for s-polarized light. A subwavelength slit surrounded on each side by periodic grooves has been fabricated in a gold film and covered by a thin dielectric layer. The excitation of s-polarized dielectric waveguide modes inside the dielectric film strongly increases the s-polarized transmission. A 25 fold increase is measured as compared to the case without the dielectric film. Transmission measurements are compared with a coupled mode method and show good qualitative agreement. Adding a waveguide can improve light transmission through subwavelength apertures, as both s and p-polarization can be efficiently transmitted.

Enhanced optical transmission (EOT) through subwavelength apertures is usually obtained for p-polarized light. The present study experimentally investigates EOT for s-polarized light. A subwavelength slit surrounded on each side by periodic grooves has been fabricated in a gold film and covered by a thin dielectric layer. The excitation of s-polarized dielectric waveguide modes inside the dielectric film strongly increases the s-polarized transmission. Transmission measurements are compared with a coupled mode model and show good qualitative agreement. Adding a waveguide can improve light transmission through subwavelength apertures, as both s and p-polarization can be efficiently transmitted.

The miniaturization of photodetectors often comes at the expense of a smaller photosensitive area. This can reduce the signal and thus limit the image quality. One way to overcome this limitation is to reduce the photosensitive area but with no reduction of signal i.e. harvest the light. Here we investigate, theoretically and experimentally, light harvesting with nanostructured metals. Nanostructured metals can also give additional functionality such as polarization filtering which is also investigated. After defining the figure of merits used when characterizing light harvesting and polarization filtering structures, we detail the fabrication and measurement process. Structures were made on glass substrate, as a post process step on CMOS fabricated detectors and directly in the CMOS fabrication of the detectors. The optical characterization results are presented and compared with theory. Finally, we discuss the challenges and advantages of integrating metallic nanostructures within the CMOS process.

In this paper, we present the design, fabrication, and characterization of wire grid polarizers. These polarizers show high extinction ratios and high transmission with structure dimensions that are compatible with current complementary metal-oxide-semiconductor (CMOS) technology. To design these wire grids, we first analyze the transmission properties of single apertures. From the understanding of a single aperture, we apply a modal expansion method to model wire grids. The most promising grids are fabricated on both a glass substrate and CMOS photodiode. An extinction ratio higher than 200 is measured.

An enhanced transmission is detected through a single slit of subwavelength width surrounded by grooves in a gold layer that is added as a postprocess to a standard complementary metal oxide semiconductor (CMOS) fabricated detector. The enhanced transmission results from constructive interference of surface waves, which interact with the incident light. The measured enhanced transmission shows strong qualitative agreement with that predicted by the modal expansion method. With the decreasing dimensions available in standard CMOS process, such nanostructures in metals could be used to replace current optical systems or to improve performance by increasing the signal to noise ratio and/or allowing polarization selection.

Keywords: Annular Aperture Arrays ; Field Optical-Images ; Hole Arrays ; Transmission ; Deposition Reference EPFL-ARTICLE-164812View record in Web of Science Record created on 2011-04-11, modified on 2017-05-10

Strong scattering properties are obtained for a monolayer of randomly packed polystyrene microspheres. This gives rise to structural colors in transmission. For a sphere diameter between 0.5 and 1 micron, light is mainly scattered in the forward direction. Consequently, in-plane multiple scattering can be neglected when spheres are not too close to each others. This allows one to use a single scattering approximation to reproduce transmission spectra of the system. The film color is dependent on the sphere size, but also on the observation angle. This angular dependant color is reproduced taking into account multiple scattering between spheres. These films can be useful when low reflection is needed.

Subwavelength hole arrays in thin gold films were fabricated in a low-cost and parallel fabrication process on 2" wafers. Polystyrene beads were used as an initial pattern template which is transferred into a thin gold film by sputter etching. Hole arrays with two different periodicities were characterized in optical transmission measurements in air and in liquids of varying refractive index. Despite the conical hole shape and long-range disorder of the arrays, the optical transmission spectra are similar to those obtained for precise hole arrays fabricated by serial writing methods, e.g. focused ion beam milling (FIB). We further show the use of the fabricated hole arrays for sensing of molecular binding events.

We present the characterization of short-range ordered hexagonal arrays of subwavelength holes in thin gold films. The hole arrays are fabricated by a low-cost technique using convectively self-assembled polystyrene beads as an initial pattern template. Our results suggest that corrugated, short-range ordered hole arrays allow the excitation of resonant surface plasmons. This opens the door to inexpensive, large- scale and high throughput fabrication of nanophotonic devices.