Amir Djalalian-Assl

Filling schemes at submicron scale: development of submicron sized plasmonic colour filters.

The pixel size imposes a fundamental limit on the amount of information that can be displayed or recorded on a sensor. Thus, there is strong motivation to reduce the pixel size down to the nanometre scale. Nanometre colour pixels cannot be fabricated by simply downscaling current pixels due to colour cross talk and diffraction caused by dyes or pigments used as colour filters. Colour filters based on plasmonic effects can overcome these difficulties. Although different plasmonic colour filters have been demonstrated at the micron scale, there have been no attempts so far to reduce the filter size to the submicron scale. Here, we present for the first time a submicron plasmonic colour filter design together with a new challenge - pixel boundary errors at the submicron scale. We present simple but powerful filling schemes to produce submicron colour filters, which are free from pixel boundary errors and colour cross- talk, are polarization independent and angle insensitive, and based on LCD compatible aluminium technology. These results lay the basis for the development of submicron pixels in displays, RGB-spatial light modulators, liquid crystal over silicon, Google glasses and pico-projectors.

A Chiral Plasmonic Metasurface Circular Polarization Filter

Here, we demonstrate a proof of principle circular polarization filter based on a far-field interference effect using an array of pairs of simple nanoapertures. We demonstrate computationally and experimentally device performance which show good agreement and close to a 10% difference in transmission through the structure for left- and right-circularly polarized light. This ultracompact device could prove useful for remote sensing and advanced telecommunication applications.

Surface plasmon wave plates

Here, we investigate both numerically and experimentally, the polarization conversion capabilities of a rectangular array of holes with two unequal orthogonal periodicities. We show that it is possible to tune the periodicities in such a way that the transmitted light is circularly polarized for a nominated wavelength, λCPL, when the structure is illuminated with appropriately oriented linearly polarized light at normal incidence. A device was fabricated and experiments confirmed that a degree of circular polarization of 0.89 could be achieved at the resonant wavelength.

Micro-concave waveguide antenna for high photon extraction from nitrogen vacancy centers in nanodiamond

The negatively charged nitrogen-vacancy colour center (NV− center) in nanodiamond is an excellent single photon source due to its stable photon generation in ambient conditions, optically addressable nuclear spin state, high quantum yield and its availability in nanometer sized crystals. In order to make practical devices using nanodiamond, highly efficient and directional emission of single photons in well-defined modes, either collimated into free space or waveguides are essential. This is a Herculean task as the photoluminescence of the NV centers is associated with two orthogonal dipoles arranged in a plane perpendicular to the NV defect symmetry axis. Here, we report on a micro-concave waveguide antenna design, which can effectively direct single photons from any emitter into either free space or into waveguides in a narrow cone angle with more than 80% collection efficiency irrespective of the dipole orientation. The device also enhances the spontaneous emission rate which further increases the number of photons available for collection. The waveguide antenna has potential applications in quantum cryptography, quantum computation, spectroscopy and metrology.

Tunable surface plasmon wave plates

The highest resonant transmission through an array of holes perforated in metallic screens occurs when the dielectric constant of the substrate, the superstrate, and the hole are the same. Changes in the refractive index of the homogenous environment also produce the largest shift in resonances per refractive index unit. In this Letter, we first propose and apply a technique in realization of a freestanding bi-periodic array of holes perforated in a silver film. We then show both numerically and experimentally that shifts in (1,0) and (0,1) modes in response to changes in the refractive index of the surrounding dielectric provide a mechanism for realization of a miniaturized tunable quarter-wave plate that operates in an extraordinary optical transmission mode with a high throughput and a near unity state of circularly polarized light.

Optical nano-antennas

Optical nano-antennas are nano-scaled metallic devices capable of manipulating and controlling visible light at sub-wavelength scales. Here we discuss the development of novel nanometric slot antennas and their complementary nanoparticle antennas.

Polarization effect and emission control in asymmetric cross-shaped slot antennas surrounded with periodic corrugations

We discuss progress in the development of asymmetric cross-shaped plasmonic antennas based on resonant nanoscale apertures surrounded by surface corrugations. By tailoring the aperture and the surrounding surface, we show directionality and polarization control of transmitted light.

Travelling Surface Plasmons with Interference Envelope and A Vision for Time Crystals

The influence of the film thickness and the substrate’s refractive index on the surface mode 7 at the superstrate is an important study step that may help clearing some of the misunderstandings 8 surrounding their propagation mechanism. A single sub-wavelength slit perforating a thin metallic 9 film is among the simplest nanostructure capable of launching Surface Plasmon Polaritons on its 10 surrounding surface when excited by an incident field. Here, the impact of the substrate and the 11 film thickness on surface waves is investigated. When the thickness of the film is comparable to its 12 skin depth, SPP waves from the substrate penetrate the film and emerge from the superstrate, 13 creating a superposition of two SPP waves, that leads to a beat interference envelope with 14 well-defined loci which are the function of both the drive frequency and the dielectric constant of 15 the substrate/superstrate. As the film thickness is reduced to the SPP’s penetration depth, surface 16 waves from optically denser dielectric/metal interface would dominate, leading to volume 17 plasmons that propagate inside the film at optical frequencies. Interference of periodic volume 18 charge density with the incident field over the film creates charge bundles that are periodic in space 19 and time. 20

Thin Nanoporous Metal-Insulator-Metal Membranes.

Insulating nanoporous materials are promising platforms for soft-ionizing membranes; however, improvement in fabrication processes and the quality and high breakdown resistance of the thin insulator layers are needed for high integration and performance. Here, scalable fabrication of highly porous, thin, silicon dioxide membranes with controlled thickness is demonstrated using plasma-enhanced chemical-vapor-deposition. The fabricated membranes exhibit good insulating properties with a breakdown voltage of 1 × 10(7) V/cm. Our calculations suggest that the average electric field inside a nanopore of the membranes can be as high as 1 × 10(6) V/cm; sufficient for ionization of wide range of molecules. These metal-insulator-metal nanoporous arrays are promising for applications such soft ionizing membranes for mass spectroscopy.

Polarization manipulation with subwavelength nanoapertures

Manipulation of polarization states is an important feature of many applications including in telecommunication, remote sensing and photonic computing technologies. Here we present two plasmonic nanoaperture based devices for creating and filtering circularly polarized light. One acts as an ultra-compact quarter wave plate, the other, based upon a planar chiral design, leads to asymmetric transmission of left and right circularly polarized light.