Transmissive Suppressed-Order Diffraction Grating (SODG)

We present a novel type of Suppressed-Order Diffraction Grating(SODG). An SODG is a diffraction grating whose diffraction orders have all been suppressed except one that is selected to provide electromagnetic deflection. The proposed SODG is a transmissive grating that exhibits high-efficiency refraction-like deflection for all angles, including large angles that are generally challenging to achieve, while featuring a deeply subwavelength thickness, as required in the microwave regime. We first present the design rationale and guidelines, and next demonstrate such a 10.5 GHz SODG that reaches an efficiency of 90% at 70 degrees

Compact grating coupler using asymmetric waveguide scatterers

We demonstrate a novel grating coupler design based on double asymmetric and vertically oriented waveguide scatterers to efficiently couple normally incident light to a fundamental mode silicon waveguide laying on a buried oxide layer.Comment: 4 pages, 1 figur

Photonic Gap Antennas Based on High Index-Contrast Slot-Waveguides

Optical antennas made of low-loss dielectrics have several advantages over plasmonic antennas, including high radiative quantum efficiency, negligible heating and excellent photostability. However, due to weak spatial confinement, conventional dielectric antennas fail to offer light-matter interaction strengths on par with those of plasmonic antennas. We propose here an all-dielectric antenna configuration that can support strongly confined modes ($V\sim10^{-4}\lambda_{0}^3$) while maintaining unity antenna quantum efficiency. This configuration consists of a high-index pillar structure with a transverse gap that is filled with a low-index material, where the contrast of indices induces a strong enhancement of the electric field perpendicular to the gap. We provide a detailed explanation of the operation principle of such Photonic Gap Antennas (PGAs) based on the dispersion relation of symmetric and asymmetric horizontal slot-waveguides. To discuss the properties of PGAs, we consider silicon pillars with air or CYTOP as the gap-material. We show by full-wave simulations that PGAs with an emitter embedded in the gap can enhance the spontaneous emission rate by a factor of $\sim$1000 for air gaps and $\sim$400 for CYTOP gaps over a spectral bandwidth of $\Delta\lambda\approx300$ nm at $\lambda=1.25$ \textmu m. Furthermore, the PGAs can be designed to provide unidirectional out-of-plane radiation across a substantial portion of their spectral bandwidth. This is achieved by setting the position of the gap at an optimized off-centered position of the pillar so as to properly break the vertical symmetry of the structure. We also demonstrate that, when acting as receivers, PGAs can lead to a near-field intensity enhancement by a factor of $\sim$3000 for air gaps and $\sim$1200 for CYTOP gaps

Hybrid Epsilon-Near-Zero Modes of Photonic Gap Antennas

We demonstrate that in photonic gap antennas composed of an epsilon-near-zero (ENZ) layer embedded within a high-index dielectric, hybrid modes emerge from the strong coupling between the ENZ thin film and the photonic modes of the dielectric antenna. These hybrid modes show giant electric field enhancements, large enhancements of the far-field spontaneous emission rate and a unidirectional radiation response. We analyze both parent and hybrid modes using quasinormal mode theory and find that the hybridization can be well understood using a coupled oscillator model. Under plane wave illumination, hybrid ENZ antennas can concentrate light with an electric field amplitude $\sim$100 times higher than that of the incident wave, which places them on par with the best plasmonic antennas. In addition, the far-field spontaneous emission rate of a dipole embedded at the antenna hotspot reaches up to $\sim$2300 that in free space, with nearly perfect unidirectional emission.Comment: 5 figures, 6 page

Photonic Gap Antennas for the Manipulation and Generation of Light

RÉSUMÉ: RÉSUMÉ Le développement des antennes optiques a énormément progressé au cours des deux dernières décennies. De manière semblable à leurs homologues à plus grande longueur d’onde (radio et micro-ondes), les antennes optiques convertissent le rayonnement électromagnétique du champ lointain en champ proche localisé et vice versa. Alors que la transmission dans les antennes à grande longueur d’onde est générée par des courants électriques alternatifs, les antennes optiques sont généralement excitées par des faisceaux lumineux incidents ou des émetteurs uniques tels que des atomes, des molécules ou des points quantiques. Une extrac-tion efficace de l’énergie électromagnétique de ces émetteurs nécessite une forte localisation du champ électrique proche. Pour y parvenir, la grande majorité des travaux théoriques et expérimentaux se sont concentrés sur l’utilisation d’antennes métalliques sub-longueur d’onde. La réponse des métaux aux champs électriques oscillant à des fréquences visibles et infrarouges est dominée par les plasmons de surface qui permettent une localisation très in-tense des champs électriques oscillants, dans un volume beaucoup plus petit que la longueur d’onde. La résonance des plasmons de surface convertit l’énergie du champ électrique, source de capacitance, en énergie cinétique des électrons libres, source d’inductance cinétique. Cela est différent du mécanisme d’opération des antennes à grande longueur d’onde et des an-tennes diélectriques, où l’énergie oscille principalement entre le champ électrique et le champ magnétique. La capacité des antennes plasmoniques à manipuler ou à renforcer l’émission d’émetteurs uniques proches s’est avérée utile à la fois pour les dispositifs émettant de la lumière et pour les sources de photons uniques de pointe. De plus, leur capacité à concentrer la lumière a trouvé des applications importantes, par exemple dans les senseurs, l’optique non linéaire, la photonique intégrée et l’imagerie. L’objectif de cette thèse est d’explorer le potentiel des structures diélectriques à faibles pertes en tant qu’antennes optiques. Dans les diélectriques à faibles pertes, les résonances du matériau sont absentes dans la bande de fréquence qui nous intéresse, de sorte que nous pou-vons nous concentrer uniquement sur les résonances structurelles de l’antenne. Contrairement aux métaux, les diélectriques ont des électrons (ou des charges) liés, et le courant de déplace-ment correspondant soutient l’oscillation uniquement entre l’énergie du champ électrique et celle du champ magnétique. Le courant de déplacement dans les diélectriques n’est pas limité à la surface mais est disponible dans tout le volume de la structure de l’antenne. Avec une polarisabilité moléculaire croissante du matériau diélectrique, la structure de l’antenne peut être réduite à une taille plus petite pour augmenter l’intensité du champ électrique et il n’y a pas de perte d’énergie sous forme de chaleur. ABSTRACT: ABSTRACT Antennas are ubiquitous in wireless electronic devices, ranging from radio-controlled toys and smartphones to satellites in space. In the past three decades, a new type of antenna has emerged, operating as a transducer for light waves instead of radio waves. These optical antennas efficiently receive and transmit electromagnetic radiation, acting as transducers between nanoscale dipoles such as atoms, molecules, or quantum dots and light. Therefore, the performance of optical antennas hinges on their ability to concentrate light at a deep subwavelength level. To achieve this goal, most theoretical and experimental efforts have been dedicated to utilizing sub-wavelength metallic antennas. Metals support a collective oscillation of electrons known as surface plasmons at visible and infrared frequencies, enabling deep sub-wavelength localization of oscillating electric fields. This localization is achieved by converting the energy of the electric field, which acts as a source of capacitance, into the kinetic energy of free electrons, serving as a source of kinetic inductance. In contrast, long-wavelength and dielectric antennas predominantly involve energy oscillation between electric and magnetic fields. Plasmonic antennas have proven valuable in manipulating and enhancing the emission of nearby emitters, benefiting light-emitting devices and state-of-the-art single-photon sources. Additionally, their light-concentrating capabilities have found crucial applications in sensing, nonlinear optics, integrated photonics, and imaging. The objective of this thesis is to explore the potential of low-loss dielectric structures as optical antennas. In low-loss dielectrics, material resonances are absent in the frequency region of interest, so we can focus only on the antenna’s structural resonances. In contrast to metals, dielectrics have bound electrons (or charges), and the corresponding displacement current supports the oscillation only between electric and magnetic field energy. The displacement current in dielectrics is not limited to the surface but is available throughout the entire volume of the antenna structure. With increasing molecular polarizability of the dielectric, the antenna structure can be scaled to a smaller size to enhance the electric field intensity and there is no energy waste as heat. From the radio antennas made by Hertz to the metal optical antennas, the field enhancement in the gap of the antenna structure has been the gateway to their applications. Here we explore the potential of the gap in optical dielectric antennas to enhance the electric field in its vicinity and to tune the directional strength of the light radiation into the far field region. In addition, we demonstrate their unique abilities in transforming the wavefront of the light when arranged in an array

Wireless Communication System Design for Underground Mine

Deployment of Wireless Sensor Networks (WSN) and wireless communication system has become indispensable for better real-time data acquisition from the ground monitoring devices, gas sensors, and equipment used in the underground mines as well as to locate the miners. The conventional methods i.e. use of wire for communication is found to be inefficient and ineffective at the time of mine hazards such as roof falls, fire hazard etc. Before the implementation of any wireless system, the variable path loss indices for different workplace should be determined. This helps in better signal reception and localization of sensor nodes. This also enhances the way of tracking the miner carrying the wireless device. An attempt has been made for the determination of parameter of a suitable radio propagation model. It includes the results of an experiment carried out in GDK-10A incline, SCCL, India. The path loss indices at different areas along with other essential parameters for accurate localization have been determined using XBee module and ZigBee protocol at 2.4 GHz frequenc

Large-Angle, Broadband and Multifunctional Gratings Based on Directively Radiating Waveguide Scatterers

Conventional surface-relief gratings are inefficient at deflecting normally-incident light by large angles. This constrains their use in many applications and limits the overall efficiency of any optical instrument integrating gratings. Here, we demonstrate a simple approach for the design of diffraction gratings that can be highly efficient for large deflection angles, while also offering additional functionality. The gratings are composed of a unit cell comprising a vertically-oriented asymmetric slot-waveguide. The unit cell shows oscillating unidirectional scattering behavior that can be precisely tuned as a function of the waveguide length. This occurs due to interference between multiple modes excited by the incident light. In contrast to metasurface-based gratings with multiple resonant sub-elements, a periodic arrangement of such non-resonant diffracting elements allows for broadband operation and a strong tolerance for variations in angle of incidence. Full-wave simulations show that our grating designs can exhibit diffraction efficiencies ranging from 94% for a deflection angle of 47$^\circ$ to 80% for deflection angle of 80$^\circ$. To demonstrate the multifunctionality of our grating design technique, we have also proposed a flat polarization beamsplitter, which allows for the separation of the two orthogonal polarizations by 80$^\circ$, with an efficiency of 80%