Theory of a Directive Optical Leaky Wave Antenna Integrated into a Resonator and Enhancement of Radiation Control

We provide for the first time the detailed study of the radiation performance of an optical leaky wave antenna (OLWA) integrated into a Fabry-P\'erot resonator. We show that the radiation pattern can be expressed as the one generated by the interference of two leaky waves counter-propagating in the resonator leading to a design procedure for achieving optimized broadside radiation, i.e., normal to the waveguide axis. We thus report a realizable implementation of the OLWA made of semiconductor and dielectric regions. The theoretical modeling is supported by full-wave simulation results, which are found to be in good agreement. We aim to control the radiation intensity in the broadside direction via excess carrier generation in the semiconductor regions. We show that the presence of the resonator can provide an effective way of enhancing the radiation level modulation, which reaches values as high as 13.5 dB, paving the way for novel promising control capabilities that might allow the generation of very fast optical switches, as an example.Comment: 10 pages, 14 figure

Social Media as A Source of Self Organizing City: Bridging the Gap Between Policy Making and Public Act

Cities are complex systems, which creates spontaneous movements and reactions in urban space. These selforganized networks and environment continuously reproduce each other by involving series of social and cultural communication patterns, ideas and decision-making processes. Unlike conventional participation tools ICT, social media and mobile technologies provide an alternative, virtual platform, that enables citizens to connect with decision makers, share information, comment and vote for changes, and self-organizing their environment. This new platform delivers a practical tool to decision makers for accessing a wider interest group, collecting location based, real time data and enables citizens to get involved in the planning process. In recent years Turkey has gone through many urban conflicts, and social media tools, especially Facebook, and Twitter densely used for information sharing and to be heard by government. In this study, the usage of social media as a participation tool was discussed in two parts. Firstly, A literature review on the engaging potential of mobile participation tools was given. Secondly, the usage and the impact of social media and mobile platforms was evaluated over examples from Turkey

Silicon Nitride Waveguides for Plasmon Optical Trapping and Sensing Applications

We demonstrate a silicon nitride trench waveguide deposited with bowtie antennas for plasmonic enhanced optical trapping. The sub-micron silicon nitride trench waveguides were fabricated with conventional optical lithography in a low cost manner. The waveguides embrace not only low propagation loss and high nonlinearity, but also the inborn merits of combining micro-fluidic channel and waveguide together. Analyte contained in the trapezoidal trench channel can interact with the evanescent field from the waveguide beneath. The evanescent field can be further enhanced by plasmonic nanostructures. With the help of gold nano bowtie antennas, the studied waveguide shows outstanding trapping capability on 10 nm polystyrene nanoparticles. We show that the bowtie antennas can lead to 60-fold enhancement of electric field in the antenna gap. The optical trapping force on a nanoparticle is boosted by three orders of magnitude. A strong tendency shows the nanoparticle is likely to move to the high field strength region, exhibiting the trapping capability of the antenna. Gradient force in vertical direction is calculation by using a point-like dipole assumption, and the analytical solution matches the full-wave simulation well. The investigation indicates that nanostructure patterned silicon nitride trench waveguide is suitable for optical trapping and nanoparticle sensing applications

Electric field enhancement with plasmonic colloidal nanoantennas excited by a silicon nitride waveguide

We investigate the feasibility of CMOS-compatible optical structures to develop novel integrated spectroscopy systems. We show that local field enhancement is achievable utilizing dimers of plasmonic nanospheres that can be assembled from colloidal solutions on top of a CMOS-compatible optical waveguide. The resonant dimer nanoantennas are excited by modes guided in the integrated silicon nitride waveguide. Simulations show that 100 fold electric field enhancement builds up in the dimer gap as compared to the waveguide evanescent field amplitude at the same location. We investigate how the field enhancement depends on dimer location, orientation, distance and excited waveguide modes

Recent advances in nanoparticles as antibacterial agent

Recently, the rapid increase in antibiotic-resistant pathogens has caused serious health problems. Researchers are searching for alternative antimicrobial substances to control or prevent infections caused by pathogens. Different strategies are used to develop effective antibacterial agents, and in this respect, nanoparticles are undoubtedly promising materials. Nanoparticles act by bypassing drug resistance mechanisms in bacteria and inhibiting biofilm formation or other important processes related to their virulence potential. Nanoparticles can penetrate the cell wall and membrane of bacteria and act by disrupting important molecular mechanisms. In combination with appropriate antibiotics, NPs may show synergy and help prevent the developing global bacterial resistance crisis. Furthermore, due to characteristics such as enhanced biocompatibility and biodegradability, polymer-based nanoparticles enable the development of a wide range of medical products. Antibacterial applications of nanoparticles range from antimicrobial synthetic textiles to biomedical and surgical devices when nanoparticles are embedded/loaded/coated into different materials. In this review, the antibacterial mechanisms of nanoparticles and their potential for use in the medical field are discussed

High Data Rate Inter-Satellite Omnidirectional Optical Communicator

We are developing an inter-satellite omnidirectional optical communicator (ISOC) that will enable up to 1 Gbps data rates over a distance up to 200 km in free space. Key features of the ISOC include full sky coverage and its ability to maintain multiple links simultaneously. The ISOC outer frame is a truncated icosahedron small enough to deploy out of a CubeSat. The frame contains photodetector receivers and gimbal-less scanning MEMS mirrors for transmit beam steering. We have developed miniature transmitter housings (“telescopes”) that include a single mode laser diode and a MEMS mirror. The frame’s vertices feature fast photodetectors for reception and direction finding. In this paper we present design considerations and testing results for an ISOC built to operate at 850 nm. We also discuss a mission concept, labeled Q4, which is being proposed to demonstrate the omnidirectional capabilities of the ISOC. Q4 includes (4) 6U CubeSats furnished with ISOCs and advanced ADCS systems for proper beam pointing. We present design considerations for the Q4 CubeSats and an overall description of the Q4 mission including expected results

Tera-sample-per-second Real-time Waveform Digitizer

We demonstrate a real-time transient waveform digitizer with a record 1 TSa/s (Tera-Sample/sec) sampling rate. This is accomplished by using a photonic time stretch preprocessor which slows down the electrical waveform before it is captured by an electronic digitizer.Comment: 13 pages, 6 figures, submitted to Applied Physics Letters, Apr 200