In this work, we show how we can improve the image resolution capabilities of a Phase Conjugating (PC) lens as well as the angular resolution of Luneburg lens antennas by employing signal processing techniques, such as the Correlation Method (CM), the Minimum Residual Power Search Method (MRPSM), the sparse reconstruction method, and the Singular-Value-Decomposition (SVD)-based basis matrix method. In the first part, we apply these techniques for sub-wavelength imaging in the microwave regime by combining them with the well-known phase conjugation principle. We begin by considering a one-dimensional microwave sub-wavelength imaging problem handled by using three signal processing methods, and then we move on to two- or three-dimensional problems by using the SVD-based basis matrix method. Numerical simulation results show that we can enhance the resolution significantly by using these methods, even if the measurement plane is not located in the very near-field region of the source. We describe these proposed algorithms in detail and study their abilities to resolve at the sub-wavelength level. Next, we investigate the sparse reconstruction method for a normal Luneburg lens antenna, and the Correlation Method and the SVD-based basis matrix method for a flat-base Luneburg lens antenna to estimate the Direction-of-Arrival (DOA). Numerical simulation results show that the signal processing techniques are capable of enhancing the angular resolution of the Luneburg lens antenna, enabling the lens to locate multiple targets with different scattering cross-sections, and achieving higher angular resolution.
Invisibility has been a tantalizing concept for mankind over several centuries. With recent developments in metamaterial science and nanotechnology, the possibility of cloaking objects to incoming electromagnetic radiation has been escaping the realm of science fiction to become a technological reality. In this article, we review the state-of-the-art in the science of invisibility for electromagnetic waves, and examine the different available technical concepts and experimental investigations, focusing on the underlying physics and the basic scientific concepts. We discuss the available cloaking methods, including transformation optics, plasmonic and mantle cloaking, transmission-line networks, parallel-plate cloaking, anomalous resonance methods, hybrid methods and active schemes, and give our perspective on the subject and its future. We also draw a parallel with cloaking research for acoustic and elastodynamic waves, liquid waves, matter waves and thermal flux, demonstrating how ideas initiated in the field of electromagnetism have been able to open groundbreaking venues in a variety of other scientific fields. Finally, applications of cloaking to non-invasive sensing are discussed and reviewed.
In this paper we present an alternative approach to addressing the problem of scattering reduction for radar targets, which have recently been dealt with by using the Transformation Optics (TO) algorithm which typically calls for the use of Metamaterials (MTMs) that are inherently narrowband, dispersive and highly sensitive to polarization as well as to the incident angle. The present design utilizes realistic lossy materials that can be conveniently fabricated in the laboratory, and are wideband as well as relatively insensitive to polarization and incident angle of the incoming wave. A modified interpretation of the TO algorithm is presented and is employed the design of RCS-reducing absorbers for arbitrarily shaped targets, and not just for canonical shapes, e.g., cylinders, for which cloaks have been designed by using the TO. The paper also briefly examines the topic of performance enhancement of absorbers by using graphene materials and embedded Frequency Structure Surfaces (FSSs). We begin by presenting the design procedure for planar absorbers, and then examine how well those designs perform for arbitrarily-shaped objects. Finally, we discuss how the planar design can be modified by tailoring the material parameters of the coating for specific object shapes. A number of test cases are included as examples to illustrate the application of the proposed design methodology, which is a modification of the classical TO paradigm.
Assessment of biodiversity of pollinators on the landscape scale or estimation of fluxes of disease-transmitting biting midges constitutes a major technical challenge today. We have developed a laser-radar system for field entomology based on the so called Scheimpflug principle and a continuous-wave laser. The sample-rate of this method is unconstrained by the round-trip time of the light, and the method allows assessment of the fast oscillatory insect wing-beats and harmonics over kilometers range, e.g., for species identification and relating abundances to the topography. Whereas range resolution in conventional lidars is limited by the pulse duration, systems of the Scheimpflug type are limited by the diffraction of the telescopes. However, in the case of sparse occurrence of the atmospheric insects, where the optical cross-section oscillates, estimation of the range and spacing between individuals with a precision beyond the diffraction limit is now demonstrated. This enables studies of insect interaction processes in-situ.
Tracing the dynamics of electrons inside atoms molecules or solids as they occur in real time resides at the forefront of modern science and technology. Advances in attosecond physics over the last decade and beyond are now enabling this essential experimental capability. Here we discuss some of the key developments in light sciences that made possible attosecond metrology and control of electronic processes inside matter on native time scales. These developments hold the promise for new, fundamental insights into the innerworkings of the microcosm as well as the identification of innovative routes for light-based electronic and photonic devices operating at PHz rates.
In many ways light and nanoscience do not mix well. By convention light can be focussed to a spot no smaller than about a micron whereas nano structures by definition are three orders of magnitude smaller in scale. However recent theoretical advances show how to control light at the nanoscale, provided we can find the correct materials for our devices. I shall describe these new theories, and how they enable us to concentrate light to better than a nanometre. In this way light can detect single molecules, and the huge concentrations of optical energy can force photons to interact with one another which they normally do not do.
With the advancement of wireless networks and cloud computing, people are becoming increasingly surrounded by a variety of displays - rich electronic devices: TV, Phone, Pad, Notebook and other portable or wearable devices. These electronic products put high demands on the quality of the visual interface. Paper-like displays are reflective and do not require a backlight. They have received much attention after electrophoretic-based electronic paper displays were commercialized in 2004. Paper-like displays combine excellent reading experience with ultra-low power consumption. In particular, their outdoor readability is superior to transmissive liquid crystal displays (LCDs) and organic light emitting devices (OLEDs). In this paper, we give an overview onvarious paper-like display technologies with emphasis of the status and future development of electrophoretic display and electro-fluidic display principles. We focus on both technologies because electrophoretic displays have been commercialized successfully, and electro-fluidic display has high potential to deliver video and full color.
In this paper, a number of different application fields of inorganic luminescent materials are being discussed. In a tutorial manner, it will be shown how device requirements are being translated into properties the luminescent materials need to have. To this end many different material properties that have a strong influence on the device performance are discussed, such as the shape, the spectral position of the absorption- and emission bands and the decay time of the emission. The light yield under excitation with ionizing radiation, the energy resolution and the occurrence of afterglow are being treated as well. Subsequently, strategies are shown how to optimize these properties. Examples are given for light sources (fluorescent lamps and LEDs), radiation sources used for disinfection purposes and also for devices used in medical imaging and in horticultural applications.
Here we realize a broadband absorber by using a hyperbolic metamaterial composed of alternating aluminum-alumina thin films based on superposition of multiple slow-wave modes. Our super absorber ensures broadband and polarization-insensitive light absorption over almost the entire solar spectrum, near-infrared and short-wavelength infrared regime (500-2500 nm) with a simulated absorption of over 90%. The designed structure is fabricated and the measured results are given. This absorber yields an average measured absorption of 85% in the spectrum ranging from 500 nm to 2300 nm. The proposed absorbers open an avenue towards realizing thermal emission and energy-harvesting materials.
We present a multi-color STED fluorescence microscope providing far-field optical resolution down to 20 nm for biomedical research. The optical design comprises fiber lasers, beam scanners, and a set of active and passive polarizing elements that cooperatively yield an optically robust system for routinely imaging samples at subdiffraction length scales.
We provide a critical account of the dynamics of laser induced refractive index changing mechanisms in nematic liquid crystals which may be useful for all-optical switching and modulation applications in the visible as well as the Terahertz and long-wavelength regime. In particular, the magnitude and response times of optical Kerr effects associated with director axis reorientation, thermal and order parameter changes, coupled flow-reorientation effects and individual molecular electronic responses are thoroughly investigated and documented, along with exemplary experimental demonstrations. Emphases are placed on identifying parameter sets that will enable all-optical switching with much faster response times compared to their conventional electro-optics counterparts.
The generic foundry approach will lead to a revolution in micro and nanophotonics, just as it did in microelectronics thirty years ago. Generic integration leads to a drastic reduction in the entry costs for developing Photonic Integrated Circuits. Integrated circuits using generic integration open up a whole new range of applications including data communications, fiber-to-the-home, fiber sensors, gas sensing, medical diagnostics, metrology and consumer photonics. Present status and prospects of InP-based photonic foundry technology are reviewed.
Photoacoustic tomography (PAT) is an emerging imaging modality that shows great potential for preclinical research and clinical practice. As a hybrid technique, PAT is based on the acoustic detection of optical absorption from either endogenous chromophores, such as oxy-hemoglobin and deoxy-hemoglobin, or exogenous contrast agents, such as organic dyes and nanoparticles. Because ultrasound scatters much less than light in tissue, PAT generates high-resolution images in both the optical ballistic and diffusive regimes. Over the past decade, the photoacoustic technique has been evolving rapidly, leading to a variety of exciting discoveries and applications. This review covers the basic principles of PAT and its different implementations. Strengths of PAT are highlighted, along with the most recent imaging results.