Transformation Optics and the Control of Light

Light Harvesting: Non-Local and Quantum Tunnelling Effects

Metallic nanoparticles that support localized surface plasmon resonances can concentrate light into a deep-subwavelength volume, thereby achieving very large field enhancements. Many emerging nano-photonic technologies rely on the careful control of this field enhancement, including cancer therapy, improved photovoltaic devices, and optical antennas for enhanced light-matter interactions. However, at deep subwavelength scales, classical continuum electrodynamics fails to describe the optical responses of nanoparticles owing to nonlocal screening and the spill-out of electrons. Electron correlations that are driven by these effects require a new model of nonlocal transport, which is crucial in nanoscale optoelectronics. In this talk, I will present a systematic strategy, based on transformation optics, to study analytically the plasmonic interaction at subnanometer scales. Our approach incorporates radiative, nonlocal, and quantum tunnelling effects, and thus can be applied to design realistically sized plasmonic systems. As an example, I will use this method to elucidate the optimum shape of a nanoparticle that maximizes its absorption and field enhancement capabilities.

Metamaterial High-Directivity and Conformal Antennas

This talk mainly focuses on how metamaterials can be used to control direction of the emission of an EM source. In the first part of this presentation, I will introduce and compare three different approaches to achieve directive emission with metamaterials, i. e. by embedding a single line source in a slab of (a) a zero-refractive-index metamaterial (b) an extremely anisotropic metamaterial (c) a transformation medium with a spatially-variant refractive-index. The emitted energy is concentrated around the surface normal of the slab, and thus a far-field directive radiation can be achieved. In the second part of my talk, I will show that a transformed current distribution with an appropriately designed metamaterial coating produces similar radiation characteristics as the original antenna. This method thus provides a possible route to achieve conformal antennas.

The 60 GHz band has been an active subject of research during the last 15 years. This is due to its unique properties: a worldwide unlicensed bandwidth, a small wavelength and a high path loss. Several standards have emerged and integrated transceivers in CMOS processes following these standards have been published. This opens the path to low cost solution for high volume market 60 GHz modules. The Antenna-in-Package is here the chosen approach. We will study it using several technologies through its conception and measurement.

In this talk, I will present a 2.45 GHz wireless microphone for cochlear implant. The transmitting part of the system consists in an analog part (ramp generator and comparator) from a simple ramp ADC (Analog-to-Time converter only) as well as the RF transmission part. The digital part of the ADC is shifted to the receiver, where the signal picked-up by the antenna is amplified by an LNA and then demodulated into its OOK form by an envelope detector. The PWM signal is sent to a counter and transformed into digital for which the equivalent number of bits depends on the clock frequency of the DSP and the envelop detector performance. Especially the digital part is replaced by an analog filter in order to restore the analog signal.

The fundamental concepts of radiometers (passive imaging) and imaging arrays (active imaging) will be covered. This includes the definition of responsivity, noise-equivalent power (NEP), Dicke switching and 1/f noise, integration time and NEDT, antenna coupling efficiency especially when using on-chip antennas, will be first presented. The talk will then cover some of the latest chips developed by academia and industry at 94-160 GHz (radiometers) and 160-800 GHz (detectors and active imaging arrays) using SiGe, CMOS and advanced CMOS SOI nodes.

A hybrid simulation algorithm judiciously combines several numerical solvers to fully exploit the accuracy of rigorous schemes and the efficiency of approximate schemes to provide viable design tools. This approach is particularly important when dealing with the electrically small and large (in terms of the wavelength of the signals) features within the same geometry/modeling space, which is often the case in the sub-mm/THz devices, systems and in a large complex Radio propagation environment.
In this Seminar we describe a hybrid EM modelling technique based on combining ray tracing method with FDTD method, which uses ray tracing to analyze wide areas and FDTD to treat areas close to complex discontinuities, where ray based solutions are not sufficiently accurate. Besides much improved accuracy, the hybrid method only applies FDTD to a small portion of the entire modeling environment, which ensures practicality in terms of computational resources.
The hybrid method also enables the study of effects of generic indoor structural features, furniture, inhomogeneity inside walls and any objects that may have significant effect on signal coverage and statistics inside buildings. Furthermore, the method provides solution to the problem of outdoor-indoor signal coupling in the presence of inhomogeneous walls by using the ray tracing - FDTD – ray tracing approach. The method makes it possible to study the effect of inhomogeneity inside walls more accurately without adding much to the computational complexity; especially when the incident waves can be approximated by plane waves and the wall structure is periodic. Examples are given to show that in the areas where the specular signal is blocked by metallic structures, the proposed method can accurately predict signal coverage by taking into account the fields scattered by the inhomogeneity inside walls while the ray tracing method is not satisfactory. The ability of the developed method to analyze fading in signal strength, Doppler spread and time dispersion caused by multipath is also demonstrated in this seminar.    

Integration of all photonic components on a single solid state platform has long been a critical issue for optical community. One of the most promising techniques for optical integrated circuit is the Photonic Crystal (PC) technology. In the recent years, emerging PC technology compatible with Complementary Metal-Oxide Semiconductor (CMOS) technology, has paved the way for implementation of an integrated hybrid optics and electronic circuit. Using PC, compact optical elements can be implemented on a solid state platform. The bottleneck of this technology and in general optical integrated circuit is the strong polarization dependence of wave propagation. Thus, the performance and propagation characteristics of the integrated circuit elements are polarization dependent. Hence, our goal here is to overcome the polarization sensitivity of PC integrated circuit by introducing integrated PC based polarization controlling devices that are capable of controlling and manipulating of the polarization of the propagating wave. One of the crucial elements of polarization controlling devices is the polarization rotator. The polarization rotator is utilized to manipulate and rotate the polarization of light. In this work, we have proposed, designed and implemented an ultra-compact passive PC based polarization rotator.
Passive polarization rotator structures are mostly composed of geometrically asymmetric structures. The polarization rotator structure here consists of a single defect line PC slab waveguide. The geometrical asymmetry has been introduced on top of the defect line as an asymmetric loaded layer. The top loaded layer is asymmetric with respect to the z-axis, the propagation direction. To synchronize the power conversion and avoid power conversion reversal, the top loaded layer is alternated around the z-axis periodically. The structure is called periodic asymmetric loaded PC slab waveguide.
We also extended the method to SOI based PC membrane technology for sub-mm/THz applications. The device layer is made of highly resistive silicon to maintain low loss propagation for THz wave. The PC slab waveguide and polarization rotators were fabricated employing this technology. Finally, a-SiON based PC slab waveguide structures were also fabricated at low temperature for optical applications. This technology has the potential to be implemented on any substrate or CMOS chips.    

High-gain and high-performance waveguide slot arrays in millimeter-wave band are being developed in our laboratory for commercial applications. In the first half of this talk, the realization of a plate-laminated double-layer waveguide slot array in Q-band will be presented. The antenna is designed for a broadband point-to-point fixed wireless access (FWA) system with the maximum throughput of 1 Gbps. The designed antennas are fabricated by diffusion bonding of laminated thin metal plates, which is a promising process of high-precision and high mass-productivity. In a practical manner, the installment of antenna on the wireless terminal as well as the isolation enhancement between two antennas for simultaneous transmission and reception are also investigated. In the second half of this talk, an E-band waveguide slot array with a larger bandwidth will be presented. A PMC termination associated with the symmetry of the feeding waveguide is newly proposed to realize dense and uniform slot arrangement free of high sidelobes. A 16x16-element array with uniform excitation is designed and fabricated by diffusion bonding of laminated thin copper plates. The antenna efficiency of 83.0% is measured at the center frequency. The 1dB-down gain bandwidth is no less than 9.0% and a wideband characteristic is achieved.

From the effective medium theory, the periodic structures with sub-wavelength elements can be viewed as homogeneous metamaterials, for example, left-handed materials, zero-index materials, epsilon-negative medium, mu-negative medium, anisotropic metamaterials, and chiral medium. Some unusual electromagnetic properties have been found with homogeneous metamaterials, such as the negative refraction and perfect imaging. However, inhomogeneous metamaterials which are composed of non-periodic structures can provide much more freedom to control electromagnetic waves. In this presentation, I will mainly focus on the experimental verification to the control of electromagnetic waves using inhomogeneous metamaterials in the microwave frequency. There are three approaches to design inhomogeneous metamaterials: the geometrical optics method (gradient-index metamaterials), the quasi-conformal mapping (all-dielectric metamaterials), and the transformation optics (anisotropic metamaterials). We have designed, fabricated, and measured a couple of inhomogeneous metamaterial devices in the microwave frequencies, including the two-dimensional (2D) and three-dimensional (3D) ground-plane cloaks, gradient random surface, electromagnetic black hole, 3D flattened Luneburg lens, and the illusion-optics devices.

Metamaterials have attracted great attentions due to their ability to control electro- magnetic waves and the unusual properties. This presentation will be focused on the application of metamaterials in microwave antennas, exploring better performance and/or new features of antennas. Three types of metamaterial antennas are presented: zero-index material antennas, small patch antennas for wireless communications, and metamaterial lens antennas.
We propose and experimentally demonstrate two kinds of anisotropic zero-index materials (AZIMs) in the Cartesian and cylindrical coordinates, respectively. The Cartesian AZIMs (such as z component of permittivity or permeability tensor equals zero) are shown to generate perfectly plane waves in the z direction, resulting in high-directivity antennas. We make two-dimensional (2D) and three-dimensional (3D) experiments to verify such new features. On the contrary, the radially AZIMs (radial component of permittivity or permeability tensor in the cylindrical coordinate equals zero) will always produce omnidirectional radiations regardless the numbers and positions of sources inside AZIM. We also show experimentally the powerful ability of AZIM to reach high-efficiency spatial power combination for the omnidirectional radiations.
We experimentally demonstrate efficient methods to improve the bandwidth and radiation efficiency of patch antennas and reduce the coupling among patch antenna array using metamaterials, which are important to the wireless communications (e.g., MIMO systems).
We present two kinds of metamaterial lens antennas. First, we demonstrate a series of 3D broadband, low loss, dual polarization, and high-directivity planar lens antennas which are realized using gradient-index metamaterials, which have excellent features and superior performance than traditional antennas (horns or Rotman lenses). Second, we propose and realize a 3D Luneburg lens with flattened focal surface using the transformation optics. The novel 3D lens has great advantages to the conventional uniform-material lens and spherical Luneburg lens with no aberration, zero focal distance, a flattened focal surface, and the ability to form images at extremely large angles. It can be directly used as a high-gain antenna to radiate or receive narrow beams in large scanning angles for dual polarizations.

The linear PAs for advanced system, such as 4G and beyond, should handle signals with high PAPR. For amplification of the signals, the efficiency of the PAs is degraded significantly due to the operation at a low power region. To improve efficiency of the PAs, advanced design architectures are developed. These architectures are based on a highly efficient amplifier and try to maintain the high efficiency at a low power level. The representative architectures are Doherty amplifier, LINC, ET technique, class-S amplifier, and some digital PAs.
Doherty is the main force in mobile infrastructure PA and can provide a high efficiency for the amplification of signal with a high PAPR. There is a significant progress in the broad banding but the bandwidth is still limited. Recently, the performance of the LINC PA is improved significantly by increasing the power combining efficiency. The distortion is cancelled successfully using DPD technique.
ET is the most popular architecture for the handset application since this PA is very flexible, suitable to the multimode and multiband operation, together with high efficiency. This technique can be applied easily to a low-high mode PA, also. One variation of the technique is average power tracking (APT) amplifier, controlling VDC according to the average power level using a buck DC-DC converter.
As transistors are scaled down with higher speed, the digitally configured circuit can be applied for the RF signal amplification. The digital circuit can be very flexible and can be used for multimode/multiband application but the performance is not up to the expectation, yet. For the digital amplification, the I-Q modulated signal is normally up-converted to a polar signal. The amplitude information is digitized at the base band speed or the RF frequency and is applied to the digital PA. The digital bit can be amplified by the thermo-coded cells, which is a digital amplifier.  The digitizing can be done using sigma-delta modulator and the digitized bit can be applied to a PA, either as an input or as a bias voltage. The resulting amplifier is a class-S PA. I-Q modulated signal can be directly up-converted as a digital form using sampling technique and is applied to the thermo code cells. These digitally configured PAs are actively studied for handset application and will progress continuously.
These various advanced architectures for the next generation PA will be introduced in this talk.

Tapered slot-line antenna (TSA) is a well known printed end-fire antenna with traveling wave feature. In order to further improve its performances and extend its functions, several techniques with patents were developed in SEU, and summarized in this article. Here include: grating-loaded TSA for gain enhancement, CPW-feeding TSA for bandwidth broadening, asymmetric TSA structure for beam shaping, coupled TSA with hybrid network for mono-pulse beam forming. Both conceptual illumination and simulated/measured results are described.

With the development of satellite navigation technology, many countries have started to build their own satellite navigation systems. Nowadays, satellite navigation systems are intensively used. The American GPS and the Russian GLONASS are already operating world-wide. The Chinese Compass system has also provided a partial service. Future satellite navigation receivers will be provide multimode operation utilizing different satellite navigation systems to improve their positioning accuracy and reliability, so the design of terminal antenna for multimode satellite navigation systems is practically desirable.
A multimode satellite navigation receiver is required to cover several frequency bands for GPS, GLONASS, GALILEO and COMPASS systems. Each GNSS system has several frequency bands. The challenges in the design of a multiband receiver antenna come from two requirements – the antenna needs to provide right-hand circular polarization with a low axial ratio and also maintain a low VSWR over multiple frequency bands. In this talk several designs of dual band and tri-band GNSS antennas will be covered and their operating principles will be discussed.

In this seminar, Prof. Dou Wenbin will introduce Southeast University, College of Information Science and Engineering (former Department of Radio Engineering) and the State Key Laboratory of Millimetre Waves. The presentation will provide details on the accurate measurement of complex permittivity of dielectric material based on Quasi-optical open cavity technique at millimetre waves, as well as introduce the measurement of complex permittivity of material at microwaves using strip line technique. Finally some work on antennas, radomes and imaging will be presented.

Metamaterials are artificial photonic materials that show unconventional electromagnetic properties arising from their structural effect. Symmetry, coupling and interference between different excitation processes play important roles in introducing novel functionalities. Examples include a new type of Mobius symmetry, gigantic chirality that breaks mirror symmetry, and plasmon induced transparency that mimicks the electromagnetic induced transparency (EIT) in atomic systems. In this talk, I will present a number of functional metamaterials and plasmonic devices, passive or active, based on the mechanism of coupling and symmetry, including a chirality switching metamaterial, a plasmonic demultiplexer with continuum mediated anti-Hermitian coupling, and a metamaterial with interference induced asymmetric transmission.

Wave Penetration into a Human Head, a Bi-anisotropic Body of Arbitrary Shape

The advancement of electromagnetic engineering has been driving the need to develop efficient time domain techniques for transient analysis of transmission, propagation and reception of electromagnetic pulses. This presentation addresses one method based on numerical inversion of Laplace transform (NILT), which overcomes the restrictions in previous approaches, leads to good accuracy in both late and early time, and has a simple algorithm, short calculation time, small required memory size and readily controlled error. To our knowledge, this would be the first time that systematically treats the theory of NILT and its application in the transient analysis of electromagnetic waves. This talk highlights how to overcome the restriction that numerical inversion of Laplace transform has high demands on image functions, and places the emphasis on how to extend and apply this method to a variety of cases. The correctness and effectiveness of this work are validated through the comparisons between our results and those published in the literature. Meanwhile, the results that cannot be achieved with the previous approaches are also provided. Moreover, this talk presents some applications of the new technique in diverse engineering fields, including ultra wideband technology, electromagnetic compatibility and material science.

This talk introduces research on wireless communications and microwave technologies at Shanghai University, China.  For wireless communications, we focus on the use of 2.4-GHz ISM band in City Metro Networks. I show that RF interferences between wireless data communication systems and the variety of existing users of this band become a critical issue. To solve the EMC and security problems, many approaches have been adopted in China where Shanghai University has played a leading role and offered valuable suggestions. For microwave technologies, Shanghai University has long been recognized as a Centre of Excellence in China.  I briefly touch on miniaturization of microstrip antennas, wireless power transmission, invisibility techniques, radio frequency device and integrate circuits.

Microstrip patch antennas have become favorites of antenna designers.  Depending on the application, it is desirable for the antenna under design to be circularly polarized or multi-band.  A simple way of achieving these characteristics is by means of cutting suitable slots on the patch.  This talk presents some of the recent work by the author and his collaborators on this method.  After an overview of single-feed circularly polarized patch antennas, the use of slots in enhancing the performance of these antennas is described, followed by a design which achieves polarization reconfigurability. The talk concludes with a technique of designing dual and triple band linearly polarized patch antennas.

As a major remote sensing sensor, Synthetic aperture radar (SAR) can produce high resolution images from a moving platform, such as an airplane or a satellite, and is being widely used in many civilian and military applications. The main advantage of SAR is that images of the illuminated area can be obtained independent of time-of-day or weather conditions (e.g., fog, cloud level, rain, and snow). Compressive sensing (CS) is a new developing novel theory that enables perfect recovery of signals and data from what appear to be highly sub-Nyquist-rate samples. It offers the possibility to effectively reduce data size, complexity, weight, power consumption and costs of SAR systems. As an example, a novel spaceborne SAR wide-swath imaging approach based on Poisson disk-like nonuniform sampling and compressive sensing is used to illustrate the CS-SAR application and some processing issues are discussed in details.

Nonlinear Imaging and Inversion Approaches for Large-Scale Geophysical Electromagnetic Measurements

The marine controlled-source electromagnetic (CSEM) technology has attracted much attention for its capability in directly detecting thin hydrocarbon reservoirs. The approach is based on comparing the electric field amplitude as a function of the source-receiver offset with a similar measurement for a non-hydrocarbon bearing reservoir. The presence of hydrocarbon raises the amplitude of the measured electric field indicating the existence and to some degree determining the horizontal extent of the hydrocarbon zone; however with this approach it is difficult to know the reservoir's depth and shape. A more rigorous approach to address this type of application is the full nonlinear inversion. In this presentation we present two rigorous nonlinear inversion algorithms.

The first method is the so-called pixel-based inversion (PBI). In this approach the investigation domain is subdivided into pixels, and by using an optimization process the conductivity distribution of the investigated domain is reconstructed. The optimization process uses the Gauss-Newton minimization method augmented with various types of regularization. This PBI approach has demonstrated its ability to retrieve reasonably good conductivity images. However, the reconstructed boundaries and conductivity values of the imaged anomalies are still not adequately resolved. Nevertheless, the PBI approach can provide some useful information on the location, the shape and the conductivity of the hydrocarbon reservoir.

The second method is the so-called model-based inversion algorithm (MBI), which uses a priori information on the geometry to reduce the number of unknown parameters and to improve the quality of the reconstructed conductivity image. This PIA approach can be also used to refine the conductivity image that we obtained using the PBI algorithm. The PIA also adopts the Gauss-Newton minimization method. The parameters that govern the location and the shape of an anomaly include the depth and the location of the user-defined nodes for the boundary of the region. The unknown parameter that describes the physical property of the region is the conductivity.

We will show some inversion results of synthetic and field data to illustrate the PBI and MBI approaches. We further show that by combining both inversion algorithms we arrive at a better interpretation of the controlled-source electromagnetic data. This work is a joint work with T.M. Habashy, M. Li, and G. Pan

Future Perspectives of SAR Polarimetry with Applications to Multiparameter Fully Polarimetric POLSAR Remote Sensing

With the un-abating global population increase our natural resources are stressed as never before, and the global day/night monitoring of the terrestrial covers from the mesosphere to the litho-sphere becomes all the more urgent. Microwave radar sensors are ideally suited for space imaging because those are almost weather independent, and microwaves propagate through the atmosphere with little deteriorating effects due to clouds, storms, rain, fog aerosol and haze. Globally humidity, haze and aerosols next to cloudiness are increasing at a rather rapid pace, whereas only 20 years ago all of those covered 48% of the globe, today those have increased to about 62% and within another 20 years may exceed 80% for irreversible reasons. Thus, optical remote sensing from space especially in the tropical and sub-tropical vegetated belts is already and will become ever more ineffective, and microwave remote sensing technology must now be advanced strongly and most rapidly hand in hand with digital communications technology because operationally it is more rapidly available especially for disaster mitigation assistance. The basic radar technologies to do the job at day and night are the multimodal Synthetic Aperture Radar (SAR) sensors, first developed for air-borne sensing implemented as for example in 1978 with the first space-borne digital Sea-Sat L-Band SAR which had severe limitations in that it was of fixed wide swath-width at a single arbitrary polarization (HH) and of rather poor 25m resolution. In the meantime, fully polarimetric multi-modal high resolution SAR systems at multiple frequencies and incidence angles were introduced first with the multi-band AIRSAR of NASA-JPL culminating in the once-only pair of SIR-C/X-SAR shuttle missions of 1994 April and October, which laid the ground work for true day/night space remote sensing of the terrestrial barren and vegetated land and ocean covers using multi-band polarimetric SAR. Thereafter, the Canadian CCRS, the German DLR and the Japanese NASDA & CRL {now JAXA & NICT} took over introducing and steadily advancing the Convair-580, the E-SAR (now F-SAR) and Pi-SAR airborne highly advanced fully polarimetric sensors platforms, respectively. These separate international multi-modal fully polarimetric and also interferometric airborne SAR developmental efforts culminated in a well coordinated group effort of three independent teams eventually launching and operating Fully Polarimetric Satellite SAR Sensors at L-Band (ALOS-PALSAR launched by JAXA/Japan in 2006 January - and to be followed by ALOS-PALSAR-2 &3); at C-Band (RADARSAT-2 launched by CSA-MDA in 2007 December - to be followed by independent RADARSAT-3&4) and at X-Band (TerraSAR-X launched by DLR-Astrium in 2007 July with the follow-on tandem mission TanDEM-X launched in June 2010) . Thus, international collaboration on advancing day & night global monitoring of the terrestrial covers was demonstrated with the launch of the three fully polarimetric multi-modal SAR Satellites at L-, C-, X-Band and its first tandem satellite-pair update of the DLR TanDEM-X. Recently NASA-JPL is joining these global efforts again, and all of these efforts will be topped by the near-future joint DLR-JPL DESDynI/Tandem-L wide-swath, high-resolution fully polarimetric sensor implementation.

The use of judiciously engineered metamaterials in novel class antennas and microwave devices is presented. In this seminar, I will review the research activities of the IEF/PSud in the field, discussing the motivations of this research as well as the applications for aeronautical and telecommunication domains.