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In the quest to decipher the chain of life from molecules to cells, the biological and biophysical questions being asked increasingly demand techniques that are capable of identifying specific biomolecules in their native environment, and can measure biomolecular interactions quantitatively, at the smallest possible scale in space and time, without perturbing the system under observation. The interaction of light with biomolecules offers a wealth of phenomena and tools that can be exploited to drive this progress. This Roadmap is written collectively by prominent researchers and encompasses selected aspects of bio-nano-photonics, spanning from the development of optical micro/nano-spectroscopy technologies for quantitative bioimaging and biosensing to the fundamental understanding of light–matter interaction phenomena with biomolecules at the nanoscale. It will be of interest to a wide cross-disciplinary audience in the physical sciences and life sciences.

In this paper, the authors investigate analytically the transformation from the initial guided mode distribution to the stationary state and the effects of the bidimensional roughness profile, in multimode polymeric buried waveguides. In these structures, due to the geometrical dimensions and the operating wavelength, about a thousands of guided modes can propagate, even for weak core/cladding dielectric contrast. The coupling coefficients are computed by exploiting the geometrical features of the optical channels, such as the waveguide dimensions and the roughness surface statistics. The analysis gives insight on the guided/guided and guided/radiated mode interaction, and higher order solution is proposed, in the case of a great number of modes interacting over distances that are extremely long as compared to the signal wavelength and the roughness correlation length. Experimental results are valuated by means of semicontact atomic force microscopy as well as compared with existing numerical models.

An accurate investigation of an integrated optical polariser has been presented. The transverse magnetic (TM)-passing property for an asymmetrical slab with anisotropic cladding that behaves as negative or positive uniaxial crystal has been evaluated. After a modal analysis, the polarisation of the electromagnetic (EM) field is evaluated by means of transmission line matrix-integral equation (TLMIE) method which performs a 3D full-wave modelling of the structure (i) including dielectric losses and (ii) for different slant angle of the laminated cladding. The TLMIE method permits to maximise the TM-passing property for a single-mode channel with anisotropic cladding.

An effective tool for accurate analysis and design of a wide range of optical devices involving three-dimensional (3-D) photonic crystals is provided. The advantages of using transverse resonance in conjunction with full-wave numerical solvers in order to characterize this kind of structures are highlighted. This paper focuses on the study of a practical example of an asymmetric crystal slab and shows the features of the proposed method in terms of accuracy and flexibility. The concept of Floquet modes of a periodic crystal is applied, and a multimode transverse equivalent network is developed in the aim of obtaining the resonant 3-D modes of the slab containing the photonic crystal

In this paper, an accurate model of the far-field radiation of a tapered optical fiber, which is widely used in communication optics and biomedical tomography, is presented. The authors first analyze the far field that is radiated from the normally cut fiber then extend the model to a fiber with a tapered end by considering the different phase contributions of the emitted rays. The proposed technique shows the effects of the cut with a view of obtaining a high efficiency both in coupling and radiation pattern characteristics

A new simple form of a rib-waveguide polarizer is proposed and investigated. The cladding consists of a dielectric multilayer based on Si and SiO2; the core is a single-mode MO (magnetooptic) channel waveguide in Ce-substituted Yttrium Iron Garnet (YIG). The TM-passing property of the anisotropic cover filters out the unwanted polarization. The authors first develop a modal analysis of the rib waveguide and then perform a full-wave modeling of the polarizer by means of the transmission-line matrix integral equation (TLMIE) method. The TLMIE is an efficient three-dimensional (3-D) hybrid technique that combines the advantages of the numerical transmission-line matrix (TLM) method in dense finite regions, and those of the analytical Green's functions where available. The TLMIE method validates the modal analysis, yields an accurate physical insight of the polarization selection, and, it provides a tool for the optimization of the device

In this work, an analytical model of the frequency shift experienced by an optical signal passing through a traveling wave modulating channel is derived. The model starts from the well-known coupled-mode theory but holds for an arbitrary temporal envelope of the optical signal and for any time dependence of the slowly varying modulating field; it provides an analytical and accurate explanation of various effects such as those due to losses or microwave-optical group velocity mismatch. The practical example of a modulated optical Gaussian pulse is provided.

This paper presents a rigorous and general approach to the analysis of multimode traveling-wave electrooptical modulators. Starting from the linear model derived by Di Donato et al. in 2004, where we demonstrated the accuracy of this approach for single mode electrooptic modulators and for quasi-degenerate modes, we now provide a compact, analytical solution to the system of coupled transmission-line equations describing multimode and multipolarization interaction. In addition, the analysis will consider the joint effect of a continuous and a time-space varying voltage. Small dielectric perturbations induced by the microwave fields (/spl Delta//spl epsiv//spl Lt//spl epsiv/) and large difference between the optical and modulating signal frequencies are the only hypotheses used in deriving the linear model by Di Donato et al. Some examples are discussed in order to demonstrate the main characteristics of the electrooptic modulators and some suggestions on the electrooptic modulator design are provided in order to realize polarization-independent devices.

Photonic devices based on stacked multilayer waveguides are widely used in optical integrated architectures like polarizers, filters, photodetectors, laser, transducers for sensing applications, and microelectromechanical systems. In this paper, we present an accurate modeling of a waveguide polarizer based on an antiresonant reflecting optical waveguide (ARROW) structure utilizing birefringence form. The ARROW polarizer is the case of a structure with severe "aspect-ratio" that most of numerical technique cannot handle. The electromagnetic analysis is performed by means of a transmission-line matrix integral-equation (TLMIE) method-based solver. TLMIE is a three-dimensional full-wave hybrid technique that combines the advantages of the numerical transmission-line matrix method in dense finite regions and those of the integral-equation method in homogeneous regions where analytical and/or numerical Green's functions are available. An accurate investigation of propagation/radiation properties of TE/TM modes is performed. Theoretical results of TE/TM losses are compared to measured data showing very good agreement. Starting from this validation, it seems possible to provide design criteria for the optimization of the polarizer.

The theoretical investigation of waveguides having non-uniform cross-section is an attractive and challenging problem which arises serious interest. In this paper, we develop the analysis of laminated multilayered 3D-waveguide, by the three following steps: (i) Coupled Mode theory (CM) is generalized and compared with Local Mode theory (LM). The latter is a rigorous technique which accounts for propagation, diffraction and coupling in a non-uniform environment. (ii) The two approaches are then applied to the problem of polarization coupling in a laminated rib-waveguide Si:H–SiO2. For moderate optical axis slant (low hybridization) and fixed layer thickness the two theories yields similar results, while LM becomes mandatory when hybridization is important. (iii) Finally, we validate and complete the EM analysis by using the finite element method (FEM) for the 3D modelling of the structure. Copyright © 2005 John Wiley & Sons, Ltd.

The theoretical investigation of waveguides having nonuniform cross-sections is an attractive and challenging problem which deserves serious interest. In this paper, we present a novel analysis of laminated multilayered three-dimensional waveguide, based on two modes: 1) a new coupled transmission line approach that considers the sloping of the layers along the longitudinal direction and 2) a transmission line matrix integral equation (TLMIE) modeling that complete and extends the investigation of the field propagation. In method 1), we neglect radiation modes and their EM coupling. All physical effects instead are accounted for by the full-wave TLMIE method. By using TLMIE, we validate the EM analysis and calculate TE/TM losses, arising from radiation modes.

Polarization beam-splitters (PBSs) and polarization switches based on the birefringence of periodically laminated dielectric thin films are important tools in modern optics. In this paper, we present a rigorous analysis of multilayer PBSs by evaluating: 1) the fields outside the structure and 2) the electromagnetic coupling in laminated polarization splitters behaving as negative uniaxial crystals, in the case of Bragg condition. This analysis has been applied to an artificial anisotropic dielectric realized by means of layers of a-Si:H and SiO/sub 2/.

This paper investigates transverse-electric-transverse-magnetic (TM) conversion properties of an integrated optical polarization switch realized by means of a TM-pass waveguide polarizer, whose cladding consists of an obliquely deposited thick film. This waveguide polarizer is more compact, stable, and inexpensive to realize than a hybrid waveguide polarizer using birefringent crystal as cladding. By utilizing the TM-passing property of the anisotropic cover of a rib waveguide, the polarization is selected by means of the electrooptic effect.

In this paper, we propose exact transmission-line matrix (TLM) boundary conditions for closed homogeneous waveguides. This approach is based on applying mode matching at the absorbing boundaries to the time-domain TLM algorithm. The absorbing condition in the time domain is achieved by the convolution of the modal characteristic impedances following inverse Fourier transform. The method is demonstrated for thick inductive irises in rectangular waveguide, showing excellent wide-band match of the fundamental mode, as well as of higher order modes excited by the discontinuity.

In this work we describe a novel kind of scanning probe microscope carried out through an optical fiber extrinsic microcavity. The micro-cavity is realized by approaching a single mode fiber to a sample placed on a piezo-scanner. The distal end of the fiber and the sample realize the optical resonator. The probe is fed by a low-coherence source and the reflected intensity is acquired by an optical spectrum analyzer. The resonant behavior of the cavity enables to overcome the conventional Rayleigh limit. For this system the transverse resolution is not defined by the NA of fiber but it is a function of the transverse electromagnetic field inside the micro-cavity. The lens-free system paves the way towards quantitative measurements in air and liquid environment.

Real circuits involve metallic edges with finite conductivity and nonideal dielectrics. Usually it is more or less implicitly assumed that fields and induced currents behave as if conductors and dielectrics were ideal. In this paper, we show that this assumption is partially erroneous and that the presence of real conductors and dielectrics seems to lead to a simpler and more physical picture, where longitudinal currents are shown to be nonsingular.

In a companion paper (Rozzi et al., 1998), experimental validation was provided for a transient three-dimensional numerical model of the process by which a rotating workpiece is heated with a translating laser beam. In this paper, the model is used to elucidate the effect of operating parameters on thermal conditions within the workpiece and to assess the applicability of an approximate analysis which is better suited for on-line process control. From detailed numerical simulations, it was determined that the thickness of a surface thermal layer decreases with increasing workpiece rotational speed and that the influence of axial conduction on the workpiece temperature distribution increases with decreasing laser translational velocity. Temperatures increase throughout the workpiece with increasing laser power, while the influence of increasing beam diameter is confined to decreasing near-surface temperatures. Temperature-dependent thermophysical properties and forced convection heat transfer to the laser gas assist jet were found to significantly influence the maximum temperature beneath the laser spot, while radiation exchange with the surroundings and mixed convection to the ambient air were negligible. The approximate model yielded relations for calculating the radial temperature distribution within an r-φ plane corresponding to the center of the laser source, and predictions were in reasonable agreement with results of the numerical simulation, particularly in a near-surface region corresponding to the depth of cut expected for laser-assisted machining.

Laser-assisted machining (LAM), in which the material is locally heated by an intense laser source prior to material removal, provides an alternative machining process with the potential to yield higher material removal rates, as well as improved control of workpiece properties and geometry, for difficult-to-machine materials such as structural ceramics. To assess the feasibility of the LAM process and to obtain an improved understanding of governing physical phenomena, a laser assisted machining facility was developed and used to experimentally investigate the thermal response of a rotating silicon nitride workpiece heated by a translating CO2 laser. Using a focused laser pyrometer, surface temperature history measurements were made to determine the effect of rotational and translational speed, as well as the laser beam diameter and power, on thermal conditions. The experimental results are in good agreement with predictions based on a transient three-dimensional numerical simulation of the heating process. With increasing workpiece rotational speed, temperatures in proximity to the laser spot decrease, while those at circumferential locations further removed from the laser increase. Near-laser temperatures decrease with increasing beam diameter, while energy deposition by the laser and, correspondingly, workpiece surface temperatures increase with decreasing laser translational speed and increasing laser power, In a companion paper (Rozzi et al., 1998), the detailed numerical model is used to further elucidate thermal conditions associated with laser heating and to assess the merit of a simple, analytical model which is better suited for online process control.

We propose a full-wave numerical model of a three-dimensional (3-D) photonic crystal with the absolute photonic bandgap (PBG) centered at /spl lambda//spl sim/1.6 /spl mu/m. The analyzed structure is widely used in integrated optical circuitry. The electromagnetic analysis is performed by using the finite-element method (FEM) and transmission line matrix-integral equation (TLMIE) method. We analyze the reflection properties and compare theoretical results to experimental data. Due to its exact boundary conditions, TLMIE shows much higher accuracy with respect to FEM in the PBG optical band. As a demonstration, we have realized and analyzed a holographic polymer dispersed liquid crystal grating.

We present a fully ab initio, nonperturbative description of the optical limiting properties of a metal-free phthalocyanine by simulating the effects of a broadband electric field of increasing intensity. The results confirm reverse saturable absorption as the leading mechanism for optical limiting phenomena in this system and reveal that a number of dipole-forbidden excitations are populated by excited-state absorption at more intense external fields. The excellent agreement with the experimental data supports our approach as a powerful tool to predict optical limiting in view of applications. © 2014 American Physical Society.

The coaxial suspended strip configuration in elliptical cross section is often found in transitions from ordinary coax to planar circuits and other geometries. Using elliptical coordinates makes the problem separable, leading to closed-form solutions for the fundamental TEM mode and the TE/TM higher modes. It is emphasized that the presence of the thin strip is dealt with analytically by this approach. Mode patterns and TEM characteristic impedance are reported. The cutoff frequencies versus eccentricity are computed for the first eight modes.

The field nearby a thin iris discontinuity can be found in an exact manner by solving the wave equation in an appropriate coordinate system. To this end, it is necessary to select a coordinate system that fits the iris boundary. As an example, capacitive and inductive irises in rectangular waveguides have been solved by considering the Helmholtz equation in the elliptic-cylinder coordinate system. The presence of the waveguide environment is then enforced either by using the aperture field solution in a variational expression of the equivalent shunt susceptance or by taking images. The advantage of the new solution is that a single term solution, apart from being very accurate and numerically efficient, also contains the correct frequency dependence; thus providing results over the entire band. Moreover, wide-band equivalent circuits with frequency independent elements of the Foster's canonical form descend directly from the field analysis.

The well known bound modes of open microstrip do not constitute a complete spectrum, for, continuous radiation and localized (reactive) modes are excited at discontinuities in microstrip circuits and antennas. This part of the spectrum has not been investigated before so that, up to date, radiation problems in microstrip are being investigated by nonmodal methods, such as the moment method. We derive here for the first time the complete spectrum of open microstrip, including one or more bound modes and a continuum, and demonstrate its straightforward application to a practical problem such as the excitation by a cylindrical probe of finite radius. Application of Lorentz's reciprocity principle is now possible in complete analogy to the problem of excitation of a close waveguide by a probe. Mode patterns, the equivalent circuit of a via-hole and its radiation pattern are characterized as a practical application of the foregoing theory. >

In this paper we analyze the effects of radiation in Y-junctions in rib waveguide by combining the effective dielectric constant method and the concept of local modes of a five-layer slab guide. The evaluation of the fields of the junction is performed together with the analysis of the radiation effects at the end of the transition; various kinds of junctions are examined and discussed, in both LSE and LSM polarizations. >

A novel method is proposed for the analysis of transients in dielectric guide, e.g., when excited by a Gaussian beam pulsed in time and modulated by a cosine waveform. This approach, utilizing the full modal spectrum of the guide, results more reliable than existing numerical techniques, while, by virtue of its analytical nature, greatly reducing the computational complexity of the problem. >

Photolithographic techniques permit the realization of complex circuits totally confined to the E-plane of millimetric rectangular guides with high precision and low cost. This work contains a detailed analysis of an E-plane diplexer configuration recently introduced. Its main feature is the matching section of the three port junction, a simple abrupt E-plane one tuned by means of an inductive post realized on the same mask as the branching filters. On the basis of this analysis, we also demonstrate the application of a recently developed diplexer synthesis technique. Many prototypes, in K/sub a/-band were designed and tested, showing good performances and good agreement between theory and experiment. >

Compact waveguide bends with low return loss over the full waveguide band width are realized by placing properly selected discontinuities inside the curve. The component is designed by using an extremely efficient computer code which employs the local modes approach to analyze curved sections, while discontinuities are rigorously accounted for by considering their multimode equivalent circuit. A simple technique to select the appropriate matching elements is described and examples of full-band matched bends are provided.

The microstrip loaded inset dielectric waveguide has been proposed as a transmission medium alternative to microstrip, and as a useful antenna medium at X-band and millimetric frequencies. In the present analysis we consider the case where a multi-layer, multi-conductor microstrip circuit may be housed within inset dielectric waveguide. A generalised transverse resonance diffraction method is developed in the space domain for analyzing such structures. Experimental and theoretical results for the propagation characteristics of the fundamental and first higher order mode of a few different configurations are presented showing good agreement. >

The GTEM (GigaTEM) cell is proving a useful tool for characterizing the EM emission of objects under laboratory conditions. In order to enhance its practical use, however, it is essential to be able to identify and predict differences between tests in "open site" and in cell environment. The modes of the empty cell were previously reported. In this contribution, we address in the first time the problem of excitation by dipoles in the non uniform environment of the cell. Moreover, we present an analytical model of the scattering by a dielectric or conducting sphere in the cell. Numerical results are compared with experimental data, when possible, and with theoretical results for scattering by the same object in free space, showing very good agreement as regards the resonant frequencies. >

This paper presents a novel analysis of air-bridges in open CPW, including the effects of finite thickness metallisation, using the complete modal spectrum of the CPW. This is a technique which, in comparison with other methods, allows the common features of CPW circuitry to be extracted and preprocessed without consideration of the particular problem in hand, that is, a suitable basis upon which to build a CAD package for smaller computers. Using this approach, scattering parameters, radiation and substrate leakage patterns of isolated bridges have been derived for both types of fundamental mode incidence and compared, where possible, to those obtained from other methods. Furthermore, pairs of bridges, coupled by both the near and far fields, have been analysed. >

The modes of open waveguides with nonseparable cross sections are derived by means of an extension of the resonance equation for the electromagnetic field. Such modes, forming a continuous spectrum, allow us to apply to discontinuity problems in open environments the techniques originally developed for closed waveguides. In this paper, the resonance equation is generalized according to functional analysis considerations. By this approach, it is possible to derive the modal spectrum from the simultaneous diagonalization of the real and imaginary parts of the admittance of the structure. A variational interpretation of the solution of the generalized resonance equation gives additional insight into the modes of open waveguides. The generalized resonance equation, when applied to three-dimensional objects, provides the well-known characteristic modes of these structures. The relationship between continuous spectrum, characteristic modes, and leaky waves is also discussed. >

The analysis of discontinuities in open waveguides, particularly strongly radiating discontinuities, requires a knowledge of the complete modal spectrum of the guide. The continuous spectrum of nonseparable open waveguides, a category which includes many useful high-frequency structures, may be developed from a characteristic Green's function approach. The continuous hybrid spectrum of the inset dielectric guide (IDG), a structure that shows promise for both propagation and antenna applications, is presented as an example. As a verification, this spectrum is used in the analysis of strongly radiating rectangular waveguide to IDG transitions, and a good correlation with experimental data is achieved. >

In this work, we analyze the problem of the electromagnetic field radiated from apertures in coaxial fed metal enclosures loaded with metal inserts. Such situations are found, for example, in PC environments where slots and apertures are used for the purpose of heat dissipation, CD-ROMs, cable penetration etc. We derive an accurate model of the entire structure, including the coaxial line-to-loop-to-cavity feed and the inner metal planes, simulating the presence of the circuitry inside. The analysis is developed by means of the hybrid transmission line matrix-integral equation (TLM-IE) method and theoretical results are compared with experimental ones showing very good agreement. The evaluation of the reflection coefficient and of the level of radiated emission as functions of the metal plates position is very helpful toward the engineering design of the entire structure. The numerical simulations require rather low computational effort.

Non-destructive sensor for the measurement of thickness and refractive index of polymeric layers deposit on glass bases. The sensor is oriented to the manufacture of polymers for O-PCB interconnects. Michelson FOLCI configuration has been applied. Article not available.

The inset dielectric guide (IDG) represents an easy-to-fabricate alternative to the image line that is also less sensitive to loss radiation at discontinuities. Two IDG geometries were analyzed, the so-called deep and shallow IDG structures, operating in the LSE and LSM polarizations, respectively. The propagation constants of single and coupled symmetrical IDGs have been calculated as well as the coupling coefficients of coupled guides. The transverse resonance diffraction method with variational formulation was used. Measured values show very good agreement with predicted values for the propagation constants of coupled deep slot IDGs. The information is a prerequisite for the design of directional couplers in IDG. >

The general problem of multiple coupled rib waveguides, where energy may be leaked from one guide to the other via the substrate and radiation mode, is treated. Rigorous results including substrate and air modes coupling are sought for the general case of coupling of two or more different guides. The analysis, developed in terms of a cascade of the transverse steps, utilizing a variational solution with a single trial function and making explicit use of edge singularities at the dielectric corners in order to produce an effective and rigorous solution, is presented. Multiple coupled rib guides are then reduced to a cascade of interacting step discontinuities in the transverse direction. When comparison is possible, the numerical results obtained by the method are seen to be as accurate as those obtained by the finite element method (FEM)/finite difference method (FDM), but with a fraction of the computer time and memory involved. >

The continuous spectrum of the rib waveguide is derived by a method that ensures orthonormality and completeness of the spectrum. A relatively simple approximation of this continuum for most cases of common interest is obtained. The theory is applied to the abrupt step discontinuity in the E-plane of the rib guide under LSE polarization and to the abrupt termination problem, including radiative effects never before investigated. >

The continuum of an open waveguide describes radiation as simply, in principle, as the discrete spectrum of a classical guide describes any physical field in it. This part of the spectrum, however, has received little attention for guides of nonseparable two-dimensional cross-sections. To illustrate its derivation, the authors establish the continuum of a flange-backed rectangular waveguide slotted on its narrow wall. As a demonstration for its use, they determine the transmission and radiation properties of the junction between an ordinary and a slotted guide. >

Nonlinear propagation in dielectric slab waveguides is discussed in the framework of a phase-plane approach. It is shown that qualitative aspects, such as integrals of motion in phase-plane, emerge from the analysis. Systematic consideration of these quantities narrows the range of possible solutions and provides a direct physical interpretation of them. Particularly suggestive, in this respect, are the interpretations of the appearance of higher order modes and of the energy/boundary conditions constraints typical of the nonlinear problem. Results for the TE and TM cases are presented. >

An inset dielectric guide (IDG) with a multilayer dielectric filling is studied, using the transverse resonance diffraction, technique. The convergence and numeric efficiency of the analysis are good, and comparisons with experimental measurements of phase constant show the validity of the data produced. Those aspects of the IDG structure that limit its monomode bandwidth when it is filled with a single dielectric are investigated. It is shown how the monomode bandwidth of such an IDG may be made greater than that of rectangular metal waveguide by appropriate choice of aspect ratio. It is also shown how the simple use of two dielectric layers in the IDG slot can yield a guide whose monomode bandwidth is 66%, which is much greater than the typical operating bandwidth of a standard double ridge waveguide (40%). In the maximum bandwidth configuration, variation in the position of the boundary between the dielectrics produces little change in bandwidth. Hence, it appears that multilayer IDG is an attractive transmission media for wideband applications at both microwave and millimeter-wave frequencies. >

Modified matched spatial filters capable of recognition and discrimination are described. Synthesis of these filters in the frequency rather than the space domain is considered. Synthesis of a deconvolution and a binary frequency filter are discussed, and initial results are presented.

This work analyzes a new simulation approach to the evaluation of the time-domain electromagnetic (EM) field by reducing the number of equations to solve. Scalar Helmholtz-equations are utilized in order to determine the electric and magnetic Hertzian-potentials that yield the EM field. The method is applied to the example of optical waveguide arrays by considering the field-perturbation effect due to high dielectric contrast and dielectric discontinuities. The rigorous Hertzian potentials formulation is extended to bi-dimensional structures.

The modeling of a GTEM cell which consists of a tapered rectangular waveguide loaded with an eccentric sloping plate conductor is discussed. The fields of the cross section of the uniform structure are derived by transverse resonance diffraction. The local modes approach is applied to the study of the longitudinal field distribution. Results show the structure to be actually overmoded rather than quasi-TEM. Numerical results agree with those in the literature, where available. The treatment is highly accurate and requires no more computer power than that of a desktop computer. >

We present a novel optical sensor able to mea- sure the distance between the tip of an endoscopic probe and the anatomical object under examination. In medical endoscopy, knowledge of the real distance from the endo- scope to the anatomical wall provides the actual dimen- sions and areas of the anatomical objects. Currently, en- doscopic examination is limited to a direct and qualitative observation of anatomical cavities. The major obstacle to quantitative imaging is the inability to calibrate the ac- quired images because of the magnification system. How- ever, the possibility of monitoring the actual size of ana- tomical objects is a powerful tool both in research and in clinical investigation. To solve this problem in a satisfac- tory way we study and realize an absolute distance sensor based on fiber optic low-coherence interferometry FOLCI. Until now the sensor has been tested on pig tra- chea, simulating the real humidity and temperature 37°C conditions. It showed high sensitivity, providing correct and repeatable distance measurements on biologi- cal samples even in case of very low reflected power down to 2t o 3n W, with an error lower than 0.1 mm. © 2008 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2870138

Thanks to the low-coherence interferometry it is possible to characterize the transmission of highly dense multimode polymeric waveguides for the O-PCB. In particular the attenuation and the multi-modal dispersion are directly deduced by interferometry patterns.

We present the experimental evidence of the interplay between the variation of the linewidth and effective mass of electrons in image potential states on a Cu(1 1 1) surface induced by a selective alteration of the hot-electron gas density generated by ultra-short laser pulse excitations. (C) 2008 Elsevier B.V. All rights reserved.

Guided, hybrid propagation in a slotline at microwave and millimeter-wave frequencies is discussed. The analysis is carried out rigorously in the space domain, involving the variational solution of a singular integral equation for an E, field tangential to the slot. Data are obtained for field distributions, dispersion, and characteristic impedance, and are compared with data available in the literature. Results are reported on power lost by the propagation mode in the conductors and in the dielectric substrate. The analysis highlights the onset of leakage into a sufficiently thick substrate due to the excitation of a TM (transverse magnetic) surface wave. This sets a high-frequency limit for lossless operation. >

The inset dielectric guide (IDG) is an alternative to the image line, retaining most if its advantages without its main disadvantages. In particular, IDG makes it possible to realize low-cost leaky wave antennas with very pure polarization properties by laying thin metal strips (dipoles) on the air-dielectric interface. The scattering properties of thin metal strips are analyzed by means of a Ritz-Galerkin variational approach, taking into proper account the edge singularities. A variational expression for the equivalent circuit of the radiating dipole is derived, and this information is applied to the design of a tapered linear array by network methods. The array was built and tested, and it showed excellent performance. >

We study the use of individual multimode fibers for the purposes of microendoscopy. We discuss the question of image decomposition in the several modes propagating over the fiber and their scattering at the truncated fiber end. We derive analytically the scattering matrix of the "fiber-to-air" interface, we quantify the extent of intermodal coupling, and we evaluate the radiation diagram from the fiber end. Results show that intermodal coupling is weak, so that it appears possible to "capture" an external image and transmit the same through the fiber, after appropriate phase correction, without excessive distortion.