The merging of silicon microfabrication techniques with surface functionalization biochemistry offers new exciting opportunities in developing microscopic biomedical analysis devices with unique characteristics. Micro-mechanical transducers for chemical and biosensing applications represent one possibility. Microcantilevers can transduce a chemical signal into a mechanical motion with high sensitivity. In this review we summarize how cantilever-based sensors can be operated, and their working principle is presented in few selected biosensing experiments which have been performed recently in our groups in the study of biotin–streptavidin and antigen–antibody interactions, and specific surface charge development of organic molecules. We also discuss the advantages of this novel technique as well as its potentials.

Micromechanical cantilever-based biosensors

We present the light-propagation characteristics of OmniGuide fibers, which guide light by concentric multi-layer dielectric mirrors having the property of omnidirectional reflection. We show how the lowest-loss TE01 mode can propagate in a single-mode fashion through even large-core fibers, with other modes eliminated asymptotically by their higher losses and poor coupling, analogous to hollow metallic microwave waveguides. Dispersion, radiation leakage, material absorption, nonlinearities, bending, acircularity, and interface roughness are considered with the help of leaky modes and perturbation theory, and both numerical results and general scaling relations are presented. We show that cladding properties such as absorption and nonlinearity are suppressed by many orders of magnitude due to the strong confinement in a hollow core, and other imperfections are tolerable, promising that the properties of silica fibers may be surpassed even when nominally poor materials are employed.

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Low-loss asymptotically single-mode propagation in large-core OmniGuide fibers.

Many novel materials and device designs have been proposed as photonic analogs to electrical diodes over the last four decades. This paper seeks to revisit these materials and designs as advanced technologies may enable experimental realization that was not possible upon conception of several of these designs. The background behind integration challenges, including waveguide birefringence, fabrication tolerances, garnet/semiconductor mismatch, and optimized interfaces will hopefully spark new ideas that will finally enable the realization of integrated optical isolators and circulators.

Integrated Magneto-Optical Materials and Isolators: A Review

Plasmonics provides a possible route to overcome both the speed limitations of electronics and the critical dimensions of photonics. We present an all-plasmonic 116–gigabits per second electro-optical modulator in which all the elements—the vertical grating couplers, splitters, polarization rotators, and active section with phase shifters—are included in a single metal layer. The device can be realized on any smooth substrate surface and operates with low energy consumption. Our results show that plasmonics is indeed a viable path to an ultracompact, highest-speed, and low-cost technology that might find many applications in a wide range of fields of sensing and communications because it is compatible with and can be placed on a wide variety of materials.

High-speed plasmonic modulator in a single metal layer

Silica-based photonic crystal fibre has proven highly successful for supercontinuum generation, with smooth and flat spectral power densities. However, fused silica glass suffers from strong material absorption in the mid-infrared (>2,500 nm), as well as ultraviolet-related optical damage (solarization), which limits performance and lifetime in the ultraviolet (<380 nm). Supercontinuum generation in silica photonic crystal fibre is therefore only possible between these limits. A number of alternative glasses have been used to extend the mid-infrared performance, including chalcogenides, fluorides and heavy-metal oxides, but none has extended the ultraviolet performance. Here, we describe the successful fabrication (using the stack-and-draw technique) of a ZBLAN photonic crystal fibre with a high air-filling fraction, a small solid core, nanoscale features and near-perfect structure. We also report its use in the generation of ultrabroadband, long-term stable, supercontinua spanning more than three octaves in the spectral range 200–2,500 nm. A low-loss ZBLAN micro-structured fibre is used to generate a supercontinuum spanning from the UV to the mid-IR (200 nm–2,500 nm). The material has high resistance even after extended operation and can withstand large spectral power densities.

Deep-ultraviolet to mid-infrared supercontinuum generated in solid-core ZBLAN photonic crystal fibre

A passive polarization converter free of longitudinally-periodic structure

A new numerical method for analyzing birefringence and dispersion characteristics of birefringent optical fibers is presented. A major advantage of the method, based on the solution of full‐vectorial Maxwell equations, is its high accuracy no matter how great the geometrical anisotropy of the optical fiber. To verify the reliability of our numerical procedure, the modal birefringence and the form‐induced polarization mode dispersion in elliptical core fibers with different eccentricities are investigated and their values compared with some theoretical and experimental results.

Theoretical analysis of birefringence and form‐induced polarization mode dispersion in birefringent optical fibers: A full‐vectorial approach

A full-vectorial integral expression is derived to compute the effective mode area of any Kerr-type nonlinear-optical waveguide working in a self-phase-modulation regime. In order to highlight the correction brought by the vectorial approach in a strong guidance situation, we compare the effective area of a tapered fiber computed by the usual scalar expression with the one obtained with the full-vectorial approach.

Nonlinear self-phase-modulation effects: a vectorial first-order perturbation approach.

Nonlinear propagation constants and related nonlinearity coefficients of the fundamental modes of tapered fibers and step-index elliptical-core fibers are determined by the use of a new numerical approach for solving vectorial Maxwell’s equations, assuming a Kerr-type nonlinearity. A numerical method based on a finite-element scheme and the iteration procedure are reported. Nonlinear modal parameters computed from solutions of the scalar Helmholtz equation and vectorial Maxwell’s equations are compared with those obtained by the use of scalar and vectorial first-order perturbation methods. For both devices, the limitation of the scalar approach is clearly demonstrated. For tapered nonlinear fibers, the validity of the full-vectorial first-order perturbation method for some ranges of the input power is established. Physical interpretation of the results and their potential applications are given.

Nonlinear modal parameters of optical fibers: a full-vectorial approach

Recently, there has been increased interest in the analysis of passive polarization converters made with longitudinally-periodic structures owing their great polarization conversion efficiency. Three kinds of passive polarization converters made with periodic structures are presently reported in the literature: asymmetric loading section converters, tilted waveguiding section converters and asymmetric angled facet section converters. The most promising version so far is the angled facet converter recently proposed by van der To1 et al [ 1,2]. This polarization converter contains a series of N waveguide sections with right-asymmetric (RAS) and left-asymmetric (LAS) cross-sections with angled facets. Simplified structure of RAS and LAS cross-sections with angled facet are shown in Fig. 1. For any converters made of longitudinally-periodic structures, the main factors limiting the performance of the devices are the losses which occur at the junction between the neighboring sections and the difficulty of fabricating the multi-section devices. In this paper, using a vectorial finite-element propagation method to model angled facet converters, it is shown that polarization rotation effects in such devices can be maximized with an appropriate choice of the facet angle a and the base rib width w. Optimization of structure design achieves a device free of longitudinally-periodic structure with a very short converting length and low losses.

Velko P. Tzolov

Papers

A passive polarization converter free of longitudinally-periodic structure

Theoretical analysis of birefringence and form‐induced polarization mode dispersion in birefringent optical fibers: A full‐vectorial approach

Nonlinear self-phase-modulation effects: a vectorial first-order perturbation approach.

Nonlinear modal parameters of optical fibers: a full-vectorial approach

Modeling of a Passive Polarization Converter Free of Longitudinally-Periodic Structure