Thirty years ago, Coullet et al. proposed that a special optical field exists in laser cavities bearing some analogy with the superfluid vortex. Since then, optical vortices have been widely studied, inspired by the hydrodynamics sharing similar mathematics. Akin to a fluid vortex with a central flow singularity, an optical vortex beam has a phase singularity with a certain topological charge, giving rise to a hollow intensity distribution. Such a beam with helical phase fronts and orbital angular momentum reveals a subtle connection between macroscopic physical optics and microscopic quantum optics. These amazing properties provide a new understanding of a wide range of optical and physical phenomena, including twisting photons, spin-orbital interactions, Bose-Einstein condensates, etc., while the associated technologies for manipulating optical vortices have become increasingly tunable and flexible. Hitherto, owing to these salient properties and optical manipulation technologies, tunable vortex beams have engendered tremendous advanced applications such as optical tweezers, high-order quantum entanglement, and nonlinear optics. This article reviews the recent progress in tunable vortex technologies along with their advanced applications.

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Optical vortices 30 years on: OAM manipulation from topological charge to multiple singularities

Optical Waveguide Theory

In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

The index of refraction n of the many mammalian tissues is an important but somewhat neglected optical constant. Archival and oral papers have quoted the use of values of n for tissue generally ranging from 1.35 to 1.55. However, these values are frequently without experimental basis. They have arbitrarily used values near that of water, which is a major component of mammalian tissue, or have calculated a theoretical n from the weighted elemental composition of tissue. Since these values have not been precise and little information is available on specific indices for each tissue, a study was undertaken to develop a simple, rapid, and reliable method for the experimental determination of n. This was done using the ubiquitous quartz optical fiber. By substituting the usual cladding found on commercial quartz optics by the tissue in question and utilizing the principle of internal reflection, the value of n for the specific tissue can be calculated. This is done by utilizing the known indices for air and quartz and measuring the angle of the emergent cone of light from the output of the optical fiber. A number of indices for mammalian tissue (bovine, porcine, canine, and human) have been determined at 632.8 nm. With few exceptions, for tissues at this wavelength, n was in the 1.38-1.41 range. The species type did not appear to be a factor. Bovine muscle showed normal dispersion characteristics through the visible wavelengths. The denaturation of tissue was shown to alter significantly the refractive index.

Refractive index of some mammalian tissues using a fiber optic cladding method.

Introduction, J.C. Spain Strategies for Aerobic Degradation of Nitroaromatic Compounds by Bacteria: Process Discovery to Field Application, S.F. Nishimo, J.C. Spain, and Z. He Molecular Biology of Nitroarene Degradation, R.E. Parales Perspectives of Bioelimination of Polynitroaromatic Compounds, H. Lenke, C. Achtnich, and H-J. Knackmuss Identification of Genes Involved in Picric Acid and 2,4-Dinitrophenol Degradation by mRNA Differential Display, R. Ross, D.M. Walters, H-J. Knackmuss, and P.E. Rouviere Microbial Degradation of Mononitrophenols and Mononitrobenzoates, G.J. Zylstra, S-W. Bang, L.M. Newman, and L.L. Perry The Role of Nitrate Ester Reductase Enzymes in the Biodegradation of Explosives, R.E. Williams and N.C. Bruce Anaerobic Transformation of TNT by Clostridium, F. Ahmad and J.B. Hughes Fungal Degradation of Explosives: TNT and Related Nitroaromatic Compounds, W. Fritsche, K. Scheibner, A. Herre, and M. Hofrichter Phytoremediation and Plant Metabolism of Explosives and Nitroaromatic Compounds, J.G. Burken, J.V. Shanks, and P.L. Thompson Biodegradation of RDX and HMX: From Basic Research to Field Application, J. Hawari Subsurface Chemistry of Nitroaromatic Compounds, S.B. Haderlein, T.B. Hofstetter, and R.P. Schwartzenbach Composting (Humification) of Nitroaromatic Compounds, D. Bruns-Nagel, K. Steinbach, D.Gemsa, and E. von Low Application and Costs for Biological Treatment of Explosive-Contaminated Soils in the United States, D.E. Jerger and P.M. Woodhull

Biodegradation of Nitroaromatic Compounds and Explosives

A new method for tracing rays through graded-index media is presented. The method essentially consists of transforming the ray equation into a convenient form and solving the resulting equation using a standard numerical technique. A detailed comparison of this method with existing methods has also been made, and it is shown that for obtaining a desired accuracy this method requires much less computational effort.

Tracing rays through graded-index media: a new method

The role of the mode field diameter in the characterization of single-mode fibers is examined. The most relevant definitions of this parameter are reviewed, and a comparative analysis of methods for its measurement is performed. All the discussed measurement methods have reached a repeatability and reproducibility which are quite satisfying. Emphasis is given to the requirements posed by the new fiber designs, such as the polarization-maintaining structures. Most of the discussed techniques have been industrialized, and a number of instruments based on them are commercially available; however, it is predicted that the evolution of fiber design will impose new requirements on some of these instruments. >

Mode field diameter measurements in single-mode optical fibers

In this paper, we present two approximations for the fundamental mode of graded-index fibres. The first is a one-parameter analysis which involves computational effort comparable to that involved in the Gaussian approximation and yet gives much better results. The second is a two-parameter analysis which gives much better results than other existing approximations for all values ofV for most graded-index fibres.

The fundamental mode of graded-index fibres: simple and accurate variational methods

A model for a step-index fiber in the form of an equivalent slab guiding structure is presented. This model simplifies the analysis of fiber directional couplers and coupler half-blocks with dielectric and metallic superstrates. Simple empirical formulas to obtain the model parameters are also given. The use of this model is illustrated with some numerical examples. >

Analysis of fiber directional couplers and coupler half-blocks using a new simple model for single-mode fibers

Fiber optic evanescent wave absorption sensors based on four different designs are described. The launching condition and the geometry of the sensing region are found to be the main parameters that can influence the sensitivity of the sensor. High sensitivity is achieved by launching the selected rays into the fiber having tapered sensing regions. The experimental results obtained are qualitatively explained using a simple model based on meridional rays.

Anurag Sharma

Papers

Tracing rays through graded-index media: a new method

Mode field diameter measurements in single-mode optical fibers

The fundamental mode of graded-index fibres: simple and accurate variational methods

Analysis of fiber directional couplers and coupler half-blocks using a new simple model for single-mode fibers

Fiber optic evanescent field absorption sensor: effect of launching condition and the geometry of the sensing region