Showing papers in "Journal of Optics in 2002"
TL;DR: In this article, the laser diode self-mixing (or feedback) interferometric technique is reviewed as a general tool for remote sensing applications and the operating principle is outlined, and the attainable performance is compared to conventional coherent detection.
Abstract: The laser diode self-mixing (or feedback) interferometric technique is reviewed as a general tool for remote sensing applications. The operating principle is outlined, and the attainable performance is compared to conventional coherent detection. Applications to metrology and to new sensing schemes are described, experimental results are reported and the overall performance of the sensors are assessed.
554 citations
TL;DR: In this article, the authors used a Puffin model UTC 341 high resolution monochrome Pasecon tube video camera, fitted with a f/4 macro lens and integral low heat LED illumination, to measure floc size, settling velocity and density simultaneously.
Abstract: Morphodynamical predictive simulations of estuarine sediments require in situ mud floc data for model verification and calibration purposes. The limiting factor in many previous studies were the devices used for sampling, as flocs are very fragile. Instruments such as Niskin bottles, pipettes or the Owen tube are all very disruptive. This could be the reason that previous studies tended to show a much lower floc size range than is now known to exist. The presence of large estuarine macroflocs was observed by in situ photography and in situ laser particle size measurements, but these techniques still provided no indication of settling velocity or effective density, which are variable amongst floc populations. In contrast, the video camera based instrument developed at the University of Plymouth, INSSEV (in situ settling velocity), measures floc size, settling velocity and density all simultaneously. This operates whereby flocs are trapped in an upper decelerator chamber and then allowed to fall into a settling column located underneath. A Puffin model UTC 341 high resolution monochrome Pasecon tube video camera, fitted with a f/4 macro lens and integral low heat LED illumination, views the flocs through a window in the side of the settling column, and hence the floc characteristics can be obtained. The camera utilizes a back-illumination system (i.e. a silhouetting technique) in which particles appear dark on a light background; this reduces image smearing and makes the floc structure more clearly visible. A selection of INSSEV flocs are presented from deployments conducted in the upper Tamar Estuary during 1998. Low concentration neap tides revealed that optimum ambient flocculation conditions produced macroflocs approaching 0.75 mm in length and settling velocities of 4–5 mm s−1. These macroflocs typically resembled 'comets' or 'long stringers'. However, these stringer configuration macroflocs were in the minority and on average only represented 30–40% of the total suspended matter concentration. Throughout the more turbulent and higher concentration spring tides, INSSEV was found to be very effective at measuring floc characteristics, even within concentrated benthic suspension layers of 8 g l−1. Ideal flocculation conditions (in terms of floc size) transformed 95% of the ambient suspended particulate matter concentration present into large, fast settling, more rounded cluster-type macroflocs with settling velocities of 8–15 mm s−1 and effective densities under 50 kg m−3. A number of the smaller macroflocs had their settling characteristics significantly improved by becoming interlinked with organic matter to form stringers with a string-of-pearls configuration. Although stringers were seen to occur during both neap and spring tides, the former ambient conditions tended to produce stringers which were only a third of the size of those typically observed at springs, and thus the neap tide stringers had comparatively lower settling velocities.
102 citations
TL;DR: In this paper, the evolution of the electromagnetic field intensity provides a physical understanding of the behavior of dispersion curves and of lifetime discontinuities in Wood-Rayleigh anomalies in particular.
Abstract: In transmission metallic gratings, quasi-total transmission of light is achieved by two different mechanisms, which are the excitation of horizontal and vertical surface-plasmon resonances. Both resonances are represented on complex photonic band structures for a wide range of grating thicknesses. The evolution of the electromagnetic field intensity provides a physical understanding of the behaviour of dispersion curves and of lifetime discontinuities in Wood–Rayleigh anomalies in particular. Both radiative and non-radiative processes are distinguished in the resonances' width, giving limits for the use of metallic gratings in photonic devices.
94 citations
TL;DR: In this article, the complex refractive index of a planar slab from normal-incidence intensity reflectance and transmittance was derived. But the analysis was restricted to planar planar slabs.
Abstract: Analytical expressions are derived that allow one to calculate the complex refractive index of a planar slab from normal-incidence intensity reflectance and transmittance.
90 citations
TL;DR: The variational principle is employed to study chirped solitons that propagate through optical fibres and is governed by the dispersion-managed nonlinear Schrodinger's equation as discussed by the authors.
Abstract: The variational principle is employed to study chirped solitons that propagate through optical fibres and is governed by the dispersion-managed nonlinear Schrodinger's equation. In this paper, we have considered both kinds of fibres, namely polarization preserving and birefringent types. The study is extended to obtain the adiabatic evolution of the parameters of such solitons in the presence of perturbation terms for both types of fibres.
87 citations
TL;DR: In this article, the authors studied the propagation of light pulses through scattering media using the time-dependent radiative transfer equation in the space-frequency domain and showed that the diffusive regime is attained at long times only for thick slabs.
Abstract: We study the propagation of light pulses through scattering media using the time-dependent radiative transfer equation. A standard discrete-ordinate method is used to solve this equation in the space-frequency domain. We present calculations of diffuse transmission through scattering slabs, in the presence of absorption and anisotropic scattering. We show that the diffusive regime is attained at long times only for thick slabs. Comparisons with diffusion theory show that the proper choice of the diffusion constant is an important issue for time-dependent transport.
84 citations
TL;DR: In this paper, the optical forces due to the radiation of a thermal source were studied using the Lifshitz model and two contributions were found: a repulsive "wind" component and a dispersive "surface wave" component.
Abstract: We study the optical forces due to the radiation of a thermal source. Our model consists of a particle modelled by a dipole above a half-space at temperature T. The fluctuating fields are computed using the Lifshitz model. We find two contributions to the force: a repulsive 'wind' component and a dispersive force mainly due to the contribution of thermally excited surface waves. It is found that for SiC material, the latter is repulsive in the very near field. The usual van der Waals force is larger by a factor of approximately ten for submicron size particles.
80 citations
TL;DR: Improved Zernike moments are presented, with theory and experiments that show that the improved ZERNike moments not only have better rotation invariance, but also have scale invariance.
Abstract: Zernike moments have many desirable properties, such as rotation invariance, robustness to noise, expression efficiency, fast computation and multi-level representation for describing the shapes of patterns, but there is a major drawback with Zernike moments: they need to normalize an image to achieve scale invariance. This introduces some errors since it involves the re-sampling and re-quantifying of digital images, and leads to inaccuracy of classifier. In this paper, we present improved Zernike moments, with theory and experiments that show that the improved Zernike moments not only have better rotation invariance, but also have scale invariance. Invariance of the improved Zernike moments shows great improvement over previous methods.
68 citations
TL;DR: In this article, the theoretically gain recovery dynamics in a semiconductor optical amplifier (SOA) when a short saturating pulse (pump) is either co-propagative or counter-probative with the probe are investigated.
Abstract: We study theoretically gain recovery dynamics in a semiconductor optical amplifier (SOA) when a short saturating pulse (pump) is either co-propagative or counter-propagative with the probe. An explanation of the gain overshoot in the temporal dynamics of the SOA gain is given. Analyses of high input probe power and injected current effects are included.
66 citations
TL;DR: In this article, a model based on coupled mode theory was proposed to predict the peak positions and isolations of long-period fiber gratings, in the range 30-1200 °C.
Abstract: Long-period fibre gratings are written in non-hydrogenated standard single-mode fibres, using electric discharge. We have obtained a transmitted spectrum with low insertion loss (<0.2 dB) and resonance peak isolation of -24 dB at 1545 nm. The model, based on coupled mode theory, predicts reasonably well the peak positions and isolations. We have performed very high temperature characterizations of the realized gratings, in the range 30-1200 °C. We have shown a specific spectral shift of the resonance peaks with temperature. We report a modal dependence of wavelength shift with temperature. Temperature annealing of the gratings, at 200, 400 and 600 °C show high thermal stability compared with CO2 and UV-induced ones, but annealing at 800 and 900 °C exhibit an irreversible spectral shift. The temperature sensitivity values are in good agreement with recently published works. These characterizations will help us to understand the writing mechanism of the grating by an electric discharge in standard single-mode fibres.
66 citations
TL;DR: In this article, an off-line fiber optic sensor based on evanescent field absorption in a test solution formed by the reaction of nitrite compounds in water with suitable chemical reagents is described.
Abstract: A fibre optic technique for detecting trace amounts of nitrite compounds in water is described. The off-line fibre optic sensor outlined here is based on evanescent field absorption in a test solution formed by the reaction of nitrite compounds in water with suitable chemical reagents. A short unclad portion of a plastic clad silica fibre acts as the sensing region. The experimental results clearly establish the usefulness of the present technique for detecting very low concentrations of the order of 1 ppb (parts per billion) of nitrite compounds with a large dynamic range of 1–1000 ppb. Such a high sensitivity enables the present device to be used for measuring the nitrite content in drinking water.
TL;DR: In this paper, a quantitative study of the fabrication process of two-dimensional plastic microlens arrays fabricated using deep lithography with protons is presented, which involves the proton irradiation of a PMMA (poly(methyl methacrylate)) sample in regions with a circular footprint followed by a diffusion of MMA vapour into the bombarded zones to cause a lens-shaped volume expansion.
Abstract: We present a quantitative study of the fabrication process of two-dimensional plastic microlens arrays fabricated using deep lithography with protons. Our process involves the proton irradiation of a PMMA (poly(methyl methacrylate)) sample in regions with a circular footprint followed by a diffusion of MMA vapour into the bombarded zones to cause a lens-shaped volume expansion. In the first part of this paper we give a detailed description of our fabrication technique and of the calibration procedure that goes with it. We demonstrate the flexibility of our approach with the fabrication of different types of array: highly uniform microlens arrays and arrays of microlenses with varying sags (maximum height of the spherical lenscap) and pitches. All lenses under test feature diameters of 200 ± 2µm, root-mean-square (RMS) roughnesses on the top of the lenses of λ/30 @ 632 nm and lens sags ranging from 10 to 70 µm. We also present the optical performances and the aberrations of the microlenses, measured using a dedicated transmission Mach–Zehnder interferometer. The focal lengths of the lenses under study range from 166 to 1444 µm, corresponding to a range of sags between 9.77 and 69.73 µm and to focal numbers between 0.83 and 7.22. Typical values for the RMS and peak-to-valley aberrations of 0.209λ and 1.057λ respectively were observed. To conclude, we analyse and discuss the strengths and weaknesses of this fabrication method.
TL;DR: In this article, the Fourier modal method was extended to the case of lamellar gratings that are periodic in two directions, and numerical evidence that improved convergence rates can be obtained for dielectric and metallic gratings.
Abstract: We extend our original parametric formulation of the Fourier modal method to the case of lamellar gratings that are periodic in two directions. We provide numerical evidence that improved convergence rates can be obtained for dielectric and metallic gratings.
TL;DR: In this article, the transfer matrix method is modified for study of optical wave propagation in layered media with conducting interfaces, and the TE and TM mode transfer matrices are derived and their properties are discussed.
Abstract: In this paper, the transfer matrix method is modified for study of optical wave propagation in layered media with conducting interfaces. Both the TE and TM mode transfer matrices are derived and their properties are discussed. As examples, the reflection and transmission coefficients of a single conducting interface and the dispersion equation of a Kr¨ onig–Penney photonic crystal are obtained, all being in agreement with previous results. Also, the coupling coefficients of two slab waveguides with conducting interfaces are found for TE and TM polarizations.
TL;DR: In this article, the main and unique properties of blazed-binary diffractive elements are reviewed and the consequences for monochromatic imaging systems are considered for the resonance domain.
Abstract: Blazed diffractive elements are currently fabricated with continuous profiles or with staircase approximations. Blazed-binary gratings are more recent diffractive elements which implement continuous phase delays through a gradient-index artificial material with subwavelength binary etches. The performance of these diffractive elements in the resonance domain opens up new perspectives for manufacturing fast lenses. The objective of this paper is to review the main and unique properties of blazed-binary diffractive elements and to consider the consequences for monochromatic imaging systems.
TL;DR: In this article, the application of optical holography to the recording of plankton in both captive (tank) and natural (open-water) environments is reviewed and an overview of the development of the technique from the first work of Katz, performed in 1966, to the latest deployment of the new HOLOCAM camera in October 2001.
Abstract: We review the application of optical holography to the recording of plankton in both captive (tank) and natural (open-water) environments. Holography offers a unique ability to record the true three-dimensional spatial coordinates of both zooplankton and phytoplankton with high optical resolution in large volumes of water. Recent developments in the technology now enable volumes approaching one hundred litres to be recorded using the off-axis technique at a resolution of a hundred micrometres and smaller volumes of a few litres to be recorded using the in-line technique at a resolution of 10 μm or better. We discuss the principles of holographic recording and replay, and the special factors that must be considered when the objects are recorded in water but their images are replayed in air. Finally, we present an overview of the development of the technique from the first work of Katz, performed in 1966, to the latest deployment of the new HOLOCAM camera in October 2001, and speculate on future trends in the deployment of holographic cameras.
TL;DR: In this paper, a simple paraxial geometrical optical matrix theory is extended to the simulation of off-axis optical elements and differential ray tracing is used to model incoherent micro-optical systems.
Abstract: The simulation of micro-optical systems, especially those including microlens arrays, is still a challenging task. There are of course traditional methods which can be applied under certain circumstances. This paper will discuss several geometrical optical and diffraction-based methods for the simulation of micro-optical systems. A simple paraxial geometrical optical matrix theory will be extended to the simulation of off-axis optical elements. Ray tracing will be used to model incoherent micro-optical systems. The propagation of Gaussian beams through off-axis optical systems using differential ray tracing will be discussed. The angular spectrum of plane waves will be used to propagate a scalar complex wave amplitude in free space simulating non-paraxial diffraction effects. Finally, a model will be proposed which combines ray tracing and wave propagation methods by converting a complex wave amplitude into rays and vice versa. In the case of wavefront warping a decomposition of the wave into elementary waves has to be performed. This combined model can take into account non-paraxial effects such as aberrations of optical elements and also diffraction effects.
TL;DR: In this article, the Talbot effect with a Ronchi grating is applied to measurement of shift, and it is shown that by using a measurement procedure based on the Fourier transform, a cosine grating can be replaced by a Ronchis grating.
Abstract: In this study the Talbot effect with a Ronchi grating is applied to measurement of shift. It is shown that by using a measurement procedure based on the Fourier transform a cosine grating can be replaced by a Ronchi grating. Two different methods for data reduction and some experimental results are given.
TL;DR: In this paper, Raman peak shifting and broadening were observed and analysed in polymethyl methacrylate (PMMA) core polymer optical fibres in the 200-6800 cm−1 range using an Ar+ ion laser.
Abstract: Raman spectra from polymethyl methacrylate (PMMA) core polymer optical fibres (POFs) in the 200–6800 cm−1 range were investigated using an Ar+ ion laser Raman peak shifting and Raman spectra broadening were observed and analysed in the POFs Polarized laser-induced birefringence in an azobenzene-doped PMMA fibre material was investigated We found both a fast response mode and a slow response mode in the rise and decay process of the laser-induced birefringence It is demonstrated that the characteristics of polarized laser-induced birefringence were strongly dependent on the pump laser power
TL;DR: In this paper, Li's Fourier-modalgorithm is extended to cross gratings, which reduces the diffraction problem to the search for eigenvalues and eigenvectors of a particular matrix.
Abstract: The extraordinary optical transmission of a metallic film pierced by a two-dimensional subwavelength hole array, observed by Ebbesen et al, is explained using rigorous electromagnetic analysis and a phenomenological approach. The analysis is based on Li's Fourier-modal method extended to crossed gratings, which reduces the diffraction problem to the search for eigenvalues and eigenvectors of a particular matrix. The computation of the eigenvalues allows us to find a new channel for light transmission through the subwavelength holes, which differs from the transmission channel in the one-dimensional case (lamellar or rectangular-rod grating). It is demonstrated that the enhanced transmission is due to the excitation of a surface plasmon on the lower metallic surface.
Journal Article•
TL;DR: In this paper, the Talbot effect with a Ronchi grating is applied to measurement of shift, and it is shown that by using a measurement procedure based on the Fourier transform, a cosine grating can be replaced by a Ronchis grating.
Abstract: In this study the Talbot effect with a Ronchi grating is applied to measurement of shift. It is shown that by using a measurement procedure based on the Fourier transform a cosine grating can be replaced by a Ronchi grating. Two different methods for data reduction and some experimental results are given.
TL;DR: In this paper, optical components developed for a three-dimensional imaging system based on integral photography are described, including an image transfer screen 300 mm × 300 mm with 125 µm pitch lenses formed in photoresist and high quality replica arrays with a 100% fill factor and pitch value of 850 µm moulded from diamond-machined masters.
Abstract: This paper describes optical components developed for a three-dimensional imaging system based on integral photography. A variety of lens arrays with differing specifications were required and, by suitable choices and refinements to manufacturing techniques, lens arrays were developed specifically for various stages of the imaging system. Major achievements include an image transfer screen 300 mm × 300 mm with 125 µm pitch lenses formed in photoresist and high-quality replica arrays with a 100% fill factor and pitch value of 850 µm moulded from diamond-machined masters. Correction: In the previously published version of this paper, there were three occasions where the incorrect unit "nm" was printed instead of "mm". The first occurrence was in the abstract (which has been corrected above), and the other two were on page S19 where the text should read as "300 mm × 300 mm" and "150 mm × 150 mm". This error is reported separately as a Corrigendum in the next issue and the full text files attached below have been corrected.
TL;DR: The conception of a twofold modulation frequency laser range finder based on the phase-shift measurement method with two modulation frequencies, one giving the distance within a wide range and a second one leading to high resolution measurement, leading to a quite simple development and low cost system.
Abstract: The purpose of this paper is to present the conception of a twofold modulation frequency laser range finder. The system is based on the phase-shift measurement method with two modulation frequencies, one giving the distance within a wide range and a second one leading to high resolution measurement. The measurement method is based on intermediate frequency sampling associating the under-sampling technique with digital synchronous detection. Its main advantage is a global simplification of the electronic system, leading to a quite simple development and low cost system. There is only one phase-shift measurement stage but the twofold modulation frequency is possible thanks to the heterodyne technique. The emission and detection parts are designed for wideband operation and are digitally controlled. The whole system has been designed with only one digital phase locked loop reducing the phase noise and improving the resolution. Because of the global structure and the different digitally controlled parts the necessary calibration process could be introduced. From the design of the prototype it is possible to move towards a smart laser range finder.
TL;DR: In this paper, the authors present a review of the devices enabled by colloidal heterostructures, along with an envelope approximation used to efficiently study their properties, and provide a comparison between the envelope approximation and a tight-binding method used to study defects in photonic crystals.
Abstract: Photonic crystal heterostructures are concatenations of photonic crystals differing in refractive index or lattice geometry. They can be fabricated using self-assembly of colloidal spheres. In this paper we present a review of the devices enabled by such colloidal heterostructures, along with an envelope approximation used to efficiently study their properties. We show that the approximation is well suited for studying polymer photonic crystals. We also provide a comparison between the envelope approximation and a tight-binding method used to study defects in photonic crystals.
TL;DR: In this paper, a prototype imaging pulsed time-of-flight laser range finder is presented, which produces an image with 36 pixels, each containing distance and reflectivity information.
Abstract: Range-imaging devices are useful in various applications, both on the ground and in space. In this paper a prototype imaging pulsed time-of-flight laser range finder is presented. The range finder produces an image with 36 pixels, each containing distance and reflectivity information. The scannerless structure is robust and provides instantaneous snapshot-type imaging. An integrated video camera provides high-resolution grey-level images.
TL;DR: In this article, the effect of neglecting these reflections of the diffuse radiation is discussed and significant differences in the effective scattering and absorption coefficients, computed by inversion from diffuse reflectance spectra, are obtained when they are evaluated taking into account the reflection of the incident diffuse radiation at the front interface of the coating, in comparison with values obtained from the standard approach which neglects these reflections.
Abstract: Diffuse reflectance spectra of light scattering and absorbing coatings are considered in terms of the Kubelka–Munk theory Partial reflection of the incident diffuse radiation in the front interface of the coating, and internal reflection of backward diffuse radiation at this interface, are taken into account by means of an inversion method from which the effective scattering and absorption coefficients are obtained The effect of neglecting these reflections of the diffuse radiation is discussed Significant differences in the effective scattering and absorption coefficients, computed by inversion from diffuse reflectance spectra, are obtained when they are evaluated taking into account the reflection of the diffuse radiation at the front interface of the coating, in comparison with values obtained from the standard approach which neglects these reflections
Journal Article•
TL;DR: In this paper, an absolute distance interferometer for measurements in the range of several meters is presented, where a grating-stabilized tunable extended-cavity diode laser without AR coating and a stabilized helium-neon laser are used to generate a variable synthetic wavelength.
Abstract: In this paper an absolute distance interferometer for measurements in the range of several metres is presented. A grating-stabilized tunable extended-cavity diode laser without AR coating and a stabilized helium-neon laser are used to generate a variable synthetic wavelength. The phase distortion of analogue filters in the presence of non-linear laser tuning is discussed. A linearization of the laser frequency course and a suppression of sound-induced spectral line-broadening is achieved by electronic feedback from a homodyne fibre interferometer. The first experimental distance measuring results are shown.
TL;DR: A series of dinuclear ruthenium complexes with 1,2-dicarbonylhydrazido (DCH) ligands having various substituents were prepared in order to study the correlation between their optical, electrochemical behaviour and the electron density within the bridging ligands.
Abstract: A series of dinuclear ruthenium complexes with 1,2-dicarbonylhydrazido (DCH) ligands having various substituents were prepared in order to study the correlation between their optical, electrochemical behaviour and the electron density within the bridging ligands. As the average donor strength of the substituent increases, the oxidation potential shifts to a lower value and the metal-to-metal charge transfer (MMCT) band shifts to a higher energy. A strong MMCT absorption in the near-infrared region makes these compounds potentially useful for optical attenuation. The intrinsic attenuation property of these materials depends mainly on the concentration of ruthenium content in the complexes. The first dendritic DCH–Ru complex was prepared and showed a strong electrochromism at around 1550 nm and a fast switching speed of less than 2 s. A variable optical attenuator device based on the crosslinked ruthenium dendrimer is demonstrated with 18 000 switching cycles.
TL;DR: In this article, an absolute distance interferometer for measurements in the range of several meters is presented, where a grating-stabilized tunable extended-cavity diode laser without AR coating and a stabilized helium-neon laser are used to generate a variable synthetic wavelength.
Abstract: In this paper an absolute distance interferometer for measurements in the range of several metres is presented. A grating-stabilized tunable extended-cavity diode laser without AR coating and a stabilized helium–neon laser are used to generate a variable synthetic wavelength. The phase distortion of analogue filters in the presence of non-linear laser tuning is discussed. A linearization of the laser frequency course and a suppression of sound-induced spectral line-broadening is achieved by electronic feedback from a homodyne fibre interferometer. The first experimental distance measuring results are shown.
Journal Article•
TL;DR: The laser diode self-mixing (or feedback) interferometric technique is reviewed as a general tool for remote sensing applications and the attainable performance is compared to conventional coherent detection.
Abstract: The laser diode self-mixing (or feedback) interferometric technique is reviewed as a general tool for remote sensing applications. The operating principle is outlined, and the attainable performance is compared to conventional coherent detection. Applications to metrology and to new sensing schemes are described, experimental results are reported and the overall performance of the sensors are assessed.