Showing papers in "Pure and Applied Optics: Journal of The European Optical Society Part A in 1995"
TL;DR: In this paper, an analytic expression for the reflection coefficient for a multi-layer antireflecting stack, with elements of arbitrary thickness and oblique illumination, is given, and an approximate method for calculating the reflection coefficients of stratified media is discussed.
Abstract: An approximate method for calculating the reflection coefficient of stratified media is discussed. An analytic expression is given for the reflection coefficient for a multi-layer antireflecting stack, with elements of arbitrary thickness and oblique illumination.
102 citations
TL;DR: In this paper, a white-light channelled spectrum interferometer for absolute distance measurement in the range of 8 mu m to 1.9 mm, using a diffractive element and a linear detector array to scan the interference signal.
Abstract: We describe a white-light channelled spectrum interferometer for absolute distance measurement in the range of 8 mu m to 1.9 mm, using a diffractive element and a linear detector array to scan the interference signal. The local phase of the spectral fringe pattern is obtained from synchronized sampling with four samples per fringe period. The absolute distance is calculated from the slope of the measured phases against wavelength. First, the distance is determined to better than lambda /8 in order to overcome the phase ambiguity. Then, one of the measured local phases can be used to determine the exact distance with interferometric accuracy. Test results showed an accuracy of better than 2 nm for a distance of 125 mu m and better than 12 nm for any position within 50 mu m to 150 mu m.
100 citations
TL;DR: In this article, two and multiple-beam interference fringes are used to measure the refractive index of graded index fibres and a general expression considering the refraction of the beam by the graded index fibre has been derived, from which expressions for homogeneous and skin core fibres can be obtained.
Abstract: Two- and multiple-beam interference fringes are used to measure the refractive index of graded index fibres. A general expression considering the refraction of the beam by the graded index fibre has been derived, from which expressions for homogeneous and skin-core fibres can be obtained. Comparison between the results with the method used when neglecting refraction is dealt with using Philips, LDF (TM) optical fibres and drawn polypropylene. Considering the derived expressions in the refractive index determination gives a correction even when a matching liquid is used, this suggests that the refraction method should be used especially for graded index fibre.
64 citations
TL;DR: In this article, a new approach is proposed for analysis of scattering by a periodically corrugated dielectric layer with non-identical faces, which combines the simultaneous use of several different coordinate systems and the generalized S-matrix formalism.
Abstract: A new approach is proposed for analysis of scattering by a periodically corrugated dielectric layer with non-identical faces. The method combines the simultaneous use of several different coordinate systems and the generalized S-matrix formalism. The program has been tested by comparisons with results given by the integral method.
40 citations
TL;DR: In this paper, the authors compare three phase retrieval methods for applications in optical diffraction tomography (ODT) using realistic computer simulations, which include noise and lens aberrations, and show that the PSI method determines the phase accurately.
Abstract: We compare three different phase retrieval methods for applications in optical diffraction tomography (ODT). The first method is based on Gabor holography and is limited by the 'twin-image' problem. The second is an iterative approach for which the uniqueness of the retrieved phase is questionable. In the third method the phase is measured by phase shifting interferometry (PSI), but this technique is more demanding experimentally. Using realistic computer simulations, which include noise and lens aberrations, we show that the PSI method determines the phase accurately. The iterative method gives equally accurate results in most cases. But in some cases this method produces a false phase. This problem is demonstrated using both simulated and experimental intensity data. The images reconstructed from the false phases are found to be severely distorted. We also show that the uniqueness problem can be avoided by increasing the distance between the scattering object and the measurement line.
40 citations
TL;DR: An efficient and reliable method is presented for computing the eigenfunctions associated with scattering by elliptical cylinders based on reformulating the computational task as an eigenvalue problem.
Abstract: An efficient and reliable method is presented for computing the eigenfunctions associated with scattering by elliptical cylinders. While the classical method is based on recurrence relations and infinite continued fractions, the new method is based on reformulating the computational task as an eigenvalue problem. In contrast with the classical method, the new method requires no initial estimates of the eigenvalues, and the computations can be performed using readily available computer library routines.
36 citations
TL;DR: In this article, the authors studied the forces exerted by a Gaussian laser beam on a small dielectric sphere in water as a function of beam-off centring, i.e. the distance between the beam axis and the sphere center.
Abstract: For pt. I see ibid., vol. 2, p.261, (1993). We study the forces exerted by a Gaussian laser beam on a small dielectric sphere in water as a function of beam-off centring, i.e. the distance between the beam axis and the sphere centre. Our experimental data are from the first part work of Angelova and Pouligny who studied the levitation of polystyrene latex spheres, a few micrometres in radius, by a couple of vertical laser beams in water. We also report on newly acquired results, particularly the observation of sustained oscillations of the levitated sphere in water. These data are analysed from the viewpoint of radiation pressure forces, which we calculate using the generalized Lorenz-Mie theory (GLMT). We find that calculated equilibria fit those experimentally recorded with beams of unequal intensities. Experiments with equally intense beams lead to instabilities in the levitated particle position. This is also well explained by GLMT, but the instability threshold is found to be very sensitive to uncontrolled water convection around the particle.
34 citations
TL;DR: In this article, two definitions and three measurement schemes for polarization mode dispersion are presented and a connection with the dynamical equation for the principal polarization states is made, and first results from the COST 241 interlaboratory measurement campaign are also presented.
Abstract: Two definitions and three measurement schemes for polarization mode dispersion are presented. Their relations, advantages and drawbacks are discussed. A connection with the dynamical equation for the principal polarization states is made. First results from the COST 241 interlaboratory measurement campaign are also presented.
31 citations
TL;DR: In this article, the Chandezon formalism is extended to accommodate three-dimensional modulation profiles, and the basic feature lies in the use of a coordinate system that maps the interface onto a plane.
Abstract: The author extends the rigorous Chandezon formalism (1982) to accommodate three-dimensional modulation profiles. The basic feature lies in the use of a coordinate system that maps the interface onto a plane. As in the two-dimensional case, one is led to a linear system of differential equations whose solution is obtained through the calculation of the eigenvalues and eigenvectors of a matrix dependent on the geometry and on the index of the medium. Results are compared with those obtained by the methods of others.
25 citations
TL;DR: In this article, a digital control system for length-varying fiber drawing from standard preforms has been developed, which allows fibres with the necessary length dependence of the chromatic dispersion to be fabricated.
Abstract: The technology for length-varying fibre drawing from standard preforms has been worked out It allows fibres with the necessary length dependence of the chromatic dispersion to be fabricated Fibres with varying dispersion can have a lot of applications in soliton propagation control Such fibres allow one to realize both the regime of effective amplification and the effective compression of optical solitons This technology is based on a digital control system and can be used in the conditions of a standard drawing installation
23 citations
TL;DR: In this paper, an analysis of the electrical response (so called "optoelectronic signal") to a passing optical signal is given, where the optoelectronic response changes sign at an inversion threshold.
Abstract: Laser amplifiers based on semiconductor diodes are discussed with respect to their multifunctional possibilities including signal and power amplification, switching, phaseshift, photodetection and non-linear properties. The analysis is given of the electrical response (so called 'optoelectronic signal') to a passing optical signal. Experimental data are obtained on photoresponse, inversion threshold and phaseshift measurements in InGaAsP/InP SOA diodes. The optoelectronic response changes sign at an inversion threshold ('transparency current') thus the latter can easily be measured in lasers and amplifiers. This allows electrical diagnostics of the operation mode. An amplifier-photoreceiver may be a suitable device for optoelectronics.
TL;DR: In this paper, the analysis of a non-linear directional coupler consisting of two planar waveguides separated by a nematic liquid crystal is presented, which is caused by an opticallyinduced reorientational effect occurring in homeotropic or planar oriented nematic layers and is enhanced by an external electric field.
Abstract: The analysis of a non-linear directional coupler consisting of two planar waveguides separated by a nematic liquid crystal is presented. The non-linear effect is caused by an optically-induced reorientational effect occurring in homeotropic or planar oriented nematic layers and is enhanced by a DC external electric field. Both fields cause changes in the effective refractive index of the nematic layer due to the optical non-linearity and due to the direct action of the additional electric field. It is shown that the non-linear optical effect has a threshold of the nature of the optical Fredericks transition and the effect is discussed in classical geometries corresponding to splay, twist and bend deformations of a nematic liquid crystal. The results obtained are applied to analyse the action of a non-linear directional coupler in comparison to non-linear couplers with the Kerr-type non-linearity previously investigated.
TL;DR: In this article, exact solutions for two-dimensional scattering of an arbitrary, scalar or electromagnetic wave by perfectly reflecting elliptical cylinders, strips and slits are derived, and explicit expressions are given for the exact solutions due to a line source.
Abstract: Exact solutions are derived for two-dimensional scattering of an arbitrary, scalar or electromagnetic wave by perfectly reflecting elliptical cylinders, strips and slits. First exact solutions are presented for scattering of a plane wave normally incident on the cylinder axis, and then corresponding solutions are derived for an arbitrary incident wave. While the exact solutions for a plane incident wave are expressed in terms of angular Mathieu functions, the corresponding solutions for an arbitrary incident wave are expressed in terms of integrated angular Mathieu functions. Therefore, an efficient and reliable method for computing the integrated angular Mathieu functions is presented. As an example, explicit expressions are given for the exact solutions due to a line source.
TL;DR: In this paper, a non-contacting optical profilometer is presented based on the principle of focus multiplexing by wavelength encoding due to a phase Fresnel lens, and decoding is performed by lateral dispersion.
Abstract: A non-contacting optical profilometer is presented based on the principle of focus multiplexing by wavelength encoding due to a phase Fresnel lens. The decoding is performed by lateral dispersion. The surface profile is reconstructed after automatic point by point scanning with submicrometre height resolution.
TL;DR: In this paper, an inhomogeneous thin film model where the real part of the refractive index has a parabolic profile through the film thickness is supposed and a procedure for the unequivocal determination of the model parameters from normal incidence spectro-photometric measurements of T(lambda), R( lambda) and R'(lambda) is outlined.
Abstract: The characterization of inhomogeneous thin film has been a widely studied topic. In the present work an inhomogeneous film model where the real part of the refractive index has a parabolic profile through the film thickness is supposed and a procedure for the unequivocal determination of the model parameters from normal incidence spectro-photometric measurements of T(lambda), R(lambda) and R'(lambda) is outlined. The parabolic model can be useful in the initial stage of investigation on a film material, which is suspected of being inhomogenous, as the model parameters, the gradient and curvature of the n parabolic profile, provide a quantitative evaluation of the film inhomogeneity even when the parabolic model is not realistic.
ENEA1
TL;DR: In this paper, a model with a parabolic k-profile was proposed to evaluate the inhomogeneity of the complex refractive index n-ik throughout the thickness of a thin optical film.
Abstract: The evaluation of the inhomogeneity of the complex refractive index n-ik throughout the thickness of a thin optical film is an important topic. In a previous work, regarding the n inhomogeneity, we found that the assumption of a model with a parabolic n profile throughout the film thickness allows us to characterize inhomogeneous films and to evaluate the n inhomogeneity even when the parabolic model is not realistic. Here the author completes the work by introducing a film model which also has a parabolic k profile and by describing a procedure for the unequivocal determination of the complex parabolic model parameters from normal incidence spectrophotometric measurements of T( lambda ), R( lambda ) and R'( lambda ).
TL;DR: The exact solutions to the complex Ginzburg-Landau equation should not be searched for by perturbing some linear equation as discussed by the authors, and there exist methods to deal in one go with the full nonlinear equation.
Abstract: The exact solutions to the complex Ginzburg-Landau equation should not be searched for by perturbing some linear equation. Indeed, there exist methods to deal in one go with the full nonlinear equation. These are easier to implement than the perturbative methods and they rely only on the deepest feature of the equation, namely the structure of its singularities.
TL;DR: In this article, micro-echography was used to characterize crosslinking gradients in photopolymers, because this technique can produce acoustic images of amplitude variations of local mechanical properties.
Abstract: Microechography was used to characterize crosslinking gradients in photopolymers, because this technique can produce acoustic images of amplitude variations of local mechanical properties. A frequency of 25 MHz was chosen due to the high absorption of the investigated material at high frequencies. Two sets of samples were studied. The former, which had been polymerized through a test mask and displayed sharp gradients, were used to check the sensitivity of the technique; the latter were insulated through a chromium apodizing filter with a radial density variation and allowed the resolution of the apparatus to be determined. Results obtained on the exposed sample surfaces and on cross sections showed that this technique is well suited to the study of crosslinking gradients in, photopolymers despite the resolution loss resulting from the use of low frequencies. The method is exemplified by the study of mask pattern transfer into a polymer.
TL;DR: In this article, it was demonstrated that reflection gratings with any type of chirp can be written into photosensitive fibres using holographic phase masks. But the length dependence of induced chirps was designed to be linear or quadratic in wavelength.
Abstract: It is demonstrated that reflection gratings with any type of chirp may be written into photosensitive fibres using holographic phase masks. Chirped bandwidths of 5-15 nm have been achieved in 8 mm long gratings with reflectivities up to 98%. The length dependence of the induced chirp was designed to be linear or quadratic in wavelength. Reasonable agreement is shown with theoretical calculations. These gratings have also been used for the first time to re-compress 400 fs pulses broadened to approximately 30 ps after transmission through an optical fibre at 1560 nm. Nearly complete re-compression is observed with a compression ratio of approximately 65.
TL;DR: In this paper, the vibrational and anharmonic parameters of the methylthio (CH3S) radical in a supersonic jet environment were determined by a least-squares fit of the progressions involving the symmetric nu3 vibration in the A 2A1 - X 2E3/2 excitation spectra and involving both the nu2 and nu3 progressions in the dispersed fluorescence spectra.
Abstract: Laser-induced fluorescence excitation and wavelength-resolved emission spectra have been recorded for the methylthio (CH3S) radical in a supersonic jet environment. Twenty one vibronic bands have been obtained in excitation in the 360-387 nm region with about 0.2 cm-1 resolution and assigned to the A 2A1 - X 2E3/2 and A 2A1 - X 2E1/2 electronic transitions. Fluorescence from five vibronic bands (000, 301, 302, 312 and 201310) has been individually dispersed by a 0.6 m monochromator with a resolution of 0.3 nm. To the best of our knowledge, the wavelength-resolved emission spectra of CH3S for the 312 and 201310 bands are being reported here for the first time and these provide new vibrational intervals hitherto unobserved. Fundamental vibrational frequencies have been determined for the nu2 (umbrella) and nu3 (C-S stretch) modes of CH3S for both the excited A 2A1 state and the ground X 2E state: nu'2=1096 cm-1, nu'3=402 cm-1, nu2=1328 cm-1 and nu3=742 cm-1. In addition, the nu6 (rocking) mode vibrational frequency has been obtained for the A 2A1 state, i.e. nu'6=628 cm-1. Vibrational and anharmonic parameters have been determined by a least-squares fit of the progressions involving the symmetric nu3 vibration in the A 2A1 - X 2E3/2 excitation spectra and involving both the nu2 and nu3 progressions in the dispersed fluorescence spectra.
TL;DR: In this article, the authors proposed an amplifier based on Pr doped fluoride fibres for the 1.3µm window of the optical fiber network, which is the second transmission window of silica at 1.5 µm.
Abstract: Silica optical fibre technology for communication networks has grown rapidly in the last 15 years, and its development has made possible broadband telecommunications. The bandwidth of silica-based passive optical network (PON) is many orders of magnitude larger than that of copper coaxial cables (~20 MHz over 3-5 km). As a result, optical fibres have revolutionised telephone networks. Current figures suggest that approximately 80% of British telephone traffic is carried by optical fibres. By the year 2015, the entire Japanese telephone network will be optical fibre-based, enabling it to carry data and video via telephone cables into every home. A large component of the world-wide optical fibre system constitute the terrestrial networks which utilise the second transmission window of silica at 1.3µm. At this wavelength, no optical amplifier is as yet commercially available, necessitating the use of electronic repeaters. By contrast, for the lowest-loss window at 1.5µm, efficient high gain Er doped optical amplifiers have been developed and are widely available. Compared with optical amplifiers, electronic repeaters are more expensive, slower and less flexible in operation. The major motivation for the current project is the need for an efficient optical fibre amplifier operating in the 1.3µm window. The purpose of the project is to design and develop such amplifier based on Pr doped fluoride fibres.
TL;DR: In this article, the authors present the preliminary results about the paraxial design of graded-index (GRIN) bifocal spectacle lenses fabricated by a local ion exchange technique in glass.
Abstract: We present the preliminary results about the paraxial design of graded-index (GRIN) bifocal spectacle lenses fabricated by a local ion-exchange technique in glass. Paraxial formulae for the optical power are calculated for two refractive index profiles modelling the GRIN region, Erfc and Gaussian, which correspond to a linear and nonlinear ion-exchange regime, respectively.
TL;DR: In this article, the model of oscillating dipoles that explains the existence of the Brewster angle in isotropic media can be extended to transparent birefringent crystals if we take into account the electric polarization (crystal with dielectric anisotropy) or the magnetization (Crystal with magnetic anisotropic).
Abstract: In this work, we show that the model of oscillating dipoles that explains the existence of the Brewster angle in isotropic media can be extended to transparent birefringent crystals if we take into account the electric polarization (crystal with dielectric anisotropy) or the magnetization (crystal with magnetic anisotropy). This extension is applicable to biaxial and uniaxial crystals when the incidence plane is a principal plane.
TL;DR: In this paper, the Anderson variational method was used to study Gaussian beam propagation in planar GRIN waveguides with non-linear refractive index, and analytical expressions for oscillations of both the beam waist and the center of the beam were derived.
Abstract: Gaussian beam propagation in planar GRIN waveguides with non-linear refractive index has been studied by means of the well known Anderson variational method, improved with a more general trial function. Analytical expressions for oscillations of both the beam waist and the centre of the beam have been derived. The solutions obtained yield a very simple picture of the behaviour of Gaussian light beams in this kind of media and are in excellent agreement with the numerical calculations presented.
TL;DR: In this article, the Fourier transform is used to calculate the radiance due to an isotropic point source in an infinite, homogeneous, anisotropic scattering medium.
Abstract: We present a method to calculate the radiance due to an isotropic point source in an infinite, homogeneous, anisotropically scattering medium. The method is an extension of a well known method for the case of isotropic scattering. Its basic mathematical ingredient is the Fourier transform. Its great advantage is that it also works very close to the source and not just far away from it, as is the case with most other methods. In principle, the method works for any phase function that can be expanded in a finite number of Legendre polynomials. Here, the simple example of linear anisotropic scattering is worked out numerically and the result is compared with Monte Carlo simulation. Good agreement is found between the two.
TL;DR: In this article, high energy ion implantation on ion-exchanged glass is explored as a new suitable method to obtain waveguiding structures that contain small silver clusters, and optical and compositional measurements on these systems are presented.
Abstract: High energy ion implantation on ion-exchanged glass is explored as a new suitable method to obtain waveguiding structures that contain small silver clusters. Optical and compositional measurements on these systems are presented.
TL;DR: A method of shearing interferometry for evaluating the basic statistical quantities of randomly flat and randomly rough curved surfaces of solids is presented in this paper, which can be used for characterizing the randomly rough surfaces of both transparent and opaque solids.
Abstract: A method of shearing interferometry for evaluating the basic statistical quantities of randomly flat and randomly rough curved surfaces of solids is presented. Using this method the root-mean-square (RMS) values of heights and slopes, the values of autocorrelation lengths, autocorrelation coefficients and one-dimensional height distribution functions of surface irregularities of these surfaces can be determined. The method can be utilized for characterizing the randomly rough surfaces of both transparent and opaque solids. The results of the statistical analysis obtained by this method for chosen samples of randomly rough surfaces agree very well with those achieved by means of a stylus-type surface instrument.
TL;DR: In this article, some phenothiazine derivative dyes and triphenylmethane dyes doped into water-swollen gelatin matrices were studied with respect to their ability of hologram formation with a low power conventional HeNe laser source.
Abstract: Some phenothiazine derivative dyes and triphenylmethane dyes doped into water-swollen gelatin matrices were studied with respect to their ability of thick hologram formation with a low power conventional HeNe laser source. The highest light diffraction efficiencies measured in a self-diffraction experiment were obtained for the well known methylene blue dye but also for other dyes related to it: Giemsa and May-Grunwald stains. For the first time to our knowledge hologram formation abilities were found for crystal violet and brilliant blue dyes in water-swollen gelatin.
TL;DR: In this article, the authors present reasoning as to why optical solitons are most suitable in fiber-based transmission systems emphasizing integrability and controllability of the soliton.
Abstract: Optical solitons are now considered to be the most promising choice as the information carrier of the next generation ultra-high speed and long distance transmission system. The talk presents reasoning as to why optical solitons are most suitable in fibre based transmission systems emphasizing two intrinsic properties of solitons, integrability and controllability.
TL;DR: In this paper, an analytical method to recover the high light level probability density function (PDF) P( Omega ) of a random field from the knowledge of its PDF p(n) in photon-counting mode is described.
Abstract: We describe an analytical method to recover the high light level probability density function (PDF) P( Omega ) of a random field from the knowledge of its PDF p(n) in photon-counting mode. The inversion of the Poisson transform that relates the two PDFs is performed as follows: the characteristic function (CF) Phi ( omega ), Fourier transform P( Omega ) is first approximated using a Taylor-type series whose coefficients are the p(n); Pade approximants are then used to gain convergence in the high values of omega where the Taylor series diverges. A procedure making use of the application of constraints and consistency with the data is developed to select the most appropriate Pade approximant to the CF. A few illustrations of the inversion procedure are presented with application to astronomical speckle interferometry. Simulated numerical results have given very good results even for a very low number of photons per pixel and a reduced statistical average.