Erna Frins

Bio: Erna Frins is an academic researcher from University of the Republic. The author has contributed to research in topic(s): Interferometry & Polarization (waves). The author has an hindex of 15, co-authored 79 publication(s) receiving 573 citation(s). Previous affiliations of Erna Frins include Deutsche Telekom & Goethe University Frankfurt.

Single-element interferometer

Abstract: A very simple and stable interferometer using a single optical element – a beam-splitter cube – is presented. The device resembles a two-arm interferometer in which the arms are together in one collimated beam, and the two beam halves interfere with the help of the beam-splitter cube. The proposed device produces simultaneously two interferograms with a relative phase-shift of π (rad). Since the period of straight interference fringes can be stably controlled, the device has potential application in spatial-carrier interferometry and for flexible writing of fiber Bragg gratings.

Rotation of the polarization plane in optical fibers

Abstract: The rotation of the polarization plane of a light wave traveling in an optical fiber that lies on a space curve based on parallel transport is described. An estimation of the effect due to winding the fiber is presented.

Tomographic multiaxis-differential optical absorption spectroscopy observations of Sun-illuminated targets: a technique providing well-defined absorption paths in the boundary layer.

Abstract: A novel experimental procedure to measure the near-surface distribution of atmospheric trace gases by using passive multiaxis differential absorption optical spectroscopy (MAX-DOAS) is proposed. The procedure consists of pointing the receiving telescope of the spectrometer to nonreflecting surfaces or to bright targets placed at known distances from the measuring device, which are illuminated by sunlight. We show that the partial trace gas absorptions between the top of the atmosphere and the target can be easily removed from the measured total absorption. Thus it is possible to derive the average concentration of trace gases such as NO2, HCHO, SO2, H2O, Glyoxal, BrO, and others along the line of sight between the instrument and the target similar to the well-known long-path DOAS observations (but with much less expense). If tomographic arrangements are used, even two- or three-dimensional trace gas distributions can be retrieved. The basic assumptions of the proposed method are confirmed by test measurements taken across the city of Heidelberg.

Precision synchronous polarimeter with linear response for the measurement of small rotation angles.

Abstract: A synchronous polarimeter was set up for the measurement of small rotation angles of the polarization plane of light. The polarimeter is based on a polarizer–Faraday modulator–analyzer structure with a synchronous detection scheme, which produces a linear system response. The theoretical background is studied, and the system performance is investigated experimentally. We achieved an accuracy of the order of 10-4 deg, or 5 mg/dl of glucose in a 1-cm light path.

A new scheme for phase-shifting ESPI using polarized light

Abstract: A new scheme for achieving electronic speckle pattern interferometry (ESPI) is presented, in which two polarizing cube beam splitters placed together are used to achieve the superposition of orthogonal polarized light waves coming from the reference and the test object, respectively. Polarization phase stepping occurs by changing the so-called Pancharatnam's phase by means of the rotation of a polarizer situated in front of a digital camera. Experiments were carried out to show the feasibility of the system. A compact system that uses a micropolarizer camera for achieving instantaneous ESPI is also proposed.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Abstract: A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Spin-to-orbital conversion of the angular momentum of light and its classical and quantum applications

Abstract: A few years ago the possibility of coupling and inter-converting the spin and orbital angular momentum (SAM and OAM) of paraxial light beams in inhomogeneous anisotropic media was demonstrated. An important case is provided by waveplates having a singular transverse pattern of the birefringent optical axis, with a topological singularity of charge q at the plate center, hence named 'q-plates'. The introduction of q-plates has given rise in recent years to a number of new results and to significant progress in the field of orbital angular momentum of light. Particularly promising are the quantum photonic applications, because the polarization control of OAM allows the transfer of quantum information from the SAM qubit space to an OAM subspace of a photon and vice versa. In this paper, we review the development of the q-plate idea and some of the most significant results that have originated from it, and we will briefly touch on many other related findings concerning the interaction of the SAM and OAM of light.

Measuring Stokes parameters by means of a polarization grating.

Abstract: Ordinary gratings act on the amplitude and (or) the phase of a wave front. Polarization gratings produce instead a periodic modulation of the state of polarization. A simple grating of the latter type is constituted by a linear polarizer whose orientation varies periodically along a line. It is shown that, for a generic polarization state of the incident field, such a grating gives rise to first-order diffracted beams with counterrotating circular polarizations. It is also shown that such a grating can be used for measuring the Stokes parameters of a light beam in an achromatic manner. Several extensions are briefly discussed.

Electromagnetic mode conversion in photonic crystal multimode waveguides

Abstract: A method for converting electromagnetic (EM) energy between guided modes of a photonic crystal waveguide (800) having a waveguide axis (810), the method including: (i) providing the photonic crystal waveguide (800) with a mode coupling segment (820) comprising at least one bend (830) in the waveguide axis (810), wherein during operation the mode coupling segment (820) converts EM energy in a first guided mode to a second guided mode; (ii) providing EM energy in the first guided mode of the photonic crystal waveguide (800); and (iii) allowing the EM energy in the first guided mode to encounter the mode coupling segment to convert at least some of the EM energy in the first guided mode to EM energy in the second guided mode.