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At least 919 records · Page 51Linked to original sources
PubMed2006

Optical characterization of an unknown single layer: Institut Fresnel contribution to the Optical Interference Coatings 2004 Topical Meeting Measurement Problem.

We present the characterizations performed at the Institut Fresnel for the Measurement Problem of the Optical Interference Coatings 2004 Topical Meeting. A single layer coated on a fused-silica substrate of unknown composition and parameters is analyzed in terms of optogeometrical parameters, uniformity, and scattering. We determine the refractive index and the average thickness of the coating, then provide the localized determination of the thickness with a 2 mm spatial resolution. Topography measurements include atomic force microscopy and angle-resolved scattering measurements. These results are completed thanks to a Taylor Hobson noncontact 3D surface profiler.

Journal Article↗
PubMed2003

Measurement of modal dispersion in optical fiber by means of acousto-optic coupling.

We show that frequency-wavelength tuning characteristics of acousto-optic coupling can be used for measuring the difference of effective index, group index, and chromatic dispersion between core and cladding modes in single-mode fibers. Chromatic dispersion measurements of a 30-cm-long conventional single-mode fiber, a nonzero dispersion-shifted fiber, and a dispersion-compensating fiber with this new method are presented for the wavelength range 1500-1600 nm. Qualitative agreement with independently measured data is obtained.

Journal Article↗
PubMed2003

Distribution measurement of Raman-gain and optical-loss characteristics in optical fibers.

We propose a test method with which to measure the longitudinal distribution of Raman-gain characteristics in connected optical fibers. We describe a technique for obtaining the pump-loss distribution, knowledge of which is necessary for deriving the Raman-gain efficiency distribution, by the bidirectional measurement of Raman amplification. Based on this technique, we performed experiments and demonstrated that the Raman-gain efficiency distribution can be evaluated with the same equipment.

Journal Article↗
PubMed2005

Two-loop-based low-coherence multiplexing fiber-optic sensor network with a Michelson optical path demodulator.

A two-loop-based low-coherence multiplexing fiber-optic sensor network is proposed and demonstrated. It greatly extends the multiplexing capacity of this kind of sensor. A practical implementation of this scheme uses a popular amplified spontaneous emission light source and standard single-mode fiber, which are commonly used in the communications industry. The sensor's two-loop topology is completely passive. Absolute length measurements can be obtained for each sensing fiber segment for use in measuring the quasi-distribution strain or temperature. For large-scale smart structures this technique not only extends the multiplexing potential but also provides a redundancy for the sensing system. This means that the two-loop sensor network can break down at several points and the sensing system will still work even if some of the embedded two-loop sensors have been destroyed. The robustness of the nine-sensor two-loop sensing network is investigated and discussed.

Journal Article↗
PubMed2006

Active optical compensation of low-quality optical system aberrations.

We describe a method for the correction of slowly varying wavefront aberrations of low-quality telescope mirrors by using a DM in an active optical compensation system. Our goal is to reduce the surface wavefront error of low-cost multimeter-diameter mirrors from approximately 10 waves peak-to-valley (P-V), at a 1 microm wavelength, to approximately 1 wave or less. In a proof-of-concept demonstration using a 0.3m telescope at a wavelength of 633 nm, the rms wavefront error improved to 0.05 waves (0.26 waves P-V) from the original value of 1.4 waves rms (6.5 waves P-V). The Strehl ratio improved to 89% from the original value of 0.08%. The types of aberrations corrected include astigmatism, coma, defocus, trefoil, and higher-order aberrations.

Journal Article↗
PubMed2006

High-speed fiber-optic spectrometer for signal demodulation of inteferometric fiber-optic sensors.

We demonstrated a spectrometer that is capable of acquiring the spectra from interferometric fiber-optic sensors at high speed. The high spectrum acquisition rate is enabled by transforming the spectral information from frequency domain to time domain using a dispersive element and high-speed data acquisition devices. Preliminary results show that the prototype system can record 10,000 frames of spectra per second and achieve a spectrum measurement resolution of 15 nm. Better performance could be realized by using a Raman amplifier and by optimizing the parameters of the system and data processing methods.

Journal Article↗
PubMed1991

[Multisubstance analysis. Detection of changes in the optical density in individual layers of the optic fundus].

A promising method for noninvasive objective diagnosis and monitoring of the course of a therapy is spectrometric investigation of the human ocular fundus. Application of this method in clinical practice depends on the development of suitable procedures for deconvolution of the measured spectra. The availability of microcomputers permits the performance of complicated calculations directly at the measuring device. Based on the two-photon flux theory, the influence of absorption and scattering in anatomically determined layers of the fundus will be considered. For this reason, an iterative principle for radiation transport into the fundus is introduced, allowing derivation of a physical model for calculation of the spectral course of the reflected light. In the multisubstance analysis a measured spectrum is approximated by the model function. During this analysis the optical densities of photosensitive and nonphotosensitive pigments and the reflection at intermediate layers can be calculated. As an example of multisubstance analysis, the deconvolution of foveal reflection spectra of normals and type I diabetics is demonstrated. This method makes it possible to show that early diabetic alternations occur in the choroid.

Adolescent↗
PubMed1990

Polarization-optical investigation (topo-optical analysis) of the structure of the human erythrocyte glycocalyx. Influence of pH, ionic strength and diamide-induced spectrin cross linking.

The value of membrane anisotropy after fixation and topo-optical analysis of erythrocytes stained with toluidine blue is a measure for the degree of spatial order of the dyestuff-binding acidic residues of the glycocalyx and thus a parameter for the characterization of the glycocalyx structure. Lowering the pH value and/or the ionic strength of the staining medium results in a decrease of membrane anisotropy indicating a lower order of the anionic residues. In agreement with the findings of other authors this phenomenon seems to be connected with an expansion of the glycocalyx. Diamide-induced oxidative crosslinking of spectrin before fixation and staining with toluidine blue at physiological pH and ionic strength also results in a decreased anisotropy. This indirect influence on the glycocalyx structure may be caused by an increase of the charge density within the glycocalyx due to a diamide-induced rearrangement of the membrane skeleton and of the transmembrane proteins bound to it.

Diamide↗
PubMed1985

Aiding the vision in albinism--optical and non-optical means considered.

Not 'Low Vision Aids' alone, but the full range of methods of helping sight in these visually handicapped persons--a much wider range than is generally realised--and which includes many non-optical manoeuvres and various 'gadgets' available to all forms of defective vision, as well as the newer electronic aids is described. The difficulty for the ophthalmologist in knowing how best to help patients with albinism should be resolved by 'customer research'; this paper attempts to do so by analysis of a questionnaire to members of the Albino Fellowship.

Adolescent↗