Isabelle Verrier

High resolution group refractive index measurement by broadband supercontinuum interferometry and wavelet-transform analysis

In this paper we propose group refractive index measurement with a spectral interferometric set-up using a broadband supercontinuum generated in an air-silica Microstructured Optical Fibre (MOF) pumped with a picosecond pulsed microchip laser. This source authorizes high fringes visibility for dispersion measurements by Spectroscopic Analysis of White Light Interferograms (SAWLI). Phase calculation is assumed by a wavelet transform procedure combined with a curve fit of the recorded channelled spectrum intensity. This approach provides high resolution and absolute group refractive index measurements along one line of the sample by recording a single 2D spectral interferogram without mechanical scanning.

Broadband supercontinuum interferometer for high-resolution profilometry

In this paper, it is shown that a white light supercontinuum source generated in an air-silica microstructured optical fiber pumped with picosecond pulses offers the possibility to improve fringes visibility in interferometric acquisitions. Consequently, this source combined with a spectral interferometer, reaches high-resolution profilometric measurements. Phase calculation based on seven point algorithm can perform theoretically a subnanometer resolution. This method provides a one line profile of large surfaces from the analysis of a single shot image, without any mechanical scanning.

Linear and nonlinear optical fibre devices

The authors give the fundamental concepts of all-fibre devices and the basic technology that has been developed to realise those concepts. In addition, they present a review of the state of the art in the design and performance of linear and nonlinear optical all-fibre devices with particular emphasis on recent progress in such devices in he field of lightwave technology including optical fibre communications, optical fibre sensing and optical signal processing.

Imaging through a scattering medium with an interferential spectrometer by selection of an amplitude modulation correlator

Low-coherence interferometric systems provide three-dimensional imaging through scattering media by measurement of the objects temporal response. An optical correlator is presented that allows direct recording of the signal issued from the object under reflection. The filtering technique enhances the image visibility and allows one to obtain an image with a good signal-to-noise ratio. The performance of two particular imaging systems, point-to-point and vertical-slice imaging, is discussed with an object comprising two cover plates that are attached.

Imaging with polarized light : the vectorial modulation transfer function of a polarizing plate

A vectorial modulation transfer function or spatial frequency response of optical imaging systems including linearly polarizing components is defined, calculated and compared to experimental results and to the classical scalar paraxial theory. This exact linear polarizer modulation transfer function calculus could be of particular interest in new ellipsometric measurement methods accuracy, especially for high resolution metrology and polarization imaging analysis.

Efficient ball lens coupling between a single-mode optical fiber and a silica microguide at 1.3 μm

An efficient coupling between a single-mode optical fiber and a silica guide by a ball lens is demonstrated. We investigate this coupling scheme by a theoretical analysis and by the experiment. The contribution of all the loss factors is evaluated. The tolerances of the fiber positionment are studied and then, this coupling solution is compared to the current butt-coupling.

Measurements of Mode Propagation Time in Multimode Fibers using a Real Time Interferometric Amplitude Correlator

The method we propose consists in a modified version of the one presented above, because the amplitude correlator is different and has the avantage of directly displaying in real time the correlation function. This amplitude correlator has already been used for autocorrelation measurement with short laser pulses and is modified here to achieve cross-correlation with cw wide bandwidth laser light.

Low-loss plasmon-triggered switching between reflected free-space diffraction orders

Surface plasmon coupling of a TM polarized free space incident beam by means of the + 1st or the -2nd order of a smooth corrugation grating at a metal surface causes the cancellation of the diffracted -1st order free space beam and a maximum of the 0th order Fresnel reflection whereas the converse occurs midway between these two conditions. This implies that angular tilting of the element or wavelength scanning provokes the switching between the -1st and 0th reflected orders. This plasmon-mediated effect on propagating free-space beams exhibits remarkably low absorption losses.

Measurement of mode times of flight in multimode fibers by an interferometric method using polychromatic light: theoretical approach and experimental results

The propagation of several modes in an optical fiber is not easy to study. The experiment that we propose permits us to measure the difference in time propagation between two successive modes of a multimode fiber. The same laser beam is coupled into the fiber to be tested and into the reference single-mode fiber. The correlation of output electric fields of the modes propagated by each fiber is realized by an interferometric system.

Temporal analysis of optical complex structures: application to tomography through scattering media

Optical Coherent Tomography (OCT) technique is based on an interferometric device bringing to the inter-correlation between a short reference pulse and the signal issued from the medium. This correlation is obtained by mechanical length modulation of the interferometer reference arm. We propose here an original technique using the SISAM (“Spectroscope Interferentiel a Selection par l’Amplitude de la Modulation”: Interferential Spectrometer by Selection of Amplitude Modulation) correlator, which allows to obtain directly without length modulation, the inter-correlation signal between the reference and the tests waves. With a large spectral bandwidth light source, the temporal depth of the original pulse is short compared to the signal diffused in the complex medium, and the inter-correlation function may be reduced to the impulse response of the structure to be studied. This temporal analysis could be very interesting to obtain both amplitude and phase parameters on the waves propagated in the medium, and could induce significant data on the medium and its structure. We will present the experimental SISAM device and results obtained in imaging through turbid media with this technique. We will also discuss about efficiency of this method in terms of accuracy and of ability to characterize complex structures and media.