David Le Coq

Infrared glass fibers for in-situ sensing, chemical and biochemical reactions

Infrared optical fibres based on chalcogenide glasses have been designed for evanescent wave spectroscopy. The sensitivity of the optical sensor is improved in tapering the sensing zone by chemical etching and the working optical domain of the system has been tested on a chloroform sample. This original remote sensor, based on the analysis of infrared signatures, has been applied to follow the fermentation process in cider fabrication as well as to detect and monitor a bacterial biofilm.

Infrared chalcogen glasses: chemical polishing and fibre remote spectroscopy

Inorganic vitreous polymers based on the combination of the chalcogen elements Se, Te and As are investigated on account of their unique transparency in the infrared spectral domain leading to applications in night-vision systems as well as in IR remote fibre spectroscopy. An original procedure of chemical polishing using a congruent dissolution process of the glass is developed in order to produce outstanding optical quality surfaces. The same methodology is applied to produce tapered chalcogen glass fibres used as IR evanescent wave chemical sensors. In reducing the fibre diameter by chemical etching, a significant improvement in the sensitivity of the optical sensor operating in the 2 to 12 μm spectral region is observed. This original optical configuration is applied to some in situ chemical or biological analysis.

Direct laser writing of buried waveguide in As2S3 glass using a helical sample translation

We report the fabrication and the characterization of buried waveguide in As(2)S(3) glass. It is well known that the interaction of femtosecond pulses with this material at high laser repetition rates results in a mainly negative refractive index variation, due to heat accumulation effect. However, we show here that a helical translation of the sample parallel to the laser beam, allows the inscription of a core of positive refractive variation, with full control over its magnitude and diameter. An example demonstrating the high symmetry of the guided mode is given.

A new approach of preform fabrication for chalcogenide fibers

Abstract A new approach is investigated for the fabrication of double index chalcogenide glass fibers. The preform is obtained by an original technique based on ‘build-in casting’ inside a sealed silica container. The two glasses, chosen in the Te–As–Se system, are prepared separately by purification, melting and homogenization of the raw elements under vacuum. The core/clad structure is obtained by using a core composition, which is enriched with tellurium. A strict control of the fabrication parameters allows one to obtain well-defined core/clad diameter ratios. The preform is drawn at 270 °C and coated on line by a protective polymer.

Direct laser writing of a low-loss waveguide with independent control over the transverse dimension and the refractive index contrast between the core and the cladding

In this Letter, we present the realization of a low-loss waveguide in a chalcogenide glass by direct laser writing technique in a particular configuration that allows the independent control over the diameter of the core and the magnitude of the refractive index contrast with the cladding. The waveguide is of multicore type and composed of 19 channels arranged on a hexagonal lattice. Each channel is obtained by stacking voxels of refractive index variation obtained by static exposure to femtosecond laser pulse burst. The distance between the channels can be used to vary the diameter of the waveguide, while the duration of laser burst controls the magnitude of the effective index and the propagation loss. We demonstrate that it can be reduced down to 0.11 dB/cm.

New strategy for direct laser writing of low loss waveguide

Two geometries are usually considered for direct laser writing of waveguide in glass that differ mainly from the way the sample is translated in regard to the laser beam propagation direction, namely transversely or longitudinally. In this contribution we report on waveguide of multi-core type composed of positive refractive index channel aligned on a hexagonal lattice and written using an alternative method. Every channel is obtained by stacking voxels of refractive index variation obtained by femtosecond laser pulse burst in a static position. The dimension of the core is determined by the number of channels and its refractive index contrast with the cladding is controlled by the laser burst duration. Therefore all the characteristics of the waveguide can be fully and independently accessed through simple experimental parameters. We apply this technique to waveguide writing in chalcogenide glass and show that the propagation loss can be reduced down to 0.11 dB/cm. Moreover repeated measurements during 18 month of this loss demonstrate the temporal stability of this value.