Laurent Calvez

Low loss microstructured chalcogenide fibers for large non linear effects at 1995 nm

Microstructured optical fibers (MOFs) are traditionally prepared using the stack and draw technique. In order to avoid the interfaces problems observed in chalcogenide glasses, we have developed a new casting method to prepare the chalcogenide preform. This method allows to reach optical losses around 0.4 dB/m at 1.55 µm and less than 0.05 dB/m in the mid IR. Various As(38)Se(62) chalcogenide microstructured fibers have been prepared in order to combine large non linear index of these glasses with the mode control offered by MOF structures. Small core fibers have been drawn to enhance the non linearities. In one of these, three Stokes order have been generated by Raman scattering in a suspended core MOF pumped at 1995 nm.

Structural Investigations of Glass Ceramics in the Ga2S3―GeS2―CsCl System

Transparent glass ceramics have been prepared in the Ga(2)S(3)-GeS(2)-CsCl pseudoternary system using appropriate heat treatment time and temperature. In situ X-ray diffraction at the heat treatment temperature and (133)Cs and (71)Ga solid-state nuclear magnetic resonance have been performed in function of annealing time to understand the crystallization process. Both techniques have evidenced the nucleating agent role played by gallium with the formation of Ga(2)S(3) nanocrystals. On the other hand, cesium is incorporated very much later into the crystallites during the ceramization. Moreover, the addition of CsCl, which is readily integrated into the glassy network, permits us to shift the optical band gap toward shorter wavelength. Thus, new glass ceramics transmitting in the whole visible range up to 11.5 mum have been successfully synthesized from the (Ga(2)S(3))(35)-(GeS(2))(25)-CsCl(40) base glass composition.

An innovative approach to develop highly performant chalcogenide glasses and glass-ceramics transparent in the infrared range

An innovative way to produce chalcogenide glasses and glass-ceramics for infrared devices is reported. This new method of synthesis at low temperature combining ball-milling and sintering by SPS (Spark Plasma Sintering) is a technological breakthrough to produce efficient infrared chalcogenide glasses and glass-ceramics. This technique will offer the possibility to strongly decrease the cost of infrared devices and to produce new chalcogenide glasses. It will also permit to increase the potential of some glass compositions by allowing their shaping at desired dimensions.

Large-mode-area infrared guiding in ultrafast laser written waveguides in Sulfur-based chalcogenide glasses

Current demands in astrophotonics impose advancing optical functions in infrared domains within embedded refractive index designs. We demonstrate concepts for large-mode-area guiding in ultrafast laser photowritten waveguides in bulk Sulfur-based chalcogenide glasses. If positive index contrasts are weak in As2S3, Ge doping increases the matrix rigidity and allows for high contrast (10(-3)) positive refractive index changes. Guiding with variable mode diameter and large-mode-area light transport is demonstrated up to 10 μm spectral domain using transverse slit-shaped and evanescently-coupled multicore traces.

Second-order optical nonlinearity and ionic conductivity of nanocrystalline GeS2–Ga2S3–LiI glass-ceramics with improved thermo-mechanical properties

IR-transparent chalcogenide glass-ceramics were fabricated through a careful ceramization process of the as-prepared 65 GeS(2) x 25 Ga(2)S(3) x 10 LiI glasses at a temperature of 403 degrees C for various durations. Owing to the precipitation of Li(x)Ga(y)S(z) crystals with a Ga(2)S(3)-like structure, clear second-harmonic generation was observed in the sample crystallized at 403 degrees C for 60 h, which has a greatly improved resistance to environmental impairment. Additionally, it is found that the shorter crystallization process (< or = 60 h) contributed to the enhancement of Li(+) ionic conductivity, whereas a longer heat-treatment (80 h) would impair that of the glass-ceramics. The micro-structural origin of these varied properties was elucidated in detail. The corresponding results will be of benefit for the optimization of designed transparent chalcogenide glass-ceramics with improved thermo-mechanical properties, a permanent second-order optical nonlinearity, or a well-enhanced ionic conductivity for application in amorphous solid electrolytes.

Reversible giant photocontraction in chalcogenide glass

It is shown that chalcogenide glasses with suitably underconstrained network can undergo reversible giant photocontractions up to a micron depth. These effects result from the combination of two attributes particular to these glasses, (i) the high photosensitivity characteristic of low coordination floppy networks and (ii) the wide window of structural configuration characteristic of fragile glass former. Interestingly these effects are reversible and subsequent irradiation with high intensity results in giant photoexpansion in the same glass. The combination of subsequent photocontraction and photoexpansion on the same glass surface has good potential for the design of complex optical elements.

Photonic Bandgap Propagation in All-Solid Chalcogenide Microstructured Optical Fibers

An original way to obtain fibers with special chromatic dispersion and single-mode behavior is to consider microstructured optical fibers (MOFs). These fibers present unique optical properties thanks to the high degree of freedom in the design of their geometrical structure. In this study, the first all-solid all-chalcogenide MOFs exhibiting photonic bandgap transmission have been achieved and optically characterized. The fibers are made of an As38Se62 matrix, with inclusions of Te20As30Se50 glass that shows a higher refractive index (n = 2.9). In those fibers, several transmission bands have been observed in mid infrared depending on the geometry. In addition, for the first time, propagation by photonic bandgap effect in an all-chalcogenide MOF has been observed at 3.39 µm, 9.3 µm, and 10.6 µm. The numerical simulations based on the optogeometric properties of the fibers agree well with the experimental characterizations.

Halo-tellurite glass fiber with low OH content for 2-5µm mid-infrared nonlinear applications

We report the fabrication of new dehydrated halo-tellurite glass fibers with low OH content (1ppm in weight) and low OH-induced attenuation of 10dB/m in 3-4 µm region. It shows halo-tellurite glass fibers a promising candidate for nonlinear applications in 2-5µm region.

Similar behaviors of sulfide and selenide-based chalcogenide glasses to form glass ceramics

In this paper, the strong influence of alkali halide in chalcogenide glasses is reminded, leading for the first time to highly transparent glasses from the visible range up to 11μm. The behavior of crystallization has been demonstrated to be similar in sulfide and selenide glasses containing gallium as well. The structural evolution of several glass compositions from the Ge-Ga-S or Ge-Ga-Se systems leading to reproducible glass ceramics has been studied by XRD, NMR and thermal analysis. Whatever the composition, gallium plays a fundamental role as nanosized domains appear by phase separation between Ge rich regions and Ga rich regions. The determination of the appropriate crystallization time and temperature has permitted to obtain new passive and active glass-ceramics with a broadened transmittance region thanks to the incorporation of various alkali halides. In the first case, the controllable generation of nanocrystals leads to an increase of the main thermo-mechanical properties. In the second case, the incorporation of rare-earth ions inside the glass ceramics has exacerbated their photoluminescence properties. The possibility to combine the ceramization process with the shaping has also been demonstrated.

Composition dependence and reversibility of photoinduced refractive index changes in chalcogenide glass

Photoinduced refractive index changes are investigated as a function of composition in Ge–As–Se chalcogenide glass by measuring the formation of Bragg reflectors photo-imprinted in polished glass discs. It is shown that the glass network connectivity has a strong effect on the photostructural changes which decrease dramatically when the rigidity percolates through the structure at coordination numbers r > 2.4. The Bragg reflector formation is also affected by the refractive index of the glass which varies sharply with r and correlates directly with the glass density. The photoinduced refractive index change is shown to reverse upon annealing near the glass transition following a non-exponential kinetic that closely matches the kinetics of structural enthalpy relaxation. The Bragg reflectors can also be reversibly erased and readjusted to a new wavelength through subsequent irradiation with a different photon energy. The composition dependence of photosensitivity is discussed in terms of structural constraints. It is suggested that over-constrained networks remain rigid despite photoexcitation of bond constraints therefore precluding photostructural rearrangements.