Pascal Etienne

Spectroscopic characterization of intrinsic losses in an organic–inorganic hybrid waveguide synthesized by the sol–gel process

Abstract A promising way of fabricating integrated optics components is based on the sol–gel synthesis and photocuring of hybrid materials. However, the presence of OH groups in these materials is a major factor in optical amplification inhibition. In particular, high losses at 1550 nm are mainly due to non-condensed OH groups originating from the sol–gel process at low temperature. Thus, improvement of the final properties of these materials is correlated with the inhibition of OH group concentration. In this study, we used 29 Si NMR and near infrared spectroscopy to demonstrate the catalytic effect of zirconium (IV) n -propoxide on the condensation reactions of silanol groups. 29 Si NMR showed the absence of silanol species at the end of the synthesis. This result is attributed to the zirconate hydrophilic effect which consumes OH groups by catalysing the polycondensation of Si–OH bonds. In parallel, near-infrared experiments showed the presence of a high proportion of OH species at the end of the synthesis showing that the remaining OH groups are only present in the zirconium species.

Active erbium-doped organic–inorganic waveguide

Abstract The existence of optical amplification at 1550 nm wavelength in channel waveguides using erbium doping and 980 nm laser pump involves as low a OH group quantity as possible. Moreover, a high refractive index variation between the guide and the cladding is necessary to induce a maximum confinement and then increase the doping efficiency. This field is now limited to pure inorganic materials or semiconductors. We propose to extend this field to hybrid organic–inorganic materials. In such a way, we have developed a new composition based on hydrophobic sol–gel precursors to reduce the OH quantity, and on a diacrylate monomer whose reactivity allows a high refractive index change under UV light exposure. Signal enhancement is observed for the first time in a hybrid organic–inorganic channel waveguide.

Sol-gel channel waveguide on silicon: fast direct imprinting and low cost fabrication

Abstract Development of integrated optical devices depends on the possibility to realize them for the lowest cost. In this paper we present an improved technique based on the sol-gel process enabling to fabricate low loss (

Photocurable Sol-Gel Coatings: Channel Waveguides for Use at 1.55 μm

The development and characterization of channel waveguides using wet-process, low temperature sol-gel chemistry is described. Two structures have been developed. The first one is a one-layer structure, composed of a sol-gel solution which is a mixture of photopolymerizable organosilicate and organozirconate precursors. The other is a multilayer structure with a buffer under the guide and a protective coating. The layers are deposited by the dipping technique. The devices are obtained by UV light exposure of the coating through a predefined mask (channel waveguides). The refractive index increase is sufficient enough to allow the use of waveguides in the 1.55 μm telecommunication window.These waveguides are thick enough to reduce the coupling losses with an optical fiber below 0.5 dB. Also, because of our sandwich structure, the propagation losses are less than 0.1 dB.

Integrated optics based on organo-mineral materials

Abstract New technologies based on organic–inorganic materials are shown to be very flexible, while they present interesting performance. The process needs only four steps, and the local refractive index change necessary to guide the light may be imprinted with a simple UV exposure. Several solutions are given to design basic structure of guides and hence to make optical circuits which cover the domain of power splitters to wavelength division multiplexers, including directional couplers, gratings, etc. Optical amplification is also shown to be possible, and the connection problem is tackled.

Direct printing of gratings on sol-gel layers

The sol-gel process is an interesting alternative for making glass integrated-optics components. Reasonable performance can be reached with low-cost fabrication. We show a one-step method for imprinting gratings on a thin layer made through the sol-gel process, thus enlarging the field of application in integrated optics to filters, out-ofplane connections, etc. The efficiency of the grating is studied through diffraction measures and computations.

Tribological Properties of Ormosil Coatings

Transparent plastics are not scratch resistant. The damage leads to a loss of optical properties. Coatings prepared using either tetraethoxysilane or colloidal silica particles embedded in “glymo” is a way to avoid these disadvantages. Tribological experiments are carried out to better understand the surface modification due to a sliding friction. It is shown that the wear track is not directly related to usual mechanical properties such as Youngs modulus and the hardness of the coating. The different stages leading to material loss are discussed in term of particle removal and debris circulation (accumulation or elimination) through the friction track. The mechanical properties of the film combined with the film to substrate adhesion are expected to play an important role as it can be deduced from results obtained as a function of the coating composition.

Mechanical properties of nanocomposite organosilicate films

Nanocomposite coatings have been deposited on plastic substrates by the dipping–drawing technique. The coatings were constituted by a matrice of a hybrid organomineral gel and a reinforcement made of amorphous silica. Two methods by which increase the silica content were investigated: silica was added via a silicon alkoxide compound or via dense silica particles of 10 nm size. Youngs modulus and the hardness of the coating were measured using home-built equipment, and results compared to literature models. It is shown that the agreement between models and experimental values depends on the method of preparation of the nanocomposite coating. On the other hand, deviations appear when the volume fraction of reinforcement surpasses the three-dimensional percolation threshold.

Mechanical Properties of Gel-Derived Materials

The mechanical behaviour of xerogels and aerogels is generally described in terms of brittle and elastic materials, like glasses or ceramics. The main difference compared to silica glass is the order of magnitude of the elastic and rupture moduli which are 104 times lower. However, if this analogy is pertinent when gels are under a tension stress (bending test) they exhibit a more complicated response when the structure is submitted to a compressive stress. The network is linearly elastic under small strains, then exhibits yield followed by densification and plastic hardening. As a consequence of the plastic shrinkage it is possible to densify and stiffen the gel at room temperature. These opposite behaviours (elastic and plastic) are surprisingly related to the same two kinds of gel features: the silanol content and the pore volume. Both elastic modulus and plastic shrinkage depend strongly on the volume fraction of pores and on the condensation reaction between silanols. On the mechanical point of view (rupture modulus and toughness), it is shown that pores and silanols play also an important role. Pores can be considered as flaws in the terms of fracture mechanics and the flaw size, calculated from rupture strength and toughness is related to the pore size distribution. Different kinds of gels structure (fractal or not fractal) have been synthesized by a control of the different steps of transformation such as sintering and plastic compaction. The relationships between structural and the elastic properties are discussed in terms of the percolation theory and fractal structure.

WDM based on multimode interference-coupler built in an organic-inorganic material

Abstract The WDM phasar, which is a key element in optical telecommunication systems, is shown here to be made with a very low cost and promising technology based on organic–inorganic material, and with a design based on MMI devices for the splitter and the combiner instead of star couplers or gratings. A realization of a first 4×4 MMI phasar, for use around 1.55 μm wavelength, demonstrates the application of these two specific aspects. Experimental measurements and theoretical results are compared.