Heavy Oxide gLass ceramIcs and Glasses foR innovAtive opticaL fibErs. – HOLIGRALE

The various approaches described in this project are:
- The synthesis of new tellurite glassy compositions (with or without rare earth ions doping).
- Preparation of glassy preforms of various chemical compositions.
- The realization of first vitreous optical fibers obtained from new materials studied, as well as optical fibers including metallic wires whose could be useful as électrodes.
- The development of crystalline materials with nonlinear optical properties (particularly that of second harmonic generation).
- Manufacture of various bulk glass-ceramics, by using conventional techniques of devitrification of a glass, but also from non-conventional techniques (eg SPS).
- The development of «composite« approaches to incorporate nanoscale crystalline entities or inserting metal nanoparticles.
- Optical characterization related to the demonstration of lasing under different regimes.

Objective 1:
Fibers 40 meters long with an average diameter of 150 microns were obtained from the compositions 80TeO2-10TaO5 / 2-10ZnO and 80TeO2-15TaO5 / 2-5ZnO. The attenuation measurements provide values of the optical losses of the order of 5 dB.m-1.
Fibers from the TeO2-WO3-Nb2O5 system were developed by the technique of «build-in-casting« method to achieve double-index preforms with heart/sheath interface of excellent quality. Optical losses measured in the heart of these dual indices fiber are equivalent to those of monoindice fibers. Purification (low water content) of the glasses within the TeO2-ZnO-PbO system has resulted in a transmission fiber up to a wavelength of 4.5 microns. Pumping of such microstructured fibers from purified glass, supercontinuum extending beyond 3 microns were then obtained.
Objective 2:
The study of the TeO2-GeO2-K2O-Nb2O5 system has allowed exploring the precipitation of non centrosymmetric phases such as K [Nb1/3Te2/3]2O4.8 and the elaboration of glass-ceramics for second order nonlinear optics. Clusters partially crystallized in star shape appear in the bulk glass and generate a local second harmonic signal (SHG). The transmission can be maintained at a level of 50% in the range 450 nm-2 microns. New glasses and glass-ceramics in the TeO2-WO3 system were shaped by a non-conventional technique: SPS. The optical transparency in the visible of such glass-ceramics is nowadays too limited, but that in the near IR reaches 45%.
Objective 3:
From the 74.25TeO2-19.8Nb02.5-4.95WO3-1NdO1.5 glass and deposits reflecting layers on the surfaces of glass, a miniature laser source was constructed. We got a near 1064 nm laser emission with continuous operation regimes or self-triggering.

The prospects are naturally included in the logical sequence of objectives and challenges identified in this project. For example, there may be mentioned the start of work on ceramic tellurite fibers which like others defined objectives will be pursued. The idea is to co-fiberize a glass tube (sheath) containing a glass powder (the heart). Several tens of meters of fiber dual index, but without obtaining guidance for the moment have been obtained (TeO2-Nb2O5-WO3 system).

Tests as microlasers are under development on the transparent polycrystalline ceramic composition 75TeO2-12.5Bi2O3-12.5Nb2O5

- Patents :
1)S ; Danto, F. Désévédavy, Y. Petit, F. Smektala, T. Cardinal, L. Canioni, « Fibre optique ruban en verre photosensible », CNRS-Université de Bordeaux
2) G. Delaiizr, S. Chenu, J. carreaud, M. Allix, « Vitrocéramiues et céramiques transparentes à base de TeO2 », BNT219911FR00
- Publications:
1) A. Bertrand, et al. A Comprehensive Study of the Carbon Contamination in Tellurite Glasses and Glass-Ceramics Sintered by Spark Plasma Sintering (SPS), J. Amer. Ceram. Soc., 97 (2014) 163.
2) Guery G. et al.; Influence of Hydroxyl Group on IR Transparency of Tellurite-Based Glasses, International Journal of Applied Glass Science, 5 (2014) 178.
3)S. Danto et al., Adv. Opt. Mater. 4 2016) 162
4)A. Bertrand et al., Adv. Opt. Mater. (2016)
5)J. C. Desmoulin et al ;, J ; applied. Physics, 118 (2015) 213104
6) T ; Lo et al. Applied Physics Letters, 106 (2015) 161901
- international conferences:
1) A. Bertrand et al. Highly transparent tellurite glasses and glass ceramics elaborated by non conventional spark plasma sintering, 2nd International Symposium on Inorganic and Environmental Materials (ISIEM 2013), Rennes, 27-31 Octobre 2013.
2) H. Dardar, et al., Glass and glass-ceramics elaborated within the (Nd3+, Yb3+) doped TeO2-Nb2O5-WO3 systems for microlaser applications, 2nd Int. Symp. on Inorganic and Environmental Materials 2013 (ISIEM 2013), Rennes (France), 27-30 octobre 2013.
3) S. Danto, et al. «Tellurite glasses for the near-IR: from material design to fiber fabrication«, Glass and Optical Materials Division (American Ceramic Society) and Deutsche Glastechnische Gesellschaft Joint Annual Meeting 2015, 17-21 Mai 2015, Miami (USA).
4) Synthesis, structure, nonlinear optical and lasing properties of tellurium oxide based glasses and glass-ceramics. P. Thomas et al.; The 7th International Conference on Optical, Optoelectronic and Photonic Materials and Applications (ICOOPMA), Montréal (Québec, Canada), 12-17 June 2016.

Fiber Lasers are nowadays changing the idea people have regarding laser systems by allowing reaching high powers, higher compactness and easy use (compared to classical laser systems). In particular, fiber lasers are expected to occupy 30 to 40% of the laser market. The main interests of the optical fiber devices remain in their unique geometry which provides their adaptability to be used in various environments and allows minimizing the thermal effects induced by the laser emission. Even though the advantages of the fibers are obvious, important issues remain to be solved and it appears clearly that the silica based materials are definitely not, for several applications, the best candidates to meet the challenge.
Tellurite glasses and glass-ceramics will offer new opportunities to extend the operational wavelength range in the near infrared (above 1µm up to 5-6 µm) and will allow accessing high second order and third order optical nonlinearities.
Glass-ceramics have been considered in the past as very attractive materials for photonics but their use has led so far only to limited applications, mainly due to technological difficulties in relation with the complex nature of the materials in fiber form. However, the benefit of achieving glass-ceramics fibers would be considerable and real, justifying completely this project. Several issues, specific to glass-ceramics, will have to be addressed. In particular, the size of nanocrystals disseminated within the glassy matrix will have to be carefully controlled to avoid their excessive growth. As well, a small refractive index difference between the crystallites and the glassy matrix will constitute a key focus to maintain optical scattering losses at a low level. In addition, the low phonon energy intrinsic to the tellurite glass matrix, combined to that of selected crystals, will be essential parameters to reach important laser efficiency for the targeted applications above 1µm and up to 5-6 µm. Finally, glass-ceramics should present higher laser damage thresholds, in comparison to the “equivalent” glass compositions, due to their improved mechanical properties.
Thus, in order to guaranty the success of the HOLIGRALE project, the strategy will be to select the most adapted materials for the fabrication of fibers for Gain and fibers for Non-Linear Optics, to develop the drawing technique, to test and adopt innovative geometries for fibers and to establish some correlation between fiber architectures, materials chemistry and optical properties. This unique project will rely on the excellence of the French expertise in the aforementioned fields of research, and on the quality of the consortium created by the gathering of the laboratories implied.