Ceramic Optical Fiber for Laser Applications – FOCAL

The project is composed of 4 main objectives:
1. Active fiber composed of doped nano-crystals in silica matrix (SiO2 – Na2O – ZnO – Ga2O3)
2. Active fiber composed of doped nano-crystals in germanate matrix (GeO2 – Na2O – ZnO – Ga2O3)
3. Active ceramic fiber doped with rare-earth or transition metal ions (Sr3Al2O6 or Sr1+x/2Al2+xSi2-xO8)
4. Passive ceramic fibers with high transmission in infra-red (Sr3Al2O6)

The organization of the project is summarized as follows:
Task 0: Coordination (Leader: CEMHTI)
Task 1: Selection and elaboration of raw bulk glass, glass-ceramic and ceramics compositions
(CEMHTI, XLIM, SPCTS)
- Specification and selection of compositions
- Elaboration of raw glass materials for fiber drawing
- Determination of bulk materials crystallization parameters
- Structural and optical characterizations of bulk materials
Task 2: Fiber Fabrication (XLIM, SPCTS)
- Preform design and preparation
- Fiber fabrication
- In-line or post-drawing heat treatment for partial (glass-ceramic) or full (ceramic) fiber
ceramization
- Structural and microstructural characterization of fibers
Task 3: Optical characterizations of bulk and fiber materials (SPCTS, XLIM)
- Linear optical characterizations
- Luminescence properties
Task 4: Dissemination and exploitation of results (CEMHTI, XLIM, SPCTS)

1 - We have elaborate an optical fiber with an active glass-ceramic core showing optical loss < 2 dB/m, similar to the best materials currently reported in the litterature.
2 – We have elaborated an optical fiber with a glass-ceramic core and doped with Cr3+. When pumped at 532 nm, this fiber emits at around 700 nm, a wavelength similar to the emission of the bulk material. This result is at the level of the current state of the art in the litterature.

We think that if it is possible to further reduce the optical loss in our doped and undoped fibers by playing around with the fiber drawing parameters and with the compositions (especially via the optimization of the doping level contents). This should enable to elaborate highly performing materials, and especially to overcome those recently presented in the literature (Samson et al. 2002, Qiu et al. 2015). This is why we plan to restrain, in the near future, the valorization of our results in order to preserve the possibility to depose a patent and to publish in a high impact journal.

Regarding the elaboration of new transparent polycrystalline ceramic materials by full and congruent crystallization from glass, we have recently published two articles

The next step of the project will be dedicated to the reduction of optical loss in the developped glass-ceramic fibers. The ultimate goal would be to demonstrate a laser effect in glass-ceramic fibers doped with Ni2+ and Ti3+. In parallel, attempts to draw ceramic fiber compositions will be performed in order to limit Si diffusion (drawing from large inner diameters, drawing at lower temperature, diffusion barrier, etc.)

PUBLICATIONS:
1. A.Bertrand, J.Carreaud, S.Chenu, M.Allix, E.Véron, J.-R.Duclère, Y.Launay, T.Hayakawa, C.Genevois, F.Brisset, F.Célarié, P.Thomas, G.Delaizir, Scalable and Formable Tellurite-Based Transparent Ceramics for Near Infrared Applications, Advanced Optical Materials, (in press)
2. M.Boyer*, A.J.Fernandez Carrion, S.Ory, A.I.Becerro , S.Villette, S.V.Eliseeva, S.Petoud, P.Aballea, G.Matzen and M.Allix*, Transparent Polycrystalline SrREGa3O7 Melilite Ceramics: Potential Phosphors for Tuneable Solid State Lighting, J. Mater. Chem. C, 4 3238-3247 (2016)

PATENT:
1. -« Ceramics and/or glass-ceramics based on tellurite oxide, use and elaboration process «, deposited in France on 14/03/2016 under number 16521131.

FOCAL is an original basic research project aiming to demonstrate the feasibility of new functional doped-ceramic and glass-ceramics optical fibers. It is based on the association of three key elements: transparent (500nm-6µm) glass-ceramic and ceramic compositions recently patented by CEMHTI and compatible with thermo-mechanical constraints of optical fiber fabrication processes, the “powder-in-tube” process developed at XLIM and the expertise in structural and optical characterizations of the SPCTS. The objective is to develop laser applications over a large spectral range. The 700nm-1µm domain, hardly attained up to now, will be the heart of the project, a doubling and/or a tripling of the frequency would then enable an extended access toward ultraviolet and so multiple potential applications: medical, military, environmental and nano-machining. Given their thermal properties, these fibers will reach high damage threshold and power resistance compared to classic glass fibers.
Fiber lasers are expected to occupy 40% of the laser market within a few years against 10% nowadays. As a matter of fact, they enable i) higher compactness compared to classic bulk lasers, ii) beam transportation and iii) easier use through very good heat dissipation and vibration immunity. Even though silica-based glass fibers are the most used today, their properties (high loss out of the 0.6-2µm domain and limited number of available radiative transitions) strongly limit the applications of associated lasers. Ceramized fibers are an interesting alternative for photonic applications as they present much larger transparency windows and are promised to efficient use of numerous radiative transitions. However, so far their development has been limited, mainly because of technical barriers related to the control of devitrification. Achieving glass-ceramic and polycrystalline ceramic optical fibers, the objective of the FOCAL project, would be a considerable scientific and technological breakthrough. In order to overcome this bottleneck, an original fiber drawing process is required and the microstructure of the ceramized core material will have to enable high transmittance. In the case of glass-ceramics, the precise control of the nanocrystals size and a small refractive index difference between the crystals and the glass matrix will be the key points to minimize optical scattering loss. Concerning polycrystalline ceramics obtained by full congruent crystallization from glass, they will have to be optically isotropic (non birefringent) and exhibit very thin grain boundaries in order to avoid any light scattering.
To that end, we propose to draw the compositions elaborated at the bulk state by CEMHTI (gallo-germanate and gallo-silicate compositions for glass-ceramics and aluminate/aluminosilicate compositions for ceramics). The addition of rare-earth (Tm3+, Pr3+, Sm3+) or metal transition ions (Cr3+, Ti3+) to dope the crystals will be key points to attain efficient luminescence properties for further laser applications in wavelength domains hardly used in laser fibers. Among selected materials, germanate and aluminate compositions are low phonon matrices which will enable high photonic efficiency and extension of the operational wavelength range toward the near infrared (up to 6 µm). This result will be an important technological breakthrough giving access to a spectral domain with very few laser sources. Fiber drawing will be performed at XLIM via an original "powder-in-tube" process well adapted to our compositions and the structural characterizations will be realized at the SPCTS in order to better understand and tailor the optical properties. Preliminary experiments demonstrating the feasibility of the project have been undertaken, more precisely on transparent gallo-silicates nanostructured glass-ceramics and Sr3Al2O6 ceramics.