Lasers fibrés UV/Moyen-IR: nano-hybridation des technologies photoniques et semiconductrices – QuantumLight
The aim of this proposal is to study original composite fibres in order to develop tuneable laser sources emitting at new wavelengths (especially for the unconventional UV-visible and mid-IR ranges) for applications in information storage, remote sensing of molecules, processing of medical diagnostics and therapeutics. For this purpose, the optical gain media of these fibres will be composed of the exciting semiconductor nanoparticles, namely 'Quantum Dots (QDs)', which can be simply incorporated by the sol-gel process. These dots present the strong advantage of easily tuned emission wavelengths in a wide range (several hundred nanometers) through changes in their dimensions due to the quantum confinement effect. They also possess narrow emission lines combined with broad excitation wavelengths, which make them suitable to reach multiple emission wavelengths by starting from the same pump wavelength. Finally, the ability of the photonic crystal technology to simultaneously tailor the core material (dopant) and the optical properties of the fibre (through the microstructured cladding) gives an unique opportunity to study optically-pumped QD laser systems. QD lasers have been extensively studied since the early 90's, but only recently QD lasers are finding new interesting and exciting applications in research and industry. However, taking advantage of the well established semiconductor laser technology, most significant breakthroughs have occurred in electrically-pumped QD lasers on semiconductor substrates. Optically-pumped QD lasers are still a promising frontier with no lack of challenges. Here, we propose to extend these studies to the fibre field where the QDs are going to open a wide field of applications. This study will constitute a very original work in the fibre domain. Indeed, in the last years, the most important advance was the air-silica microstructured fibre (or PCF for Photonic Crystal Fibre) which allows remarkable control of key optical properties such as dispersion, birefringence or nonlinearity thanks to the specific interaction between the air-holes and the electric field of the guided modes. Their realizations by the 'stack and draw' method have overcome some conventional limitations and, as a result, many new applications of optical fibres are emerging. Perhaps the most spectacular ones are the development of hollow-core photonic bandgap fibres fibres where the light is guided in the air-core by a photonic bandgap effect over kilometric lengths and also, the development of compact light CW sources reaching the kWatt level by rare earth doping of silica. However, the emissions in rare earth doped fibre lasers occur at specific wavelengths intrinsically dictated by combinaison of radiative transitions of rare earth ion and pumping frequency. As a consequence, emission is somewhat limited to infrared (IR) range with few exceptions in visible and mid-IR. Moreover, no direct transition in the UV domain has been observed yet. In this context, the development of new active media is now the next required step towards developing original sources. As shown in the literature, the use of QDs, synthesized by the sol-gel chemical technology via the well established colloidal route, seems to be one of the most promising way. Our group has an expertise in both the fibre domain and the sol-gel processes (used here just for nanoparticules integration in a silica matrix and not to develop QDs, already commercially available). Indeed, we have developed the first doped optical fibres with a core composed of zirconia nanocrystals in a silica matrix. This work includes the deposit of few layers of the silica/zirconia sol onto the inner wall of a tube which then constitutes the preform. Then, after the accurate annealing, the preform is drawn into a fibre. Up to now, this work has allowed to develop composite fibres with low loss and optimisations of the process are still in progress. Consequently, by combining the available commercial QDs, our know-how in both fields and our in-house facilities, QDs liquid-core fibres and QDs hollow/solid-core fibres will be developed. Next, their luminescence properties and finally innovative fibre-based laser systems will be proposed. Due to the unique opportunities offered in terms of wide tuneability of emission wavelengths (including an access to new UV-visible and mid-IR wavelengths), narrow and stable emission lines and also the large absorption cross section and optical gain (QDs concentration up to 30%) compared to the traditional rare earth doping route (maximum 4%), strong impact are expected for academic research as well as industrials.
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