Periodic Reporting for period 4 - NCLas (NanoCrystals in Fibre Lasers)
Reporting period: 2023-01-01 to 2023-12-31
In the NCLas project, a disruptive technology for the synthesis of glasses containing functional nanocrystals (NCs) will be introduced and developed. It is based on a novel hybrid nanosintering process, which allows for the incorporation of a large variety of NCs and functionalization of glasses in different formats for various applications. Previous attempts to either grow NCs inside glass by glass heat treatment or incorporate NCs during glass formation showed unconvincing results. In this nanosintering process, key enabling steps include reducing the sintering temperature, developing specialized NC core-shell structures and adjusting the glass composition, thus achieving a chemically inert environment and matching the refractive index of NCs and glass. This technology will be exploited to produce low-loss, NC-functionalised glass fibres. Fibre lasers are energy efficient, compact and offer maintenance-free operation, ultra-short pulses, high power, and low noise. Today’s commercial fibre lasers are fabricated from robust, durable silica glass. The operation of oxide fibre lasers can be extended to an enormous spectral range (~400 – 3000 nm) by doping oxide glasses with laser-active nanocrystals optimized for particular laser wavelengths, thus enabling a huge variety of new applications. We will demonstrate two highly relevant fibre lasers: (i) a Ti3+:sapphire-NC (Ti:Sa) fibre laser tuneable around 800 nm for biophotonic applications; (ii) a Pr3+:yttria-NC 1300-nm fibre laser enabling a much-awaited wavelength extension in telecommunications and also fitting into one of the biophotonic windows. An interdisciplinary team mitigates the high risk of NCLas with demonstrated experience in their fields and highly complementary backgrounds. The consortium challenges all steps from material synthesis to device demonstration. NCLas makes a significant contribution to Key Enabling Technologies such as Nanotechnology, Photonics and Advanced Materials.
The NCLas project concentrated mainly on the investigation, characterisation and provisioning of the matrix glass nanoparticles as well as the laser-active nanocrystals Ti3+:sapphire and Pr3+:yttria.We were able to observe the formation of YPO4 NCs from the initially present Y2O3 NCs and the phosphate matrix glass during sintering and glass melting experiments. We were following up on this encouraging result and focused on this material system. Firstly, we successfully demonstrated that this phase change from Y2O3 to YPO4 can also be achieved while drawing a fiber on the draw tower and keeping the laser active ion in the new crystalline phase. Interestingly, the unique Pr3+ luminescence was ascribed to Pr3+ into the YPO4 host lattice. Neither Pr3+ emission from Y2O3 nor from the glass was detected, indicating that all Y2O3 was turned into YPO4. The next important idea was start out with the more stable YPO4 NCs in order to avoid the phase changes and demonstrate the NC survival during the fiber drawing process. Ytterbium was chosen as alternative ion for future laser experiments.The new NCs required also the consideration of new matrix glasses to allow refractive index matching. The work package WP4 was again the most active and most collaborative effort during RP3. The temperature stability of the new actively doped YPO4 NCs together with selected matrix glasses were investigated in series of sintering experiments using an oven and a flux inductor. Subsequently, preforms were prepared with a powder mix of matrix glass particles and active NCs (ANCs) in a suitable cladding tube, i.e. using the glass powder doping process. The pre-treatment of the powder mix was investigated using different compaction processes of pressing and pre-sintering like cold and hot isostatic pressing (CIP & HIP) as well as advanced temperature cycles directly at the draw tower. This resulted in the successful demonstration of the survival of the NCs during a fiber drawing process using glass powder doping and it was shown using both above mentioned phosphate matrix glasses. We researched the fluorescence properties of the YPO4:Yb3+ NCs to better understand their spectra, lifetimes, and quenching mechanisms also with the final goal to determine the most suitable Yb3+ doping level in the NCs for highest laser gain. The fluorescence was also compared to the lifetimes in fibers with surviving NCs. Due to the improvements of optical fibres, we were able to estimate the background losses for the first time, which are now dominated by scattering losses. Unfortunately, they are approximately 20dB/cm and too high to demonstrate any net gain. Nevertheless, we conducted an amplification experiment to establish the relative gain coefficient (pumped vs. unpumped) and achieved a relatively high value of 1dB/cm. While this value is much smaller than the loss coefficient, it shows the potential if these high losses can be avoided.
Thus, future work would need to concentrate on the reduction of scattering loss by employing smaller NCs and improving the refractive index matching between the NCs and the matrix glass by synthesizing an adequate phosphate glass. While there is still much research to be conducted, we were able to demonstrate that NC-doped fibres using the glass powder doping is a valid technology to add new functionalities to optical fibres.
Thus, future work would need to concentrate on the reduction of scattering loss by employing smaller NCs and improving the refractive index matching between the NCs and the matrix glass by synthesizing an adequate phosphate glass. While there is still much research to be conducted, we were able to demonstrate that NC-doped fibres using the glass powder doping is a valid technology to add new functionalities to optical fibres.
To the best of our knowledge, this is the first comparative study on synthesis, characterisation and luminescence properties of Pr3+:Y2O3: nanocrystals. Because the FET Open format focuses on future technologies in an early stage of research, the main impact of NCLas during the duration of the project will be generated on the scientific and technological side. The radically new nanosintering process will offer unprecedented parameter control over a wide range of material combinations and will establish a new class of functional hybrid materials. The incorporation of a wide variety of new functional NCs into hybrid materials, especially in fibres and waveguide, is expected to trigger new research directions towards the exploitation of new functionalities. Such a process can be exploited not only in the field of lasers, but also for active coatings or new metamaterials with properties that combine in a synergistic manner the properties of glass and the NCs. However, the nanosintering process itself is also expected to be a valuable research tool in materials science. To foster exchange within the scientific community and beyond, the project partners have developed a communication and dissemination strategy, that includes the organisation of a Summer School, an official NCLas website, a project video, scientific and other publications.
we were able to show that glass powder doping process (nanosintering) is viable route to add new functionality to optical fibres by demonstrating that NCs can survive a fibre drawing process and retain their favourable properties. For fibre lasers, the main obstacle at this point is the high scattering loss mainly due NC size and lack of better refractive index matching. Alternatively, fibre sensors are an application field that is much more tolerant towards propagation loss. Our research on core-shell NPs is also laying out a path to generalize our results and transfer this approach to other crystalline materials for other laser transitions or applications.
we were able to show that glass powder doping process (nanosintering) is viable route to add new functionality to optical fibres by demonstrating that NCs can survive a fibre drawing process and retain their favourable properties. For fibre lasers, the main obstacle at this point is the high scattering loss mainly due NC size and lack of better refractive index matching. Alternatively, fibre sensors are an application field that is much more tolerant towards propagation loss. Our research on core-shell NPs is also laying out a path to generalize our results and transfer this approach to other crystalline materials for other laser transitions or applications.