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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SUPUVIR (SUPercontinuum broadband light sources covering UV to IR applications)

Teaser

Summary

The laser offers coherent radiation, which is millions of times brighter than sunlight and can be focused to a tiny spot. It has an immense range of applications spanning basic science over industrial applications to everyday consumer products. A standing challenge has been to use nonlinear processes to convert laser light to new wavelengths as lasers only operate efficiently at distinct wavelengths. Supercontinuum generation offers an elegant solution to this, as it massively broadens the laser spectrum. In its simplest case a powerful narrowband laser is sent into a short piece of fibre to generate a rainbow of colours at the output, pertaining the brightness and spatial coherence of the laser. This allows access to both new wavelengths and new applications exploiting coherent broadband laser radiation that cannot be generated in a laser directly. The scientific challenge addressed in the project SUPUVIR is to overcome current shortcomings of supercontinuum sources in terms of wavelength coverage, noise, power density and robustness to offer a truly unique and disruptive technology for societal challenges, such as pollution monitoring, bio-imaging, and disease detection.

Photonics is an intersectoral, interdisciplinary technology that enables many other industries. Economic and social impacts are enhanced by the fact that photonics technologies are now emerging as one of the most promising technologies in the knowledge-based economy and society, supporting further progress in several key industrial segments. SUPUVIR will provide the co-evolution of technology and applications, and hence contribute to the strategic transition of Europe to a knowledge-based society, driving the transformation of industry towards higher added value and sustainable development.

The growing industry within supercontinuum broadband light sources will require highly skilled and trained employees that can efficiently tackle a broad range of technical challenges related to their development and applications. The aim of SUPUVIR is to combine the efforts of 6 academic and 4 non-academic beneficiaries to train 15 early-stage researchers by providing them with extensive knowledge in silica and soft-glass chemistry, preform design and fibre drawing, linear and nonlinear fibre and waveguide characterization, nonlinear fibre optics, supercontinuum modelling and system design, patent protection, and in-depth knowledge of a broad range of the main current applications of supercontinuum sources in for example spectroscopy and imaging. The knowledge and experience in these complementary disciplines are present in the consortium and will contribute to significant advancements in the field.

SUPUVIR aims to solve the current challenges of supercontinuum sources by 1) advancing current supercontinuum techniques, which requires highly nonlinear fibres or waveguides specifically tailored or developed for the purpose, and 2) improving current applications and developing novel applications, enabled by the advances achieved in the project. The state-of-the-art supercontinuum results will ultimately be tested in the specific applications. Thus, both scientific advances and aspects of commercial sources are in focus, both existing in synergy and together pushing the boundaries of supercontinuum sources and their applications.

Work performed

The results achieved so far at the half-way stage have shown a significant exchange of knowledge between the members of the consortium. We have successfully executed 3 of the planned training courses for the fellows, where they learned about the various building blocks behind a supercontinuum laser source, and how to draw the optical fibres in which the spectral broadening takes place. A significant achievement at the training courses has been to spark a remarkable interaction between the fellows and the senior researchers, clearly demonstrating how the various projects truly benefit from being in a large interdisciplinary consortium. These courses were open to other students as well (as the future courses will be), which means that the training does not just benefit the fellows of the present consortium, but also others.

Scientifically, the major advances achieved so far are:
1. A multi-modal microscope has been developed that currently works in the visible, and it will now be extended to use UV lasers and thereby test the various UV sources from partners.
2. In the visible and near-IR various efforts have been made to improve the supercontinuum sources. A major focus is on non-soliton based sources where the usual sources of noise and instability are suppressed. Also novel fibre platforms are investigated, including multimode fibres and new air-cladding or all-solid photonic crystal fibres.
3. For the development of the fibres for the mid-IR, the consortium is currently investigating a new type of graded-index fibre, made by stacking a high number of small rods of various refractive index compositions. In addition to this, a significant effort has been made to develop new glasses suitable for highly nonlinear and broadband interaction in various ranges of the mid-IR.
4. The mid-IR supercontinuum research has been focused on near-IR pumping schemes, as this is where the pump lasers are most mature. The results are emerging to push the supercontinuum beyond 3 Î¼m, and various fibers and waveguides are being tested.
5. For applications the consortium has already developed a new, powerful near-IR photoacoustic imaging system as well as a mid-IR multi-modal optical coherence tomography system and tested them on various samples. The consortium is also developing a source for multi-tone spectroscopy covering 1-4 Î¼m and is working on developing a short-range laser sensor for monitoring the temperature distribution in thermal devices like boilers.

Final results

In the UV range, we address the 200-400 nm range to achieve brighter supercontinuum sources extending further into the UV (down to 200 nm) and with better noise properties. In the visible and near-IR range (400-2,000 nm), in which supercontinuum sources are most mature, the key aspects are to improve the supercontinuum sources for applications to open new markets; this concerns topics like stability, coherence, noise, fibre lifetime and pulse energy. The mid-IR range (2,000-20,000 nm) is an emerging scientific area, so many aspects still need to be addressed, including nonlinear host material issues, fibre fabrication, durability of fibre materials, alternatives to fibres represented here by waveguides in quadratic nonlinear crystals, proof-of-principle supercontinuum experiments to achieve as broadband a supercontinuum as possible and to increase the average power as much as possible. Also, novel supercontinuum applications will be investigated in the areas of drug screening, photoacoustic imaging, food quality monitoring, multi-modal spectroscopy and Lidar-based process monitoring. Such novel applications are currently driving the research and development of supercontinuum sources.