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Multi-scale fibre-based optical frequency combs: science, technology and applications

Periodic Reporting for period 1 - MEFISTA (Multi-scale fibre-based optical frequency combs: science, technology and applications)

Reporting period: 2020-02-01 to 2022-01-31

To respond to the huge demand for qualified experts on optical frequency combs (OFC) technologies, MEFISTA will deliver research and training collaborations that will help 6 Early-Stage Researchers (ESRs) to acquire unique knowledge and research skills on OFC technology from the theory to implementation. In particular, the project goal is the development of novel mode-locking techniques and speciality fibres and waveguides for mode-locked femtosecond lasers (MLFLs), mid-infrared (mid-IR) tuneable dual combs sources for molecular fingerprinting, design, and characterisation of dual-comb MLFLs and MLFLs manufacturing. A special focus will be on the industrial applications related to the development and trial tests of MLFLs in the context of autonomous driving (car-object distance ranging, object recognition, moving objects speed tracing: Doppler LIDAR).
Coordinated by Aston University (ASTON), UK, MEFISTA consortium boasts a collaboration between academic and industrial world-leading groups working in photonic technologies, which have already made important contributions to this field. The consortium consists of: i) 5 high profile academic groups, being Aston Institute of Photonic Technologies (AiPT) at Aston University (UK); Universitat polytecnica de Catalunya, UPC (Spain); Universite de Lille, ULille (France); Ecole polytechnique federale de Lausanne, EPFL (Switzerland) and Technical University of Denmark, DTU (Denmark); alongside ii) two industrial partners NKT PHOTONICS A/S, NKT (Denmark) and RICHMOND DESIGN & MARKETING Limited, RDM (UK).
ERSRs reached progress as follows.
ESR1 (WP1)- During these experiments in a standard passive fibre ring cavity, without FBG, Stefano discovered that the synchronization mismatch of the pump vs the cavity has a significant and unexpected impact on the modulation instability side lobe shape. He focused on that process since that is unknown and should also affect the generation of gain through filtering frequency combs. A theory had been developed and numerical simulations and experiments are in agreement. These results had been published in one conference proceedings and two journal papers have been prepared.
ESR2 (Nayeem Akhter) contributed to WP2 by developing the software package for the study of nonlinear multimode fibre, repeating the turbulence study, repeating the proof of nonlinear self-cleaning concept, and presently is at the stage of delivering a result for active (non-Hermitian) self-cleaning. This should result in the first article submission in a few months.
ESR3 (Moritz Bartnick) was involved in WP3 by characterising experimentally the thulium-doped fibre was characterized in terms of emission properties, dispersion, nonlinearity and mode-locking at 2 microns. However, because of delays in deliveries and difficulties in manufacturing during the pandemic, the components/fibre were only just recently delivered (within the last month). The results have been published in two conference proceedings.
ESR4 (Qing Wang) contributed to WP4 by developing a new theoretical model of complex polarisation dynamics in Er-doped fibre laser mode-locked based on nonlinear polarisation rotation (NPR). Results of the theoretical modelling are in use to explain experimentally observed polarisation dynamics. It is a plan for the first journal article submission in a few months. Also, without ESR4, a new model of Er-doped fibre laser accounting for the electrostriction effect leading to excitation of the torsional acoustic modes in the transverse section of the laser has been developed to explain experimental data on harmonic mode-locking. These results have been published in the Photonics Research journal.
ESR5 (Albero Rodriguez Cuevas) contributed to WP4 by design and experimental and theoretical characterization of the polarization-multiplexed system capable of generating two optical frequency combs with repetition rate differences in the range of a few hundred Hz. He has also tested of the system’s stability and demonstrated a small drift of 6Hz over 6 hours. The experimental and theoretical analyses of polarization dynamics concluded that this polarization-multiplexed dual-comb source can be used to design the polarimetric LIDAR able to recognize the object's texture based on the polarimetric signatures. Results have been submitted to Optics Letters journal.
ESR6 (Anamika Nair Karunakaran) is currently working on contributing to WP4: (i) by combining NKT laser technology with planar microresonator comb devices, (ii) by developing robust comb stabilization algorithms and characterising comb stability, (iii) packaging the comb laser to achieve a single stand-alone compact turn-key comb module.
WP1 is focused on the experimental and theoretical characterisation of a novel gain through the losses mode-locking technique. The potential impact is in developing new physical concepts towards developing new laser sources with specifications required in spectroscopy and metrology.
WP2 is related to the development of novel mode-locking techniques based on unconventional (non-Hermitian) fibre structuring. The non-Hermitian potentials introduce unidirectional coupling towards higher or lower transverse modes (depending on the parity of the potential) therefore the coherence of multimode dynamics can be potentially controlled. The control of coherence properties in multimode fibres is crucial for the application of multimode fibres for frequency combs.
WP3 aims to design, characterise, and validate a wavelength stabilized thulium-doped mode-locked laser at 2 microns. The potential impact is developing new laser sources with specifications required in green gases spectroscopy.
WP4 is focused on the development and tests of ellipsometric Optical Frequency Comb (EOFC) in the context of distance ranging. The potential impact is in developing new types of LIDARs with the additional option of the objects’ texture recognition.

The outcomes of MEFISTA advances pushing the research frontiers beyond the state-of-the-art by developing
1. New mode-locking techniques.
2. New approaches to the design of dual-frequency comb sources with specifications required in spectroscopy, metrology, and medical diagnostics
3. New theoretical models and approaches to studying and performance optimisation of the dual-comb sources.
We anticipate that MEFISTA outcomes will open new horizons in the area of laser science and technology – pushing boundaries of the existing laser systems in terms of optical bandwidth and acquisition speed and resulting in new applications.

MEFISTA project has true potential for strengthening the European "Innovation Union” by
• Contributing to the EU’s scientific excellence and leadership in future hot topic technology such as optical frequency combs generation.
• Contributing to the EU’s industrial and business competitiveness through the creation of new services and products, based on improved optical frequency combs technologies in science (molecular spectroscopy) and industry (LIDARs, automotive sector and self-driving cars, aerospace industry).
• Creating a team of highly qualified young experts able to be leaders in the future economic and societal challenges of the EU.
• Promoting results and findings on optical frequency combs technologies beyond the photonics and autonomous driving sectors achieving a broad impact in the society.
MEFISTA 2nd part Induction, online
OTAWI, held in November 2021, in person at Lille, FR