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Multiscale optical frequency combs: advanced technologies and applications

Periodic Reporting for period 2 - MOCCA (Multiscale optical frequency combs: advanced technologies and applications)

Reporting period: 2021-02-01 to 2023-01-31

Growth of the Photonics market and great potential of Photonics in addressing global challenges creates a huge demand in innovative solutions and qualified experts with multidisciplinary skills in photonics and micro- and nano-technologies able to advance photonic technologies towards applications ranging from spectroscopy to LIDARs. The focus of the MOCCA scientific research programme was on developing the new generation of optical frequency combs (OFC).

MOCCA provided for 4 early-stage researchers (ESRs) a world-class advanced training programme which brought them to the level of the next generation of leaders in the field of photonics. The training was implemented through the unique combination of the “hands-on” research training, non-academic placements and advanced inter/multidisciplinary/inter-sectoral training to attain scientific skills (nonlinear optics and laser physics, micro- and nano-technologies) and transferable skills training. This equiped ESRs with a unique knowledge base and skill set required to address the global challenges such as global warming, improving medical diagnostics and accuracy and precision in metrology and autonomous driving etc. that underpins innovative technological development across the range of photonics-based disciplines: laser physics and engineering, micro- and nano-photonic components and circuits.

The unique Research Programme addressed demand in innovative solutions by developing a new generation of the optical frequency comb (OFC) techniques based on expertise world-leading academic (Aston University, UK; Sapienza Università di Roma, Italy; CNRC-C2N, France; RWTH Aachen University, Germany; Univ. Paris Diderot, France) and industrial centres such as (Thales, France; III-V Labs, France; AMO Gmbh, Germany).
The core of the scientific work is performed in WP1-4, while WP5 covers the network-wide and transferable skills training, career development, WP6 covers the project management, recruitment, dissemination and outreach, and WP7 covers ethics requirements.

All achieved specific Research Objectives in MOCCA are listed below:
RO1. Design, fabrication (CO2 laser annealing and/or femtosecond laser inscription), theoretical and experimental characterisation of wideband OFCs with low frequency and equidistant spectrum (of 100 MHz distance between lines) based on Aston SNAP bottle resonators 5 6 7
RO2. Design, fabrication, theoretical and experimental characterisation of wideband OFCs with low frequency and equidistant spectrum (200 GHz distance between lines) based on Thales photonic crystal platform.
RO3. Simulation, design and development of OFC devices based on pioneering work by AMO by utilizing surface modification techniques and/or strain to increase nonlinear optical effects in silicon photonic structures.
RO4. Design, fabrication, theoretical and experimental characterization of ultralow power threshold microresonator OFC sources based on C2N and III-V Labs new nonlinear semiconductor platforms.
RO5. Development and proof-of-concept tests of the dual comb spectrometers based on different combinations of the microresonators (Aston) and microcavities (Thales) with an active fibre cavity.
RO6. Theoretical characterisation of the dynamics and the phase noise of the comb OFC source developed in Aston and Thales.

The consortium organised 12 scientific training events, 3 Transferable Skills Training Workshops and 4 Annual Project Network Meetings. All ESRs prepared their career development plans (CDP) in the beginning of the project, and regularly updated it during their studies. Closer to the end of MOCCA they prepared a final CDP with short-term and long-term goals.

In the management WP6 the full cohort of ESR has been recruited and maintained throughout the project, all ESRs completing their secondments to industrial/academic partners. ESR3, Francesco Talenti, awarded his PhD degree on 10th January 2023.
The extensive project website has been built and will be maintained for at least 2 years after the project ends. The project has a presence of several social media platforms, generating over 100,000 impressions, and attracting influential followers to the account. In total 11 management meeting took place at regular intervals.

MOCCA ESRs planned and delivered a myriad of outreach and public engagement activities reaching all sectors of society. They visited both primary and secondary schools to enthuse young mines about photonic sciences. ESRs engaged with industry during secondments but also by attending trade fairs, where they represented MOCCA and its research. MOCCA produced brochures, pamphlets, posters, etc and ran live events with different target audiences. To disseminate their research, the 4 ESRs in MOCCA contributed published 8 peer reviewed journal papers, gave 10 peer-reviewed conference presentations, prepared 5 conference posters, and submitted 12 scientific deliverables, all of which are open access.
WP1 was focusing on new concepts for microresonator comb generation.

WP2 aimed to develop new nonlinear semiconductor material platforms for ultralow-power threshold comb sources. It was, therefore, the prime goal of the MOCCA project to explore novel concepts and material platforms and device designs that can drastically reduce the pump threshold, while improving power conversion efficiency. The new material platforms chosen for the MOCCA sources would allow to co-integrate the nonlinear microresonator with an electrically pumped microlaser in a monolithic approach, thereby drastically reducing footprint and cost while expanding the versatility and application potential of the devices.

WP3 aimed to embed comb sources developed in WP1, WP2 into the fibre cavity. The methodology explores the frequency spitting between clockwise and counter-clockwise modes of the microresonator combined with dual direction mode-locking based on an embedded comb source. Finally, the performance of SNAP-, nonlinear semiconductor material platform- and photonic crystal-based miniature dual-comb generators will be experimentally tested in the context of proof-of-concept applications in metrology and gas spectroscopy.

WP4 was focused on the theoretical study of the role of cavity dispersion for maximum spectral broadening, and how gain, path length fluctuations and environmental factors (such as temperature drifts) may influence the stability of the intra-cavity nonlinear spectral broadening process.

The outcomes of MOCCA advances pushing the research frontiers beyond the state-of-the-art by developing
1. New insight on microresonator and microcavity fabrication technologies
2. New approaches to the development 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 MOCCA 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.
Figure 4 MOCCA Workshop in Rome
Figure 2 MOCCA Workshop in Paris
Figure 3 MOCCA TSW1
Figure 5 MOCCA ESRs and Supervisors