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Multiscale optical frequency combs: advanced technologies and applications

Periodic Reporting for period 1 - MOCCA (Multiscale optical frequency combs: advanced technologies and applications)

Reporting period: 2019-02-01 to 2021-01-31

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. EID MOCCA address challenges in huge demand of qualified experts by providing for 4 early-stage researchers (ESRs) a world-class advanced training programme which will bring them to the level of the next generation of leaders in the field of photonics. The TP will be 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 provided by synergistic merging the expertise of 3 academic, 2 non-academic beneficiaries and 1 non-academic and 2 academic partners from 4 countries. This will equip 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 (RP) will address 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).
Students are working across several work packages. They reached progress as follows.

ESR1 (WP1-WP3) reached progress in developing microresonator based on Aston technological platform by (i) mastering all the steps of the experimental procedure, from chemical etching to scanning; (ii) programming and automating all technological steps the stages and automatized all the devices used in the fabrication: everything is controlled from the computer; (iii) exploring the technique allowing to create a resonator using tapering, and (iv) by gathering knowledge from theory and recent works in the field and applying it to create a numerical model preceding the fabrication in the lab.

ESR2 (WP1and WP2) achieved the following results: (i) bibliography on salient concepts and the state of the art related to quadratic and cubic combs generation has been collected; (ii) linear optical properties of already fabricated photonic crystal cavities for further nonlinear experiments have been characterised; (iii) the concept of the nanoscale cavity with evenly spaced modes has been implemented in the so-called hybrid silicon/III-V platform developed at C2N.

ESR3 (WP3 and WP4) made a progress in the development of a numerical model for the description of chirped pulses coupled inside micro-resonator for the solitons dynamics formation, namely (i) bibliography on the state of the art of the frequency combs has been collected; (ii) theoretical study of a novel comb generation scheme with amplitude/phase-modulated pump has been done; (iii) numerical simulations of microresonator comb experiments at the Max Planck Institute of Potsdam (Germany) has been started.

ESR4 (WP2) Simulations were performed to design the required racetrack resonator. The final device parameters from the simulation were used to create a mask for stepper lithography. A 6-inch wafer is used for stepper lithography and then patterned into the design using etching processes like RIE (Reactive Ion Etching) etc. Silicon dioxide is used for encapsulation followed by 2d material transfer. Edge couplers are used for coupling light from fibre to the waveguide which will then transfer to the resonator.

Training activities (WP5) organized include MOCCA Workshop I (Fig.2) and 2 and Transferable skills workshop I (Fig.3) and II.
WP1 is focusing on novel approaches to the design of microresonators developed in Aston and Thales. The performance of the developed miniature comb generators will be experimentally analysed, compared with each other, and prepared for industrial applications in high-precision metrology.

WP2 aims to develop new nonlinear semiconductor material platforms for ultralow-power threshold comb sources. It is, 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 aims 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 is 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.

MOCCA project has true potential for strengthening European "Innovation Union” by
• Contributing to the EU’s scientific excellence and leadership in future hot topic technology such as optical frequency combs generation.2028
• 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.
Figure 1
Figure 3 MOCCA TSW1