The research programme of the consortium embraced four work packages pushing frontiers of the microresonator frequency
comb technology in the areas of (1) signal processing and optical communication, (2) spectroscopy, metrology and astronomy,
(3) hybrid integration and packaged solutions for comb generator modules, and (4) frequency conversion using chi(2) nonlinearity.
In (1), the consortium explored applications associated with RF and THz signal processing based on micro-comb technologies
developed numerical and theoretical models and made integrated devices for these applications. We achieved progress
on microresonator applications for wavelength division multiplexing in optical communications and developed space
division multiplexing for massively parallel transmission. We have achieved several results in generating
ultra-broadband combs and demonstrated novel comb-based optical arbitrary waveform generation and detection schemes.
In (2), we developed comb self-referencing on a chip, realised dual-comb spectroscopy with two microcombs of
slightly different repetition rates and explored comb generation in the mid-infrared for molecular spectroscopy applications.
We developed electrically pumped mode-locked lasers on a silicon platform for an integrated dual-comb spectrometer.
Extending combs to visible and infrared was achieved in LiNbO_3-on-insulator waveguide and resonators with cascaded nonlinearity.
(3) The outside-laboratory applications of frequency combs require developing packaged solutions. We developed
the first such devices using microcombs for astro and optical data processing applications. Our technique uses the
so-called photonic wire bonds to connect the different components. We have also explored a more advanced solution
to the problem: using chip-scale light sources integrated on the same chip with a microresonator using the heterogeneously
integrated mode-locked lasers with III/V gain sections, amplifiers, and saturable absorbers that are
all electrically pumped on a single silicon chip.
In (4), the consortium developed the first microcombs based on cascaded second-order nonlinearities using several
material platforms. We demonstrated the first Turing pattern combs in lithium niobate and explored the thin-film
lithium niobate resonators and waveguides for comb generation. Our work on cadmium-silicon-phosphate allowed
us to generate microcombs in the mid-infrared. To achieve these results, we have fabricated whispering-gallery
microresonators for frequency doubling, providing the highest quality factors to date, 10^8.
We predicted and observed first spectrally staggered combs. We have explored gallium-phosphate
and its mixed chi(2) and chi(3) nonlinear response to develop comb sources in the visible.
The significant elements of the training programme delivered by the project consortium were transferrable skills
workshops, hands-on lab courses, webinars and scientific schools. The consortium delivered four transferrable skills workshops
to boost early-stage researchers' employability. These workshops were:
-Computational methods for nonlinear photonics,
-Taking an idea to a product,
-Entrepreneurial challenges and IP management in small and medium R&D businesses,
-Space for physicists (R&D career in space industry).
Training in specific technical skills in demand in the photonics industry and university labs, and essential for
the success of the consortium research programme, were addressed by a series of courses, which included –
-Modern coherent optical communications;
-Large scale photonic integration (two parts);
-Full-field photonic components and integrated circuits;
-Femtosecond laser-based comb technology.
The consortium has organised three scientific schools collocated with conferences for the early-stage researchers,
which attracted many external participants and world-leading experts in the area.
These events have raised the international profile of the research done by the consortium, facilitated the flow of ideas,
dissemination of results and provided practical training in communication skills and life contact with potential employers
for the consortium researchers. Training materials and research outcomes were regularly uploaded to the consortium
website at
https://www.microcomb-eu.org/(opens in new window) and further disseminated using the @microcomb twitter hashtag.
