Ultra-High-Q Integrated Optical Microresonators for Frequency Comb Generation

ntegrated photonics is a major emerging technological field with the potential for massive impact on the biomedical, security, defence, transportation, telecoms and other sectors. Specifically, integrated high-Q optical microresonators could form the basis for a vast array of new devices including handheld optical clocks, trace gas detectors, ultraprecise lidar, narrow-linewidth lasers, low-noise microwave sources, biosensors, gyroscopes and optical data transmitters. This project addresses two of the main challenges in bringing such devices to fruition: achieving ultra-high-Q waveguide ring resonators and integrating these with semiconductor lasers on the same chip.
The project will focus on developing silicon nitride waveguide ring resonators with Q factors approaching 108 and above, building upon the latest and most advanced techniques for deposition, nanolithography and etching, and modelling the waveguide geometry to optimise dispersion. The resonators will then be used for frequency comb generation, with emphasis on self-referenced octave-spanning combs for optical clocks and dual-comb spectroscopy. Time permitting, the student will also research techniques to integrate III-V semiconductor lasers with the silicon platform of the silicon nitride resonators in order to realise self-contained monolithic devices.
The new knowledge generated by this project will bring us closer to commercialising a range of exciting on-chip ultra-high-Q microresonator-based technologies.

Complementing our Pathways to Impact document, here we state the expected real-world impact, which is of course the leading priority for our industrial partners. Their confidence that the proposed CDT will deliver valuable scientific, engineering and commercial impact is emphasized by their overwhelming financial support (£4.38M from industry in the form of cash contributions, and further in-kind support of £5.56M).

Here we summarize what will be the impacts expected from the proposed CDT.

(1) Impact on People
(a) Students
The CDT will have its major impact on the students themselves, by providing them with new understanding, skills and abilities (technical, business, professional), and by enhancing their employability.
(b) The UK public
The engagement planned in the CDT will educate and inform the general public about the high quality science and engineering being pursued by researchers in the CDT, and will also contribute to raising the profile of this mode of doctoral training -- particularly important since the public have limited awareness of the mechanisms through which research scientists are trained.

(2) Impact on Knowledge
New scientific knowledge and engineering know-how will be generated by the CDT. Theses, conference / journal papers and patents will be published to disseminate this knowledge.

(3) Impact on UK industry and economy
UK companies will gain a competitive advantage by using know-how and new techniques generated by CDT researchers.
Companies will also gain from improved recruitment and retention of high quality staff.
Longer term economic impacts will be felt as increased turnover and profitability for companies, and perhaps other impacts such as the generation / segmentation of new markets, and companies receiving inward investment for new products.

(4) Impact on Society
Photonic imaging, sensing and related devices and analytical techniques underpin many of products and services that UK industry markets either to consumers or to other businesses. Reskilling of the workforce with an emphasis on promoting technical leadership is central to EPSRC's Productive Nation prosperity outcome, and our CDT will achieve exactly this through its development of future industrially engaged scientists, engineers and innovators. The impact that these individuals will have on society will be manifested through their contribution to the creation of new products and services that improve the quality of life in sectors like transport, dependable energy networks, security and communications.

Greater internationalisation of the cohort of CDT researchers is expected from some of the CDT activities (e.g. international summer schools), with the potential impact of greater collaboration in the future between the next generations of UK and international researchers.