Industrial Pathway to Micro-Comb Lasers

In 2005, the Nobel Prize in Physics was awarded to Hall and Hänsch for their breakthrough in spectroscopy and metrology. They created a laser called an "optical comb". Combs are often referred to as optical rulers: their spectrum consists of a precise sequence of discrete, equally spaced narrow laser lines, which represent precise "marks" in frequency. This achievement led to a revolution in metrology. Thanks to these peculiar lasers, high-precision atomic clocks could be developed which unveiled a new world in just a few years, allowing measurement in astronomy, particle physics, biology and geology with unprecedented accuracy.

The possibility of miniaturizing such sources is pursued by scientists around the world, to create tiny ultra-precise "optical hearts" for future high-tech devices. Linked to an atomic reference, a micro-comb can be a fundamental part of a miniature atomic clock, envisioned in the UK as a breakthrough 2.0 quantum technology.

A clock is generically constituted by a reference and a counter, respectively the pendulum and the clockwork in old-fashioned clocks. In state-of-the-art atomic clocks, such parts are an atomic optical reference and an optical frequency comb. When locked, for example, to narrow atomic transitions, the optical frequency comb acts as the counter of an atomic clock and can enable accuracies of 10^(-18)s.

The realization of these optical sources in compact forms based on small-scale, micro-metre size devices, will represent a fundamental breakthrough, especially in terms of complexity management, power consumption, costs and handling. Presently, optical comb technology is bulky, fitting the size of a small car. Low footprint, low-power consuming comb sources (enabling battery-powered or wall-plug operation, and thus portable implementations) would represent a revolution in many fields.

A micro-comb based atomic clock is a transformative technology, strategic in keeping pace with our ever-increasing need for high-precision timing in computing, financial transactions and communication, fundamentally affecting the way we build our social infrastructure.
It will also open up new possibilities for innovation and research across many areas of technology. These tiny pulsating devices could be used to enable measurement of low concentrations of gases, as part of an instrument for breath analysis, or for detecting gas leakages in quality control and safety.

They will be used in space to measure the red-shift of the stars, as part of extremely sensitive gravitational sensors mapping the surface of the earth helping our agricultural system or the development of complex city underground-infrastructures. They will become incorporated into and reduce the size of many types of new and existing sensors and they will be used as a precise time reference in navigation equipment.

Backing up this vision, the objective of this proposal is to establish and translate novel technology for the development of compact micro-combs, capable of producing a set of precise optical laser lines.
The micro-comb is generated on a micrometric scale resonator, which will be produced by laser engraving of glass rods or with commercial optical fibre technology. This device will be inserted in a fibre laser cavity, to produce a robust and broadband optical radiation composed of equally spaced laser lines.

We will study strategies to link these lines to precise optical references, which could be eventually replaced by state-of-the-art atomic references, obtained by trapping a single ion or cooling a few atoms.

The technology transfer will be maximised by strong industrial partnerships and use of commercial, off-the-shelf, optical technologies, resulting in a turn-key prototype ready for the UK commercial exploitation.

This proposal aims to bring to industrial maturity, from technology readiness level (TRL) 3 to 6, a transformative technology for compact optical frequency combs based on an optical micro-cavity nested in a fibre laser. Together with MSquared and NPL, established UK industrial companies and potential commercialisation partners, we will work to maximise the industrial potential of the technology.

1 Technology Transfer and Advancement of Knowledge. The photonics academic/R&D communities will benefit from the advancement of fundamental knowledge on high-challenge problems in the field, e.g. understanding the nonlinear rules of wave interaction in oscillators and the degrees of freedom for wavelength manipulation of a comb in micrometre size optical resonators.
Researchers engaged in the development of atomic clock technology and the photonics industry are the direct beneficiaries of a tailored transfer of knowledge from the field of micro-combs: e.g. how a micro-comb can be effectively produced with off-the-shelf optical components, how it can be locked to an atomic reference and how this enables key development in the industry of atomic clocks. Eventually, this research will enable the atomic and quantum academic communities to transfer methods and approaches to application and industry.

2 Economy and Industry. Proof of concept devices (TRL4-6), are a direct deliverable of this research. This proposal exploits micro-cavities that recently reached the market (Lenterra, OEWaves) or can be fabricated with commercial fibre technologies. The final device targets the market of optical frequency comb lasers, proposing a product with dramatically improved performance in terms of power consumption and compactness. Partner teams at MSquared and NPL are expected to benefit directly both from the transfer of know-how (e.g. micro-cavity lasers) from the generation of joint IP and commercialisation. Industry sectors involved in fibre technology and ion beam deposition, which we will approach as possible partners in the dissemination of this proposal, are potential beneficiaries. Routes for licensing University-generated IP to industry will be developed during the proposal. In the long term, these devices will be vital sub-systems in high-accuracy, commercial portable atomic clocks.

4 Cross-disciplinary scientific and societal impact. Compact and practical micro-combs will provide portable atomic clocks, answering the need for exceptional timing accuracy in a practical form factor. Specifically, telecommunications and financial market will require high temporal accuracy for the next generation of 5G systems and timestamps on transactions, respectively. In the longer term, in conjunction with state-of-the-art quantum gravimeters and accelerometers, atomic clocks are expected to revolutionise navigation systems. In the medium term, combs are striking tools for high precision spectroscopy: miniature combs can have key application in the monitoring of hazardous gases in the atmosphere, breath control, improving the security and health of the population, but also in the manufacturing process of the electronics and pharmaceutical industries.

5 Training of highly qualified personnel, and development of new skills. This proposal involves two PhDs and one PDRA who will receive advanced training on nonlinear photonics techniques, laser mode-locking, ultra-fast electrical measurements, micro-resonators as well as broader skills in project management, communication and presentation. The team that I direct at Sussex will acquire the necessary skills for establishing itself as international leader in the field. Personally, I will strengthen my leadership skills by expanding my knowledge base of industrial and market needs. As a Rutherford fellow, I will shape a fully independent research program based on an academic/industrial network, while providing the UK with a state-of-the-art prototype technology.