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.
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