COMPACT VISIBLE FREQUENCY COMBS: THE MISSING LINK IN A VISION OF PERVASIVE QUANTUM TIMEKEEPING

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Informed by the requirements of future precision atomic clocks, this project targets the development of an "optical frequency comb" -- a laser providing a thousands of regularly spaced optical frequencies which form a ruler in frequency that is a critical component in quantum timekeeping devices.Quantum technology research in the UK and internationally is developing small atomic clocks to which the frequency of a special laser (not a laser comb) can be locked with extremely high stability. Yet these clocks "tick too fast": the clock laser oscillates at about 500 trillion "ticks per second", far too quickly to allow it to be interfaced to real-world systems like computer networks and electronic navigation devices. The laser comb can be used like a gearwheel to reduce this rate to one more appropriate for everyday applications of about 10 billion ticks per second. In this sense the comb works exactly like the clockwork mechanism in a pendulum clock, reducing the faster ticks of the pendulum to less frequent increments in the positions of the minute and hour hands.To date, practical laser combs with the right technical characteristics have been difficult to produce, even with lab-scale dimensions. This project will address the need for compact combs as sub-systems within a practical optical clock--and the current absence of such technology--by developing a disruptive laser-comb architecture. This will be compatible with visible clock transitions in new ion-based time standards, and will have a scale suitable for integrating into quantum timekeeping devices needed by sectors from security, energy, geodesy, finance and defence.Our approach will leverage advances in ultrafast lasers and integrated nonlinear photonic devices, complementary technologies in which the investigators at Heriot-Watt and Glasgow Universities are world leaders. Areas of emphasis are the development of robustly packaged infrared pulsed lasers operating at around 10 GHz (10 billion "ticks per second"), and the efficient extension of these to the visible region by using chip-scale "super-continuum" devices prototyped in the material gallium arsenide and finally to be made from the material silicon nitride. The output of these lasers will be made into a frequency comb by using a combination of optical and electronic stabilization techniques.The project will be developed in close association with several academic and industrial partners who will contribute resources and expertise in lasers (Laser Quantum Ltd.), optoelectronic manufacturing (Optocap Ltd.), optical frequency metrology (NPL), optical frequency standards (EPSRC UK Quantum Technology Hub in Sensors and Metrology), optical systems engineering (Fraunhofer Centre for Applied Photonics) and expertise in end-user applications of combs (Dstl).Our partners have committed up to £527.5K cash and £182K in-kind support, and span the supply chain from devices and systems, to verification and end-users. This breadth and depth of commitment will ensure that the project gains real-world traction and will have an enduring impact.The modular comb targeted by the project resonates strongly with EPSRC's Photonics for Future Systems priority and addresses key portfolio areas of Optical Devices & Subsystems, Optoelectronic Devices & Circuits, Quantum Devices, Components & Systems and RF & Microwave Devices. By the end of the project we expect to have demonstrated and evaluated this novel laser-comb technology, as well as created considerable new knowledge and IP in the areas of ultrafast lasers and integrated nonlinear photonics. This will leave us in a strong position to translate the technology into systems of commercial and scientific benefit to our industrial and academic partners and wider society.