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

根据未来精密原子钟的需求，该项目的目标是开发一种“光学频率梳”--一种提供数千个规则间隔的光学频率的激光器，这些频率形成频率的尺子，这是量子计时设备中的关键部件。英国和国际上的量子技术研究正在开发小型原子钟，特殊激光(而不是激光梳子)的频率可以以极高的稳定性锁定到该频率上。然而这些时钟“滴答滴答地走得太快了”：时钟激光以大约500万亿“每秒滴答”的速度振荡，太快了，无法与计算机网络和电子导航设备等现实世界的系统连接。激光梳子可以像齿轮一样使用，将这一速度降低到更适合每天大约100亿刻度每秒的应用。从这个意义上说，梳子的工作原理就像钟摆时钟中的发条装置，将钟摆的较快滴答声减少到分针和时针位置上不太频繁的增量。到目前为止，即使是实验室规模的尺寸，也很难生产出具有正确技术特征的实用激光梳子。该项目将通过开发一种颠覆性的激光梳子结构，解决将紧凑型梳子作为实际光学时钟中的子系统的需求，以及目前缺乏此类技术的问题。这将与基于离子的新时间标准中可见的时钟转换兼容，并将具有适合集成到安全、能源、大地测量、金融和国防等部门所需的量子计时设备的规模。我们的方法将利用超快激光和集成非线性光子设备的进步，这是Heriot-Watt大学和格拉斯哥大学的研究人员处于世界领先地位的互补技术。重点领域是开发工作在约10 GHz(100亿“每秒刻度”)的坚固封装的红外脉冲激光器，并通过使用以砷化镓材料为原型并最终由氮化硅材料制成的芯片级“超连续”器件，将这些脉冲激光器有效地扩展到可见光区域。这些激光的输出将通过光学和电子稳定技术的组合被制成频率梳。该项目将与几个学术和工业合作伙伴密切合作开发，这些合作伙伴将在激光(激光量子有限公司)、光电子制造(OptoCap有限公司)、光学频率计量(NPL)、光学频率标准(EPSRC英国传感器和计量技术中心)、光学系统工程(弗劳恩霍夫应用光子学中心)和最终用户应用梳子(DSTL)方面的专业知识方面提供资源和专业知识。我们的合作伙伴已承诺提供高达527.5K现金和182K实物支持，并跨越从设备和系统到供应链的整个供应链提供给核查人员和最终用户。这一承诺的广度和深度将确保该项目获得现实世界的吸引力并将产生持久的影响。该项目的目标是模块化梳子，与EPSRC的面向未来系统的光子学优先事项产生强烈共鸣，并涉及光学器件和子系统、光电器件和电路、量子器件、组件和系统以及射频和微波器件的关键投资组合领域。到项目结束时，我们预计将演示和评估这种新的激光梳状技术，并在超快激光和集成非线性光子学领域创造相当多的新知识和知识产权。这将使我们处于有利地位，将技术转化为有利于我们的工业和学术合作伙伴以及更广泛的社会的商业和科学利益的系统。

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.