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

根据未来精密原子钟的要求，该项目的目标是研制一种“光频梳”--一种激光器，它提供数千个规则间隔的光频，这些光频形成一个频率标尺，是量子计时设备的关键部件。英国和国际上的量子技术研究正在研制小型原子钟，一种特殊激光的频率可以与之匹配。（不是激光梳）可以以极高的稳定性锁定。然而，这些时钟“走得太快了”：时钟激光器的振荡速度约为500万亿“每秒走”，太快了，以至于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。激光梳可以像齿轮一样使用，以将该速率降低到更适合于每秒约100亿次滴答的日常应用的速率。从这个意义上说，激光梳的工作原理与摆钟中的发条装置完全相同，将钟摆的快速滴答声减少到分针和时针位置的不太频繁的增量。迄今为止，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。该项目将通过开发一种破坏性的激光梳结构来解决对紧凑型梳作为实用光学时钟内的子系统的需求，以及目前缺乏这种技术的问题。这将与新的基于离子的时间标准中的可见时钟转换兼容，并将具有适合集成到安全，能源，大地测量，金融和国防部门所需的量子计时设备中的规模。我们的方法将利用超快激光和集成非线性光子器件的进步，这些互补技术在赫瑞瓦特和格拉斯哥大学的研究人员中处于世界领先地位。重点领域是开发工作在10 GHz（每秒100亿次“滴答”）左右的坚固封装的红外脉冲激光器，并通过使用砷化镓材料原型的芯片级“超连续”器件将这些有效扩展到可见光区域，最后由氮化硅材料制成。这些激光器的输出将通过使用光学和电子稳定技术的组合制成频率梳。该项目将与几个学术和工业合作伙伴密切合作，他们将贡献激光器的资源和专业知识（Laser Quantum Ltd.），光电制造（Optocap Ltd.），光频计量（NPL）、光频标准（EPSRC UK Quantum Technology Hub in Sensors and Metrology）、光学系统工程（Fraunhofer Centre for Applied Photonics）以及在最终用户应用方面的专业知识（Dstl）。我们的合作伙伴承诺提供高达52.75万英镑的现金和18.2万英镑的实物支持，并涵盖从设备和系统到验证和最终用户的供应链。该项目所针对的模块化梳与EPSRC的未来系统光子学优先事项产生了强烈的共鸣，并解决了光学器件和子系统，光电器件和电路，量子器件，组件和系统以及RF和微波器件的关键投资组合领域。到项目结束时，我们预计将展示和评估这种新型激光梳技术，并在超快激光器和集成非线性光子学领域创造大量新知识和知识产权。这将使我们处于有利地位，将技术转化为对我们的工业和学术合作伙伴以及更广泛的社会有益的商业和科学系统。

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.