MacV: Miniaturised atomic clocks using VCSEL pump sources

基于相干布居捕获（CPT）的微型原子钟需要低功率、单模激光二极管，其可以在几千兆赫兹下直接调制。垂直腔面发射激光器（VCSEL）是这种应用的理想选择，主要是因为它们具有非常低的功耗、宽的波长调谐系数、降低的光反馈敏感度、延长的器件寿命和小的器件尺寸。商用VCSEL具有约50-100 MHz的线宽，虽然这对于许多其他激光光谱应用可能是一个问题，但它基本上不会损害CPT谐振的质量。相反，由于圆形光束轮廓，VCSEL特别容易受到偏振不稳定性的影响;然而，可以实施几种新颖的设计修改来解决这个问题。目前，英国没有可靠和强大的微型原子钟VCSEL的来源或任何供应链，全球开发最佳波长（Cs D1 - 894 nm）VCSEL的商业制造商数量非常有限。我们的项目将建立一个英国的战略能力，专注于VCSEL激光源的开发和批量生产，专门为支持采用的原子钟应用而定制。这个研究团队将专注于设计在894 nm下以最大调制速度工作的外延层，同时保持合理的线宽。它将有助于设计制造的结构，以确保一个单一的极化。它也将有助于芯片规模的原型和测试结构的特性，快速反馈到外延生长和评估设计的结构在芯片级。

Coherent population trapping (CPT) based miniature atomic clocks require low power, single mode laser diodes that can be directly modulated at a few gigahertz. Vertical Cavity Surface Emitting Lasers (VCSELs) are ideal for this application primarily due to their very low power consumption, wide wavelength tuning coefficient, reduced sensitivity to optical feedback, extended device lifetime, and small device footprint. Commercially available VCSELs have linewidths of ~50-100 MHz, and while this can be a problem for many other laser spectroscopy applications, it does not substantially compromise the quality of a CPT resonance. Conversely, due to the circular beam profile, VCSELs are particularly susceptible to polarisation instabilities; however, there are several novel design modifications that can be implemented to address this issue. Currently, there are no UK sources or any supply chain of reliable and robust VCSELs for miniature atomic clocks and a very limited number of commercial manufacturers globally developing VCSELs at the opimium wavelength for the application (Cs D1 - 894nm). Our project will establish a UK strategic capability focussed on the development and volume production of VCSEL laser sources, tailored specifically for to support the adoption of miniaturised atomic clock applications.This research team will focus on designing the epitaxial layers for operation at 894nm with maximum modulation speed, while maintaining a reasonable linewidth. It will contribute to the design of the fabricated structure to ensure a single polarisation.It will also contribute to the characterisation of chip scale prototypes and test structures for fast feedback to the epitaxial growth and for evaluation of the designed structures at the chip level.