MacV: Miniaturised atomic clocks using VCSEL pump sources

基于相干种群捕获（CPT）的微型原子钟需要低功率单模激光二极管，可以直接调制到几兆赫兹。垂直腔面发射激光器（VCSELs）是这种应用的理想选择，主要是因为它们的功耗非常低，波长调谐系数宽，对光反馈的灵敏度降低，器件寿命延长，器件占地面积小。商用vcsel的线宽为~50-100 MHz，虽然这对于许多其他激光光谱应用来说可能是一个问题，但它不会实质上损害CPT共振的质量。相反，由于圆形光束轮廓，vcsel特别容易受到极化不稳定性的影响；然而，有几个新颖的设计修改可以实现来解决这个问题。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，全球范围内非常有限的商业制造商在应用的最佳波长（Cs D1 - 894nm）上开发vcsel。我们的项目将建立一个英国战略能力，专注于VCSEL激光源的开发和批量生产，专门为支持小型化原子钟应用而定制。本研究团队将专注于设计可在894nm以最大调制速度工作的外延层，同时保持合理的线宽。这将有助于制造结构的设计，以确保一个单一的极化。它还将有助于芯片规模原型和测试结构的特征，以便对外延生长进行快速反馈，并在芯片级对设计结构进行评估。

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.