MacV: Miniaturised atomic clocks using VCSEL pump sources

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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.