Effects of surface roughness and top layer thickness on the performance of Fabry-Perot cavities and responsive open resonators based on distributed Bragg reflectors

TL;DR

This paper analyzes how surface roughness and top layer thickness affect the quality factor of DBR-based Fabry-Perot and open resonators, highlighting the importance of minimizing roughness for optimal performance.

Contribution

It provides a comprehensive analysis of the effects of surface roughness and layer thickness on DBR resonator performance, emphasizing practical implications for device fabrication.

Findings

Surface roughness reduces the quality factor significantly.

Maximum achievable quality factor is limited by surface roughness.

Designs must account for roughness to optimize resonator performance.

Abstract

Optical and acoustic resonators based on distributed Bragg reflectors (DBRs) hold significant potential across various domains, from lasers to quantum technologies. In ideal conditions with perfectly smooth interfaces and surfaces, the DBR resonator quality factor primarily depends on the number of DBR pairs and can be arbitrarily increased by adding more pairs. Here, we present a comprehensive analysis of the impact of top layer thickness variation and surface roughness on the performance of both Fabry-Perot and open-cavity resonators based on DBRs. Our findings illustrate that even a small, nanometer-scale surface roughness can appreciably reduce the quality factor of a given cavity. Moreover, it imposes a limitation on the maximum achievable quality factor, regardless of the number of DBR pairs. These effects hold direct relevance for practical applications, which we explore further through two case studies. In these instances, open nanoacoustic resonators serve as sensors for changes occurring in dielectric materials positioned on top of them. Our investigation underscores the importance of accounting for surface roughness in the design of both acoustic and optical DBR-based cavities, while also quantifying the critical significance of minimizing roughness during material growth and device fabrication processes.