A brief review of Whispering Gallery Mode in sensing

The Whispering Gallery Mode (WGM) operates on principles akin to those of acoustics. It involves an optical micro-cavity with an echo wall structure, where light waves undergo continuous reflection along the micro-cavity boundary, resulting in the formation of a high quality factor (Q) value. This mode finds applications in various fields, including miniature lasers, sensors, light filters, and optical switches. In comparison to alternative laser technologies, those based on the WGM principle, such as liquid crystal (LC) droplet resonators, solid resonators, and all-optical tunable micro-cavity lasers, exhibit superior sensitivity and high Q. Numerous research groups are actively exploring the potential applications of the WGM. This paper aims to provide a comprehensive introduction to WGM concepts. This article aims to introduce the concept of WGM comprehensively. This paper introduces the fundamental parameters of WGM, conducts a theoretical analysis of the electromagnetic field within the micro-cavity, and explores the optical and sensing characteristics of LC. Furthermore, the paper presents various types of WGM lasers, encompassing solid active resonators, solid passive resonators, liquid active resonators, and liquid passive resonators. The final section of the paper offers a concise overview of the application of resonant cavities based on the WGM in biochemical molecular studies, life sciences, and physical sensing. The paper aims to elucidate the principles and applications of WGM, thereby contributing to the advancement of this promising area of research.