(INVITED)Investigation of liquids with microcavity in-line Mach-Zehnder interferometers – impact of the microcavity shape on the sensing performance

Abstract

In this work, we review microcavity in-line Mach-Zehnder Interferometers (µIMZI) obtained in optical fibers using femtosecond (fs) laser micromachining. These structures can be considered as a great solution satisfying the requirements mentioned above for small-volume RI sensing applicable in label-free biosensing. Furthermore, application of the femtosecond laser facilitates tailoring of the microcavity's shape with high degree of flexibility. Over the years, various µIMZI have been reported, where RI sensing has been mainly analyzed but no impact of the microcavity shape has been shown up to date. Thus, on top of the review on µIMZIs, in this work, we discuss the impact of the shape of the on the sensing performance of the device. We use two representative examples of microcavity shapes, i.e., U-shape and V-trench, made in a standard single-mode fiber. Despite different shapes, both structures offer similar and high RI sensitivity (exceeding 13,000 nm/RIU in the RI range 1.333–1.340 RIU). However, the performance of the structures in microfluidic systems is different. Based on the experimental results and numerical simulations, the advantages and disadvantages of different shapes are discussed for their application in investigations of liquids and biosensing.