Study of the Vernier Effect Based on the Fabry–Perot Interferometer: Methodology and Application

Haitao Gao,Yanan Zhang,Danping Xu,Chaoyang Li,Junxian Wang,Shubing Zhang,Jian Shen

doi:10.3390/photonics8080304

Abstract

The optical Vernier effect is a powerful tool for improving the sensitivity of an optical sensor, which relies on the use of two sensor units with slightly detuned frequencies. However, an improper amount of detuning can easily cause the Vernier effect to be unusable. In this work, the effective generation range of the Vernier effect and the corresponding interferometer configuration are suggested and experimentally demonstrated through a tunable cascaded Fabry–Perot interferometer structure. We further demonstrate a practical method to increase the magnification factor of the Vernier effect based on the device bandwidth. Only the optical path length of an interferometer probe and the sensitivity of the measurement parameters are needed to design this practical interferometer based on the Vernier effect. Our results provide potential insights for the sensing applications of the Vernier effect.

Highlights

Methodology and Application.The fiber Fabry–Perot interferometer (FPI) has been widely used in many fields due to its stable interference fringes, easy demodulation, and compact structure [1,2,3,4]
The structure of the fiber optic FPI sensor can be grouped into two categories: (i) an intrinsic Fabry–Perot interferometer (IFPI), where the light is reflected by the reflector inside the fiber, a typical example is how the IFPI can be formed by a pair of Bragg gratings separated by a small gap [9], and (ii) an extrinsic Fabry–Perot interferometer (EFPI), where the light exits the fiber and propagates inside the external cavity
We studied the relationship between the optical path length (OPL) ratio of two interferometers and the accordion phenomenon, and it is found that the Vernier effect can be stably generated in the ratio range of 0.67 to 1.5

Summary

Introduction

In 2021, Yi, G et al reported a high-temperature sensor based on the parallel double FPI structure This separate configuration prevents the reference interferometer from being affected by temperature [29]. In another report by the author, the use of a modal interference combined with extreme optical Vernier effects to produce a measurable envelope while maintaining extremely high magnification is proposed. This method demonstrated the ultra-sensitive fiber refraction with a sensitivity of 500 μm/RIU, and the calculated magnification was higher than 850 times that of normal magnification [32]. Our research results provide a reference for the practical application of the Vernier effect

Device

In shown in Figure

Experiments and Discussion

12. Experimental system

12. Experimental

Conclusions