In this article a Vernier effect based sensor is analyzed and demonstrated experimentally in a tri-microfiber coupler (Tri-MFC) and polarization-maintaining fiber (PMF) loop interferometer (Tri-MFC-PMF) to provide ultrasensitive refractive index and temperature sensing. The main novelty of this work is an analysis of parameters of the proposed Tri-MFC-PMF with the objective of determining the conditions leading to a “strong” Vernier effect. It has been identified by simulation that the Vernier effect is a primary factor in the design of Tri-MFC-PMF loop sensing structure for sensitivity enhancement. It is furthermore demonstrated experimentally that enhancing the visibility of the Vernier spectrum in the Tri-MFC-PMF allows to achieve an ultrahigh refractive index and temperature sensitivity with improved measurement accuracy. Specifically it is shown that small values of the total phase difference ( π / 16 + Nπ )∼( π / 4 + Nπ ), where N is an integer, accumulated over the PMF loop and Tri-MFC loop result in a “strong” Vernier effect. Experimentally an ultrahigh refractive index sensitivity of -20588 nm/RIU and temperature sensitivity of 0.019 nm/°C are demonstrated by utilizing the stronger Vernier effect with “clear” Vernier spectrum. This analysis of the parameters may be useful to future researchers seeking to increase the measurement accuracy of sensors by enhancing the spectral visibility of the Vernier effect in other types of fiber optic interferometers.

A novel micron-range displacement sensor based on a whispering-gallery mode (WGM) microcapillary resonator filled with a nematic liquid crystal (LC) and a magnetic nanoparticle- coated fiber half-taper is proposed and experimentally demonstrated. In the proposed device, the tip of a fiber half-taper coated with a thin layer of magnetic nanoparticles (MNPs) moves inside the LC-filled microcapillary resonator along its axis. The input end of the fiber half-taper is connected to a pump laser source and due to the thermo-optic effect within the MNPs, the fiber tip acts as point heat source increasing the temperature of the LC material in its vicinity. An increase in the LC temperature leads to a decrease in its effective refractive index, which in turn causes spectral shift of the WGM resonances monitored in the transmission spectrum of the coupling fiber. The spectral shift of the WGMs is proportional to the displacement of the MNP-coated tip with respect to the microcapillary’s light coupling point. The sensor’s operation is simulated considering heat transfer in the microcapillary filled with a LC material having a negative thermo-optic coefficient. The simulations are in a good agreement with the WGMs spectral shift observed experimentally. A sensitivity to displacement of 15.44 pm/µm and a response time of 260 ms were demonstrated for the proposed sensor. The device also shows good reversibility and repeatability of response. The proposed micro-displacement sensor has potential applications in micro-manufacturing, precision measurement and medical instruments.

Mechanical force sensors are critical for a wide range of advanced applications. This paper presents a high-performance whispering gallery mode (WGM) force sensor based on a glass-supported microbubble resonator (MBR). By incorporating the proposed glass support design, the proposed sensor achieves the highest force sensitivity reported for MBR-based structures, of 125.71 pm/mN and a detection limit of 52.26 μN. The sensor has a response time of 3.5 ms, enabling rapid detection of dynamic force changes. Further tests show that the sensor is capable of detecting subtle forces, such as those created by water droplets and a gentle breeze, paving the way for potential applications in health monitoring, vibration detection, and other dynamic force-sensing scenarios.

An optical fiber force sensor based on the Vernier effect in cascaded Fabry–Perot interferometers (FPIs) formed by a barium tantalate microsphere and a section of polymethyl methacrylate (PMMA) optical fiber is proposed and investigated. Optical fiber sensors offer numerous advantages over their electronic counterparts, including immunity to electromagnetic interference and suitability for harsh environments. Despite these benefits, current optical fiber force sensors often face limitations in sensitivity, reliability, and fabrication costs. The proposed sensor has the potential to address these issues. Simulations and experimental results demonstrate that the sensor achieves a sensitivity of 9279.66 nm/N in a range of up to 3 mN. The sensor also exhibits excellent repeatability, making it a promising candidate for high-performance force monitoring in various challenging environments.

This study examines the impact of a dual-bottle whispering gallery mode (WGM) microresonator on the performance of a laser structure based on a fiber ring, focusing on the modes switching and generating single- and multi-mode emissions. Through experimental analyses, we demonstrate how the unique geometry of dual-bottle resonators affects lasing behavior, providing insights that could advance applications of the proposed laser structure in telecommunications and photonic sensing systems.

This paper proposes and investigates a novel fiber Fabry–Perot interferometer (FPI) temperature sensor that leverages the Vernier effect for enhanced sensitivity. The sensor comprises a cascade of two FPIs formed by a short polymethyl methacrylate capillary, a barium titanate microsphere, and a cleaved single-mode fiber. The Vernier effect, induced by the dual Fabry–Perot cavities, amplifies the temperature sensitivity. The fabrication process involves the precise alignment and gluing of components, resulting in a simple, cost-effective sensor. The experimental results indicate a temperature sensitivity of 1.90 nm °C ⁻¹ . The sensor also exhibits excellent repeatability and stability, making it suitable for various temperature monitoring applications.