Optical measurement of mechanical parameters is gaining significant commercial interest in different industry sectors. Torsion, twist and rotation are among the very frequently measured mechanical parameters. Recently, twist/torsion/rotation sensors have become a topic of intense fiber-optic sensor research. Various sensing concepts have been reported. Many of those have different properties and performances, and many of them still need to be proven in out-of-the laboratory use. This paper provides an overview of basic approaches and a review of current state-of-the-art in fiber optic sensors for measurements of torsion, twist and/or rotation. Invited Paper

In this article, a novel miniature Fabry-Perot twist/rotation sensor using a four core fiber and quadruple interferometer setup is presented and demonstrated. Detailed sensor modeling, analytical evaluation and test measurement assessment were conducted in this contribution. The sensor structure comprises a single lead-in multicore fiber, which has four eccentrically positioned cores, a special asymmetrical microstructure, and an inline semi-reflective mirror, all packed in a glass capillary housing. A four core fiber positioned in front of a special asymmetrical microstructure and the inline semi reflective mirror defines four Fabry-Perot interferometers. Rotation of the sensors’ asymmetrical microstructure around the axis of the in-line four core fibers´ modulates the path lengths of all four interferometers simultaneously. Proper processing of path length changes of all four interferometers allows for unambiguous and temperature independent determination of the sensor’s rotation angle.

Corrosion-induced optical fiber microbending is demonstrated within this article as an efficient method for the design of sensors for the detection and localization of corrosion events on monitored metal surfaces. The proposed sensors were demonstrated in a single point and fully distributed configurations while applied successfully on bare metal surfaces and underneath corrosion-protective coatings. The intrinsic simplicity in the design and manufacturing of the proposed sensors, reliable corrosion detection, and corrosion localization are the main attributes of the proposed microbend corrosion sensing concept.

This paper describes a Fabry–Pérot sensor-based measuring system for measuring fluid composition in demanding industrial applications. The design of the sensor is based on a two-parametric sensor, which enables the simultaneous measurement of temperature and refractive index (RI). The system was tested under real industrial conditions, and enables temperature-compensated online measurement of emulsion concentration with a high resolution of 0.03 Brix. The measuring system was equipped with filtering of the emulsion and automatic cleaning of the sensor, which proved to be essential for successful implementation of a fiber optic RI sensor in machining emulsion monitoring applications.

This paper presents an all-silica microwire optical sensor designed for both fast response time and high-resolution temperature detection. The sensor consists of a thin optical microwire created at the tip of an optical fiber, configured as a temperature sensitive Fabry-Perot interferometer. For the purposes of achieving rapid response times, the sensing section of the sensor has a diameter of 11 μm. Experimental bench tests were set up to evaluate the sensor’s static and dynamic performance. The results indicate a sensor system resolution of about 5 mK and demonstrate a bandwidth of 38 Hz that corresponds to a response time of 4ms in still air. The sensor’s functionality is shown through a basic periodic gas compression method detecting small temperature fluctuations. In addition, the sensor was demonstrated for operation up to 600 degrees Celsius.

This work presents a compact fiber-integrated sensor designed for high-resolution measurement of electric currents and magnetic fields using a magneto-optic liquid microcell. The primary goal is to develop a miniature, customizable sensor capable of operating in challenging environments where electrical isolation, spatial constraints, and resistance to ambient electromagnetic noise are critical. The sensing element is based on barium hexaferrite nanoplatelets suspended in n-butanol, whose birefringent properties vary in response to external magnetic fields. Microchannels inscribed into standard optical fibers enable precise filling of the microcell with minimal liquid volume, facilitating scalable sensor fabrication. The device measures both direct and alternating currents by detecting the surrounding magnetic field generated by a current-carrying wire. A ferrite toroid core and tunable bias magnetic field improve sensitivity and define three distinct sensor configurations. Theoretical models for each configuration were experimentally validated, demonstrating resolution down to 40 μA in the highest sensitivity setup and an AC measurement bandwidth of 2100 Hz. Temperature stability tests from 25 °C to 50 °C revealed a drift of about –0.004% of the total unambiguous measuring range per °C. These results highlight the sensor’s potential for integration into systems requiring miniature, interference-immune, and adaptable current sensing solutions.