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In recent years, the performance of an interferometric fiber optic gyroscope (IFOG) has been increased a lot and widely used for dynamic angle measurement. In this paper, we present an investigation on measurement uncertainty of the IFOG and propose a comparison angular vibration calibration approach based on an IFOG. The operation principle of the closed-loop IFOG is introduced, and its error model in angle measurement is derived. Furthermore, the measurement uncertainty components in angular vibration calibration are analyzed by comparing with primary angular vibration calibration. By using a standard angular vibration system in the Nanjing Institute of Measurement and Testing Technology, China, the angular vibration calibration capability of the IFOG is evaluated within frequency range of 1–200 Hz. In addition, the traceability of this proposed calibration approach is also discussed.

Primary angular vibration calibration devices based on laser interferometers play a crucial role in evaluating the dynamic performance of inertial sensing devices. Here, we propose a sinusoidal phase-modulated angle interferometer (SPMAI) to realize angular vibration measurements over a frequency range of 1–1000 Hz, in which the sinusoidal measurement retro-reflector (SMR) and the phase generation carrier (PGC) demodulation algorithm are adopted to track the dynamic angle variation. A comprehensive theoretical analysis is presented to reveal the relationship between demodulation performance of the SPMAI and several factors, such as phase modulation depth, carrier phase delay and sampling frequency. Both the simulated and experimental results demonstrate that the proposed SPMAI can achieve an angular vibration measurement with amplitude of sub-arcsecond under given parameters. Using the proposed SPMAI, the frequency bandwidth of an interferometric fiber-optic gyroscope (IFOG) is successfully determined to be 848 Hz.

In order to accurately evaluate the dynamic performance of inertial devices, this paper proposed an angular vibration test system and method for inertial devices based on heterodyne interference technology. This system is mainly composed of the angular vibration excitation device and the angular vibration measurement device. By installing an angular reflector on the swing table, the dual-frequency laser interferometer (DFLI) can measure the real-time angle value of the swing table, then obtain its amplitude-frequency characteristics with the Fast Fourier Transform algorithm . The experimental results show that the test system can measure angular vibrations exceeding 1000 Hz. Furthermore, the frequency bandwidth of an interferometric fiber optic gyroscope (IFOG) fabricated in our laboratory is evaluated by the angular vibration test system aforementioned, and its cut-off frequency is measured as 375 Hz. Finally, a comprehensive theoretical analysis has been implemented to investigate the uncertainty factors in the DFLI of this system.

A single-mode–multimode–single-mode (SMS) optical fiber-based displacement sensing system mounted on an Ilizarov transverse tibial bone transport device for microcirculation reconstruction is reported. Wide-range displacement is approximated as a uniform extension of a spring that is connected to an SMS optical fiber structure acting as the displacement sensor and allowing full displacement characterization. Transmission spectrum changes are measured, providing a displacement range of 24 mm with a sensitivity of − 55.42 p m / m m and a resolution of 45.2 µm. The experimental results are characterized using a polynomial response curve for measuring the displacement due to transverse distraction of the Ilizarov device. The SMS fiber interrogation system is based on a macrobending fiber edge filter-based ratiometric measurement system. The use of SMS fibers together with the macrobending fiber-based interrogation system eliminates the influence of temperature on the displacement measurement. The implementation of the all-fiber sensing system of this investigation has uniquely facilitated a smart clinical device with a wide displacement range as well as operating in real-time monitoring when attached to the Ilizarov transverse tibial bone transport device. It also means that this fiber-optic sensing device can be made more cost-effective, simpler in construction, and more versatile while providing a high degree of measurement accuracy and resolution.

We propose an all-fiber multimode interferometer based on a core-offset SMS fiber structure, and demonstrate that the lateral core-offset value has a big impact on multimode interference and re-imaging phenomenon within it.

A low-cost optical fibre sensor based on two cascaded balloon-like bent fibre (BBF) structures for simultaneous displacement and temperature measurement is reported. The sensor is fabricated by cascading two balloon-like bent single-mode fibres (SMFs) which with different bending radii, generating two separate interference dips within a limited wavelength range. The wavelength of the two interference dips exhibits different responses to external displacement and temperature variations, hence simultaneous measurement of displacement and temperature is realized. Experimental results show that the proposed optical fibre sensor achieves a displacement sensitivity of −318.8 pm/μm and a temperature sensitivity of 47.4 pm/°C. Taking advantage of its low-cost, ease of fabrication, and experimentally determined high sensitivity, the sensor in this investigation can be potentially applied in both displacement and temperature measurement fields.

peer-reviewed A high sensitivity temperature sensor based on a singlemode-no-core-singlemode (SNCS) fibre structure and surrounded with alcohol within a silica capillary is described. In this investigation, no-core fibre (NCF) is used as the multimode waveguide and alcohol is chosen as the temperature sensitive medium. By packaging the alcohol solution with a short length of NCF enclosed within a silica capillary, the surrounding temperature can be detected by monitoring the variations of transmission loss at a specific wavelength. The theoretical analysis predicts this temperature sensor can provide high sensitivity, and the experimental results support this. The maximum temperature sensitivity of the sample is 0.49 dB/°C with a potential temperature resolution of 0.02 °C at the operating wavelength of 1545.9 nm. In addition, the repeatability and response time of the sensor of this investigation are investigated experimentally.

A relative humidity (RH) sensor based on a simple singlemode-side polished multimode-singlemode (SSPMS) fiber hybrid structure is investigated, which is capable of working over a relatively high-temperature range, at which many RH sensors based on moisture sensitive material coatings cannot operate. The beam propagation method is used to analyze the light transmission characteristics within the side polished multimode fiber (SPMMF) structure. Experimental results show that the SPMMF surface roughness has a significant influence on the sensor's humidity sensing performance, as a result of the adsorption and desorption of water molecules along the side polished surface. A higher surface roughness results in an increased RH sensitivity. It is concluded that the SSPMS fiber structure based RH sensor can achieve around 0.069 dB/%RH within the humidity range of 30%RH–90%RH for a temperature range of 70 °C to 90 °C. In addition, the temperature cross-sensitivity has been investigated experimentally. The developed fiber optic sensor in this investigation provides a simple and effective approach for RH measurement in a variety of production applications.

A novel relative humidity sensor based on a singlemode-side polished multimode-singlemode fibre structure coated with gelatin material is reported. The sensing principle and fabrication method of the proposed sensor are presented. The experimental method is demonstrated to provide the optimum thickness of coating layers in order to achieve the highest sensitivity of 0.14 dB/%RH and a fast response time of 1000 ms for a given relative humidity sensing range. The developed humidity fibre optic sensor based on a gelatin coating shows great potential for many applications such as industrial production, food processing, and environmental monitoring.

The paper describes a multimode-interference-effect-based single-mode–multimode–single-mode (SMS) fiber optic sensing system for wide-range displacement monitoring on an Ilizarov orthopedic external fixation device. Displacement measurement is implemented as the uniform extension of a spring, which is connected to an SMS optical fiber displacement sensor, allowing full displacement characterization. SMS fiber structures are used together with a macrobending-fiber-based interrogation system to measure temperature perturbation and hence eliminate its effect on the displacement measurement. Transmission spectra are measured, achieving a displacement measurement range of 110 mm with maximum sensitivity of −53 pm/mm and a resolution of 500 μm. The all-fiber sensing system has facilitated a clinical device with a wide displacement range operating in real-time when attached to the Ilizarov apparatus.

Many researchers from scientific and industrial fields have devoted their efforts to the laser interferometer, aiming to improve the measurement accuracy and extend the practical applications. Here, we present a modified homodyne laser interferometer based on phase modulation for simultaneously measuring displacement and angle. The active sawtooth wave phase modulation enhances immunity of this interferometer to the environmental fluctuations and laser power drift. Based on polarized optic theory and the sinusoidal measurement retro-reflector, a modified Michelson-type interferometer configuration is designed to simultaneously measure displacement and angle. Phase difference between the reference and measurement interference signals can be obtained using the sawtooth wave phase modulation and zero crossing detection technique, where the real-time displacement and angle values can be derived directly. Experimental results demonstrate our proposed interferometer has good static and dynamic performance.

peer-reviewed A novel optical fiber sensor based on a balloon-shaped bent single-mode (BSBS) fiber structure incorporating a long-period grating (LPG) for simultaneous measurement of displacement and temperature is described and experimentally demonstrated. The sensor is fabricated by splicing a BSBS fiber structure based on a Mach-Zehnder interferometer (MZI) with a long-period grating (LPG). The interference dip formed by the BSBS fiber structure is sensitive to external displacement and temperature variation, while that formed by an LPG only depends on temperature, displacement, and temperature and, therefore, can be unambiguously and simultaneously measured by this sensor. Experimental results show that this sensor offers a high displacement sensitivity of -306 pm/μ m over the displacement range of 0-80 μm and a temperature sensitivity of 42.9 pm/°C over the temperature range of 20-45 °C. Due to its high measurement sensitivities, low cost, and good repeatability, this sensor could be a realistic candidate for applications where displacement and temperature need to be measured simultaneously ACCEPTED peer-reviewed

peer-reviewed A novel, MMI-based all-fiber structure, which consists of two single-mode fibers and a multimode fiber polished on both sides, is described. The light propagation characteristics of this fiber structure, as well as its superior sensing performance, are analysed theoretically by using the beam propagation method (BPM). This fiber structure demonstrates a significant spectral response to changes of the surrounding refractive index (RI), and the measured results exhibit good agreement with the predicted data. The measured average RI sensitivity is as high as 151.29 nm/RIU over an RI range from 1.3450 to 1.4050, when the polished depth is 30 μm on both sides of the multimode fiber. This fiber structure can be an advantageous platform for various applications, especially for a lab-on-fiber type sensing application.

Single-mode-multimode-single-mode (SMS) fibre structures have attracted great attention for their sensing applications in recent years. A typical SMS fibre structure is simply fabricated by sandwiching a multimode fibre (MMF) between two single-mode fibres (SMFs). Owing to its compact structure, easy of fabrication and low-cost, SMS structures are widely applied in a variety of parameter measurements such as temperature, curvature, displacement, magnetic field, refractive index (RI) and humidity, etc. To meet the requirement of high precision measurement, some post-processes for SMS fibre structures are also intensively investigated to improve its sensing performance. The development of the SMS fibre structures based sensors is reviewed in this paper, in which also contains a briefly theoretical introduction for a traditional SMS fibre structure.

peer-reviewed A high sensitivity optical fibre temperature sensor is demonstrated based on a balloon-shaped bent single-mode (BSBS) fibre structure where the fibre retains its original protective polymer coating. The BSBS fibre structure can be simply realized by bending a coated straight single-mode fibre into the balloon shape using a section of silica capillary tube. By adjusting the bending radius of the balloon-shaped fibre section, a modal interferometer between the core mode and the coating mode can be effectively implemented at a suitable bending radius. Considering the intrinsically high thermo-optical coefficient and thermal expansion coefficient of the polymer coating, the BSBS fibre structure offers excellent temperature sensing performance. Experimental results show that the temperature sensitivity is as high as −2465 pm °C−1 with a resolution of 0.008 °C over the temperature range of 20.7 °C–31.7 °C. Based on its simple fabrication process, very low cost, and experimentally determined high sensitivity coupled with good repeatability, the temperature sensor described in this article could be a competitive candidate in many temperature sensing applications.

In this paper, a theoretical and experimental investigation of the multimode interference induced self-imaging phenomenon in a singlemode-multimode-singlemode (SMS) fiber structure is described. The simulated transmission spectra based on guided modal propagation analysis and beam propagation method are presented and compared with experimental obtained results. The temperature dependence of the self-imaging position of the SMS fiber structure is also investigated. These investigations provide excellent opportunities for multiple future applications including telecommunications and sensing.

A fibre-optic strain sensor based on a gourd-shaped joint multimode fibre (MMF) sandwiched between two single-mode fibres (SMFs) is described both theoretically and experimentally. The cladding layers of the two MMFs are reshaped to form a hemisphere using an electrical arc method and spliced together, yielding the required gourd shape. The gourd-shaped section forms a Fabry-Perot cavity between the ends of two adjacent but non-contacting multimode fibres' core. The effectiveness of the multimode interference based on the Fabry-Perot interferometer (FPI) formed within the multimode inter-fibre section is greatly improved resulting in an experimentally determined strain sensitivity of -2.60 pm/με over the range 0-1000 με. The sensing characteristics for temperature and humidity of this optical fibre strain sensor are also investigated.