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The majority of current methods for measuring the angular deflection of a laser beam enable measurement only in one selected plane. However, there are tasks in which measurements of laser beam deflections in 3D are required. In this paper, we present a way of enabling two-axial measurements of the deflection of a beam based on a single-axis sensor. The key idea is to direct a laser beam, alternately, into one of two arms of a measurement system. In the first arm, the beam is transmitted directly to the angular sensor, while in the second, the beam is directed to the sensor via a special optical element that rotates the plane of the beam deflection; in other words, this element changes the deflection in the horizontal plane into a deflection in the vertical plane, and vice versa. To alternate the path of the beam, a variable phase retarder and a polarising beamsplitter are used. The proposed technique was experimentally verified, and the results confirm its effectiveness. [ABSTRACT FROM AUTHOR]

The majority of current methods for measuring the angular deflection of a laser beam enable measurement only in one selected plane. However, there are tasks in which measurements of laser beam deflections in 3D are required. In this paper, we present a way of enabling two-axial measurements of the deflection of a beam based on a single-axis sensor. The key idea is to direct a laser beam, alternately, into one of two arms of a measurement system. In the first arm, the beam is transmitted directly to the angular sensor, while in the second, the beam is directed to the sensor via a special optical element that rotates the plane of the beam deflection; in other words, this element changes the deflection in the horizontal plane into a deflection in the vertical plane, and vice versa. To alternate the path of the beam, a variable phase retarder and a polarising beamsplitter are used. The proposed technique was experimentally verified, and the results confirm its effectiveness.

Laser distance sensors are a widespread, fast and contactless approach for distance and surface topography measurements. Main characteristics of those sensors are given by resolution, measurement speed and sensor geometry. With decreasing sensor size, the alignment of the optical components in sensor setup becomes more challenging. The depth response of optical profilers is analyzed to obtain characteristic parameters and, thus, to value the alignment and the transfer behavior of those sensors. We present a novel miniaturized sensor setup comprising of confocal and interferometric confocal signals within one sensor in order to compare both principles simply by obscuring the reference arm by an absorber. Further, we introduce a theoretical signal modeling in order to analyze influences such as spatial coherence, Gaussian beam characteristics and tilted reflectors on depth response signals. In addition to this, we show that the coherent superposition significantly reduces the axial resolution due to the confocal effect in interferometric signals compared to simple confocal signals in measurement and simulation results. Finally, an appropriate fit function is presented, in order to figure out characteristic sensor parameters from the obtained depth response signal. In this context, a good agreement to simulated and measured signals is achieved. [ABSTRACT FROM AUTHOR]

A fully automated electrically controlled tunable interference-based microwave sensor is demonstrated with broadband complex permittivity measurements of aqueous solutions within the frequency range of 12–18 GHz. To construct deep destructive interference over the above-mentioned bandwidth, two quadrature hybrids (QHs or 90° coupler) split and combine the signals of material-under-test (MUT) channel and reference liquid (REF) channel with 180° phase shift. Together with voltage variable phase shifters (PSs) and attenuators in both channels, the destructive interference nulls of the desired frequency can be easily tuned having a $Q$ -factor of $2.67\times {10}^{3}$. A coplanar waveguide (CPW) sensor design was used as the microwave sensing structure and closed microfluidic channel was designed and manufactured with polydimethylsiloxane (PDMS) to facilitate the alteration of MUT, REF, and calibration liquids. Benefiting from electrically controlled PS and attenuator, the measurement system is fully automated for accurate and fast broadband microwave liquid characterization. Measurement of 2-propanol-water solutions (isopropyl alcohol (IPA) solutions) with volume concentration of 1% is performed to illustrate automation processes and its high sensitivity. A mathematical model improved from those in the literature by taking conductor loss and mismatch effects into consideration was applied to extract MUT permittivity, generalizing the calibration procedure with the air and deionized (DI) water as calibration materials, which results in improvements in accuracy, sensitivity, and effective MUT volume. Comparing to state-of-the-art sensors, the proposed setup has an average relative error (ARE) of 1.443% for the effective volume of 5.18 $\mu \text{L}$. The complex permittivity of 2-propanol-water solutions with different mole fractions were obtained and confirmed with current literature data. [ABSTRACT FROM AUTHOR]

A highly sensitive, large throughput and wide dynamic range (in the aspect of size and material type) broadband tunable microwave interferometer based rectangular waveguide wear debris detection system is presented. Passing of (non)ferrous and (non)conductive particles through the sensor, which causes inductance and/or capacitance changes, are detected as transmission signal variations of the system. We first demonstrate the sensing principle with the aluminum particle of $800~\mu \text{m}$ and epoxy resin particle of 1 mm3 at 6 GHz. Then, the effects of particle size and flow speed are tested with aluminum particles ranging from $200~\mu \text{m}$ to 1.8 mm. The measurement results show that the system is able to measure particle sizes with known material and differentiate nonconductive particles from conductive ones. With the proposed data processing techniques, this system is capable of detecting as small as $76~\mu \text{m}$ particles within an 8 mm outer diameter tube. And with future improvements on sensitivity and particle material characterization, the proposed system has the potential to differentiate (non)ferrous and (non)conductive particles and measure their sizes as a real-time wear debris sensing devices for rotating and reciprocating machines. [ABSTRACT FROM AUTHOR]

This paper presents a novelty approach to usage of the fiber-optic phase-based sensor in railway transportation. We designed and tested the real deployment of this sensor working on the principle of light interferences within optical fibers. The proposed construction of the sensor allowed to increase the sensitivity and thanks to this can be detected and calculated individual axles and wheels of tram vehicles. We performed long-time period measurements (April to September 2019) in diverse climatic conditions, including measurements of 642 tram passages (several different construction types) in real urban traffic. The detection accuracy level was slightly above 99.4 %.

This paper presents a novelty approach to usage of the fiber-optic phase-based sensor in railway transportation. We designed and tested the real deployment of this sensor working on the principle of light interferences within optical fibers. The proposed construction of the sensor allowed to increase the sensitivity and thanks to this can be detected and calculated individual axles and wheels of tram vehicles. We performed long-time period measurements (April to September 2019) in diverse climatic conditions, including measurements of 642 tram passages (several different construction types) in real urban traffic. The detection accuracy level was slightly above 99.4%. [ABSTRACT FROM AUTHOR]

New possibilities of vibration monitoring can be found in completely different physical approaches, where all measuring technology is currently based on sensors in the electrical domain. This paper presents two different promising alternative approaches to vibration measurement, specifically in the field of fiber-optics and pneumatic sensors. The proposed solution uses a Michelson fiber-optic interferometer designed without polarization fading and with operationally passive demodulation technique using three mutually phase-shifted optical outputs. Experimentally developed sensor systems for the registration of anthropogenic seismic phenomena were complemented by standard instrumentation for measuring seismicity used as a standard. The measurement was performed under simplified conditions using a calibrated stroke as a source of dynamic loading. In addition to alternative systems, the paper also presents the results of recalculation of the measured values in a time domain and basic relationships for the conversion to basic units derived from the SI (International System of Units) system and used internationally in the field of seismic engineering. The results presented demonstrate that even systems operating on a different physical principle have great potential to replace the existing seismic devices. The correlation coefficients for both sensory devices were high (above 0.9) and the average deviations from the measured values of the amplitude of the oscillation velocity did not exceed the value of 0.02, neither with the fiber-optic or pneumatic sensor.

• Detailed FPGA resource budget analysis is provided to certify that latency is the most important factor to support large scale sensor array. • This paper presents a complete design of the interrogation controller based on FPGA with optimized pipeline to reduce latency. • To the best of our knowledge, it is the first work to build the real-time interrogation controller that can support more than 1000 sensors. Fiber-optic sensor arrays are always organized utilizing hybrid time division multiplexing (TDM)/wavelength division multiplexing (WDM) techniques to share some common optical components and reduce the cost. Modern sensor arrays can support up to several thousands of sensors by employing distributed amplification technique. They generate huge amount of data and pose other big challenge on the interrogation controller of the sensor system, such as long demodulation time and heavy computational burden. Aiming to solve these problems, we present a complete design of the interrogation controller based on a field programmable gate array (FPGA) by lending its powerful parallelism potential. The interrogation controller adopts a hardware-implementation-friendly modulation method called the rectangular-pulse binary (RPB) modulation. The functional modules in the FPGA are properly organized according to the working principle of the RPB method and carefully designed by optimizing their pipeline architecture to minimize the output latency, which is essential to increase the maximal supportable number of sensors. By analyzing the resource budget and the actual resource consumption result, it demonstrates that the controller can support up to 1000+ sensors in real time by using a single middle-end Stratix III FPGA chip. A 8-sensors array prototype is constructed to validate its functionality. This work can greatly reduce the cost of the sensor system and push it closer to the practical applications. [ABSTRACT FROM AUTHOR]

In this work, the performance of five different fiber optic sensors at cryogenic temperatures has been analyzed. A photonic crystal fiber Fabry-Pérot interferometer, two Sagnac interferometers, a commercial fiber Bragg grating (FBG), and a π-phase shifted fiber Bragg grating interrogated in a random distributed feedback fiber laser have been studied. Their sensitivities and resolutions as sensors for cryogenic temperatures have been compared regarding their advantages and disadvantages. Additionally, the results have been compared with the given by a commercial optical backscatter reflectometer that allowed for distributed temperature measurements of a single mode fiber. [ABSTRACT FROM AUTHOR]

As the infrastructure grows, space on the surface in the urban area is diminishing, and the view of the builders is increasingly moving underground. Implementation of underground structures, however, presents a number of problems during construction. One of the primary side effects of tunnel excavation is vibration. These vibrations need to be monitored for potential damage to structures on the surface, and this monitoring is an integral part of any such structure. This paper brings an original pilot comparative study of standard seismic instrumentation with experimentally developed fiber-optic interferometric and acoustic systems for the purpose of monitoring vibration caused by the blasting operation. The results presented show that systems operating on physical principles (other than those previously used) have the potential to be an alternative that will replace the existing costly seismic equipment. The paper presents waveform images and frequency spectra from experimental measurements of the dynamic response of the rock environment, due to blasting operation performed shallowly during the tunnel excavation of a sewer collector. In the time and frequency domain, there is, by comparison, significant agreement both in the character of the waveform images (recording length, blasting operation timing) and in the spectra (bandwidth, dominant maxima).

Magnetic field sensing is an important issue for many application areas, such as in the military, industry and navigation. The current sensors used to monitor this parameter can be susceptible to electromagnetic interferences, however due to their advantages over the traditional sensors, the optical fiber devices could be an excellent alternative. Furthermore, magnetic fluid (MF) is a new type of functional material which possesses outstanding properties, including Faraday effect, birefringence, tunable refractive index and field dependent transmission. In this paper, the optical fiber magnetic field sensors using MF as sensing element are reviewed. Due to the extensive literature, only the most used sensing configurations are addressed and discussed, which include optical fiber grating, interferometry, surface plasmon resonance (SPR) and other schemes involving tailored (etched, tapered and U-shaped) fibers.

In order to expand the dynamic range of fiber-optic interferometric demodulation, a novel phase compensation scheme based on the phase generated carrier arctangent algorithm (PGC-arctan) is proposed, which overcomes the limitation of the amplitude range from $- \pi /2$ to $\pi /2$ for arbitrary signals; and a Michelson interferometer measurement system is established to verify the rationality of the compensation algorithm. The phase compensation algorithm is based on analysis of the instantaneous function of the arctangent signal during the phase hopping process, while overcoming the problem of phase winding. Experimental results confirmed the feasibility of the phase compensation scheme as predicted by theoretical and simulation analysis. In particular, the new scheme was shown to be effective in responding to arbitrary large-amplitude and time-dependent vibrational input, with the additional benefit of a strong ability to suppress system and ambient noise. [ABSTRACT FROM PUBLISHER]

Heavy metal pollution in natural water environment is always a concern in both human and ecosystem health. All current systems available in the market for detecting heavy metal ions have common drawbacks such as bulky size, expensive set-up and costly maintenance. This paper presents an optical microfiber sensor functionalized with chelating agent to detect the existence of specific heavy metal ions of low concentration. To the best of our knowledge, coating of chelating agent on silica microfiber of very small diameter (3.9 μm) is the first such report. A clear spectral shift was observed when the sensor was immersed into metal ion solution of concentration 10 ppb. [ABSTRACT FROM AUTHOR]

• The demonstrated sensor possesses negligible crosstalk between the sensing elements and good stability at temperature up to 900 °C. • An in-house fabricated four-hole asymmetric pure silica microstructured optical fiber is used as the pressure sensing fiber. • Each sensing element is constructed by simply splicing the pressure sensing fiber between two single mode fibers. • The spatial frequency associated with each sensing element is separated by creating distinct optical path lengths through choosing different lengths of the pressure sensing fiber and/or by changing the mode coupling to allow different mode pairs to interfere. • Fourier technique is used to demultiplex the sensing elements. • The multi-point pressure sensor has good potential to be used in harsh environment industrial applications such as oil and gas industries. We demonstrate a multipoint optical fiber pressure sensor for high temperature operation using multimode interference. Each sensing element consists of a four-hole asymmetric multimode fiber acting as the pressure sensing fiber, spliced between two standard polarization-maintaining single mode fibers. Multiple sensing elements are serially connected for multipoint pressure sensing and demultiplexing is achieved using Fourier analysis. The spatial frequency associated with each sensing element is separated by having distinct optical path lengths. The pure silica material of the sensing fiber enables high-temperature operation. As a proof of concept, we demonstrate two-point pressure sensing at a temperature up to 900 °C with negligible crosstalk between the sensing elements and good stability. Our demonstrated sensor has potential applications in heavy industry where spatially resolved measurements of pressure at high temperature may lead to improvements in efficiency and safety. [ABSTRACT FROM AUTHOR]

In this work, the performance of five different fiber optic sensors at cryogenic temperatures has been analyzed. A photonic crystal fiber Fabry-Pérot interferometer, two Sagnac interferometers, a commercial fiber Bragg grating (FBG), and a π-phase shifted fiber Bragg grating interrogated in a random distributed feedback fiber laser have been studied. Their sensitivities and resolutions as sensors for cryogenic temperatures have been compared regarding their advantages and disadvantages. Additionally, the results have been compared with the given by a commercial optical backscatter reflectometer that allowed for distributed temperature measurements of a single mode fiber.

miniature fiber-optic Fabry-Pérot cavity interferometerA miniature fiber-optic Fabry-Pérot cavity interferometer is presented. The interferometer is fabricated at the fiber tip by wet chemical etching using hydrofluoric acid. A concave well is created on the fiber end face. Interference happens between the reflections from the fiber core and the end of the cladding. We demonstrate applications of the interferometric sensor for temperature and gas refractive index sensing. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Interferometric radar sensor. [•] Level gauge. [•] Field tests. [•] Laboratory tests. [Copyright &y& Elsevier]

Application of a fibre-optic Sagnac interferometer as a rotational seismometer is presented in this paper. It is a new device which parameters (sensitivity equal to 4.3×10−8 rad/s for 2σ) are comparable with the parameters of typical mechanical rotational seismometers. However, a direct measurement of rotation without influence of linear motions for fibre-optic rotational seismometer designed it for a direct measurement of a ground rotation component. Experimental data obtained during simultaneous application of the above two types of sensors are also presented. Research of near-field seismic events, the amplitude of which has been identified in the range of 1.5×10−6 rad/s to 2×10−7 rad/s, shows directly that, so-called, seismic rotational waves exist independently of typical seismic waves generated during earthquakes. [ABSTRACT FROM AUTHOR]

Two long-period gratings (LPGs) fabricated in series in an optical fiber form a Mach-Zehnder interferometer, producing a sinusoidal channelled spectrum within the characteristic LPG attenuation bands, which has the appearance of an interference fringe pattern. The phase of the fringes is sensitive to changes in the surrounding environmental parameters, such as refractive index. Fabrication of a number of identical cascaded LPG pairs with different separations produces independent fringe patterns of different frequencies within the attenuation bands. The application of basic Fourier techniques to analyze the transmission spectrum allows the phase of each fringe pattern to be determined independently, facilitating the differentiation of external effects acting on each interferometer [ABSTRACT FROM PUBLISHER]

A novel Mach-Zehnder interferometer (MZI) based on dual antiresonant reflecting optical waveguides (ARROWs) for sensing is proposed. By adjusting the degree of structural symmetry to control the coupling behavior of the dual ARROW, an interferometric sensor without any bending structure can be realized. Operating principles and simulation characteristics of the device are discussed in detail. The refractive-index detection limit of the order of 10-5 is achieved. [ABSTRACT FROM PUBLISHER]

In this paper, we propose an interrogation system capable of multiplexing four identical Fabry-Perot (FP) interferometric sensors using two wavelength-division multiplexing devices. One is a 40-channel DWDM channel monitor, the other a four-channel CWDM device. The sensors are connected to the output channels of the CWDM device in order to assign a portion of the spectrum to each sensor. The reflected spectra are then analyzed using the DWDM channel monitor. By monitoring the power incident on each of the DWDM channels, the four sensor reflection spectra can be reconstructed in software and information relating to the measurand obtained. Based on software simulations and previous laboratory experiments with single sensors, it is predicted that this system would be capable of interrogating four EFPI strain sensors simultaneously at frequencies greater than 5 kHz with a resolution of approximately 2 με and a range of 3000 με. [ABSTRACT FROM PUBLISHER]