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The use of sensors to detect or measure ripening changes in fruit is a growing area of interest to the scientific community. Colorimeters are commonly employed for color and shade identification; however, their usage to measure the color parameters of fruit rinds based on image analysis can be expensive. This article presents a non-invasive and low-cost optoelectronic system for detecting color changes in oranges to predict the ripening stage. The system utilises a 1 W white LED as a light source, an RGB photodiode array, and two plastic optical fibres bundled in parallel to form the head of an extrinsic sensor. A microcontroller is employed for model integration and data acquisition. The evolution of the skin color of the fruit was monitored until over-ripeness was evident. The sensor was designed to detect the color changes; the CIE L*a*b* color difference between the optoelectronic device results and those obtained by colorimetry was 2.6–4.5. To predict the ideal conditions for fruit handling and determine the maturity level, a multilevel perceptron ANN was trained, achieving an accuracy of 96.4%. In addition, an overall precision of 96.6% was achieved when classifying fruit into three maturity categories (under-ripe, ripe, and over-ripe), and the error was 3.4%. The combination of the optoelectronic device and ANN improves considerably this fruit color classification accuracy, can facilitate the determination of the optimal time for consumption, and optimize the postharvest process efficiency.

We develop a simple and cost-efficient configuration of Brillouin optical correlation-domain reflectometry (BOCDR), the setup of which does not include an additional reference path used in standard BOCDR systems. The Fresnel-reflected light from an open end of a sensing fiber is used as reference light. The limitations of spatial resolution, measurement range, and their ratio are theoretically clarified, and then, a distributed strain measurement with a <; 100-mm spatial resolution and a 4.1-m measurement range is demonstrated with a high signal-to-noise ratio. [ABSTRACT FROM PUBLISHER]

We implement the strain and temperature sensors based on multimode interference in perfluorinated (PF) graded-index (GI) plastic optical fibers, and investigate their sensing performance at 1300 nm. We obtain strain and temperature sensitivities of -112 pm/με/m and +49.8 nm/°C/m, the absolute value of which are 12.9 and over 1800 times as large as those in silica GI multimode fibers, respectively. These ultra-high strain and temperature sensitivities probably originate from the unique core material, i.e., PF polymer. [ABSTRACT FROM PUBLISHER]

A fiber Fabry-Perot interferometer (FPI) based on a bubble-expanded microcavity is investigated in this paper. Due to the expanded bubble microcavity, the FPI exhibits high strain sensitivity of 30.66 pm/με. To the best of our knowledge, such strain sensitivity is three to ten times higher than that of the fiber FPIs based on the microcavities previously reported. The strain response of the FPI with different shapes is analyzed, and the experimental results are consistent with the theoretical analysis. [ABSTRACT FROM PUBLISHER]

A fiber-optic Fabry-Perot interferometer based on UV-curable polymer microhemisphere is proposed and demonstrated. The polymer microhemisphere is formed by adhering and solidifying a liquid microdroplet of UV-curable adhesive to the end face of a cleaved single-mode fiber. The height of polymer microhemisphere could be flexibly controlled by adjusting the diameter of a single-mode fiber. The theoretical and experimental results demonstrate that the refractive index (RI) and the temperature of external environment can be simultaneously measured by the fringe contrast variation and the wavelength shift of reflection spectra separately, alleviating the cross sensitivity effectively. The obtained temperature and RI sensitivities are about 0.19 nm/°C and 260 dB/RIU in the RI range of 1.38-1.42. [ABSTRACT FROM PUBLISHER]

A kind of magnetic field sensor based on mode interference effect is proposed. The sensing arm consists of two special up-tapered joints formed on the traditional single-mode fiber by fusion tapering technique. Magnetic fluid is used as the cladding of the structure. The interference valley wavelength or the transmission loss of the sensing structure is sensitive to the external magnetic field, which is utilized for magnetic field sensing. The sensitivity of shift of interference valley wavelength with magnetic field can be up to 325.3 pm/mT in the range of 0-16 mT. The variation of transmission loss at valley wavelength with magnetic field has a sensitivity of -0.2121 dB/mT in the range of 2-30 mT. [ABSTRACT FROM PUBLISHER]

We experimentally demonstrated a strain sensor based on fiber ring cavity laser with a photonic crystal fiber (PCF) in-line Mach-Zehnder interferometer (MZI) structure, which is used as an optical band-pass filter and acts as the strain sensing component. The fiber ring cavity laser plays the role of enhancing the visibility of the resonant spectrum and narrowing the corresponding 3-dB bandwidth, thus improving the comprehensive sensing performance. The induced axial strain on the structure is measured by monitoring the central wavelengths of the laser output. A high strain sensing sensitivity of 2.1 pm/με is successfully achieved in the linear strain range of 0-2100 με. A parameter Q value describing the overall sensing performance is introduced by including the strain sensing sensitivity, sensing sensitivity relative to 3-dB bandwidth of the resonant spectrum and the corresponding visibility. Comparing with the reported strain measurements based on a PCF in-line MZI structure, the experimental results based on fiber ring cavity laser sensor present more than nine times larger Q value. [ABSTRACT FROM PUBLISHER]

We present a fiber-optic liquid level sensor that is conducted by a combination of optical interferometry and lever principle. The sensing unit is a Mach-Zehnder interferometer (MZI), which is formed by sandwiching a piece of photonic crystal fiber (PCF) between two single-mode fibers (SMFs). The measuring equipment is composed of a rotatable lever and a fixed link. The rotatable lever includes two different length arms, i.e., L1 and L2. Both ends of the MZI are glued on the tip of the L2 arm and the fixed link using ethoxyline, respectively. A hanging stick, which is dipped into a liquid tank, is directly mounted on the other end of the rotatable lever. The buoyancy will increase as the stick depth of immersion into the liquid increases. The tension the MZI subjected will increase according to the proportion of L1/L2 on account of the lever principle. The sensitivity of the sensor could be regulated with different ratios of lever arms. In our experiment, a maximum sensitivity of 111.27 pm/mm was obtained with a 1 : 7.8 ratio of two lever arms L1/L2. The demonstrated liquid level sensor has the advantages of simple structure, easy fabrication, low cost, and high sensitivity. [ABSTRACT FROM PUBLISHER]

This paper reports a vector Brillouin optical time-domain analyzer based on heterodyne detection and IQ demodulation algorithm. This approach employs an acousto-optic frequency shifter to generate a single-frequency reference, which simplifies the probe spectrum and directly features the Brillouin gain and phase shift compared with the phase modulation. In addition, the proposed IQ demodulation algorithm makes signal processing easy to implement and allows fast and real-time demodulation. A proof-of-concept experiment is carried out in an ~1.6-km standard single-mode fiber consisting of two different sections of fibers. Both the Brillouin gain and phase-shift spectrograms are successfully measured with an ~2-m spatial resolution. The temperature dependence values of the Brillouin gain and phase-shift spectra are also measured, and the temperature dependence values of the Brillouin frequency shift show excellent linearity larger than 0.999 and almost identical slopes of 1.166 and 1.159 MHz/°C, respectively. [ABSTRACT FROM PUBLISHER]

A novel localized surface plasmon resonance (LSPR) fiber sensor was proposed. This LSPR fiber sensor was primarily constructed by conducting etching of the cladding layer and core layer on a single-mode fiber, followed by plating of 1444 nanometal rings. Sensor design and relevant calculations were conducted using a semi-analytical simulation method, which integrated the exact mode solver for the cylindrical coordinate and eigenmode expansion method. It was examined that the current metallic patterns in the fiber sensor can trigger the LSPR by the electric field Er of the core mode HE11, and this is the main reason why this novel fiber sensor can obtain high performance. After performing algorithms, images showed evident excitation of the LSPR. The LSPR fiber sensor designed in this paper possesses excellent attributes of short length (185.173 μm), high resolution (approximately - 70 dB), and high sensitivity (approximately 34 257 nm/RIU). [ABSTRACT FROM PUBLISHER]

A dual-parameter sensor based on a liquid-infiltrated microstructured optical fiber (MOF) is constructed by selective liquid infiltration of one particular cladding air hole in the MOF. The fundamental core mode could be simultaneously coupled to several higher order modes of the adjacent liquid rod waveguide when the phase-matching condition is satisfied, resulting in the emergence of multiple resonance peaks with different sensing characteristics. Our proposed liquid-infiltrated MOF sensor has several advantages, such as high sensitivity and a large measurement range. Moreover, it is able to resolve the temperature-force cross-sensitivity issue that is commonly encountered in most practically deployed sensing components. [ABSTRACT FROM PUBLISHER]

A core-mode-cladding-supermode modal interferometer with all-solid photonic bandgap fiber (AS-PBF) is constructed, and a reflective Michelson-type high-temperature sensor is fabricated. Such a fiber sensor is constituted by a small segment of AS-PBF and a leading single-mode fiber. The splice region of the two fibers is weakly tapered to excite the cladding supermode. Both the interference spectra and the near-field infrared CCD images verify that the LP01 cladding supermode is effectively excited and interferes with the LP01 core mode, which agrees well with theoretical results. Benefiting from a large effective thermooptic coefficient between the two modes, temperature sensitivity up to 0.111 nm/°C at 500 °C is obtained in experiment. The proposed sensor is compact and easy to fabricate, which makes it very attractive for high-temperature sensing applications. [ABSTRACT FROM PUBLISHER]

A reflective fiber-optic interferometer for ultra-high temperature measurement is proposed and experimentally demonstrated. The device consists of a short piece of polarization-maintaining photonic crystal fiber (PM-PCF) spliced with a lead-in single mode fiber (SMF) without any offset. The hollow holes within the PM-PCF are partly collapsed due to the directional arc-heating splicing and excite two linearly polarized (LP) modes over the downstream PM-PCF. These two LP-modes are reflected at the end face of PM-PCF and backward recoupled into the lead-in SMF through the collapsed region. A superimposed interference pattern is obtained as the result of interference of the polarized modes. The proposed interferometer is demonstrated for ultra-high temperature measurement up to 1100 °C with a sensitivity of 12.3 pm/°C over repeated measurements. Meanwhile, isochronally thermal annealing has been studied to address the effect of residual stress in the sensing probe and the feasibility of further improving temperature measurement range of the device. [ABSTRACT FROM PUBLISHER]

We propose and demonstrate a novel configuration for depolarized interferometric fiber-optic gyroscopes (IFOGs). This configuration utilizes optical compensation between two orthogonal polarizations for suppressing errors induced by polarization nonreciprocity. Theoretical analysis shows that it is a new approach different from conventional IFOGs where a polarizer is mandatory. An experimental demonstration of the proposed IFOG (2097-m coil, open-loop configuration) achieves a low bias drift of 0.016 °/h in detecting the Earth's rotation rate. Furthermore, this configuration requires no polarizer or any other polarization-maintaining device. [ABSTRACT FROM PUBLISHER]