Search Results (17)

By partitioning agricultural fields into units with similar yield-limiting factors, Management Zone (MZ) delineation provides the spatial basis for variable-rate application of inputs such as nitrogen, seed, and irrigation. To evaluate the operational implementation of MZ methodologies, this paper analyzes 137 peer-reviewed papers published between 2000 and 2025, extracting data on agronomic contexts, sensing inputs, computational workflows, and validation strategies. Our analysis reveals a clear methodological shift: while early studies relied heavily on data such as soil properties, recent literature is dominated by multisource data fusion that combines static soil proxies (e.g., apparent electrical conductivity) with dynamic remote sensing vegetation indices. Methodologically, the literature relies heavily on similarity-based clustering, specifically fuzzy c-means and k-means, often applied to raw spatial grids or Principal Component Analysis (PCA) transformations. Although machine learning and optimization-based approaches have increased in recent years, rigorous agronomic and economic validation remains limited, while internal cluster validity indices (e.g., FPI, NCE) and inferential statistical tests (e.g., ANOVA) are widely used to assess delineated zones, only 13 of the reviewed papers explicitly evaluated the economic or environmental net returns of the delineated zones. To transition MZ delineation from a classification problem to an operational decision-support tool, the current literature suggests a need to shift validation efforts away from internal clustering metrics toward multi-year yield stability assessments and direct economic cost–benefit analyses. Full article

Ball resonator optical fiber sensors (OFSs) can offer multiparameter sensing capability, but their non-periodic and low-finesse reflection spectra make conventional spectral demodulation unreliable. This work proposes two sensor configurations: (i) a ball resonator and (ii) a hybrid sensor integrating a Fabry–Pérot interferometer (FPI) with a ball resonator, and compares their performance for multiparameter physiological monitoring using the Karhunen–Loève transform (KLT). The sensors were evaluated for glucose concentration (0–3 mg/mL), temperature (20–55 °C), and pH (3–9) monitoring. The ball resonator sensor, paired with KLT, achieved high linearity across all measurands (R² = 0.989, 0.919, and 0.838 in response to glucose, temperature, and pH, respectively). The hybrid sensor exhibited a higher glucose sensitivity (6.15 a.u./(mg/mL)) compared to the ball resonator (3.77 a.u./(mg/mL)), resulting in limits of detection (LODs) of 2.53 mM and 4.19 mM, respectively. In contrast, the ball resonator sensor demonstrated better sensitivity for temperature and pH sensing. Furthermore, we present a comprehensive benchmarking framework of seven spectral demodulation methods for OFSs. The results demonstrated that KLT consistently provides robust demodulation performance and highlighted the potential of KLT for multiparameter physiological sensing applications. Full article

Albendazole (ABZ) is a broad-spectrum anthelmintic drug whose residual presence in food and the environment raises public health concerns, requiring rapid and sensitive methods of detection. In this work, a sensitive Fabry–Pérot interferometer (FPI) probe was fabricated by realizing a cavity located at the tip of a single-mode optical fiber core with a molecularly imprinted polymer (MIP) for ABZ detection. The fabrication process involved the development of a photoresist-based micro-hole filled by the specific MIP via thermal polymerization. Interferometric measurements obtained using the proposed sensor system have demonstrated a limit of detection (LOD) of 27 nM, a dynamic concentration range spanning from 27 nM (LOD) to 250 nM, and a linear response at the nanomolar level (27 nM–100 nM). The selectivity test demonstrated no signal when interfering molecules were present, and the application of the sensor for ABZ quantification in a commercial pharmaceutical sample provided good recovery, in accordance with bioanalytical validation standard methods. These results demonstrate the capability of a MIP layer-based FPI probe to provide low-cost and selective optical-sensing strategies, proposing a competitive approach to traditional analytical techniques for ABZ monitoring. Full article

A highly sensitive Fabry–Pérot interferometer (FPI) is fabricated via symmetric taper fiber cleaving and centered waist-inserted assembly, a design where geometric symmetry is fundamental to the sensor’s performance. The FPI is fabricated by simple and cost-effective techniques, including fiber cleaving, splicing, and tapering. Due to the ultra-long cantilever beam with an effective length of 2.33 mm and the ultra-short Fabry–Pérot (FP) cavity with an actual length of 13.98 μm, the sensor exhibits an ultra-high strain sensitivity of 544.57 pm/με in experimental results. The sensor boasts a small temperature sensitivity of 1.02 pm/°C and a cross-temperature sensitivity of 0.0019 µε/°C in the temperature range of 25–200 °C. Furthermore, the sensor has good stability and repeatability. Owing to the symmetry-enhanced design, simple fabrication process, high strain sensitivity, as well as a stable, linearly proportional response over an extensive strain regime, the device has large potential in various sensing applications. Full article

A parallel Fabry–Perot interferometer (FPI) optical fiber sensor, enhanced with UV glue, was proposed for environmental temperature detection. The UV glue is applied to the fiber’s sensing region using a coating method, forming an FP cavity through misalignment welding, allowing the FP to function as a temperature sensor. In parallel, a reference FPI with a similar free spectral range (FSR) is connected, generating a Vernier effect that amplifies small changes in the refractive index (RI) of the sensing region. The study demonstrates that UV glue enhances the temperature-sensing capabilities of the FP, and when combined with the Vernier effect, it significantly improves the sensitivity of a single interferometric sensor. The temperature sensitivity of the parallel-connected FPI is −2.80219 nm/°C, which is 7.768 times greater than that of a single FPI (−0.36075 nm/°C). The sensor shows high sensitivity, stability, and reversibility, making it promising for temperature-monitoring applications in various fields, including everyday use, industrial production, and the advancement of optical fiber temperature-sensing technologies. Full article

Vector bending sensors can be utilized to detect the bending curvature and direction, which is essential for various applications such as structural health monitoring, mechanical deformation measurement, and shape sensing. In this work, we demonstrate a temperature-insensitive vector bending sensor via parallel Farby–Perot interferometers (FPIs) fabricated by etching and splicing a multicore fiber (MCF). The parallel FPIs made in this simple and effective way exhibit significant interferometric visibility with a fringe contrast over 20 dB in the reflection spectra, which is 6 dB larger than the previous MCF-based FPIs. And such a device exhibits a curvature sensitivity of 0.207 nm/m⁻¹ with strong bending-direction discrimination. The curvature magnitude and orientation angle can be reconstructed through the dip wavelength shifts in two off-diagonal outer-core FPIs. The reconstruction results of nine randomly selected pairs of bending magnitudes and directions show that the average relative error of magnitude is ~4.5%, and the average absolute error of orientation angle is less than 2.0°. Furthermore, the proposed bending sensor is temperature-insensitive, with temperature at a lower sensitivity than 10 pm/°C. The fabrication simplicity, high interferometric visibility, compactness, and temperature insensitivity of the device may accelerate MCF-based FPI applications. Full article

In the field of fiber-optic sensing, effectively reducing the noise of sensing spectra and achieving a high signal-to-noise ratio (SNR) has consistently been a focal point of research. This study proposes a deep-learning-based denoising method for fiber-optic sensors, which involves pre-processing the sensor spectrum into a 2D image and training with a cycle-consistent generative adversarial network (Cycle-GAN) model. The pre-trained algorithm demonstrates the ability to effectively denoise various spectrum types and noise profiles. This study evaluates the denoising performance of simulated spectra obtained from four different types of fiber-optic sensors: fiber Fabry–Perot interferometer (FPI), regular fiber Bragg grating (FBG), chirped FBG, and FBG pair. Compared to traditional denoising algorithms such as wavelet transform (WT) and empirical mode decomposition (EMD), the proposed method achieves an SNR improvement of up to $13.71 \mathrm{dB}$, an RMSE that is up to three times smaller, and a minimum correlation coefficient ($R^2$) of no less than 99.70% with the original high-SNR signals. Additionally, the proposed algorithm was tested for multimode noise reduction, demonstrating an excellent linearity in temperature response with a $R^2$ of 99.95% for its linear fitting and $99.74\%$ for the temperature response obtained from single-mode fiber sensors. The proposed denoising approach effectively reduces the impact of various noises from the sensing system, enhancing the practicality of fiber-optic sensing, especially for specialized fiber applications in research and industrial domains. Full article

Fabry–Perot interferometers (FPIs), comprising foundry-compatible dielectric thin films on sapphire wafer substrates, were investigated for possible use in chemical sensing. Specifically, structures comprising two vertically stacked distributed Bragg reflectors (DBRs), with the lower DBR between a sapphire substrate and a silicon-oxide (SiO₂) resonator layer and the other DBR on top of this resonator layer, were investigated for operation in the near-ultraviolet (near-UV) range. The DBRs are composed of a stack of nitride-rich silicon-nitride (SiN_x) layers for the higher index and SiO₂ layers for the lower index. An exemplary application would be formaldehyde detection at sub-ppm concentrations in air, using UV absorption spectroscopy in the 300–360 nm band, while providing spectral selectivity against the main interfering gases, notably NO₂ and O₃. Although SiN_x thin films are conventionally used only for visible and near-infrared optical wavelengths (above 450 nm) because of high absorbance at lower wavelengths, this work shows that nitride-rich SiN_x is suitable for near-UV wavelengths. The interplay between spectral absorbance, transmittance and reflectance in a FPI is presented in a comparative study between one FPI design using stoichiometric material (Si₃N₄) and two designs based on N-rich compositions, SiN_1.39 and SiN_1.49. Spectral measurements confirm that if the design accounts for phase penetration depth, sufficient performance can be achieved with the SiN_1.49-based FPI design for gas absorption spectroscopy in near-UV, with peak transmission at 330 nm of 64%, a free spectral range (FSR) of 20 nm and a full-width half-magnitude spectral resolution (FWHM) of 2 nm. Full article

This paper reports a fiber in-line Fabry–Perot interferometer (FPI) fabricated in a no-core fiber using the direct femtosecond laser writing technique for high-temperature sensing applications. Two in-line reflectors are directly inscribed in a no-core fiber to construct a low-finesse FPI. Fringe visibility greater than 10 dB is obtained from the reflection spectra of the fabricated no-core fiber FPIs. Temperature responses of a prototype no-core fiber FPI are characterized up to 1000 °C. The proposed configuration is compact and easy to fabricate, making it attractive for sensing applications in high-temperature harsh environments. Full article

A hybrid fiber sensor for the simultaneous measurement of pressure and temperature is proposed. The sensor is constituted of a section of silica capillary tube (SCT) whereat access channels are created with two different methods: instilling a bubble on the fiber by employing successive arc discharges on the SCT whilst under pressure and splicing the SCT with another section of SCT with a smaller inner diameter. The reflection-based sensor enhances Fabry–Perot interference (FPI) and antiresonant (AR) guidance, simultaneously, in a single sensing element of a few millimeters. A comparison study between the access channel methods reveals higher spectral visibility for the bubble method and similar pressure and temperature resolutions. For a 2.58 mm long sensor with a bubble, the sensitivity to pressure is 4.09 ± 0.01 nm/MPa and −3.7 ± 0.1 nm/MPa for the FPI and AR, respectively, while its sensitivity to temperature is −0.20 ± 0.02 pm/°C and 24.0 ± 0.5 pm/°C, respectively, for the FPI and AR, which are within the numerically calculated sensitivities. The sensor is robust and has a convenient reflective probe with easy and low-cost fabrication, granting high competitiveness in actual applications. Full article

We present a fiber-optic sensor based on the principles of a Fabry–Perot interferometer (FPI), which promptly, sensitively, and precisely detects blood clot formation. This sensor has two types of sensor tips; the first was crafted by splicing a tapered fiber into a single-mode fiber (SMF), where fine-tuning was achieved by adjusting the tapered diameter and length. The second type is an ultra-compact blood FPI situated on the core of a single-mode fiber. The sensor performance was evaluated via clot-formation-indicating spectrum shifts induced by the varied quantities of a thrombin reagent introduced into the blood. The most remarkable spectral sensitivity of the micro-tip fiber type was approximately 7 nm/μL, with a power sensitivity of 4.1 dB/μL, obtained with a taper fiber diameter and length of 55 and 300 μm, respectively. For the SMF type, spectral sensitivity was observed to be 8.7 nm/μL, with an optical power sensitivity of 0.4 dB/μL. This pioneering fiber-optic thrombosis sensor has the potential for in situ applications, healthcare, medical monitoring, harsh environments, and chemical and biological sensing. The study underscores the scope of optical technology in thrombus detection, establishing a platform for future medical research and application. Full article

A single-channel fiber-optic bolometer system based on a high-finesse silicon Fabry–Pérot interferometer (FPI) was previously reported, intended to measure plasma radiation from the magnetically confined fusion chamber. Recently, we developed a multichannel fiber-optic bolometer system with five bolometers multiplexed using a coarse wavelength division multiplexer (CWDM) and interrogated with a white-light system involving a superluminescent light-emission diode source and a high-speed spectrometer. One of the bolometers was used as the reference bolometer to compensate for the ambient temperature variations, and the other four bolometers were used for radiation measurement. The bolometers have a simple structure with a silicon pillar at the end of the single-mode fiber and a gold disk on the other side of the silicon pillar. They are also easy to fabricate without stringent requirements on the optical alignment. Analysis of the system optimization was performed to improve the noise performance and to mitigate the vibration effect that may present in the practical application. The system had a significantly enhanced measurement range compared to the previous high-finesse FPI bolometer system for measuring radiation. Test results performed in air using a 405 nm laser as the radiation source showed that the temperature resolution and the noise-equivalent power density of the sensing bolometers connected to each channel of the CWDM were, respectively, ~0.4 mK and ~0.1 W/m², with a time constant of ~220 ms, which is comparable to the previous more complicated fiber-optic bolometer systems based on high-finesse FPIs that were interrogated using wavelength-scanning lasers. Full article

Fabry–Perot interferometric (FPI) sensors are an accurate and well-established sensing technology that are used to monitor a wide range of parameters such as strain, temperature, and refractive index, among many others. Nevertheless, due to the limited number and high cost of existing interrogation techniques for FPIs, its use is often restricted to discrete measurements, not being so explored for dynamic applications. The development of an alternative interrogation technique for a high rate of acquisition may propel this type of sensor into less explored fields such as dynamic biomedical applications. In this work, we present the theoretical and experimental analyses of an FPI sensing architecture by using an alternative high rate dynamic acquisition methodology, based on frequency to amplitude conversion, where the FPI spectral shift is detuned by the convolution of the optical light source with the FPI interference pattern. The good agreement between the theoretical and experimental results verified the reliability of the proposed methodology. Moreover, preliminary results show that the developed sensing architecture can be a suitable solution to monitor biomedical parameters such as the carotid pulse wave. Full article

Drone-based remote sensing has evolved rapidly in recent years. Miniaturized hyperspectral imaging sensors are becoming more common as they provide more abundant information of the object compared to traditional cameras. Reflectance is a physically defined object property and therefore often preferred output of the remote sensing data capture to be used in the further processes. Absolute calibration of the sensor provides a possibility for physical modelling of the imaging process and enables efficient procedures for reflectance correction. Our objective is to develop a method for direct reflectance measurements for drone-based remote sensing. It is based on an imaging spectrometer and irradiance spectrometer. This approach is highly attractive for many practical applications as it does not require in situ reflectance panels for converting the sensor radiance to ground reflectance factors. We performed SI-traceable spectral and radiance calibration of a tuneable Fabry-Pérot Interferometer -based (FPI) hyperspectral camera at the National Physical Laboratory NPL (Teddington, UK). The camera represents novel technology by collecting 2D format hyperspectral image cubes using time sequential spectral scanning principle. The radiance accuracy of different channels varied between ±4% when evaluated using independent test data, and linearity of the camera response was on average 0.9994. The spectral response calibration showed side peaks on several channels that were due to the multiple orders of interference of the FPI. The drone-based direct reflectance measurement system showed promising results with imagery collected over Wytham Forest (Oxford, UK). Full article

The Karhunen-Loeve Transform (KLT) is applied to accurate detection of optical fiber sensors in the spectral domain. By processing an optical spectrum, although coarsely sampled, through the KLT, and subsequently processing the obtained eigenvalues, it is possible to decode a plurality of optical sensor results. The KLT returns higher accuracy than other demodulation techniques, despite coarse sampling, and exhibits higher resilience to noise. Three case studies of KLT-based processing are presented, representing most of the current challenges in optical fiber sensing: (1) demodulation of individual sensors, such as Fiber Bragg Gratings (FBGs) and Fabry-Perot Interferometers (FPIs); (2) demodulation of dual (FBG/FPI) sensors; (3) application of reverse KLT to isolate different sensors operating on the same spectrum. A simulative outline is provided to demonstrate the KLT operation and estimate performance; a brief experimental section is also provided to validate accurate FBG and FPI decoding. Full article