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Data storage is a problem that cannot be ignored in the long-term monitoring of a phase-sensitive optical time-domain reflectometry (Φ-OTDR) system. In this paper, we proposed a data-reduction approach for heterodyne Φ-OTDR using an ultra-low sampling resolution and undersampling techniques. The operation principles were demonstrated and experiments with different sensing configurations were carried out to verify the proposed method. The results showed that the vibration signal could be accurately reconstructed from the undersampled 1-bit data. A space saving ratio of 98.75% was achieved by converting 128 MB of data (corresponding to 268.44 ms of sensing time) to 1.6 MB. The proposed method led to a potentially new data-reduction approach for heterodyne Φ-OTDR, which also provided economical guidance for the selection of the data-acquisition device. [ABSTRACT FROM AUTHOR]

Children's lead poisoning continues to compromise children's health and development, particularly in the inner cities of the United States. We applied a global Poisson model, a Poisson with random effects model, and a geographically weighted Poisson regression (GWPR) model to deal with the spatial dependence and heterogeneity of the number of children's lead poisoning cases in Syracuse, New York. We used three environmental factors-the building year (i.e., the year of construction) of houses, the town taxable value of houses, and the soil lead concentration-averaged at the census block level to explore the spatially varying relationships between children's lead poisoning and environmental factors. The results indicated that GWPR not only produced better model fitting and reduced the spatial dependence and heterogeneity in the model residuals but also improved the model predictions for the spatial clusters, or hot spots, of children's lead poisoning across inner city neighborhoods. Furthermore, the spatially varying model coefficients and their associated statistical tests were visualized using geographical information system maps to show the high-risk areas for the impacts of the environmental factors on the response variable. This information can provide valuable insights for public health agencies to make better decisions on lead hazard intervention, mitigation, and control programs. [ABSTRACT FROM AUTHOR]

Children’s blood lead concentrations have been closely monitored over the last two decades in the United States. The bio-monitoring surveillance data collected in local agencies reflected the local temporal trends of children’s blood lead levels (BLLs). However, the analysis and modeling of the long-term time series of BLLs have rarely been reported. We attempted to quantify the long-term trends of children’s BLLs in the city of Syracuse, New York and evaluate the impacts of local lead poisoning prevention programs and Lead Hazard Control Program on reducing the children’s BLLs. We applied interrupted time series analysis on the monthly time series of BLLs surveillance data and used ARMA (autoregressive and moving average) models to measure the average children’s blood lead level shift and detect the seasonal pattern change. Our results showed that there were three intervention stages over the past 20 years to reduce children’s BLLs in the city of Syracuse, NY. The average of children’s BLLs was significantly decreased after the interventions, declining from 8.77μg/dL to 3.94μg/dL during1992 to 2011. The seasonal variation diminished over the past decade, but more short term influences were in the variation. The lead hazard control treatment intervention proved effective in reducing the children’s blood lead levels in Syracuse, NY. Also, the reduction of the seasonal variation of children’s BLLs reflected the impacts of the local lead-based paint mitigation program. The replacement of window and door was the major cost of lead house abatement. However, soil lead was not considered a major source of lead hazard in our analysis. [ABSTRACT FROM AUTHOR]

An automatic control algorithm for flattening the gain of a fiber Raman amplifier is derived from the Raman scattering equations. A pseudo-inverse gain matrix is introduced to adjust the powers of the pump lasers. The algorithm is simple, fast, effective, robust and insensitive to the length and type of the fiber. It is demonstrated experimentally that the gain flattening for Raman amplifiers comprising various types and lengths of fiber and with different target gains can be achieved automatically with this algorithm. The algorithm converges for both small and large input signal. Flattened Raman gain with a fluctuation less than 0.40 dB over a 50-nm bandwidth for a 50-km SMF or less than 0.20 dB over a 40-nm bandwidth for a 6.6-km dispersion compensated fiber is realized in the experiment. [Copyright &y& Elsevier]

Patients with moderate-to-severe atopic dermatitis (AD) experience intense chronic itch and impaired sleep. Reports from parents and teachers suggest that AD patients may also have attention problems. However, attention has not yet been directly assessed in AD patients. We utilized an objective, computer-based continuous performance test (CPT) validated for use in attention-deficit/hyperactivity disorder (ADHD) diagnosis to formally evaluate attention in adolescent AD subjects. This was a single-visit, cross-sectional, non-interventional study of moderate-to-severe (Investigator’s Global Assessment [IGA] ≥ 3) AD subjects aged 12–17 years without clinician-diagnosed ADHD. Attention was evaluated using two performance-based measures: Conners, CPT-3 and the Stroop Color and Word Test. The primary parameter was CPT-3 detectability (d’) measure. Lesional severity measures included Eczema Area and Severity Index (EASI) and body surface area (BSA) involvement. Subjects completed self-report rating scales assessing sensory responsiveness patterns (Adult/Adolescent Sensory Profile [AASP]), itch (Peak Pruritus Numerical Rating Scale [PP-NRS]), skin pain, quality of life, sleep, anxiety, and depressive symptoms. A total of 44 subjects were included in the study (61.4% female; mean age 15.0 [SD 1.78] years; mean EASI 20.4 [SD 7.8]; mean PP-NRS 7.0 [SD 1.8]). Results indicated substantial disease impact on sleep, quality of life, and comorbid anxiety and depressive symptoms. The mean (SD) Conners, CPT-3 dʹ T-score was 48.7 (SD 10.7), similar to the expected mean from a randomly selected age/gender-matched sample of the general population (50 [SD 10], by definition). Overall, 13.6% of subjects exhibited a dʹ T-score ≥ 60 (clinically significant poor performance), which was not greater than the expected general population value (15.9%). Subject-level data review by two psychologists determined that only 2 subjects demonstrated an overall response pattern that clearly indicated attention deficit. Many subjects had atypical sensory responsiveness profiles: sensory hypersensitivity (38.6%), sensory avoidance (50%), and low registration (hypo-sensitivity, 36.4%). Adolescents with moderate-to-severe AD without existing ADHD diagnosis did not demonstrate greater attention problems on performance-based measures than would be expected in age/gender-matched peers. Trial registration NCT05203380.Plain Language Summary: Atopic dermatitis (often shortened to AD) is a long-term skin disease that causes intense itching. It affects patients’ lives in many ways, including interrupting their sleep. Parents and teachers of young people with AD have sometimes suggested that AD may also cause attention problems. But this has never been tested properly. We measured the attention of 44 adolescents aged between 12 and 17 years who all had moderate-to-severe AD. We used computerized tests of attention that were developed for young people with ADHD (attention deficit hyperactivity disorder). Also, we made sure that none of the 44 patients had also been diagnosed with ADHD. The severity and extent of the patients’ AD was measured by doctors. We also used some measures that allowed the patients to report how AD affected their lives, including things like itch, skin pain, quality of life, sleep, anxiety, and depression. The adolescent patients reported that AD had a negative effect on various areas of their lives, including sleep and quality of life, and that it resulted in anxiety and symptoms of depression. However, the results of the attention tests in adolescents with AD were similar to what would usually be expected in adolescents without AD. Only 2 of the 44 patients with AD were found to have clear evidence of attention problems. The study concluded that adolescents with moderate-to-severe AD did not have any greater attention problems than would usually be expected in adolescents without AD. [ABSTRACT FROM AUTHOR]

In this paper, we propose a digital phase demodulation scheme for phase-sensitive optical time-domain reflectometer (Φ -OTDR) systems based on simulated coherence for digital phase shift, in which three-path signals with a phase interval of 120° can be obtained by employing digital simulated orthogonal coherence for phase shift instead of using a hardware 3×3 coupler and three detectors, while the high-frequency component can be eliminated through cross differential between simulated coherence signals. On this basis, the phase variation of Rayleigh backscattering (RBS) light can be analyzed by differential cross multiplication (DCM). The performance of the proposed scheme is evaluated through experiments by detecting a series of vibration signals with various sensing distances, vibration frequencies, and waveforms. The experimental results demonstrate that the phase variation caused by external vibration can be effectively reconstructed and a strain resolution of 0.5 n ɛ and the SNR of 51.03 dB can be achieved through the proposed demodulation method, which significantly simplifies the system and effectively suppresses the deviation of phase interval and noise caused by hardware demodulation. • We propose a digital phase demodulation scheme for Φ -OTDR systems based on simulated coherence for digital phase shift. • Three-path signals can be generated by the proposed scheme rather than the use of hardware couplers and three detectors. • The proposed scheme can reduce the cost of the system and suppress negative impact caused by hardware demodulation. [ABSTRACT FROM AUTHOR]

A fiber speckle sensor (FSS) based on a tapered multimode fiber (TMMF) has been developed to measure liquid analyte refractive index (RI) in this work. By the lateral and axial offset of input light into TMMF, several high-order modes are excited in TMMF, and the speckle pattern is spatially modulated, which affects an asymmetrical speckle pattern with a random intensity distribution at the output of TMMF. When the TMMF is immersed in the liquid analyte with RI variation, it influences the guided modes, as well as the mode interference, in TMMF. A digital image correlations method with zero-mean normalized cross-correlation coefficient is explored to digitize the speckle image differences, analyzing the RI variation. It is found that the lateral- and axial-offsets-induced speckle sensor can enhance the RI sensitivity from 6.41 to 19.52 RIU−1 compared to the one without offset. The developed TMMF speckle sensor shows an RI resolution of 5.84 × 10−5 over a linear response range of 1.3164 to 1.3588 at 1550 nm. The experimental results indicate the FSS provides a simple, efficient, and economic approach to RI sensing, which exhibits an enormous potential in the image-based ocean-sensing application. [ABSTRACT FROM AUTHOR]

Metasurface‐based spatial phaser, exhibiting dispersive group delay responses, is able to perform real‐time analogue signal processing on the temporal spectrum of spatial electromagnetic waves, e.g., Fourier transformation, pulse chirping, pulse spread, and compression. The functionality of a spatial phaser is closely related to its group delay dispersion slope. For instance, for an up‐chirped incident pulse, the positive‐slope‐dispersion phaser spreads the pulse whereas the negative‐slope‐dispersion one compresses the pulse. Most reported spatial phasers exhibit fixed dispersion slopes and hence perform single functionality only, which cannot meet the demand of multifunctional systems in communication and sensing applications. In this paper, a new way is proposed to control and tune the dispersion slope of spatial phasers using polarization of incident waves, which is simpler and more efficient than conventional approaches based on tunable circuits. To verify the proposed method, a first‐order spatial phaser is designed and experimentally demonstrated within 9.4–10.6 GHz. It is able to generate negative‐slope, positive‐slope, and zero‐slope group delay dispersions, in case of x‐, y‐, and ±45°‐polarized waves. Such a reconfigurable phaser may find wide applications in integrated communication and sensing. [ABSTRACT FROM AUTHOR]

We report an ytterbium (Yb) doped fiber Mach Zehnder interferometer (MZI) based on the up-taper fiber structure in a fiber ring laser (FRL) cavity. Different from the traditional FRL sensing system, in which additional filters are required, the designed structure simultaneously acts as a filter, sensor and gain medium. Furthermore, thanks to the high thermal–optical coefficient of Yb doped fiber, the temperature sensitivity of 0.261 nm/°C can be achieved in the range of 10–50 °C. In addition, benefiting from the unique characteristics of the laser system itself, the designed structure has a narrower linewidth (−0.2 nm) and a higher signal-to-noise ratio (SNR) (−40 dB) than the sensor system based on a broadband light source (BBS). Meanwhile, the refractive index (RI) response and stability of the system are measured. The RI sensitivity is up to 151 nm/RIU, and the wavelength fluctuation range within two hours is less than 0.2 nm. Therefore, the designed structure is expected to play a significant role in human life safety monitoring, aircraft engine temperature monitoring, etc. [ABSTRACT FROM AUTHOR]

This paper presented a new kind of salinity and temperature dual-parameter sensor based on a fiber ring laser (FRL) with tapered side-hole fiber (SHF) embedded in a Sagnac interferometer. The sensing structure is majorly composed of tapered SHF located in the middle of SHF inside the Sagnac interferometer loop structure. The influences of the SHF's diameters of different tapered in the Sagnac interferometer loop on the FRL sensing system are studied. The presence of air holes in the SHF makes the cladding mode easier to excite, and the interaction between the cladding mode with its surroundings is enhanced, thus having higher salinity sensitivity. Besides, the unique advantages of high resolution, narrower linewidth, and high signal-to-noise ratio (SNR) of fiber laser make the measurement results more accurate. In this experiment, the SHF with different taper diameters was made, and it was found that reducing the diameter of the taper waist diameter could further improve the salinity sensitivity. When the waist diameter was 9.70 μm, the maximum salinity sensitivity of 0.2867 nm/‰ was achieved. Temperature sensing experiments were also carried out. The maximum temperature sensitivity of the FRL sensing system was −0.3041 nm/°C at the temperature range from 20 to 30 °C. The sensor has the characteristics of easy manufacture, good selectivity, and high sensitivity, proving the feasibility of simultaneous measurement of seawater salinity and temperature. [ABSTRACT FROM AUTHOR]

We designed and characterized a chiral metamaterial circularly polarized strong circular dichroism absorber with dynamic tuning capabilities using graphene. The synergistic combination of strong circular dichroism and perfect absorption, coupled with the tunability afforded by graphene, positions this absorber as a promising candidate for advanced electromagnetic applications. Employing a frequency-domain solver in electromagnetic simulation software, the impact of parameters such as the thickness of a metal U-ring, a silica dielectric layer, and the polarization angle of incident light on circular dichroism is systematically analyzed. Strong circular dichroism can be achieved by adjusting the misalignment angle of the metal U-ring, reaching a value as high as 0.91. At an incident angle of 60°, left-circularly polarized (LCP) light demonstrates outstanding wide-angle absorption performance, absorbing over 80% in the x-z plane and more than 70% in the y-z plane. Transitioning from circular to linear polarization and changing the tilt angle of the metal U-ring also achieves a 99.99% absorption peak at 1.33 THz. Moreover, in comparison to conventional absorbers, the structure presented in this study offers enhanced controllability of absorption performance through external voltage manipulation. This research not only refines the existing concepts but also introduces novel ideas for the development of tunable chiral optical devices. • Voltage-controlled, angle-dependent graphene terahertz absorber with strong circular dichroism. • The terahertz absorber functions at 1.2-1.5 THz, achieving circular dichroism of 0.91 with an 8° misalignment of the metal U-ring. • At a 60° incidence angle, LCP absorbs over 80% in the x-z plane and 70% in the y-z plane, offering superior wide-angle absorption. • Circular to linear polarization conversion achieves 99.99% absorption at 1.33 THz. [ABSTRACT FROM AUTHOR]

The detection of trace cancer markers in body fluids such as blood/serum is crucial for cancer diseases screening and treatment, which requires high sensitivity and specificity of biosensors. In this study, a peanut structure cascaded lasso (PSCL) shaped fiber sensing probe based on fiber laser demodulation method was proposed to specifically detect the carcinoembryonic antigen related cell adhesion molecules 5 (CEACAM5) protein in serum. Thanks for the narrow linewidth and high signal-to-noise ratio (SNR) of the laser spectrum, it is easier to distinguish small spectral changes than interference spectrum. Adding the antibody modified magnetic microspheres (MMS) to form the sandwich structure of "antibody-antigen-antibody-MMS", and amplified the response caused by biomolecular binding. The limit of detection (LOD) for CEACAM5 in buffer could reach 0.11 ng/mL. Considering the common threshold of 5 ng/mL for CEA during medical screening and the cut off limit of 2.5 ng/mL for some kits, the LOD of proposed biosensor meets the actual needs. Human serum samples from a hospital were used to validate the real sensing capability of proposed biosensor. The deviation between the measured value in various serum samples and the clinical value ranged from 1.9 to 9.8 %. This sensing scheme holds great potential to serve as a point of care testing (POCT) device and extend to more biosensing applications. [Display omitted] • A lasso-shaped fiber laser biosensor sensitized with magnetic microspheres was proposed for the specific determination of CEACAM5. • The fiber laser biosensor held the limit of detection (LOD) of 0.11 ng/mL, which was better than many recently published paper, and adequate for clinical needs. • The sensing capability of the biosensor was validated via the test of human serum samples, and the experimental results were comparable to the data from clinical assays. • The simple preparation process allowed the sensor for mass production and extend the utility to a broader biosensing field. [ABSTRACT FROM AUTHOR]

Abstract: A finite-difference time-domain (FDTD) method combined with a periodic boundary condition is used to analyze the diffraction efficiency of an etched diffraction grating (EDG) demultiplexer coated with a metallic film at the backside. The numerical results show that the diffraction loss is mainly due to the scattering effect of shaded facets of a metal-coated grating at both the polarizations. However, the same shaded facets can produce a higher loss for a TM polarization than that for a TE polarization, which induces a higher polarization dependent loss (PDL) of the demultiplexer. [Copyright &y& Elsevier]

We demonstrate a new concept for an all-fiber inclinometer based on a tapered fiber Bragg grating (tFBG) in a fiber ring laser (FRL) with the capability of measuring the tilt angle and temperature simultaneously. The sensor performance is analyzed theoretically and investigated experimentally. The dependence of tilt angle on the spectral response in variable temperature conditions was measured. Two inclinometers with different lengths have been fabricated and characterized in FRL. The sensitivity is 0.583 dB/° and 0.849 dB/°, respectively, in the range of 0° to 90°. Thanks to the FRL system, narrow 3-dB bandwidth (<0.1 nm) and high optical signal-to-noise ratio (~60 dB) are achieved. The tFBG in the FRL system can be used for working as a temperature insensitive inclinometer. The results suggested that the proposed inclinometer has the advantages of compact size and convenient manufacture, enhancing its potential for application prospect. [ABSTRACT FROM AUTHOR]

Introduction/Background Dupilumab has previously shown to significantly improve signs, symptoms, and quality of life in patients with moderate-to-severe atopic hand and foot dermatitis. Objective To investigate the efficacy of dupilumab across morphological subtypes in patients with moderate-to-severe atopic hand and foot dermatitis. Methods: The phase 3, randomized, double-blind LIBERTY-AD-HAFT (NCT04417894) trial enrolled patients aged =12 years with moderate-to-severe (Investigator's Global Assessment [IGA] score of 3/4) atopic hand and foot dermatitis. Patients were randomized to dupilumab monotherapy 300 mg every 2 weeks (q2w) in adults; 200/300 mg q2w in adolescents, or placebo for 16 weeks. This analysis reports the percent change from baseline in modified total lesion sign score (mTLSS) by hand and foot morphological subtypes: chronic dry fissured, hyperkeratotic (palmar/plantar), and other. Results: 133 patients enrolled into this study and were randomized to dupilumab (n = 67) or placebo (n = 66). Atopic hand and foot morphologies were reported in 3 categories: chronic dry fissured (n = 63), hyperkeratotic (palmar/plantar; n = 37), and other (n = 33) In the "other" category, dyshidrotic was the most frequent morphology (n = 13). mTLSS values were similar at baseline for all morphological subtypes. At Week 16, greater improvements were seen in the percent change from baseline (SE) in mTLSS for patients receiving dupilumab vs placebo in all categories: chronic dry fissured (-65.6% [5.1] vs -31.5% [6.2]), hyperkeratotic (palmar/plantar; -58.2% [7.6] vs -11.8% [7.7]), and other (-64.5% [11.6] vs -29.9% [9.0]). Safety was consistent with the known dupilumab safety profile in patients with atopic dermatitis. Conclusions: The efficacy of dupilumab remains consistent across different hand and foot dermatitis morphologies and shows higher treatment benefit across subtypes compared with placebo. [ABSTRACT FROM AUTHOR]

A novel temperature-insensitive tilt sensor is proposed based on two fiber Bragg gratings (FBGs), which were embedded in a cylindrical cantilever-based pendulum in two orthogonal planes. Tilt-induced bending of the pendulum changes bandwidths and hence reflected optical powers of the two FBGs. Intensity-measurements of two-dimensional (2D) tilt angles can be realized without temperature dependence. Theoretical analysis and experimental verification have been carried out. Sensitivity of 42.97 nW/° with measurement accuracy of 0.27° has been achieved over a range up to ±15°. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:344-346, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27281 [ABSTRACT FROM AUTHOR]

In this work, we theoretically present a reconfigurable plasmonic chiral metasurface based on a sandwiched metal–insulator–metal structure, which can strongly, spin-selectively absorb circularly polarized light. Through finite-difference time-domain simulation, the absorption of left- or right-handed circularly polarized light can reach nearly 100% at the resonant position, and the magnitude of the circular dichroism can be 80%, which is larger than most of the previously reported value. This strong chiroptical effect originates from plasmonic resonances induced by the incident circularly polarized light. Furthermore, the proposed plasmonic chiral metasurface is able to be reconfigurable by either changing its intrinsic or extrinsic chirality, which can be numerically confirmed by the change of the sign and magnitude of the CD. Such a reconfigurable plasmonic chiral metasurface could find many potential applications in chirality detection/sensing, polarimetric imaging, spin–orbit communications, etc. [ABSTRACT FROM AUTHOR]

In this work we discussed a label-free biosensing application of long-period gratings (LPGs) optimized in refractive index (RI) sensitivity by deposition of thin tantalum oxide (TaO x) overlays. Comparing to other thin film and materials already applied for maximizing the RI sensitivity, TaO x offers good chemical and mechanical stability during its surface functionalization and other biosensing experiments. It was shown theoretically and experimentally that when RI of the overlay is as high as 2 in IR spectral range, for obtaining LPGs ultrasensitive to RI, the overlay's thickness must be determined with subnanometer precision. In this experiment the TaO x overlays were deposited using Atomic Layer Deposition method that allowed for achieving overlays with exceptionally well-defined thickness and optical properties. The TaO x nano-coated LPGs show RI sensitivity determined for a single resonance exceeding 11,500 nm/RIU in RI range n D = 1.335–1.345 RIU, as expected for label-free biosensing applications. Capability for detection of various in size biological targets, i.e., proteins (avidin) and bacteria (Escherichia coli), with TaO x -coated LPGs was verified using biotin and bacteriophage adhesin as recognition elements, respectively. It has been shown that functionalization process, as well as type of recognition elements and target analyte must be taken into consideration when the LPG sensitivity is optimized. In this work optimized approach made possible detection of small in size biological targets such as proteins with sensitivity reaching 10.21 nm/log(ng/ml). • Long-period grating (LPG) has been coated with tantalum oxide nano-coating. • Optimized refractive index sensitivity for a single resonance exceeds 11,500 nm/RIU. • Determination of the coating thickness at sub-nanometer level is crucial. • The LPGs were applied for detection of bacteria and proteins. • At LPG optimization one must consider functionalization process and the target. [ABSTRACT FROM AUTHOR]

In our bioassay protocol, the Ag@4MBA@DNA-biotin probes were synthesized by linking biotin-modified DNA and 4-mercaptobenzoic acid-covered Ag nanoparticles, and the Si@Ag@anti-digoxin/digoxin-DNA substrate was fabricated by immune linking of digoxin-DNA and anti-digoxin immobilized on a Ag-coated wafer. Then, the probes, miRNA-21 and the substrate were constructed into a “sandwich structure” to detect the variation in the SERS signals with respect to miRNA-21 concentrations. Next, streptavidin and extra probes were alternately introduced to implement the cascade amplification of the SERS signal to increase the detection sensitivity. The results show that the limit of detection (LOD) with cascade amplification is remarkably improved from 97.81 pM to 38.02 fM, which is three orders of magnitude higher than the original data without cascade amplification. Furthermore, the SERS-based cascade amplification mechanism was analyzed and is attributed to the “hot spots effect” of the noble metal nanostructure. The biotin-streptavidin (B–S) system was introduced into the SERS detection platform, and the novel SERS-based cascade amplification bioassay protocol has significant creativity for the detection of nucleic acids. [ABSTRACT FROM AUTHOR]

Highlights • To achieve a high sensitivity, the cascaded two Fabry-Perot interferometers sensor with the Vernier effect was proposed. • For the intensity interrogation, the sensor system only required a broadband light source and the photo detector. • The reaction between the Streptomycin monoclonal antibody and Streptomycin-BSA was measured by the sensor for the biosensing application. Abstract In this paper, a novel high-sensitivity optical sensor based on cascaded two Fabry-Perot interferometers (FPIs) has been investigated theoretically and experimentally. In order to improve the sensitivity, the two FP interferometers were designed with slightly different free spectrum ranges (FSRs) to produce Vernier effect. The experimental results showed that the sensitivity of the sensor is 23,794.6 nm/RIU for the wavelength interrogation and 4602.3 dB/RIU for the intensity interrogation, much higher than that of the conventional sensors for the bulk refractive index (RI) sensing. Finally, the reaction between Streptomycin monoclonal antibody and Streptomycin-BSA was measured, showing a great potential for low-cost and portable systems in biochemical sensing. [ABSTRACT FROM AUTHOR]

Besides distinct features on RF/optical signal generation, optoelectronic oscillators (OEOs) have also been rapidly developed as emerging techniques towards sensing, measurement, and detection. In this paper, we start with the conceptual architecture and the analytical model of OEOs. Then, three operation principles behind sensing, measurement, and detection applications are categorized, including the variation on the time delay of loop, the passband reconfiguration of microwave photonic filter in loop, and the oscillation gain from injection locking, which clearly clarify the X-to-frequency mapping (X denotes target parameter or signal) for supporting practical solutions and approaches. Next, a comprehensive review to advances in OEO-based sensing, measurement, and detection applications is presented, including length change and distance measurement, refractive index estimation, load and strain sensing, temperature and acoustic sensing, optical clock recovery, and low-power RF signal detection. As a new application example, a novel approach for in-line position finding is proposed. When a long fiber Bragg grating inserted into OEO is locally heated to slightly broaden its reflection spectrum, the target position heated is mapped into the oscillating frequency shift, according to the first operation principle. A sensitivity of 254.66 kHz/cm is obtained for position finding in the experiment. Afterward, solutions for calibration and stabilization are briefly introduced, which enable us to improve the accuracy and reliability. Finally, features and future prospects on the sensing, measurement, and detection applications are discussed, such as compact and integrated OEOs. [ABSTRACT FROM AUTHOR]

High-resolution Doppler frequency shift (DFS) estimation in a wide frequency range is essential for radar, microwave/millimeter-wave, and communication systems. In this paper, a photonic approach to DFS estimation is proposed and experimentally demonstrated, providing a high-resolution and frequency-independent solution. In the proposed approach, the DFS between the transmitted microwave signal and the received echo signal is mapped into a doubled frequency spacing between two target optical sidebands by using two cascaded electrooptic modulators. Subsequently, the DFS is then estimated through the spectrum analysis of a low-frequency electrical signal generated from the frequency beating of the two target sidebands with an improved resolution by a factor of 2. In the experiments, DFSs from -\90 to 90 kHz are successfully estimated for microwave/millimeter-wave signals at 10, 15, and 30 GHz, where the estimation errors are lower than \pm \5 \times \10^-10 Hz. For radial velocity measurement, these results reveal a range from 0 to 900 m/s and a resolution of \1 \times \10^-11 m/s at 15-GHz frequency band, or a range from 0 to 450 m/s and a resolution of \5 \times \10^-12 m/s at 30-GHz band. To eliminate the estimation ambiguity, a reference branch is introduced for generating an indicator frequency to discriminate the sign of DFS and the direction of radial velocity for approaching or receding motion. In addition, extended discussions on the signal-to-noise ratio, the minimum measurable DFS, and other detection features of the proposed approach are presented. [ABSTRACT FROM AUTHOR]

We demonstrate a distributed Bragg reflector (DBR) fiber laser sensor for simultaneous measurements of axial strain and transverse load, this sensor might be applied in structure health monitoring. In this scheme, transverse load introduces an additional birefringence and consequently a linear beat note frequency change of the orthogonally polarized lasing modes, while the axial strain can be simply deduced from the wavelength shift of the laser. The sensor’s sensitivity is measured to be 1.33 kHz/mg and 1.266 pm/με for lateral load and axial strain respectively. [ABSTRACT FROM AUTHOR]

In this study, the laser sintering technique was used to obtain Er3+/Yb3+ co-doped silica glasses for up-conversion (UC) luminescence for the first time. Further, structural analysis of the glass sample was conducted via XRD, SEM and EDS measurements. Based on the measured absorption spectrum, important spectroscopic parameters including three intensity parameters Ω t (t = 2, 4 and 6), theoretical and experimental line strengths, spontaneous transition probabilities, branching ratios and radiative lifetimes, were calculated using the Judd-Ofelt (J-O) theory. The UC properties of Er3+/Yb3+ co-doped silica glasses were investigated upon the excitation of a 976 nm laser. It has been experimentally confirmed that the green and red UC luminescences corresponding to the radiative transitions of Er3+: 2H 11/2 → 4I 15/2 (green), 4S 3/2 → 4I 15/2 (green) and 4F 9/2 → 4I 15/2 (red) were achieved. This result is consistent with those of the J-O theoretical analysis. Additionally, the energy transfer mechanism between Er3+ and Yb3+, which is responsible for the UC process, was discussed based on their dependence on the pump power. The obtained results indicated that the Er3+/Yb3+ co-doped silica glasses manufactured using the laser sintering technique can be promising for the application of short-wavelength lasers. • A non-CVD method, namely the laser sintering technique, was adopted. • Er3+/Yb3+ co-doped UC luminescent silica glasses was fabricated. • The silica glasses have exhibited excellent optical and spectroscopic properties. • Strong UC emissions were experimentally observed. • The experimental result is in agreement with those of the J-O theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a real-time multi-class disturbance detection algorithm based on YOLO for distributed fiber vibration sensing. The algorithm achieves real-time detection of event location and classification on external intrusions sensed by distributed optical fiber sensing system (DOFS) based on phase-sensitive optical time-domain reflectometry (Φ-OTDR). We conducted data collection under perimeter security scenarios and acquired five types of events with a total of 5787 samples. The data is used as a spatial–temporal sensing image in the training of our proposed YOLO-based model (You Only Look Once-based method). Our scheme uses the Darknet53 network to simplify the traditional two-step object detection into a one-step process, using one network structure for both event localization and classification, thus improving the detection speed to achieve real-time operation. Compared with the traditional Fast-RCNN (Fast Region-CNN) and Faster-RCNN (Faster Region-CNN) algorithms, our scheme can achieve 22.83 frames per second (FPS) while maintaining high accuracy (96.14%), which is 44.90 times faster than Fast-RCNN and 3.79 times faster than Faster-RCNN. It achieves real-time operation for locating and classifying intrusion events with continuously recorded sensing data. Experimental results have demonstrated that this scheme provides a solution to real-time, multi-class external intrusion events detection and classification for the Φ-OTDR-based DOFS in practical applications. [ABSTRACT FROM AUTHOR]

• Developed tapered no-core fiber coupler for ultrahigh-sensitivity biosensing. • Provide "additional" stability due to the coupler structure. • Demonstrated limit of detection of Staphylococcus aureus as low as 3.1 CFU/mL, the best value reported so far. • The sensor structure has potential for other applications such as disease,medical diagnostics and food safety inspection. An ultra-high sensitivity label-free optical fiber biosensor for inactivated Staphylococcus aureus (S. aureus) detection is proposed and investigated in this study, with additional advantages of robust and stability compared to traditional tapered fiber structure. The proposed fiber biosensor is based on a tapered singlemode- no core-singlemode fiber coupler (SNSFC) structure, where the no core fiber was tapered to small diameter (taper-waist diameter of about 10 μm) and functionalized with the pig immunoglobulin G (IgG) antibody for detection of S. aureus. The measured maximum wavelength shift of the sensor for an S. aureus concentration of 7 × 101 CFU/mL (colony forming unit per milliliter) is 2.04 nm, which is equivalent to a limit of detection (LOD) of 3.1 CFU/mL (a highest LOD reported so far for optical fiber biosensors), considering the maximum wavelength variation of the sensor in phosphate buffered saline (PBS) is ±0.03 nm over 40 min, where 3 times of maximum wavelength variation (3 × 0.03 = 0.09 nm) is defined as measurement limit. The response time of the developed fiber sensor is less than 30 min. The ultra-sensitive biosensor has potential to be widely applied to various areas such as disease, medical diagnostics and food safety inspection. [ABSTRACT FROM AUTHOR]

In this paper, a thermo-optic tuning optical waveguide sensor system based on a cascaded double micro-ring resonator is investigated. The system consists of a micro-ring resonator with the microheater as a reference ring and a micro-ring resonator with removing the upper cladding layers as a sensing ring, combined with a microfluidic control. The refractive index change of the sample is measured by the electric power change of the microheater. The experimental results show that the sensitivity of the thermo-optic tuning is 34.231 W/RIU (refractive index units), and the measurement range is 4.325 × 10−3 RIU, almost eight times larger than that of the cascaded double micro-ring resonator without thermo-optic tuning for the intensity interrogation. [ABSTRACT FROM AUTHOR]

A critical barrier for the successful development of fiber sensors for bio-chemical processes is their limitedly improved sensitivity, restricted by the sensor structural design. To solve this, in this paper, a novel concept was proposed using functionalised modified magnetic microspheres (MMSs) to "amplify" the effect of target bio-chemical analytes to significantly improve the fiber sensor's sensitivity, which has been demonstrated using human chorionic gonadotropin (hCG) as an example. Two types of antibody hCG, ( β and α , both can specifically bind with hCG), were adhered on the surface of fibre sensor and MMSs respectively. Both hCG and MMSs will be specifically captured by the fibre sensor, where MMSs act as an "amplifier" to improve the sensor sensitivity. Experimentally immunomagnetic detection limit of 0.0001 mIU/mL has been achieved, which is the highest reported so far. This newly developed methodology opens a new direction for sensitivity improvement and could be further explored to applications require ultrahigh sensitivity detections such as earlier medical diagnostics. • Use surface modified magnetic microspheres (MMSs) to "amplify" the signal of target analyte. • Provide "additional" sensitivity improvement for the fabricated sensor. • Demonstrated limit of detection of human chorionic gonadotropin as low as 0.0001 mIU/mL, the best value reported so far. • The concept will be pivotal for applications require ultra-high sensitivity detection such as early medical diagnostics.. [ABSTRACT FROM AUTHOR]