Maintaining a near-zero magnetic field condition is a requisite for atomic magnetometer under the spin-exchange relaxation-free (SERF) regime. Therefore, the precise determination of the residual magnetic fields is of great significance. Herein, we proposed an in-situ measurement method of residual magnetic fields in a dual-beam atomic magnetometer based on a transient response of the transverse polarization along the probe beam direction after switching off the pump beam. Proceeding from the Bloch equation, we established a complete evolution expression of the polarization vector under any static residual magnetic field with the pump beam switched off. On this basis, we analyzed the transient response of the transverse polarization by numerical simulation under different situations of residual magnetic fields. Besides, we also considered two possible conditions when the residual magnetic fields are relatively large or small, respectively. Accordingly, we presented an efficient and convenient estimation method of the residual magnetic fields based on certain time characteristics of the transient response. We verified the feasibility of our method by experiment and achieved a triaxial residual magnetic fields measurement within 0.5 s. This method can realize an in situ and real-time measurement of the residual magnetic fields in a fast and convenient way. Furthermore, this method can evaluate the effectiveness of different magnetic field compensation methods without introducing any modulation or extra devices.

We obtained an expression for Jones matrix of a real spun fiber which take into account a slight deviation of the fiber properties from the idealized case with polarization eigenstates in the form of right and left circular polarizations. The performed experiments with the spun fiber revealed the parameter deviations of the polarization modes of the real spun fiber from the idealized model and allowed estimation of this deviation level. The features of using the Jones matrix of a real spun fiber in the analysis of practical fiber-optic circuits and modeling their signals were considered.

A differential fiber optic gyroscope (FOG) driven by two broadband light sources with different wavelengths was demonstrated theoretically and experimentally, and bias drift and angle random walk both can be reduced considerably due to common-mode error cancellation. A 3-component fiber optic rotational seismometer based on the differential FOG was developed and successfully applied in rotational seismic observation.

Biomarker assay has evolved into an invaluable complementary method for early screening and treatment diagnosis of tumors. Limited by the bulky devices, elaborate procedures, and poor detection accuracy, conventional methods fail to meet the demand for portable, universal, as well as high-precision detection. Herein, an optical fiber lossy mode resonance (LMR) immunoprobe implemented by ITO film as the lossy mode support layer is demonstrated for the detection of prostate-specific antigen (PSA), a biomarker for prostate cancer (PCa). Theoretically, the refractive index sensing performance of the optical fiber LMR was verified by constructing a transmission matrix model, providing theoretical guidance for the application of optical fiber LMR sensors. The construction of the PSA immunoprobe was experimentally achieved by functionalizing the optical fiber LMR sensor. The relationship between wavelength shift and PSA concentration was quantified by resonance wavelength interrogation, and the detection limit (LOD) was calculated to be as low as 0.144 ng/mL, making it ideal for early risk management and prognostic diagnosis of PCa. For clinical application, multiple serum samples were analyzed by the optical fiber LMR immunoprobe with favorable precision. Taken together, this work demonstrates considerable promise in applications of label-free, low-cost, compact-size, and convenient early screening for suspected PCa.

In this paper, we have considered the refractive index measurement resolution limits of a core-cladding intermodal fiber optic interferometer based on SMF-28 optical fiber, with spectral interrogation in the C-band. The resolution was calculated using the Cramer-Rao bound. To achieve this, we found the sensitivities of the cladding mode propagation constants to the refractive index of the surrounding medium, as well as the cladding mode attenuation coefficients, through full-vector numerical simulation. These calculations were performed for two fiber configurations: with and without a metal coating on the cladding. Our numerical results demonstrate that the refractive index measurement resolution improves when higher-order cladding modes are used. Also we demonstrated that the use of additional thin metal coating of the cladding and plasmon modes does not enhance the interferometric sensor's resolution in this case because their huge losses.

The paper describes the results of Raman spectroscopy and SERS for the study of fluorescent components of Baltic amber via the extraction method. Using SERS, it was possible to confirm in amber: tetracene and benzanthracene and others components. It has been shown that SERS methods are effective for the detection of aromatic and non-aromatic compounds. SERS be used to distinguish between different types of amber and isolate the necessary amber components. The obtained results are promising for compiling spectral maps of ambers for their possible classification by their place of origin and age.

Temperature is undoubtedly one of the most important parameters in human life, production, and technological activities, and plays a crucial role in both daily life and industrial production. Fiber temperature sensors, with their advantages of small size, fast response, high sensitivity, and so on, have been widely studied and used. Ultrasensitive fiber temperature sensor based on the Fabry Perot interferometer (FPI) and vernier effect has been composed. Single mode fiber (SMF), polydimethylsiloxane (PDMS), and capillary have been used to fabricate two FPIs. The sensor was cascaded by a sensing FPI (FPIs), a "SMF-PDMS-SMF" cavity with FSR of 6.27 nm, and a reference FPI (FPIr), a "SMF-capillary-SMF" cavity with FSR of 6.47 nm. Temperature measurements have been performed on both individual sensing FPIs and cascaded sensor, and it is found that they both have excellent linear response with linearity of more than 0.998. The sensitivity of the single sensing FPI is 1.037 nm/°C; The temperature sensitivity of the sensor based on the cursor effect is 32.39 nm/°C, with an amplification factor of 31.58, which is very close to the theoretical M-factor. This ultrasensitive temperature sensor can meet the demand for high-precision temperature measurement.

The paper is devoted to the analysis and review of optical resonance gyroscopes on low-coherence radiation sources. The main advantages of using low-coherence radiation sources in optical resonance gyroscopes are considered. The circuit design options for their implementation developed to date, their operating principle, achieved characteristics, common problems of such gyroscopes and methods for solving them are analyzed.

Lithium-ion batteries (LIBs) experience intense electrochemical reactions during high-rate charge/discharge cycles, resulting in significant differences in state characteristics between the inside and outside of the battery. However, most monitoring techniques are severely limited in safety and accuracy due to the intense redox reactions inside LIBs. Thus, we propose a highly stable fibre-optic microcavity sensor based on the Fabry-Perot (F-P) interference principle, which is capable of real-time, in-situ monitoring of the state characteristics inside the LIBs. The degree of electrochemical reactions inside the battery is reflected by extracting the internal gas pressure state characteristics of LIBs at different charging and discharging rates. This experimental result demonstrates that the voltage is closely related to the gas pressure inside the battery and that the cyclic gas pressure increases greatly with the charge/discharge rate increase. This fibre-optic sensing approach provides a promising tool for monitoring in-situ battery state characteristics and safety.

Grating interferometers with high accuracy, strong robustness and multi-dimensional measurement ability have become a main approach in ultra-precision positioning. However, the installation errors, especially the nonideal rotation and translation of the grating, will affect the phase of diffraction beam, resulting in displacement calculation errors. In this paper, a common phase variation model of grating interferometer regarding to the mechanical errors is proposed. A simplified geometric model of general grating interferometers base on the principle of optical-path-unfolding is first established for convenience and universality. Optical path tracing algorithm and the ray vector analysis method are adopted to analyze the phase variations due to optical-path length change and Doppler effect. The experiment results indicate that when the grating moves 100 mm in X-direction with a rotation of 100 arcseconds around Y-axis, a non-linear error of 11.4 nm is generated. For deflection angles of 300 arcseconds around three axes, cross-talk errors between translation axes will reach 45.6 μm in a range of 30 mm for the measurement system illustrated. The Unfolding-Based model proposed in this paper can be applied to most of the grating interferometers. Calculation errors can be effectively quantified through the model and algorithm, which provide a reference for the optimization of optical path as well as the design of calibration algorithm. The results further improve the necessity of six degree-of-freedom measurement ability in ultra-precision positioning.

Distribute acoustic sensors (DAS) based on linear frequency modulation (LFM) has advantages flexible sensitivity adjusting and less affection from interference fading. The time delay estimation (TDE) is commonly used in interferogram movement caused by frequency shift compensation to acquire quantitative strain. While, jump demodulation error may occur when large dynamic strain is applied to detection fiber, limits the dynamic range of sensing system. In this paper, we established a frequency band characteristic model of LFM-DAS optical signal envelope, the relationship between phase change and interferogram envelope shift in different bands is investigated. The simulation and experiment result shown that envelope of high frequency band has lower energy and SNR. Low-pass Filters (LPF) related can used to stabilize the envelope shape and increased correlation coefficient. In addition, part of the jump error is eliminated, which enhances the strain demodulation accuracy. 41.2 km, 100Hz, 53.81nε sinusoidal disturbance DAS has been realized based on LFM pulse. The root-mean-square error (RMS) is 3.191, Power spectral density (PSD) is 60.14 rad²/Hz.

The grating interferometer possesses inherent advantages such as high robustness , compact structure, and the ability to measure multiple degrees of freedom in displacements. However, traditional models primarily focus on translational displacements while overlooking rotational displacements. This oversight leads to micrometer-range errors that diminish the precision of measurement algorithms in multiple interferometers, hindering accurate positioning in motion stages.To address this problem First, a mathematical model for the phase-shift of the interference signal is formulated based on the principles of spatial analytical geometry and the Doppler effect. The model is subsequently simplified through Taylor series expansion to eliminate non-linear terms. By utilizing four grating interferometers symmetrically arranged in a square configuration around a centrally positioned motion stage, the redundant measurement data facilitates the computation of the 6-DOF displacements of the motion stage. Simulation results confirm that the algorithm effectively reduces the translational error to below ±4.85 × 10⁻² nm and the rotational error to below ±2.28 × 10⁻¹⁰ rad, while requiring computational times of only 6.257 × 10⁻² ms and 2.906 × 10⁻² ms, respectively.

The condition and concept of confocality for ring resonators are considered. The advantages and limitations of such a design and its prospects for application in passive optical gyros are considered. It is also shown that earlier proposed scheme with toroidal reflecting surfaces can be substituted by the ring cavity with the internal axially symmetrical lens (GRIN-lens).

Temperature is a significant control parameter in the silicon-based MEMS fabrication process, and the uneven distribution of the temperature on the surface of a silicon wafer can have a huge impact on the entire process. In this study, an FBG temperature sensing network was used to monitor temperature trends and abnormal temperature regions during the manufacturing process. The measurement of wafer surface temperature using FBG arrays often only records limited spatio-temporal temperature data, rather than the temperature distribution across the entire surface. Therefore, a reconstruction algorithm is needed to reconstruct the temperature field on the wafer surface. In order to find the optimal FBG sensor arrangement while improving the reconstruction accuracy of the wafer surface temperature field, this paper discusses the influence of the number of sensors and the sensors’ placement. COMSOL is used to simulate the process of wafer heating. Sparse temperature data are obtained by numerical calculations to reconstruct the temperature field with both linear and fan-shaped sensor position arrangements. The RMSE between the temperature field obtained by the optimized layout and the simulation results is smaller than 2.5°C. The FBG network layout proposed in this paper can provide an application basis for temperature field reconstruction in the MEMS manufacturing process.

In response to the intrinsic constraints of traditional single-parameter pipeline leakage detection, this paper proposes a hybrid ultra-weak fiber Bragg grating (UWFBG) array with alternating chirped and narrowband gratings of low reflectivity. The microporous Pt/WO₃ sensing material is combined with narrowband gratings to fabricate hydrogen sensors, while adjacent chirped gratings form vibration sensors. The demodulation system incorporates wavelength division multiplexing (WDM) to integrate homodyne coherent detection with tunable laser-based distributed wavelength demodulation, facilitating simultaneous monitoring of pipeline vibrations and ambient hydrogen concentration. This configuration enables multi-parameter sensing of hydrogen concentration and vibration in hydrogen transportation pipelines. Under constant pressure conditions, the experiment designed in the lab simulated hydrogen pipeline leaks with varying hole sizes, resulting in hydrogen accumulation around the leakage site. The hybrid UWFBG array was helically deployed along the pipeline. The findings revealed a quadratic correlation between the time-domain standard deviation of the leakage vibration signal and the leakage hole size, alongside a quartic relationship between the slope of wavelength shift and the leakage hole size. This validates the viability of utilizing the hybrid UWFBG array for leakage detection in hydrogen pipelines. Moreover, the integration of hydrogen concentration and vibration signals offers novel perspectives for subsequent leakage classification and localization.

This study presents a portable multi-component gas sensing system based on Fiber-Enhanced Raman Spectroscopy (FERS). The system achieves efficient gas collection, precise analysis, and rapid response times by leveraging the unique advantages of hollow-core optical waveguides. The large aperture and high reflectivity of silver-coated capillary (SCC) minimize optical power loss and improve the collection efficiency of Raman signals, ensuring high sensitivity and accuracy in gas detection. And by combining SCC and lens with the gas chamber, the integration of the probe has been improved. Additionally, The system's fiber optic probe structure seamlessly connects the Raman probe to the laser and spectrometer via multimode fiber, streamlining signal transmission, allowing it to function as an independent portable probe. Experimental results demonstrate the system's capability for qualitative and quantitative analysis of multi-component gases, achieving detection limits in the low hundreds of parts per million (ppm) for gases such as CH₄, C₂H₄, and C₂H₂, along with other flammable industrial gases. Notably, the system exhibits a rapid response time of 1.5 seconds. This portable FERS-based gas sensing system offers exceptional performance for real-time gas analysis, making it a valuable tool for industrial and environmental monitoring applications due to its compact design, high sensitivity, versatility, and fast response.

Atomic magnetometers with magnetic field modulation have emerged as pivotal sensors for biomagnetic measurements. However, challenges such as crosstalk between adjacent modulation fields and the complexity of signal circuitry become increasingly serious in the development of array-based equipment with the magnetometers, especially in the miniaturized atomic magnetometer. This paper proposes an all-optical, fully integrated fiber-coupled atomic magnetometer that employs pump beam modulation. A miniaturized atomic magnetometer with a volume of 10 cm³ has been designed, incorporating an active measurement area of 3 × 3 × 3 mm³. The magnetometer operates in the spinexchange relaxation-free (SERF) regime with an ⁸⁷Rb vapor cell. An amplitude-modulated pump beam directly modulates the rubidium atomic ensembles, rather than the magnetic field modulation. The optical rotation angle is detected by an unmodulated probe beam oriented orthogonally to the pump beam. In light of the discontinuous pumping characteristics, we developed a modified theoretical model to clarify the output response of the proposed atomic magnetometer. The experimental results demonstrate that the new design achieves the same sensitivity as conventional magnetometer configurations with a smaller volume and without crosstalk of the magnetic field. This research highlights the significant potential for advancing the development of highly sensitive, miniaturized atomic magnetometers, making them particularly suitable for applications in magnetocardiography (MCG) and magnetoencephalography (MEG).

Traditional monitoring systems for older adults typically rely on a single type of sensor, resulting in limited data sources that limit the comprehensiveness and diversity of monitoring. This limitation makes it difficult for the system to effectively and comprehensively identify complex abnormal behaviors, thus failing to provide sufficient data support for decision-making. To address this problem, this study proposes a multi-sensor information fusion-based monitoring system for the elderly. The system employs an advanced fusion algorithm to fuse data from visible, infrared and other sensors. To further improve the accuracy and coverage of the system monitoring, this study introduces a fusion genetic wolf pack algorithm to optimize the sensor layout and ensure the optimal configuration of sensors in the monitoring environment. By combining multi-sensor information fusion with optimal layout, the system not only monitors the multidimensional living environment and physiological state of the elderly more accurately, and provides comprehensive and accurate monitoring of the elderly's daily activities and health status, but also provides a solid data base for the detection and processing of abnormal behaviors.

Optically pumped gradiometers have emerged as a promising tool for measuring extremely weak magnetic fields generated by nearby bio-magnetic sources, providing remarkable advantages such as high sensitivity, compact footprint, and the ability to operate in unshielded environments. However, existing gradiometer configurations often employ fixed baseline distances, which hinders the optimization of parameters such as baseline distance when dealing with magnetic sources of different sizes. Moreover, there is a lack of universal conclusions in current research regarding the optimal selection of baseline distance, measurement distance, and other parameters for various magnetic source types. To address this issue, we construct a dual-channel spin-exchange relaxation-free (SERF) gradiometer with an adjustable baseline ranging from 5 mm to 60 mm to investigate the relationships between the baseline distance of the gradiometer, the size of the magnetic field source, and the measurement distance, as well as their impact on the signal-to-noise ratio (SNR). By employing circular coils of different radii to simulate magnetic field sources, we measure the SNR of the gradiometer under the distance ranging from 40 mm to 95 mm and present normalized SNR curves that illustrate the relationship between the baseline distance, field source radius, and measurement distance. To ensure universal applicability, the specific distances are converted into multiples of the source radius. The results demonstrate that positioning the gradiometer closer to the source enhances its SNR, regardless of the source size. However, the optimal baseline distance varies depending on the source size, with smaller sources requiring relatively longer baselines to achieve better performance. We believe these findings can offer reliable evidence for optimizing gradiometer configurations in bio-magnetic measurements and other applications involving sources of different sizes

A plastic optical fiber (POF) assisted by a corrugated surface long period grating (LPG) was proposed as a refractive index (RI) sensor, and the LPG was fabricated on a POF by a simple mechanical die press print method. An influence of the diameter of a POF assisted by an LPG to the RI sensitivity was investigated. A ray theory of geometric optics was used to simulate the LPG based RI sensors, and theoretical and experimental results showed that the RI sensing performance of the LPG could be effectively improved by flattening the POF for thinned it in one dimension, or drawing the POF for thinned it in two dimensions.

A corrugated surface long-period grating (LPG) was imprinted on a flat-shaped plastic optical fiber (POF) as a liquid-level sensor. The flat shape was processed on commercial POF by a simple heat-pressing method, and the LPG was fabricated by a mechanical die-press-print method. The liquid-level sensing performance of the sensor with different structural parameters was evaluated. It was shown that the thinner flat-shaped POF assisted by an LPG exhibits better sensing performance. The LPG with deeper groove depth achieved higher sensitivity, and theoretical calculations were consistent with these results. The highest sensitivity of -0.2332dB/mm was obtained while the flat-shaped POF with a thickness of 500μm, on which was assisted by the LPG with a period of 300μm and a groove depth of 103μm. The results demonstrated that flattening the POF assisted an LPG could improve the liquid-level sensing performance.

Lung cancer is a malignant tumor with the highest morbidity and mortality rate. Early screening and treatment are crucial in effectively reducing lung cancer mortality. This study presents a novel label-free bioanalysis system integrating fiber optic sensing and two-dimensional (2D) scattering imaging technologies, offering real-time, high-efficiency detection capabilities. The cladding on the fiber surface, followed by immobilization of specific antibodies. Variations in the evanescent wave field at the fiber surface induce changes in the transmission intensity, enabling highly sensitive, realtime detection of target biomolecules. Simultaneously, the light beam transmitted through the fiber optic excites individual biological cells in the fluid chamber, while a micro-optical system captures their 2D light scattering patterns, enabling precise cell identification and classification. The integration of these two technologies allows the sensor system to perform visualized single-cell identification and classification, as well as efficient biomarker detection at the molecular level. Compared to traditional single-technology approaches, this innovative system offers significant advantages in sensitivity, specificity, and detection speed, opening new pathways for bioanalysis. It demonstrates broad application potential in areas such as label-free ion detection and cell classification, particularly in early tumor screening.

High-quality radio-over-fiber (RoF) links are desired for wireless communication and radar systems. To address challenges of power fading induced by dispersion in fiber transmission, and the decreasing sensitivity caused by large carrier-to-sideband ratio (CSR), we propose a double-sideband-modulation analog photonic link featuring power fading compensation and tunable optical CSR based on a dual-parallel polarization modulator. Through adjustment of the direct current bias voltage, dynamic compensation of dispersion-induced power fading at the working frequency can be achieved. The simulation results show successful compensation of power fading over fiber transmission distances of 25 and 40 km. In addition, the tunable optical CSR ranging from -60 dB to 60 dB is attained by tuning the polarization angle before the modulator, providing the flexibility of optimizing the RoF link performance by adjusting the optimal CSR.

Whispering-gallery-mode (WGM) microcavities has emerged as a promising alternative to traditional probes, offering high sensitivity and wide bandwidth. In our research, we propose a novel silicon dioxide WGM microprobe device, with impressive Q factors up to 10⁷. With a sensitivity of 5.4 mPa√Hz and a bandwidth of 41 MHz at -6 dB, we have successfully conducted photoacoustic imaging on various samples using this device. What’s more, it can measure the resonance spectrum of microparticles by contact. Meanwhile, our compact and lightweight device exhibits waterproof, corrosion-resistant, and pressure-resistant properties by encapsulating in a 2 mm aluminum case which shows significant application potential in photoacoustic endoscopic detection, near-field ultrasonic detection and other aspects.

A fiber optic Mach-Zehnder interferometer (MZI) sensor with sensitivity to strain, magnetic field, and bending was designed by splicing single-mode fiber (SMF) and dispersion compensation fiber (DCF). MZI is a sandwich structure of “SMF - tapered DCF - SMF”. MZI₁ and MZI₂ are prepared by pulling DCF to different lengths using a fiber optic fusion tapering machine respectively. MZI₁ with tapered structure is quite sensitive to axial strain, and the experimentally obtained axial strain sensitivity is -21.6 pm/με. Then, sticking MZI₁ and magnetostrictive material together can form a magnetic field sensor. The experiment found that within the range of 15 mT to 140 mT, there is an excellent parabolic fitting relationship between the dip wavelength of MZI₁ spectrum and magnetic field intensity, with a fitting coefficient of 0.9997. The curvature of the bending was measured using MZI₂, achieving a sensitivity of 10.1 nm/m^-1 and a linearity of 0.9906.

In modern intelligent scenarios, such as highway and ship, it is the most crucial to on-line measure the weight of vehicle by a fast and efficient way. Considering the varying body sizes of vehicles, ranging from a few meters to ten meters, it is needed to establish the relationships between the vehicle weight and the different shapes of vehicle wheel. In this paper, an on-line weight traceability measuring system of vehicle was developed by based on image sensing fusion technologies. We design some datum points to determine the geometric relationships between four optical sensors too, which located in different orientations. Finally, a series of experiments on conventional vehicle were carried out to demonstrate the weight measurements by considered of practical applications. The influence factors of weight measurement errors were also been discussed. Those results have been proven to be amenable for practical purposes through many tests so that it might be applicable to achieve intelligent weight measurements in highway toll station. Key words: weight; traceability; vehicle; optical imaging.