This PDF file contains the front matter associated with SPIE Proceedings Volume 12321, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

In this study, a plasmon sensor based on a core mismatch optical fiber structure is proposed for measuring various creatinine concentrations. Creatinine is an important clinical biomarker for diabetes, kidney disease, renal failure, and muscle atrophy. The single-mode fiber (SMF) and multi-mode fiber (MMF) are used to fabricate the SMF-MMF-SMF-MMF-SMF (SMSMS) structure. Further, SMSMS fiber structure is etched with hydrofluoric (HF) acid, that results in more evanescent fields at the core-cladding interface. Gold nanoparticles (AuNPs) are immobilized on the surface of the optical fiber structure to activate the LSPR phenomenon. To validate the sensor's performance, the sensor's sensitivity, reusability, reproducibility, and selectivity are tested. The experimental results demonstrate that the fiber-optic sensor based on the SMSMS structure is capable of measuring creatinine concentrations over a wide range in aquaculture industry. This provides an excellent opportunity for the sensor to be used in biomedicine.

Protein is a complex chemical substance essential for human survival. Traditional protein detection methods, such as colorimetry, electrochemical analysis, and enzyme-linked immunosorbent assays, have shown good specificity and accuracy for the protein detection. However, all these methods require specialized instruments, and the detection procedures are laborious and time-consuming. As a result, a rapid, sensitive, label-free protein detection method is urgently needed. Herein, we have developed an ultra-sensitive biosensor for the detection of low-concentration protein molecules, employing liquid crystal (LC)-amplified optofluidic resonator. Since the orientations of LCs highly depend on the surface biomolecular binding processes, LCs can be employed to realize the extremely sensitive detection of biomolecules. Immobilized protein molecules interfere with the orientation of LCs by reducing the vertical anchoring force from the alignment layer in which the spectral wavelength shift was monitored as a sensing parameter. A biosensing platform based on an LC-amplified optofluidic whispering gallery mode (WGM) resonator was designed and studied accordingly. Due to the simultaneous interaction of the WGM and the LCs in the optofluidic resonator, the changes caused by the injection of protein molecules will be amplified, resulting in a shift in the resonance wavelength. Total wavelength shifts scale proportionally to the molecular concentrations of the protein within a certain range. The detection limit for streptavidin (SA) can reach as low as the femtometer level, which is significantly higher than the detection limit in the classic polarized optical microscope (POM) method visible with the naked eye. In addition to SA, the LC-based optofluidic resonator can also be applied to detect a variety of protein molecules. Our study demonstrates that LC-amplified optofluidic resonator can provide a novel solution for ultrasensitive real-time characterization of biosensing and biomolecular interactions.

An all-fiber sensor for heart rate monitoring is proposed and demonstrated based on the disturbance of the evanescent field in the no-core fiber (NCF). The sensing structure is realized through splicing a piece of single mode fiber (SMF) at the ends of the NCF, respectively. When a broad-band light is injected into the structure, the vibration of the pulse signal applied to the sensing structure will lead to the disturbance of the evanescent field in the NCF and modulate the intensity of the optical output power. Therefore, when the sensing structure is placed at the wrist of a human, it can be used to monitor the heart rate. It is demonstrated that a standard electrocardiogram (ECG) signal can be obtained when 30-mm long NCF is used in monitoring the heart rate. According to the measured ECG signals, the proposed sensor can have a response to the heart pulse at different rates ranging from 60 beats per minute (bpm) to 120 bpm.

With the development of medical laboratory science, sensitive biomarkers detection has a prime role in the early diagnosis of diseases. The rapid diagnosis is crucial in acute diseases to lower mortality, e.g., acute myocardial infarction (AMI). Additionally, the dual-biomarker detection is highlighted in the bioassays. Compared to the gold standard immunoassay—enzyme-linked immunosorbent assay (ELISA) with extensive pretreatment and extended duration, the turbidimetric inhibition immunoassay (TIIA) is an ideal candidate for the fast detection with simple procedure and short reaction time. However, the low sensitivity limits its applications. Here, we presented an optofluidic laser immunosensor based on the latex-enhanced TIIA. With the dual-amplification of latex particles and laser, a fast and sensitive detection of cardiac troponin I (cTnI) was achieved. Furthermore, a dual-biomarker immunoassay was demonstrated with the optofluidic laser immunosensor by a two-step strategy to produce two types of immune complexes in the optofluidic laser. With the low minimum distinguishable detection (~fM) of dual-biomarkers of cTnI and immunoglobulin G (IgG) was achieved by the two-step strategy within 25 min. Thanks to the various commercial immunoassay kits, this method shows the potential to be employed in immunoassays for a variety of proteins, providing a unique platform for rapid and ultrasensitive dual-biomarker biosensing and an effective tool for clinical diagnosis of diseases.

Understanding the distribution of plankton in the ocean ecosystem is critical as the plankton of a broad range of species constitute the primary staple of marine species. To monitor the dynamic variation in space and time of plankton in a long term, various techniques have been used to characterize the plankton distribution in the ocean. In this article, based on shadow photographic imaging technology, a compact and miniaturized in-situ system is designed to provide highresolution spatial and temporal data on plankton abundance, biomass, and size. A 610 nm LED is used as the illumination source, which attenuates fast, and most marine organisms, including motile plankton, are least sensitive to red light, after the lighting, the plano-convex lens creates a collimated light field in a water body, to generate the shadow image of the sampling target in the water body on the CCD on the other side. And the diameter of the proposed system is only 70 mm, the length is 620 mm. In terms of the optical performance, the resolution, field of view, and depth of field are 50 um, 17.67x14.88 mm2, and 100 mm respectively, theoretically, about 26 mL of seawater parcel can be investigated with each exposure. The system has been deployed in the nearshore area of the South China Sea, deep learning technology is used to process the data acquired by the system.

On the basis of Optical Frequency Domain Reflectometry (OFDR) principles, Optical Backscatter Reflectometry (OBR) is able to convert a simple and cheap single mode fiber (SMF) into an effective spatially distributed sensor of temperature and strain. By using different spatial configurations of SMFs, it can be obtained a 2D sensing map of applied forces over a delimited surface. This can be useful in biomedical applications such as force byte measurement. Here, a 2D pressure sensing map, based on distributed fiber optic sensing technique, is presented. The two-dimensional approach is achieved by bending the optical fiber along the surface to get ten lines embedded in silicone material, thus obtaining a carpet of 2 by 6 cm. The highly resolved sensing map is achieved by setting fiber lines 2 mm apart from each other with a sensing range of 2 mm over the fiber. The distributed strain, detected by the embedded fiber, is then converted into a pressure map. The pressure sensitivity coefficient of the map has been successfully characterized. The setup has been validated for surface measurement of wavelength shift values over 9 points on the sensing carpet with 310 total sensing points (10 fiber lines, each having 31 sensing points per 6 cm length). The peculiarity of sensing surfaces based on their mechanical properties gives an opportunity for improved response to curvature due to the embedding or attaching the sensor to irregular shapes and geometries.

As a fast and accurate active ranging technique, LiDAR (Light Detection and Ranging) plays an increasingly important role in the future intelligent society. Driven by the fast-booming miniaturized robotics industries, the small-size, lightweight, and low-power LiDAR with a high update rate shows huge application perspectives and is highly desired. In this paper, a novel microwave-photonic frequency-modulated continuous wave (FMCW) LiDAR on a silicon-photonic chip is proposed, which can realize simultaneous distance and speed sensing. The FMCW generation, LiDAR signals passive processing and photoelectric detection are integrated into a single silicon photonic chip with a footprint of about 1mm×2 mm. Also, a phase-based signal demodulation scheme is proposed for this LiDAR, which makes the update rate of the LiDAR equal to the DAQ sampling rate, greatly increasing the dynamic performance of the LiDAR. Numerical verifications show this LiDAR can reach a micrometer resolution and megahertz update rate. The results of the proof-of-concept experiment will be given in the near future.

Single nanoparticle detection is demanding in fields such as early-stage diagnostics, environmental monitoring, and biochemical research. Optical whispering-gallery microcavities have high quality factors (Q factors) and small mode volumes, and mechanical oscillations can thus be excited by the strongly confined optical mode field. The mechanical mode frequency varies when the analyte attaches to the microcavity, and thus acts as an excellent sensing signal for single nanoparticle mass detection. In this work, we demonstrated the mass sensitivity dependence of mechanical modes on different cavity modes, the sensing sites, and the microcavity geometries, providing a way for optimizing the detection limit when designing a microcavity sensor.

The work is devoted to the analysis of the accuracy characteristics of rotation angle sensors using angular scales from nanostructured metasurfaces. The principle of their operation is based on the dependence of the frequency response of metasurfaces on the orientation of the incident light polarization plane. The influence of the noise characteristic of angle sensors on the measurement result is considered. It is shown that for the sensors considered in the work, it might be on the order of units of arc seconds. The influence on the accuracy characteristics of misalignments of the angular scale and thermal effects that the sensor may experience during operation is analyzed. Recommendations to reduce the influence of parasitic effects and further improve the accuracy characteristics are given.

SiO₂ cladding YAG:Yb crystal core fiber fabricated by the modified rod-in-tube method was demonstrated as a remote sensor for partial discharge faults (PD). The spectra of the crystal fiber and PD fault standard source were measured. When the applied voltage of the PD source is 36 kV, the detection pulse intensity of the sensor decays exponentially with the change of the distance from the PD source to the sensing probe (SSD). Its decay trend in the range of 0-25 cm conforms to the Beer-Lambert law. When the fixed SSD is 7 cm and the applied voltage range of the PD source varies from 35 to 39 kV, the pulse frequency detected by the sensor has a good linear relationship with the applied voltage (R² = 0.99279). The experimental results indicate that the crystal optical fiber sensor can realize the remote sensing of PD monitoring.

Fiber-optic current transformer (FOCT) is widely used in DC power transmission and transformation system of power grid. Power grid users pay attention not only to its measured output value, but also to its state quantity. They expect to find equipment failure in advance by monitoring the internal state parameters of optical path and reduce the risk of abnormal shutdown. This work mainly analyzes the modulation and demodulation process of FOCT based on PZT modulation, and extracts the condition monitoring parameters for fault diagnosis. And the influence of typical low-temperature fault process on outdoor modulation circuit devices is analyzed, and the data of performance deterioration process of modulation tank is collected through accelerated aging test, which explains the influence of performance deterioration of low-temperature devices on state parameters.

High-sensitivity sensing of multi-component gases has important applications in environmental monitoring, industrial process control, and biomedical analysis. Fiber-enhanced gas Raman spectroscopy based on node-less anti-resonant hollow-core fibers (AR-HCFs) has advantages for the detection of multi-component gases. AR-HCFs can significantly improve the collection efficiency of gas signals, but the diffusion rate of gas in AR-HCFs is slow under normal pressure, and the gas exchange in AR-HCFs requires the help of gas pressure control devices. In this work, a reflective fiber-enhanced gas Raman system is designed and only one end of the hollow-core fiber is coupled to the optical path, the other end is placed in free space which facilitates rapid gas exchange. Various gases such as CH₄, H₂, N₂, NH₃, etc. are injected into optical fibers for systematic research. It takes 70 s to fill the 0.5m-long AR-HCFs with hydrogen at 1.2 Bar, but only 8 s at 1.6 Bar. Due to the influence of the gas viscosity coefficient, the time required for CH₄ to fulfill 1m-long AR-HCFs is about 1.4 times that of H₂ under the same environment. It is proved that such an optical fiber-enhanced gas Raman system can realize fast gas filling and exchange, and has good detection ability for multi-component gas, which can be used in fields requiring the quick response of gas sensing.

Based on the microwave photonics filter technique, an FBG array for quasi-distributed strain sensing has been proposed and demonstrated. The kernel of this work is that the strain on the FBG array changes the wavelength of these FBGs, which is converted to the variation of the time delay of the time response of the generated microwave photonic filter. Results show that, there is good measurement linearity between the time delay and applied strain. The proposed scheme enjoys fast interrogation speed and high resolution, hoping to provide a valuable reference in the field of temperature, index refractive and other parameters sensing.

The article describes an optical response of metastructure consisted of two optically coupled resonant subwavelength rectangular - profile diffraction gratings, between which a layer of optically transparent dielectric was placed. The features of optical resonance transmittance and reflectance for optical PT-symmetry mode was numerical investigated and some advantages of using optical PT-symmetry for resonance transmittance (reflectance) improving was demonstrated. The spectral characteristics of the metastructure change when the pumping level changes and when the system switches from the optical parity-time-symmetry mode to the broken parity-time-symmetry mode were analyzed too.

We report on a Tm-doped self-sweeping fiber laser operating at 2 μm spectral range with a stabilized pulse repetition rate. Lasers with self-induced wavelength sweeping are bright alternative to narrow-band tunable laser sources. One disadvantage of self-sweeping lasers is fluctuations in the pulse repetition rate. In this paper for the purpose of optimization of intensity dynamics, the technique for pulse train shaping with acousto-optical modulator synchronized with laser pulses is proposed and demonstrated. Synchronization of the AOM frequency with the laser pulses allowed us to improve pulse train stability and reduce relative stability error down to 1%. The developed self-sweeping laser brings up new possibilities for remote gas analysis and LIDAR applications.

Protein detection plays an important role in the medical research. Liquid crystals (LCs), as a class of sensitive materials, exhibit a promising ability in the biosensing field. Herein, we exploited an ultrasensitive biosensor for protein detection, employing the whispering-gallery-mode (WGM) from the LC-amplified optofluidic micro-resonator. The biomolecules can trigger both light-matter interactions and the orientation transitions of LC molecules. The WGM spectral wavelength shift was recorded as the sensing indicator, and a detection limit of 15 fM for bovine serum albumin (BSA) was achieved. Our LC-amplified optofluidic biosensor provides a new solution for the ultrasensitive, real-time, and stable biological detection.

Cerium-doped lutetium yttrium oxyorthosilicate (Lu1-xYx)2SiO5:Ce crystal powders were synthesized by co-precipitation method. The properties of LYSO:Ce powders with Y3+ concentration and Ce3+ concentration were investigated using X-ray diffraction (XRD) and photoluminescence (PL). XRD results show that LYSO:Ce powder samples with different Y3+ concentration have the same crystal phase to compare with the crystal standard card. PL results show that LYSO:Ce powder has better luminescence performance when Y3+ concentration is 15 mol%. The luminescence and scintillation characteristics of the dosimeters were founded under X-ray irradiation with low dose rate of 2.284 Gy/min and compared with the dosimeter without LYSO:Ce powder material. The luminescence and scintillation properties of LYSO:Ce dosimeter indicate promising potential applications in real time remote low dose X-ray radiotherapy and radiation monitoring.

An all-fiber optic high-sensitivity displacement sensor based on 45°-spliced PM Lyot filter is proposed and its sensing performance is investigated experimentally. According to the relationships between the dips and the displacements, the sensor has a good linearity in passive mode, whose R square is larger than 0.998, and the highest sensitivity of 132.55 pm/μm is obtained in the range of 200 μm displacement variation. Moreover, it can be compatible to an intracavity displacement sensing system, achieving narrow linewidth, high signal-to-noise ratio (SNR), and high resolution. It can be found that the sensitivity of the intracavity displacement sensor can be 60 pm/μm when the PMF fiber length is about 20 cm with a linewidth narrower than 0.05 nm and a SNR higher than 55 dB.

A flat-shaped plastic optical fiber (POF) assisted by a corrugated surface long period grating (LPG) is fabricated by a simple heat pressing and mechanical die press print method. By changing the structural parameters of the flat-shaped POF with LPG, the refractive index (RI) sensing performance of the obtained sensor are evaluated. It shows that the structure parameters of sensor affect the RI sensing performance, and the sensor with a thinner flat thickness and a deeper groove depth of the corrugated surface LPG exhibits better RI sensing performance. Moreover, the sensitivity of the sensor after removing the cladding is better than that of the sensor without removing the cladding. When the POF diameter D is 1mm, the LPG period is 300μm, the thickness d of flat-shaped POF without cladding is 600μm, and the LPG groove depth h is 200μm, we obtained the highest sensitivity of 591.3%/RIU with a resolution of 2.872×10^-4RIU in the RI range of 1.3330-1.4230. The proposed sensor is a low-cost solution for RI measurement and with the features of easy fabrication, high sensitivity and intensity modulation at visible wavelengths.

In this paper, the theoretical analysis of hollow-core microstructure fiber for improving the temperature stability of fiber optic gyroscope (FOG) is carried out. The analysis shows that the thermally induced Shupe error can be reduced by a factor of about 23 in theory in a hollow-core microstructure FOG. A FOG prototype is constructed by utilizing a 300mlong 7-cell bandgap-guided hollow-core microstructure fiber, and its temperature stability is compared with that of traditional FOG under the same specification conditions. The experimental results exhibit that the hollow-core microstructure fiber in use can promote the temperature stability of FOG by 2.5 times.

In the background of modern smart grid, fiber optic current transformer (FOCT) has become a research hotspot in power system because of its high accuracy, good dynamic performance and other excellent advantages. However, lower temperatures can easily lead to failures and shutdowns, which are extremely detrimental to the safety of the grid. In this paper, the optical frequency domain reflectometry (OFDR) technology is employed to investigate the scattering characteristic of fibers used in FOCT in massively variable temperature environments. The experimental results present the variation of optical loss of various optical fibers at different temperatures, which is particularly useful for further analyzing and investigating the low-temperature failure mechanisms of FOCT.

Here we propose a visualized optical sensor based on two parallel dye-doped polymer microfibers (DPMFs) which are coupling together. The coupling region is considered the sensing unit. The fluorescence in the DPMFs is excited by the waveguiding excitation method and recorded in the microscopic images. The periodic energy distribution could be found along the coupling region, which is sensitive to the ambient refractive index (RI). The convolutional neural network (CNN) is introduced to analyze the periodic fluorescent image. With the input neurons being the structural parameters of the sensing unit, the energy distribution periods are accurately predicted by CNN according to their fluorescence images obtained under different ambient refractive indices. Further, the relationship between the periodic length and the environmental RI is established and when the RI is in the range of 1.0 ~ 1.3, the sensitivity of this visualized sensor is about 1.0 μm/RIU. This CNN-assisted visualized optical sensor, which could intuitively exhibit the change of the refractive index of the environment, has strong robustness to sensing structural parameter changes and great potential application in environmental monitoring such as gas or liquid.

We propose and experimentally demonstrate a simple directional bending sensor based on an in-line Mach-Zehnder interference structure of the single mode fiber (SMF)-multimode fiber (MMF)-asymmetrical twin-core fiber (ATCF)- MMF-SMF. Due to the asymmetric structure in twin-core fiber, this sensor can discriminate different bending directions. The interference spectrum shifts with the change of curvature. Furthermore, the sensor exhibits a linear response with a maximum bending sensitivity of 33.48 and -38.72 nm/m^-1 in the curvature range from 0 to 3.01 m^-1 for bending directions at -x (180°) and +x (0°) directions, respectively. The proposed fiber sensor has great potential in the future Internet of Things (IoT) due to its advantages, such as low cost, compactness, and high bending sensitivity.

Recent trends in long distance phase-sensitive optical time-domain reflectometer (φ-OTDR) have led to a proliferation of studies on nonlinear effects. We explores stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), selfphase modulation (SPM) and modulation instability (MI) in the φ-OTDR system both theoretically and experimentally. Results show that the analytical model of above nonlinear effects have significance for practice reference, except for MI in the case of long distance. The depletion of power and amplified spontaneous emission power density as the most effective consequences of modulation instability must be taken into account. Compared with theoretical analysis, numerical simulation provides more accurate results, and experiments support the existence of unreported intrinsic spectral component of MI around the signal.

The structural health monitoring of Prestressed Concrete Cylinder Pipes (PCCP) is still a difficult issue because the existing detection methods and pipeline protection methods require pipelines to stop running for detection and maintenance, and cannot monitor the running status of pipelines online in real time. As a result, it is impossible to prevent pipeline damage timely and effective and prevent third-party intrusion and damage. Aiming at problems such as PCCP pipeline leakage and pipe burst caused by the external third-party intrusion, pipeline aging, and other factors, this paper proposes a distributed fiber-optic acoustic sensing monitoring method based on the combination of fiber-optic back Rayleigh scattering and phase-sensitive optical time-domain reflectometry. When the pipeline is running normally, by collecting and demodulating the vibration, sound, positioning information and other data along the vibrating optical cable laid on the pipeline, the monitoring and rapid positioning of the pipeline intrusion damage and broken wire can be realized, to achieve the effect of real-time online monitoring of the structural health of the pipeline. The simulation test results show that the system can monitor the length of the pipeline up to 50km, the fault location accuracy is less than 5m, and the system has a single-point listening function, which can realize the secondary review of the fault point alarm information.

All fiber optical current transducers (FOCTs) are widely used and it is urgent demand to monitor and check the FOCTs. In this paper, a novel method to examine the state of the FOCT system and its components is proposed and demonstrated theoretically. Taking the reflective FOCT as an example, the transmittance of the FOCT, which is a function of wavelength is deduced using Jones matrix and the relationship between the transmittance and the parameters (phase shift and alignment angle) of the components such as modulator, high birefringent delay fiber, quarter wavelength plate is discussed respectively. By measuring the spectrum of the output light and processing the transmittance data, each of the parameters can be calculated and then the states of the components and whole system can be evaluated in some simple situations.

Distributed optical fiber acoustic sensing (DAS) can serve as an excellent tool for real-time condition monitoring of a variety of industrial and civil infrastructures. This paper presents a belt conveyor roller fault abnormal monitoring method based on DAS, for the low accuracy and efficiency of the existing belt conveyor rollers fault detection. This method uses the Rayleigh Backscatter of coherent pulsed light to detect and reconstruct the fault signal, and proposes a method based on the combination of power spectrum features and peak detection to recognize and locate abnormal signals under intense background noise. The field test verifies the effectiveness of the real-time monitoring scheme of the industrial conveyor belt system, with a detection accuracy rate of over 87% for simulated fault signals, and a location accuracy of ±2.5 m. It provides a new passive distributed monitoring method for the all-weather structural health monitoring of the rollers in the industrial belt conveyor systems.

This research proposes a real-time detection method for the health status of heavy-haul railways based on distributed fiber optic acoustic sensing (DAS). The DAS system detects the wheel-rail acoustic signals using the communication optical cable along the heavy-haul railway, multiple features are mixed to construct an eigenvector and a classifier to realize the typical disaster identification of the heavy-haul railway. The experimental results show that this system can realize the identification and classification of typical track diseases such as rolling contact fatigue (RCF), corrugation, unsupported sleepers on the railway, the achieved average identification rate of disease events is as high as 97.3%, and the identification time of a single event sample is 1ms. This work can achieve real-time detection of track diseases, which can be used as an important basis for workers to maintain and repair. In addition, the DAS system has also successfully monitored the train's running speed and wheel anomalies status information. This work provides a long-term online monitoring method for rail safety operation and maintenance of railway transportation and monitoring of train running status, and does not require any additional sensor arrangement.

As one of the cleanest energy sources in the 21st century, the development of hydrogen energy has attracted the attention of all countries in the world, so the monitoring of hydrogen leakage has become a current research focus. This study demonstrates a novel hydrogen sensor that combines a planar polymer grating with a Pd/Ni hydrogen-sensitive material that takes advantage of the hydrogen-absorbing expansion properties of Pd to cause the central wavelength drift of Planar Polymer Bragg Grating (PPBG) by strain transformation. The experimental results show when the hydrogen concentration is 0.3%, 0.6% and 1%, the wavelength shift of the sensor is 50 pm, 85 pm and 110 pm respectively, and the response time is approximately 30 seconds. This hydrogen sensor has the advantages of high sensitivity, low cost and compact structure, leading to great potential in industrial applications.

In the practical application of φ-OTDR system, the accuracy of the system is affected by the existence of environmental noise and so on. In order to effectively reduce the noise composition of the measured signal and better obtain the signal characteristics, this paper proposes a noise reduction method GA-VMD which combines genetic algorithm (GA) and variational mode decomposition (VMD). The method firstly optimizes the decomposition layer number (K) and penalty factor (α) of VMD by GA, and then performs multiscale permutation entropy (MPE) randomness detection of the intrinsic mode function (IMF) obtained by decomposition, so as to achieve the purpose of noise reduction. Through the processing of the measured signal, it is shown that the GA-VMD method is better than the empirical mode decomposition (EMD) and the Complementary Ensemble Empirical Mode Decomposition (CEEMD) method in terms of signal-to-noise ratio and cross-correlation coefficient. It shows that the GA-VMD algorithm is better than the EMD and CEEMDAN algorithms, which verifies the effectiveness of the method.

Rough target can cause the wavefront distortion of laser return, which shows the decoherence phenomenon and reduces the detection performance of heterodyne lidar systems. In fact, the decoherece process includes both the laser source and the rough target. The actual laser beams are usually partially coherent, and the atmospheric turbulence aggravates the coherence of laser spots on the rough target and the backscattered laser return. The backscattered laser field of rough plane is derived based on the GSM beam and the generalized Huygens-Fresnel principle. And the beam truncation effect of actual optical transceiver is also analyzed by using the hard edge aperture function. The laser return intensity variations are obtained by considering the laser beam coherence, the rough surface height fluctuation and the atmospheric turbulence. Then decoherence effects are calculated via the complex coherence degree under typical roughness parameters and laser wavelengths. For practical target, the complex coherence degree can be approximated by the Dirac delta function, and then the system efficiency and the effective coherent solid angle can also be used for further analyses. The results show a positive correlation between the decoherence effect and the roughness. The research on the scattering characteristics of rough planes expands the scattering theory and provides a reference for the design and analysis of long-range and high-precision heterodyne lidar system.

Tracking and ensuring the safety of trains is an important issue in subway operation management. Under the long-distance monitoring requirements, extracting features in real-time from large-scale stream data to track trains is a large and time-consuming task. With the support of the dynamic and distributed monitoring capabilities of ultra-weak fiber Bragg grating (UWFBG) arrays, this paper proposes a method combining the singular value decomposition (SVD) and the sequential similarity detection algorithm (SSDA) to handle the stream data to track trains in real-time. First, the vibration signal is denoised and is converted into a grayscale image using sliding window. Then, to improve the efficiency of recognition, the singular value features and the texture features are combined to build a template library for gray-scale image matching on the basis of SVD and SSDA. The details of SVD-SSDA deployment on Spark are illustrated to ensure real-time performance. Finally, the experimental results on the actual train data indicate that SVD-SSDA on Spark using ultra-weak FBG arrays can effectively identify the data stream and satisfy the requirements for real-time train tracking.

The correlation between reflected light intensity and hydrogen concentration is the basis of the end-face type hydrogen sensor with WO3 coating. However, the changes of optical propertiesofWO3 under different hydrogen concentrations have not been fully investigated, and its hydrogen sensitivity mechanism is still unclear, which restricts the improvement and optimization of hydrogen sensing performance. Therefore, the relationship between hydrogen concentration and Refractive Index (RI) of WO3 is established in this paper to explore the hydrogen sensitive mechanism. The experimental results show that the RI of WO3 changes when hydrogen is introduced, and the RI varies under different hydrogen concentration. Since there is a certain mathematical relationship between the RI value and the reflectivity of the films, the RI changes measured by ellipsometer is further verified by the intensity-tracing experiments results. Hence, we can clarify that the hydrogen sensitivity mechanism of WO3 is related to its RI changes under different hydrogen concentration, which will provide a basis for the further research and applications.

With the increasing pollution of endocrine disruptors (EDCs) to water and the development of optical fiber sensing technology, it is necessary to develop new biosensors with simplicity, sensitivity and high specificity. Herein, we demonstrated an EDCs detection device based on graphene oxide (GO) functionalized S optical fiber taper (SFT) and biotin–SA signal amplification system for the detection of E2 concentrations in water samples. In this study, the sensing element was based on compact SFT that was obtained by fusing optical fiber through a fusion splicer. The immunosensor probe was constructed by functionalizing the SFT with GO using self-assembled technique, further coupling with streptavidin and specific biotinylated monoclonal antibody against E2. The mechanism of detecting E2 relies on measuring the external refractive index changes of STF induced by the target adsorption of analyte onto the antibody. In addition, we also prepared an optical fiber immunosensor without amplification signal system as a control. By experiment, we gained an optical fiber immunosensor with a high sensitivity value of 38.3 nm/(ng/mL) that was about 1.5 times better than that of the control immunosensor produced, which was due to the signal amplification, high biotin affinity and strong specificity of SA. The detection limit of (LOD) the immunosensor for E2 was 0.01ng/mL (S/N= 3). The results revealed that the developed optical fiber immunosensor was successfully applied to the fast, online, low cost and sensitive detection of E2 in environmental samples, and its detection effect is better than the control optical fiber immunosensor

Fiber Bragg grating (FBG) sensor for marine exploration has gradually attracted people's attention because of its natural characteristics of low investment and high expansion capability. However, it is well known that FBG is not only sensitive to temperature, but also affected by strain, pressure, vibration, refractive index etc. The cross-sensitivity of FBG results in large measurement error for fiber temperature measurement. As an important error source of optical fiber temperature sensing, strain has attracted much attention of researchers. In order to eliminate the interference of strain on FBG temperature measurement, in this paper, we propose a FBG sensor for ocean applications. Two fiber Bragg gratings with different central wavelengths are cascaded to realize the decoupling of temperature and strain sensing. Experimental results show that the temperature sensitivity of the proposed sensor can reach to 9.49 pm/°C in the range from -5°C to 35°C.

Distributed acoustic sensing (DAS) technology holds considerable potential for marine geophysical surveys by transforming standard optic cable into dense arrays of seismo-acoustic sensors and gathering seismic data of shallow stratigraphic profiles. Here, a field trial with an abyss-class DAS system was carried out at 1423 meters depth in the South China Sea, and more than 600GB data was collected for 21 days. The vibration events of the marine integrated experimental base station were recorded, including entering, moving, landing and raising. The time and spectral domain characteristics were analyzed to reveal the station working statuses. The sea trial demonstrates the capability of the abyss-class DAS system for long-term seismic data acquisition in deep-sea environments.

A slope-assisted Brillouin optical time domain reflctometry system based on grade index multi-mode fiber (GI-MMF) was presented. The coherent detection was applied in this system and the Brillouin gain spectrum (BGS) was obtained by scanning work frequency. The BGS was inhomogeneously broadened by adjusting the lateral offset between single mode fiber (SMF) and GI-MMF. The bandwidth of BGS with different lateral offset was analyzed and the BGS with bandwidth of 111MHz was achieved at lateral offset of 8 μm. For realizing slope-assisted technology, a bandpass electrical filter was added behind the balanced photo-detector to realize the function of frequency selection. The strain intensity responses with different work frequency were analyzed for maintaining significant linear relationship between strain and signal intensity. The system realized the maximum strain dynamic measurement of 3000 με with the spatial resolution of 5 m along ~1 km GI-MMF at vibrational frequency of 7.83 and 15.47 Hz. The measured error of vibrational frequency was less than 0.2 and 1.5 Hz, respectively. The obtained strain intensity responses were 0.00296 and 0.00292 mV/με, respectively. The measured strain range of this system was more than three times that of traditional systems based on SMF and could be achieved at relatively low cost. The proposed scheme has potential application prospects in large dynamic strain diagnosis.

With the rapid development of high-level road traffic system and the implementation of autonomous mobility system, smart driving has become an important work toward the realization of intelligent society. Large capacity of imaging data acquired by imaging sensors and large surrounding traffic information data are required to be transferred to vehicles via in-vehicle transmission lines. Plastic optical fiber (POF) has potential for this type of next generation automotive data networks due to its relatively high bandwidth compared to current coaxial cables, easy connection due to relatively large core diameter, low cost, and immunity to electromagnetic interference. However, due to fiber mode dispersion, the bandwidth of large core POF is limited to several hundred Mega-Hertz for a hundred-meter-long transmission line. Equalization (including linear equalization and feedback equalization) was proposed to be used for eliminating inter symbol interference introduced by the limited bandwidth of the POF. In the past, fiber transfer function was supposed to be a Gaussian shape in simulations, which is not the actual situation. In this work, we first calculate the POF transfer function based on the power flow equation and the real fiber parameters. Then, we evaluate the transmission quality of raised cosine pulse sequence by observing the eye-pattern at the receiving end, which shows clear eye closure. Next, we designed a decision feedback equalizer and applied it to improve the bit rate of the transmission line. The result showed that transmission quality is improved, but the speed cannot achieve Gbps by equalizer alone.

Specific emitter identification technology has always been a hot issue for the vital research of radio-related departments in various countries. However, due to the sharp increase in the types of radiation sources and the complexity of electromagnetic space, identifying individual radiation sources has become more challenging. In order to provide a convenient and effective radiation source identification method, this paper proposes an emitter individual identification research method based on the characteristics of synchronization signal rising edges. With the help of artificial intelligence technology, the method proposed in this paper has achieved a very high individual identification rate of radiation sources by using the characteristics of synchronization signal rising edges and deep neural networks.

This paper summarizes the design methods of adaptive optical systems based on different types of platforms in recent years, classifies them according to the types of platforms they use (five categories in total), summarizes the design methods, performance indicators and achievements of each system, and reviews the feasible directions of some methods for subsequent optimization. Different adaptive optical systems need to be designed according to their goals, and the selection of computing platforms and the design of algorithms need to be considered comprehensively.

A sample of an optical monoblock ring confocal resonator is analyzed. It is a reflective prism made of S-TIH optical glass with four working surfaces located at the vertices of a square. One of the reflective surfaces is used to input and output radiation from the resonator by violating the effect of total internal reflection with the help of an auxiliary reflective prism. The spectral and other optical characteristics of a sample of an optical monoblock ring confocal resonator are studied. Its advantages over other types of optical ring resonators and the prospects for its application in optical sensors, in particular, in optical gyroscopes, are also considered.

In this paper, a novel distributed Raman distributed temperature sensing system based on pulse compression technique using hybrid modulation method is proposed. The structure of the new system and the corresponding modulation and demodulation methods are described. The system performance is verified by experiments. This scheme solves the inherent problem of mutual restrictions between spatial resolution and temperature resolution existed in conventional Raman distributed temperature sensing systems. Compared with the other scheme not using coding, the hybrid modulation method using intra-pulse sweep and inter-pulse coding not only mitigates the transient effect existed in the fiber amplifier, which results in a better performance.