The nonlinear electro-optic response of liquid crystal materials poses a fundamental constraint for the performance of liquid crystal lenses. This work proposes a curved-bottom-electrode design for modal control liquid crystal lenses (MC-LCLs) to define the spacing between the high-resistance layer and the bottom electrode, thereby enabling the lens to generate a pre-compensated electric field. Through the nonlinear electro-optic response of the LC field to this pre-compensated electric field, the MC-LCL with a pre-compensating curved electrode (PCCE-MC-LCL) achieves quasi-parabolic optical path difference (OPD) profiles across the lens. Simulation results demonstrate that within the optical power range of 1.15-2.91 m(-1), the PCCE-MC-LCL with a 5 mm aperture achieves an average RMS OPD error of 0.1115 lambda, representing a significant 69.64% reduction compared with the conventional MC-LCL (0.3673 lambda). The simulations further confirm that the curved electrode mitigates the degraded imaging performance of conventional MC-LCLs at high optical power, which originates from both their inherent lack of local electric-field modulation and the nonlinear electro-optic response of the LC.

A simple-structured hollow-core anti-resonant fiber (HC-ARF) polarization filter based on the surface plasmon resonance (SPR) effect is proposed. The polarization filter adopts fused silica as the substrate material and features a symmetric six-tube cladding structure. The gold films are deposited on the inner surface of the anti-resonant tubes along the x-direction to excite the SPR, while the nested anti-resonant tubes are introduced in the y direction to suppress the leakage loss of the y-polarized mode. The full-vector finite element method (FV-FEM) is used to systematically investigate the influence of core diameter, resonant tube inner diameter, nested tube inner diameter, gold film thickness and device length on the filtering performance. The results demonstrate that, under the optimized structural parameters, the polarization filter achieves a maximum polarization extinction ratio (PER) of -435 dB (-239 dB at 1.55 μm). It offers a bandwidth of 353 nm (1391 nm to 1481 nm and from 1518 nm to 1781 nm, which covers all the commonly used communication bands. The proposed filter features a simple structure and exhibits broad bandwidth and high PER performance, showing promising application prospects in the all-optical communication, optical fiber sensing and the other related fields.

Liquid crystal Fresnel lenses(LCFLs),as electrically tunable optical elements,have demonstrated significant application potential in recent years in fields such as augmented reality(AR)/virtual reality(VR)and adaptive optics,owing to their compact structure,tunable focal length,and capacity for large apertures.This paper provides a systematic review of the technical principles and current development status of LCFLs,with a particular focus on their phase modulation mechanisms and methods for controlling optical properties.By comparing structural differences with conventional refractive lenses,the critical role of liquid crystal anisotropy and electric field response characteristics in achieving multi-level phase profile design is summarized.Furthermore,application cases of this technology in AR/VR near-eye displays,auto-stereoscopic display systems,and adaptive optics are discussed.Finally,prospects for the future development of LCFLs are presented.

This work provides an alternative confirmation of Dirac localization in the photonic crystal fiber proposed in Light Sci. Appl.4, e304 (2015)LSAIAZ2047-753810.1038/lsa.2015.77. In weakly guiding fibers, Maxwell equations can be reduced to the wave equation, which can then be further reduced to the Helmholtz equation for time-harmonic waves. The Dirac point in the band structure of the Helmholtz equation in periodic media is analyzed. Wave localization at the Dirac point is numerically demonstrated, which confirms the finding of Light Sci. Appl.4, e304 (2015)LSAIAZ2047-753810.1038/lsa.2015.77. Coupling of Dirac modes is numerically simulated, and the results show remote coupling is feasible. Coupling strength is shown to decrease in an algebraic form with distance. This feature of coupling can be attributed to the massless property of Dirac quasiparticles, which is a precise analog of Klein tunneling of massless relativistic electrons in graphene.

Diabetes patients need to monitor blood glucose all year round. In this article, a novel scheme is proposed for blood glucose detection. The proposed sensor is based on a U-shaped microfiber prepared using hydrogen-oxygen flame-heating technology, and then 3-aminopropyltriethoxysilane (APTES) and glucose oxidase (GOD) are successively coated on the surface of the U-shaped microfiber via a coating technique. The glucose reacts with the GOD of the sensor surface to produce gluconic acid, which changes the effective refractive index and then shifts the interference wavelength. The structure and morphology of the sensor were characterized via scanning electron microscope (SEM) and confocal laser microscopy (CLM). The experimental results show that the sensitivity of the sensor is as high as 5.73 nm/(mg/mL). Compared with the glucose sensor composed of the same material, the sensitivity of the sensor increased by 329%. The proposed sensor has a broad application prospect in blood glucose detection of diabetic patients due to the advantages of miniaturization, high sensitivity, and good stability.

This study aims to develop an advanced glucose sensor based on single-mode fiber-no-core fiber-single-mode fiber (SMF-NCF-SMF) microfibers modified with glucose oxidase (GOD) for accurate and simultaneous measurement of glucose concentration and temperature, which could significantly enhance diagnostic capabilities in medical and biological applications. The sensor utilizes the evanescent wave principle to detect glucose concentration and the thermal optical effect to measure temperature. Experimental results demonstrate a concentration sensitivity of 2.07 nm/(mg/mL) within the range of 0-3 mg/mL and a temperature sensitivity of -0.35 nm/degrees C within the range of 25 degrees C-50 degrees C. These findings highlight the distinct impacts of concentration and temperature on the interference wavelength. By establishing a demodulation matrix, the sensitivities for both concentration and temperature can be separately determined. In situ temperature monitoring not only eliminates temperature interference but also ensures that GOD remains at its optimal temperature for maximum activity, thereby enhancing the sensitivity and accuracy of glucose concentration detection. Given its high sensitivity, accuracy, and simplicity, this sensor shows promising potential for widespread use in disease diagnosis and biological detection, paving the way for more advanced diagnostic technologies.

The degradation and failure of the urban water supply network may lead to serious safety hazards, including pipe breaks, water supply interruptions, water resource losses, and contaminant intrusions. The risk evaluation of water supply pipeline failure in a distribution network is a challenging task, because most of the available data cannot fully reflect pipeline failure events and many of the mechanisms still cannot be fully understood. Therefore, a predictive model is urgently needed to assess pipeline failure risk based on available data. In this paper, based on the traditional risk assessment theory, seven main factors affecting pipeline failure are selected and scored, and then a pipeline failure model is established by using the particle swarm optimization (PSO) neural network. The model uses the neural network training of historical data to evaluate the failure of the water supply pipeline, and the PSO is used to optimize the neural network to effectively improve the training time and accuracy. The model error and correlation coefficient are 0.003 and 0.987, respectively. The proposed model can be used as a powerful support tool to assist infrastructure managers and pipeline maintainers in their plans and decision-making.

Objective Wavelength Division Multiplexing(WDM)is one of the core technologies in fiber optic communication system.In WDM system,a number of optical signals with different wavelengths are transmitted simultaneously in a single optical fiber,realizing the multiplexing of the optical signals,and solving a series of problems in large-capacity,high-speed data transmission.At the receiving end of WDM system,the multiplexed optical signals are demultiplexed into a series of single wavelength optical signals,then further detected and identified to usually obtain the peak values of the signals for the next applications.Generally,the peak value of the target single-wavelength optical should be detected and identified in real time.For this purpose,we designed and developed a real-time peak detection system for multi-wavelength optical signals based on multi-window recognition,which realizes the detection and recognition of the peaks for the multi-wavelength optical signals. Methods This work proposes a real-time peak detection system for multi-wavelength optical signals based on multi-window recognition.The optical demultiplexing part uses an Fiber Fabry-Perot Tunable Filter(FFP-TF)to filter out the target single-wavelength signal from the multiple-wavelength optical signals.The driving and controlling circuit of FFP-TF and the low-noise weak optical signal conversing and detecting circuit are designed.The former is used to drive and control the FFP-TF to filter out the optical signals of the target wavelengths and the latter detects and converts the power intensity of the optical signals in real time.The detected optical signal power is converted into voltage intensity.Then the peak position and intensity in the voltage waveform are identified by using a method based on multi-window waveform identification.At last,the corresponding peak intensity and wavelength position of the optical signal waveform is obtained.The system realizes the filtering of the target wavelength optical signal,and the detecting and identifying of the peak intensity in the signal waveform at the target wavelength. Results and Discussions Firstly,a standard spectrometer is used to detect the optical signal waveform of the experiment light source.The results are illustrated(Fig.11).Secondly,the detection system proposed and developed in this work is used to determine the same experiment light source.The comparison of the results measured by the standard spectrometer and by the detection system proposed and developed in this work is shown(Fig.12).The corresponding data to Fig.11-12 are shown(Tab.1).It can be seen that the peak points of the signal waveform obtained respectively from the standard spectrometer and the detection system proposed and developed in this work agree very well.The measurement variation of the peak intensity obtained from the detection system is less than 0.01 dBm and the recognition time is less than 3 s.More experiment results illustrated in Fig.13 show that the detection range of the system proposed and developed in this work is 0--60 dBm. Conclusions In this work,a real-time peak detection system for multi-wavelength optical signals based on multi-window recognition is proposed and developed.The driving voltage of the FFP-TF is controlled to filter out the target wavelength optical signal and the weak optical signal detection circuit converts the target wavelength optical signal into a normal range of voltage.Then the multi-window waveform peak recognition method is used to identify and record the signal peaks in the waveform.The optical signals of different powers from narrowband light source are tested.The results show that the waveforms of the original optical signal and the detected one by the system is consistent.The measurement variations of peak intensity is less than 0.01 dBm,the recognition speed is less than 3 s,and the minimum detectable power of optical signal is as low as-60 dBm.

光功率检测电路的性能好坏决定了接收信号的质量,介绍了光功率检测电路中半导体光电探测器的分类以及与光电探测器相连的几种常用的跨阻放大器,并根据跨阻放大器的性能指标对比了各自的优缺点和应用范围.最后,展望了光功率检测电路的发展前景.

In order to measure humidity and temperature simultaneously, a U-shaped microfiber strain sensor coated with polyvinyl alcohol (PVA) nanofibers is proposed in this paper. The PVA nanofibers and U-shaped microfiber are prepared by electrospinning technology and hydrogen-oxygen flame heating technology, respectively. The sensing mechanism is that the radius of U-shaped microfiber will change when the temperature and humidity change, because the expansion and stress-strain properties of the coated PVA nanofibers are tightly related with inside water content which can be greatly influenced by the temperature and humidity in the environment. The temperature and humidity are measured by the wavelength changes of the resonant dips of the sensors. The experimental results show that the average sensitivity of the sensor is 0.21 nm/%RH in the range of 20 %RH to 75 %RH, and the average sensitivity is -0.19 nm/degrees C in the temperature range from 30 degrees C to 50 degrees C. Sensors with excellent performance (good repeatability, fast dynamic response, and stability) in this work are expected to play a role in practical applications in many industries.

The leak detection of water supply pipelines is significant for the protection of water resources. Acoustic detection is a common method used to investigate water supply pipeline leaks. Although some acoustic methods for the leak detection of the water supply pipeline have been developed experimentally, the theoretical investigation of said acoustic methods is still limited. Compared with aeroacoustics, the development of quantitative jet acoustic theory towards flow field calculations of liquid pipeline leak has not been reported, and the characteristics of the liquid flow field cannot be quantitatively transformed into the acoustic model. In this paper, the liquid pipeline leak is combined with piston acoustics, and the acoustic model for the leak detection of the water supply pipeline is quantitatively studied for the first time. The acoustic pressure value can be directly calculated using pipe and liquid parameters, and the validity of the model can be verified experimentally. Based on theoretical and experimental investigations, it is found that the leak sound pressure increases significantly with increasing pipeline pressure and decreases with increasing detection distance. The material composition of the pipes has little influence on the leak sound pressure. The theoretical values based on the proposed acoustic model and the experimental values agree well, where the maximum difference between them is 8.5% and the average difference is 2.6%. This study presents a foundation for the development of acoustic leak detection technology of the liquid pipeline.

Laser-induced graphene (LIG) is a porous material that can be coated on an antiresonance reflecting hollow-core optical fiber (HCF) for humidity sensing. In this study, a humidity sensor was constructed by dip coating a polyimide (PI) film on the surface of an HCF, followed by rearranging and graphitizing the PI film through laser irradiation, which led to the formation of LIG. The absorption of water vapor by the LIG film changed its refractive index, which varied the reflectivity of the HCF and produced resonance intensity changes in the transmission spectrum. Humidity experiments were conducted with LIG films under different laser parameters, that is, power. The transmission visibility of the resonance dip was evaluated. A sensitivity of 0.187 dB/% RH was obtained in an ultrawide relative humidity (RH) range of 5-95% RH. In addition, The sensor has short response and recovery times. Moreover, the proposed sensor has a wide operating temperature range and low cost, and its temperature cross-sensitivity issue can be solved using different demodulation methods. The results suggest that LIG-coated HCF is a tunable and promising solution for humidity sensing.

In the existing ellipse fitting algorithms, the Lissajous figure is used to solve the demodulation error caused by the non-ideal 3×3 couplers. However, the influence of circuit noise and phase noise on Lissajous figure are not fully considered in the studies. In this work, an ellipse fitting demodulation method based on local outlier factor (LOF) algorithm is proposed, which can effectively eliminate the outlier points in Lissajous figure caused by noises. The proposed method proves to achieve the accurate demodulation of the signals by numerical simulations. In addition, the Monte Carlo analysis is used to obtain the comprehensive error rate of about 0.13%, which verifies the stability of the proposed method. Compared with the traditional least square fitting method, this method improves the stability and accuracy of demodulated signals.

为了解决光时域反射仪(optical time domain reflectometer,OTDR)中背向散射信号受噪声干扰严重问题,本文提出了一种基于自适应噪声完备集合经验模态分解(complete ensemble empirical mode decomposition with adaptive noise,CEEMDAN)和改进小波阈值的OTDR信号去噪算法,利用CEEMDAN分解算法具有的抗模态混叠现象和降低重构误差等优点,将信号分解为若干IMF分量,根据相关系数的分析方法,找到噪声占主导的本征模态函数(intrinsic mode function,IMF)分量和信号占主导的IMF分量的临界点,去除噪声占主导的IMF分量,并将改进的小波阈值去噪方法对信号占主导的IMF分量进行去噪,最后重构信号.结果表明,本文提出的方法与传统的硬阈值方法、CEEMDAN-硬阈值方法和改进的小波阈值方法相比,能更好地抑制噪声,并达到更好的去噪效果,突显OTDR事件特征,更易于事件的检测.

Long period grating (LPG) with a small grating period (25 mu m) is inscribed with the femtosecond laser line-byline technique. The fabricated LPG consists of 500 vertical refractive index (RI) modification lines (15 mu m in length), corresponding to a compact total length of 12.5 mm. With the fabricated LPG, coupling between core modes is significantly enhanced (from previously reported <0.6 dB to similar to 11 dB). Moreover, coupling from core mode to forward- and backward-propagating cladding modes is also enabled. Thanks to the co-existence of forward- and backward-propagating cladding mode resonances, wide range and sensitive RI sensing is realized by the LPG, with a RI sensitivity more than 500 nm/RIU. In addition, the grating shows a low temperature cross-sensitivity, and the enhanced core mode resonance can serve as a monitor for temperature variation, allowing simultaneous measurement of RI and temperature. Note that these advantages are achieved with only one uniform grating. With a simple structure, the proposed grating will be a good choice for applications where wide RI sensing range and simultaneous temperature monitoring are required.

Electronically controlled gradient refractive index liquid crystal lens (EC-GRIN-LCL) is an optical lens that can change the distribution of its spatial refractive index to zoom in out by controlling the electric field. Due to the properties of variable focal length, compact structure and excellent stability, it has been attracting intensive attention in the field of optical lenses. This review introduces the basic working principle of EC-GRIN-LCL and describes four types of liquid crystal lenses driving strategies: (1) by edge electric field, (2) by discrete multi-electrode, (3) by electrode with high resistance layer, and (4) by complete electrode layer or no electrode layer. By introducing, concluding and commenting on the representative instances of the four types of EC-GRIN-LCL, this review aims to provide the readers with a clear basic knowledge, a comprehensive development history and tendency, and a reference for further research of EC-GRIN-LCL.

Monitoring glucose levels is one of the main diagnostic methods for preventing and treating diabetes. Conventionally monitoring of blood glucose through a finger-stick procedure brings pain. It is essential to develop biosensors for low concentration glucose detection in non-invasive samples. In this paper, a tilted fiber grating based localized surface plasmon resonance (LSPR) biosensor for ultrasensitive glucose detection has been demonstrated. The glucose biosensor was fabricated by immobilization of Au nanoparticles (AuNPs) onto an excessively tilted fiber grating (Ex-TFG) and subsequent biofunctionalization by coating polydopamine and concanavalin A onto the AuNPs/Ex-TFG surface. The biosensor has the response regions covering low, middle and high glucose concentrations. The resonance peak indicates a redshift of 0.24 nm, 0.06 nm and 0.48 nm in the concentration ranges of 1.0 nM $- 1.0\,\, \boldsymbol {\mu }\text{M}$ , $1.0\,\, \boldsymbol {\mu }\text{M}- 50.0\,\, \boldsymbol {\mu }\text{M}$ and $50.0\,\, \boldsymbol {\mu }\text{M}-5.0$ mM, respectively. The limit of detection (LOD) of the biosensor in pure phosphate buffered saline is 2.5 nM. The high sensitivity and specific selectivity for D-glucose detection are attributed to strong coupling between the evanescent fields from transverse magnetic (TM) cladding modes of the Ex-TFG and the localized electric fields from LSPR of the AuNPs and their biofunctionalization, and resulting in remarkable enhancement of localized effective refractive index with slightly increased D-glucose concentration. Especially, the glucose biosensor based on the Ex-TFG coupled with the biofunctionalized AuNPs, has been demonstrated to be of practical utility to detect the glucose in artificial urine, which has potential applications in non-invasive glucose monitoring for early diagnosis and better management of diabetes.

We propose and demonstrate a sensitive vector twist sensor based on a small period long period fiber grating (SP-LPFG) fabricated with a femtosecond (fs) laser. The fabricated SP-LPFG is compact in size (2.8 mm) and shows strong polarization dependent peaks in its transmission spectrum due to the vectorial behavior of high-order cladding modes. Twist sensing is realized by monitoring the polarization dependent peaks, since the polarization of input light changes with fiber twist. The proposed sensor can be interrogated by the peak intensity and wavelength, with high twist sensitivity that reaches 0.257 dB/deg and 0.115 nm/deg, respectively.

Small period long period fiber grating is fabricated by femtosecond laser line by line technique. High order Bragg resonances, which are useful for dual-/multi- parameter sensing, are significantly enhanced (from ~0.6 dB to ~11 dB).

Melatonin (MLT), a pineal neurohormone with multiple neuroprotective, is often used for peripheral nerve recovery and regenerated nerve proliferation. In this study, Polycaprolactone/Gelatin (PG) fibrous electrospun scaffolds with various percentages of MLT (0, 1, 2, and 4%wt) were fabricated for nerve cell growth, the effects of different concentrations of MLT within PG fibers (PG, PGMLT1, PGMLT2, and PGMLT4) on the proliferation and differentiation for PC12 cells were quantitatively evaluated. The microstructures and morphologies of these scaffolds were analyzed by FE-SEM and digital camera. Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), and Water Contact Angle (WCA) were used to study the composition, ratio and properties of MLT functionalized PG scaffolds. MTT and CLSM analysis showed that appropriate amount of MLT was beneficial to the proliferation of PC12 cell. MLT can also promote cell differentiation, neurite germination, the expression levels of MAP2 mRNA and protein were dramatically increased on the composite scaffolds with the increase of MLT content, moderate addition of MLT (PGMLT2, 2%) had a prominent enhancement for neurite length. This work would provide a more comprehensive reference for further researches on MLT functionalized composite scaffolds and suggest that high-performance PGMLT fibrous scaffolds could be a promising alternative for nerve repair.