Search

A Mach-Zehnder interferometer for measurement of temperature is proposed and experimentally demonstrated, which consists of two sections of single mode fiber (SMF) and a section of thin core fiber spliced between the two SMFs. The two welding areas are heated and stretched to improve the split and recombination of light. The wavelength of the resonant dip will shift when temperature varies due to the thermo-optic and thermal expansion effect. The experimental results show that a temperature sensitivity of 65 pm/°C with a linear correlation coefficient of 0.996 can be achieved in a temperature range from 25 °C to 80 °C. Due to its ease of manufacture, low cost, and high sensitivity, the fiber optic temperature sensor is suitable for temperature measurement applications. [ABSTRACT FROM AUTHOR]

Highlights • An optical fiber Mach-Zehnder interferometer has been proposed. • The RI and temperature can be measured without the cross-sensitivity. • The sensitivities are −18.1764 nm/RIU and 0.0733 nm/°C, respectively. • The advantages of cost effectiveness, robustness and easy fabrication. Abstract A Mach-Zehnder interferometer based on single-mode-multimode-thin-core-single-mode fiber structure is proposed and experimentally demonstrated for measuring refractive index and temperature simultaneously. The transmission dips of the sensor will shift when the ambient refractive index and temperature change, so it is possible to measure the refractive index and temperature by monitoring the wavelength shifts of the two transmission dips due to different interference orders. The experimental results show that the sensing sensitivities of refractive index and temperature are −18.1764 nm/RIU and 0.0733 nm/°C within the refractive index range from1.3105 to 1.3517 and the temperature range from 25 °C to 50 °C, respectively. Its cost effectiveness, robustness and easy fabrication will have attractive potential applications in chemical and biological sensing. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel planar metamaterial structure for the electromagnetically induced transparency (EIT)-like effect, which consists of a split-ring resonator (SRR) and a pair of metal strips. The simulated results indicate that a single transparency window can be realized in the symmetry situation, which originates from the bright–bright mode coupling. Further, a dual-band EIT-like effect can be achieved in the asymmetry situation, which is due to the bright–bright mode coupling and bright–dark mode coupling, respectively. Different EIT-like effect can be simultaneously achieved in the proposed structure with the different situations. It is of certain significance for the study of EIT-like effect. [ABSTRACT FROM AUTHOR]

Herein we designed a novel photoelectrochemical sensing platform based on Fe 3+ doped ZnO-Ag photocatalyst (Fe 3+ /ZnO-Ag) for ultrasensitive Hg 2+ detection by using exonuclease III-assisted target recycling and DNAzyme-catalyzed amplification. Firstly, Fe 3+ /ZnO-Ag was synthesized to provide photocurrent under visible light irradiation. Secondly, target Hg 2+ was determined by hairpin DNA probes on the Fe 3+ /ZnO-Ag modified ITO based on T-Hg 2+ -T, and then Hg 2+ was released by the digestion of exonuclease III to double-stranded DNA. Finally, the photocurrent markedly decreased due to catalysis of hemin/G-quadruplex toward 4-chloro-1-naphthol. Under optimal conditions, the photocurrents were linearly related to Hg 2+ concentrations form 0. 5 nM to 100 nM with a detection limit of 0. 1 nM at the 3 S blank criterion. More importantly, the developed biosensor exhibited good selectivity, repeatability, and stability, meanwhile, this analysis platform held great potential for testing real water samples in future. [ABSTRACT FROM AUTHOR]

Mercuric ion (Hg 2+ ) as one kind of environmental pollutants has attracted more and more attentions due to its persistence, mobility and biological enrichment. In this study, a novel photoelectrochemical biosensor for Hg 2+ detection was constructed based on dye sensitization effect induced by Y-shaped DNA transformation as signal amplification strategy. Firstly, graphene oxide-ZnO-CdS nanohybrid (GO-ZnO-CdS) as photoelectric material was synthesized by simple hydrothermal method, and was employed to modify ITO electrode. Secondly, Y-shape DNA was labeled by Au NPs in the solution, and which crosslinked on the surface of GO-ZnO-CdS modified ITO electrode by carbodiimide coupling method, which resulted in the excitation energy transfer (EET) effect between Au NPs and CdS. Finally, in the presence of Hg 2+ , the structure of DNA on the modified electrode changed from Y-shape into hairpin accompanying the proximity of dye molecule based on T-Hg 2+ -T, which eliminated EET effect and triggered dye sensitization effect for enhancing photocurrent response. Under optimal conditions, the photocurrent linearly increased with the increasing of Hg 2+ levels in the range of 5 pM − 500 pM with the detection limit of 1:5 pM(LOD = 3σ blank / s ). More importantly, the developed biosensor showed the advantages of acceptable selectivity, repeatability and stability. [ABSTRACT FROM AUTHOR]

A novel metal-insulator-metal (MIM) plasmonic waveguides structure, which is composed by stub waveguide with nanodisk and Fabry-Perot (F-P) resonator, has been proposed and numerically simulated with the finite-difference time-domain (FDTD). Based on the three-level system, the extreme destructive interference between bright and dark resonators gives rise to the distinct plasmonically induced absorption (PIA) response with the abnormal dispersion and novel fast-light feature. Simultaneously, the dramatic double plasmonically induced transparency (PIT) effect with slow-light characteristic can also be achieved in the system. The relationship between the transmission characteristics and the geometric parameters is studied in detail. By optimum design, the modulation depth of the PIA transmission spectrum of 90 % with 0.145 and 0.14 ps fast-light effect can be gained simultaneously, and the peak transmissivity of the double PIT system of 75.2 and 72.8 % with −0.38 ps slow light-effect can be achieved. The simulated transmission features are in agreement with the temporal-coupled mode theory (CMT). The characteristics of the system indicate an important potential application in integrated optical circuits such as slow-light and fast-light devices, high-performance filter, and optical storage. [ABSTRACT FROM AUTHOR]

We proposed a dual coupled-resonator system based on the metal-insulator-metal bus waveguide and numerically investigated the plasmon-induced transparency and slow light effect with the Finite-Difference Time-Domain simulations in this paper. The electromagnetically induced transparency-like spectral response will occur between two adjacent stub resonators with detuned resonant wavelength due to the phase-coupled effect. The transmissivity and group index equations were been deduced, which indicated that the system can achieve the effect of the multiple electromagnetically induced transparency-like and slow light. With the optimization, the single peak transmission can reach to as high as 92%, dual PIT transmission peaks appear, as well as group index can reach over 75. These characteristics indicate multiple applications of our system in integrated optical circuits. [ABSTRACT FROM AUTHOR]

A compact plasmonic system based on a stub metal-insulator-metal (MIM) waveguide coupled with a nanodisk resonator for plasmonic-induced transparency (PIT) has been proposed and numerically simulated by employing the finite-difference time-domain (FDTD). A reasonable analysis of the transmission features based on the temporal coupled-mode theory is given and is in good agreement with the FDTD simulation. In addition, the relationship between the transmission characteristics and the geometric parameters including the radius of the nanodisk, the coupling distance, and the deviation length between the stub and the nanodisk is studied in a step further. By optimum designing, the transmission of the PIT system can reach to as high as 90 %, as well as the group index can be over 88. The characteristics of our plasmonic system indicate an important potential application in integrated optical circuits such as optical storage, ultrafast plasmonic switch, highly performance filter and slow-light devices. [ABSTRACT FROM AUTHOR]

An in-line fiber sensor for simultaneous measurement of refractive index (RI) and temperature is proposed and demonstrated. The sensor head is composed of an asymmetric Mach–Zehnder interferometer (MZI), which is combining the single mode-multimode-single mode (SMS) fiber structure and a peanut-shape structure. The transmission dips of the sensor will shift as the ambient RI or temperature variation due to the phase changing. The different wavelength transmission dips formed by the cladding modes interfering with the core mode have different sensitivity responses, so the simultaneous measurement of the RI and temperature can be achieved by monitoring the wavelength shifts of the two transmission dips. The experimental results show that the sensing sensitivities of RI and temperature are −86.7434 nm/RIU and 0.0590 nm/°C in the RI range from 1.3105 to 1.3517 and temperature range from 25 °C to 85 °C, respectively. The novel sensor processes easy fabrication, low cost, and high sensitivity, making it offers high potential applications in physical, biological and chemical sensing. [ABSTRACT FROM AUTHOR]

Highlights: [•] We first demonstrate a sensor based on a normal FBG and a core-offset MZI for simultaneous measurement of the refractive index and temperature. [•] The new sensor can measure solutions with high stability. [•] The sensor is simple and easy for fabrication with low-cost. [ABSTRACT FROM AUTHOR]

Speckle suppression and detail preservation are a unity of contradiction during synthetic aperture radar (SAR) despeckling. In this article, an effective despeckling method is proposed based on a self-adaptive neighbourhood, which takes into account the trade-off between homogeneous region suppression and point target preservation. The size and shape of the neighbourhood depend on an adaptive threshold that is treated as a linear function of a saliency map and a threshold range estimated by the Monte Carlo algorithm based on a given significance level and the number of looks in SAR. If the saliency of the current pixel is large, which always means that the current pixels should belong to a point target, a linear object, or an edge, a relatively large threshold will be assigned to search a neighbourhood with a small size. Conversely, pixels with a small saliency value will obtain a non-local neighbourhood with a large size. A maximum-likelihood estimation is employed to estimate the real radar reflectivity based on the pixels in the adaptive neighbourhood. The comparison experiments on simulated and actual SAR data validate the effectiveness of the proposed algorithm and demonstrate its overall speckle filtering characteristics compared with other algorithms. The visual and numerical experimental results show that the proposed despeckling method provides superior performance compared with several state-of-the-art despeckling methods. [ABSTRACT FROM PUBLISHER]

Abstract: A fiber-optic sensor for liquid refractive index measurement based on a Michelson interferometer is described. The interferometer is achieved between the Fresnel reflections from the fiber ends of the coupler. The fiber ends are then in contact with the solvent and solution samples to provide reference and refractive index measurement, respectively. The refractive index of the solution is determined according to the fringe contrast of the interference fringes in the reflective spectrum of the sensor. Its ease of fabrication and low-cost offer the attractive applications in chemical and biological sensing. [Copyright &y& Elsevier]

Abstract: A simple sensor for simultaneous measurement of refractive index and temperature in solutions based on fiber Bragg grating (FBG) is proposed. The sensor contains only a normal FBG with a pigtail fiber. When the FBG is immersed in different liquids of refractive index, the side mode suppression ratio of the FBG varies due to the Fresnel reflection of the pigtail fiber. The sensor is also capable of simultaneous measurement refractive index and temperature combining the thermo-optic effect of the FBG. Its ease of fabrication and low-cost offer the attractive applications in chemical and biological sensing. [Copyright &y& Elsevier]

In this paper, a novel configuration of reflection L-band erbium-doped fiber amplifier (L-EDFA) via inserting a 980 nm pump laser diode (LD) in the input part was constructed. By selecting appropriate power ratio of the 980 and 1480 nm pump LD, gain and noise figure (NF) of the L-EDFA are greatly improved in different degree in the wavelength region from 1565 to 1615 nm. Compared to the configuration pumped by only 1480 nm pump LD with given power, the noise figure decreases 1.3–9.4 dB and the gain enhances 1.5–9.9 dB. [Copyright &y& Elsevier]

Hyperspectral unmixing decomposes the observed mixed spectra into a collection of constituent pure material signatures and the associated fractional abundances. Because of the universal modeling ability of neural networks, deep learning (DL) techniques are gaining prominence in solving hyperspectral analysis tasks. The autoencoder (AE) network has been extensively investigated in linear blind source unmixing. However, the linear mixing model (LMM) may fail to provide good unmixing performance when the nonlinear mixing effects are nonnegligible in complex scenarios. Considering the limitations of LMM, we propose an unsupervised nonlinear spectral unmixing method, based on autoencoder architecture. Firstly, a deep neural network is employed as the encoder to extract the low-dimension feature of the mixed pixel. Then, the generalized bilinear model (GBM) is used to design the decoder, which has a linear mixing part and a nonlinear mixing one. The coefficient of the bilinear mixing part can be adjusted by a set of learnable parameters, which makes the method perform well on both nonlinear and linear data. Finally, some regular terms are imposed on the loss function and an alternating update strategy is utilized to train the network. Experimental results on synthetic and real datasets verify the effectiveness of the proposed model and show very competitive performance compared with several existing algorithms. [ABSTRACT FROM AUTHOR]

The lack of labeled samples severely restricts the classification performance of deep learning on hyperspectral image classification. To solve this problem, Generative Adversarial Networks (GAN) are usually used for data augmentation. However, GAN have several problems with this task, such as the poor quality of the generated samples and an unstable training process. Thereby, knowing how to construct a GAN to generate high-quality hyperspectral training samples is meaningful for the small-sample classification task of hyperspectral data. In this paper, an Auxiliary Classifier based Wasserstein GAN with Gradient Penalty (AC-WGAN-GP) was proposed. The framework includes AC-WGAN-GP, an online generation mechanism, and a sample selection algorithm. The proposed method has the following distinctive advantages. First, the input of the generator is guided by prior knowledge and a separate classifier is introduced to the architecture of AC-WGAN-GP to produce reliable labels. Second, an online generation mechanism ensures the diversity of generated samples. Third, generated samples that are similar to real data are selected. Experiments on three public hyperspectral datasets show that the generated samples follow the same distribution as the real samples and have enough diversity, which effectively expands the training set. Compared to other competitive methods, the proposed framework achieved better classification accuracy with a small number of labeled samples. [ABSTRACT FROM AUTHOR]

The lasing wavelength shift characteristics of amplified spontaneous emission (ASE)-injected wavelength-locked Fabry-Perot laser-diodes used in the wavelength division multiplexed passive optical network are studied. The lasing wavelength shift at different injected-ASE powers and different bias currents are experimentally evaluated. The saturation effect has been found as the bias current increases. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26088 [ABSTRACT FROM AUTHOR]

Abstract: A metallic cardiovascular stent cutting system based on fiber laser was designed in this study. In order to achieve the cutting of stent, the main modules and the key technologies were analyzed and achieved. Then with the cutting system, the kerf width size was studied for different cutting parameters including laser output power, pulse length, repeat frequency, cutting speed and assisting gas pressure. Finally, a high quality of cutting of 316L stainless steel cardiovascular stent was achieved. [Copyright &y& Elsevier]

In this paper, we look at the work of a classical plasmon-induced transparency (PIT) based on metasurface, including a periodic lattice with a cut wire (CW) and a pair of symmetry split ring resonators (SSR). Destructive interference of the 'bright-dark' mode originated from the CW and a pair of SSRs and resulted in a pronounced transparency peak at 1.148 THz, with 85% spectral contrast ratio. In the simulation, the effects of the relative distance between the CW and the SSR pair resonator, as well as the vertical distance of the split gap, on the coupling strength of the PIT effect, have been investigated. Furthermore, we introduce a continuous graphene strip monolayer into the metamaterial and by manipulating the Fermi level of the graphene we see a complete modulation of the amplitude and line shape of the PIT transparency peak. The near-field couplings in the relative mode resonators are quantitatively understood by coupled harmonic oscillator model, which indicates that the modulation of the PIT effect result from the variation of the damping rate in the dark mode. The transmitted electric field distributions with polarization vector clearly confirmed this conclusion. Finally, a group delay t g of 5.4 ps within the transparency window is achieved. We believe that this design has practical applications in terahertz (THz) functional devices and slow light devices. [ABSTRACT FROM AUTHOR]

Hyperspectral Unmixing (HU), which involves decomposing mixed pixels in hyperspectral images into endmembers and abundance fractions, plays a critical role in spectral analysis. Recent advancements in deep learning methods have shown successful applications in hyperspectral analysis. This paper proposes an end-to-end network structure that combines a Convolutional Neural Network (CNN) and a Multilayer Perceptron (MLP). The 3D-CNN extracts high-level features from both spatial and spectral neighbourhoods of hyperspectral image patches, while the MLP maps these abstracted features to abundance fractions. Considering the challenge of acquiring manual labels, we adopt a Semi-Supervised learning approach that leverages unlabelled data to enhance training. We divide our training data into labelled and unlabelled subsets, defining distinct loss functions for each. Additionally, we introduce a neighbourhood similarity constraint to fully exploit spatial context information. To address scenarios where no labelled data is available, we employ Generative Adversarial Networks (GANs) to generate synthetic labelled samples. Experimental evaluations conducted on both synthetic and real datasets validate the effectiveness of our proposed method, which outperforms several commonly used and state-of-the-art HU methods. [ABSTRACT FROM AUTHOR]

A fiber optic sensor coated with molybdenum disulfide (MoS 2) hydrogel is firstly proposed for the detection of lead ion (Pb2+). By splicing a dispersion-compensating fiber (DCF) between two single-mode fibers (SMFs) to form a Mach-Zehnder interferometer (MZI), and using a fusion splicer to discharge the SMF input and output to form a thick waist cone to act as a coupler. A portion of the DCF cladding is etched to excite higher order cladding patterns and a hydrogel sensing film is applied to the etched area, the sulfur atoms in the sensing film form coordination bonds with Pb2+ and change the refractive index (RI) of the sensing film, which further leads to the wavelength shift of the resonant dip. The production process is simple and environmentally friendly. By monitoring the wavelength shift, the adsorption of Pb2+ is continuously monitored, and the sensor has a sensitivity of 3.25 × 108 nm/(mol/L) in the range of 0–1.1 × 10−8 mol/L Pb2+ in aqueous solution. The theoretical detection limit of Pb2+ concentration is 6.15 × 10−11 mol/L at a spectrometer resolution of 0.02 nm. In addition, the experimental results show that the sensor has good repeatability , selectivity and stability, and has a broad application prospect in the field of Pb2+ detection in industry and agriculture. • A SMF-DCF-SMF structure fiber sensor coated with molybdenum disulfide hydrogel is proposed for the detection of lead ion. • A sensitivity of 3.25×108 nm/(mol/L) is achieved and the theoretical detection limit of lead ion is 6.15×10-11 mol/L. • The characteristics of the sensor show applications in the field of lead ion detection in industry and agriculture. [ABSTRACT FROM AUTHOR]

Hyperspectral image (HSI) classification is one of the main research contents of hyperspectral technology. Existing HSI classification algorithms that are based on deep learning use a large number of labeled samples to train models to ensure excellent classification effects, but when the labeled samples are insufficient, the deep learning model is prone to overfitting. In practice, there are a large number of unlabeled samples that have not been effectively utilized, so it is meaningful to study a semi-supervised method. In this paper, an adversarial representation learning that is based on a generative adversarial networks (ARL-GAN) method is proposed to solve the small samples problem in hyperspectral image classification by applying GAN to the representation learning domain in a semi-supervised manner. The proposed method has the following distinctive advantages. First, we build a hyperspectral image block generator whose input is the feature vector that is extracted from the encoder and use the encoder as a feature extractor to extract more discriminant information. Second, the distance of the class probability output by the discriminator is used to measure the error between the generated image block and the real image instead of the root mean square error (MSE), so that the encoder can extract more useful information for classification. Third, GAN and conditional entropy are used to improve the utilization of unlabeled data and solve the small sample problem in hyperspectral image classification. Experiments on three public datasets show that the method achieved better classification accuracy with a small number of labeled samples compared to other state-of-the-art methods. [ABSTRACT FROM AUTHOR]

A depolarizer, a kind of optical element that converts polarized light to unpolarized light, has been found massive applications in classical optics. However, depolarizers based on metasurface which can be applied in integrated optics have rarely been proposed. In this paper, an electronically controlled metasurface depolarizer is demonstrated based on the time-domain integral average method and nano-material barium titanate. It obtains emergent light with a degree of polarization reduced to 2.5% when hit by linearly polarized light at 633 nm, and has a transmission efficiency greater than 72%. This depolarizing metasurface can be designed on-demand, immunizing the degree of the emergent light from its size, and has the simple electronic control with high-speed response. [ABSTRACT FROM AUTHOR]

In this paper, a dual guided modes ring-based photonic crystal fiber (PCF) is designed in which two channels occupying different spatial positions are independent of each other and support up to 170 + 62 orbital angular momentum (OAM) modes in the dual guided modes regions. The designed PCF consists of a large central air hole, two high refractive index rings based on Schott glass (BAK1) and cladding. The characteristics of the designed PCF are analyzed by finite element method (FEM). The results show that the proposed PCF has a sufficiently large effective refractive index difference, relatively flat dispersion, large effective mode field area and low nonlinear effects with the wavelength range from 1.45 to 1.75 μm. The energy of the light field is mainly confined to two high refractive index rings with good isolation parameters. The values of most OAM modes purity in dual guided modes regions are greater than 0.9 and the mode quality of all eigenmodes is higher than 0.93 without phase distortion over the azimuth angle. Moreover, the confinement loss of all eigenmodes are below 1.4 × 10–8 dB m−1 where the lowest value is 1.56 × 10–12 dB m−1 at λ = 1.55 μm for HE13,1 mode. The proposed PCF has a large effective mode field area, up to 316.99 μm2. The nonlinear coefficient of HE and EH modes are less than 0.55 km−1 W−1 in the outer ring and less than 1.5 km−1 W−1 in the inner ring. In conclusion, the dual guided modes ring-based photonic crystal fiber has potential applications in large capacity data transmission in optical communications. [ABSTRACT FROM AUTHOR]

A simple and cost-efficient fiber sensor based on multi-mode interference and core diameter mismatch technologies is proposed to detect the refractive index (RI) in this paper. The refractometer is fabricated by embedding a section of no-core fiber between a section of multimode fiber and dispersion-compensating fiber. Since the power distribution in the fiber will change with the effective refractive index of the cladding, the extinction ratio can be used to characterize the RI sensitivity. The experimental results show that a linear response is obtained with a RI sensitivity of 392.585 dB/RIU in the range of 1.333–1.374. Featured with high sensitivity, simple construction, easy fabrication, low cost and good repeatability, the novel refractometer has potential applications in practical chemical detecting and portable biological sensing. • A refractometer based on multi-mode interference and core diameter mismatch technologies is proposed. • The sensor head merely includes a MMF, NCF, and DCF orderly through automatic splicing without any special processing. • Utilizing extinction ratio demodulation, a RI sensitivity of 392.585 dB/RIU is achieved from 1.3330 to 1.3740, 5-7 times higher than untreated sensors. • Featured with high sensitivity, simple construction, easy fabrication, low cost and good repeatability, it holds potential for practical detection. [ABSTRACT FROM AUTHOR]

We describe a novel method for determining the degree of deacetylation (DD) of chitosans from fiber-optic measurements of refractive index. Theory analyses and the experimental setup of the method are introduced and discussed. The analytical performance of the method is described for the determination of alkaline titration end-points. Experimental results reveal that the equivalence point can be directly identified from the titration curve. The proposed method is simple, low-cost, accurate, reliable, and easy to operate for industrial application. The DD values of four chitosan samples obtained with this new method show good agreement with those yielded from H NMR. Such a mechanism of refractive-index monitor should open up a new application in the field of chitosanolytic enzymes, such as chitosanase, pectinase that are important in bioprocesses. [ABSTRACT FROM AUTHOR]

A fiber sensor for simultaneous measurement of temperature and strain based on a fiber Bragg grating (FBG) with the pigtail fiber covered with epoxy resin is presented. The side mode suppression ratio of the FBG will vary with the temperature due to the Fresnel reflection from the interface between the pigtail fiber and the epoxy resin whose refractive index is sensitive to the temperature. The sensor is also capable of simultaneous measurement temperature and strain by combining the Bragg wavelength shift characteristics as the temperature and strain of the FBG. [ABSTRACT FROM AUTHOR]

A simple fiber-optic displacement sensor based on reflective intensity modulated technology is demonstrated using a fiber collimator. The sensing range is over 30 cm, which is over 100 times that of the conventional fiber-optic displacement sensor based on the normal single-mode fiber. The measured data are fitted into linear equation very well and the values of R-square are more than 0.995. The sensitivity of the device achieves 0.426 dB/cm over the range of 5-30 cm. By applying the relative technique, the errors resulted from the fluctuation of light source and influences of environment are effectively eliminated, and the stability for wide range measurement can be improved. The simplicity of the design, high dynamic range, stability and the ease of the fabrication make it suitable for applications in industries. [ABSTRACT FROM AUTHOR]

An all-fiber comb filter with flat-top spectral response based on a Mach–Zehnder interferometer (MZI) cascading a Michelson interferometer (MI) is proposed. The proposed filter consists of a rotatable polarizer, two 3-dB couplers, and two fiber Faraday rotator mirrors (FRMs). The numerical simulation results show that the birefringence of the single mode fiber (SMF) can be neglected when the polarization state of linearly polarized incident light respect to one principle axe of fiber. By selecting the path difference of the MZI and MI and adjusting the rotation angle of the two FRMs, the flat-top comb spectral response can be obtained. [ABSTRACT FROM AUTHOR]

In this paper, an efficient L-band multi-wavelength erbium-doped fiber ring laser is demonstrated by recycling backward 1550 nm band amplified spontaneous emission as secondary pump source for the unpumped EDF section. The lasing threshold is reduced and the slope efficiency is improved. A piece of multimode fiber is used as a spatial mode-beating filter. By adjusting the polarization state of the light, the number of lasing wavelength and their spaces are controlled. In dual-wavelength laser, the power of each channel is 4 mW with 40 dB side-mode-suppression-ratio. [Copyright &y& Elsevier]

A fluorescent Fe3+ probe ((C10H7NO2)2B18H20, M1) by introducing two isoquinoline-1-carboxylic acid group into the 6,9-position of anti-B18H22 was designed and synthesized. The structure of M1 was investigated by 1H NMR, MS, FT-IR and theoretical calculation, and its optical properties were characterized with UV–Vis and PL. M1 showed aggregation induced emission enhancement (AIEE) properties in THF/H2O solution, and exhibited an excellent selectivity toward Fe3+ in THF/H2O (v/v, ƒw = 95%) solution with a detection limit of 1.93 × 10–5 M. The interaction mechanism of probe for detecting Fe3+ is attributed to the involvement of intramolecular charge transfer (ICT) process. Furthermore, a optical fiber fluorescent Fe3+ sensor based on M1 sensing film was developed, the detection limit of the optical fiber Fe3+ fluorescent sensor could be improved to13.8 pM, the ultra-low detection limit is superior to most reported fluorescent probes (or sensors) towards Fe3+. This method has the advantages of high sensitivity, anti-interference and easy to operate, and has great potential in the field of the analysis of environmental and biological samples. [ABSTRACT FROM AUTHOR]

This paper proposes an optical fiber sensor based on multimode interference (MMI) with a lateral offset structure to measure tensile strain. The coupling ratio of each higher-order mode in the coreless fiber (NCF) can be controlled by the dislocation distance. The experimental results show that the best interference fringes are obtained when the dislocation is 10 μ m and the sensitivity in the range of 0–500 μ ɛ is 28 pm/ μ ɛ. To improve the sensitivity of the sensor further, the measured data were filtered by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) to obtain a sinusoidal component, superimposed with a simulated signal to form a vernier effect. With the method of virtual vernier effect, the sensitivity is increased to 452.64 pm/ μ ɛ , which is 15.6 times the original sensitivity. Compared with the traditional vernier effect, the virtual vernier effect method does not require cascade or series method, the reference part is not affected by the environment, and the method can be widely used in many types of interferometric fiber optic sensor devices, especially to overcome the problem that MMI is not suitable for vernier effect. • An optical fiber sensor with a lateral-offset structure is proposed in this paper. • We improve the traditional method of vernier effect and propose the method of virtual vernier effect. The original sensitivity of the sensor has been increased by 15.6 times. • The method can be widely used in many types of interferometric fiber optic sensor devices, especially to overcome the problem that MMI is not suitable for vernier effect. [ABSTRACT FROM AUTHOR]

By breaking the symmetry of the structure, we obtain bound states in the continuum (BIC) in terahertz (THz) using metasurfaces which were prepared with Si and/or Si-compatible materials. With the help of the quasi-BIC with an ultra-high Q factor, the enhanced Goos–Hanchen (GH) shift can reach 5812 times of wavelength. At the same time, the high reflectance is maintained, which makes up for the defect of low reflectance when the GH shift is enhanced by the Brewster angle effect and transmission-type resonances and is convenient for experimental measurement. In addition, the metasurface can be used as an environmental refractive index sensor, and its maximum sensitivity can reach 1.27 × 107mm/RIU, which promotes the development of THz high-resolution sensors. The results could boost the development of silicon-photonics to provide low-cost, highly efficient integrated devices benefited from the same fabrication process as that of large-scale integrated circuit production. • The Goos–Hanchen shift is enhanced by quasi-bound states in the continuum. • High reflectance can be maintained while greatly enhancing the Goos–Hanchen shift. • A high sensitivity refractive index sensor is designed. [ABSTRACT FROM AUTHOR]

The authors describe an amplified photoelectrochemical immunoassay for the tumor marker carbohydrate antigen 724 (CA724). The method employs a C3N4-MoS2 semiconductor as the photoelectric conversion layer. The nanocomposite was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, and UV-vis diffuse reflectometry. The dye eosin Y was encapsulated into CaCO3 nanospheres which then were used as labels for antibody against CA724. In addition, Fe3O4 nanospheres were employed as magnetic platform for constructing photoelectrochemical sandwich immunoassay. The CaCO3 nanospheres can be dissolved with aid of ethylene diamine tetraacetic acid (EDTA) and the carried eosin Y in CaCO3 is released. The released dyes sensitizes the C3N4-MoS2 semiconductor, which induces photocurrent amplification. Under optimal conditions and at a typical working voltage of 0 V (vs. SCE), the photocurrent increases linearly in the range of 0.05 mU mL−1 to 500 mU mL−1 of CA724, with a 0.02 mU mL−1 detection limit.The C3N4-MoS2 complex, with high efficiency of electron transport, was synthesized to construct a photoelectrochemical analytical platform. A sandwich-type immunoassay was established on the surface of magnetic beads. Carbohydrate antigen 724 in sample was detected sensitively by using sensitization of released eosin Y as signal amplifiery. [ABSTRACT FROM AUTHOR]

In this paper, a new, automatic method of measuring air dew-point (DP) is presented. The system also realizes a relative-humidity sensing function, based on dew point and temperature measuring channels acquired data. The DP is detected on the surface of a lithium chloride-polyvinyl alcohol film fabricated on an optic fiber head using an optical system. The refractive index of the sensing film will be at its maximum value when the dew or frost starts to form at DP. A setup which includes a dew point sensor head and a measurement/control/data collection interface is assembled to enable automated measurements. Several programs are designed using the LabVIEW 8.6 environment to measure the dew point sensing properties of our sensor, such as response-recovery curves, temperature characteristic, and humidity calculation. Anti-interfered and good stability are its main advantages. The sensor can operate in the range of dew point temperature from 0 to 30 °C and relative humidity (RH) from 11% to 83% RH. The repeatability of the sensor was implemented with a standard deviation of 0.09 °C. The results showed that the measured dew point values and RH values were in very good agreement with reference values and with an accuracy of less than ±0.3 °C, 1% RH, respectively, over the whole temperature range. [ABSTRACT FROM AUTHOR]

A graphene-based metamaterial structure with tunable plasmon induced transparency (PIT) effect is numerically and theoretically researched in this paper. Both the collinear and parallel graphene strips serve as bright mode and a PIT window emerges due to the weak hybridization between them. The transparency window can be tuned by not only adjusting the geometry parameter of the structure but also changing the chemical potential of the graphene strips. Different from the reported tunable PIT system, the spectra width and resonance strength can be tuned with the PIT peak at a fixed frequency in this research. Moreover, the Q factor can be affected by the distance between two bright modes and a figure of merit (FOM) as high as 15.20 can be achieved in this research. These properties expand the application for PIT phenomenon in mid-infrared metamaterial devices, such as filter, modulator and sensor. [ABSTRACT FROM AUTHOR]

Graphene metasurface has attracted a lot of attentions due to the unique tunability for exotic electromagnetic properties. In this work, we propose and numerically investigate a tunable metasurface with two non-coplanar and inter-perpendicular graphene nanoribbon arrays. The variation of transmission at different substrate thickness and the coupled mode are analyzed. It is shown that the Rabi-like splitting can be achieved by the coupling between localized and delocalized graphene surface plasmon polaritons. Tunable coupling strength and positions with different gate-voltages have been discussed. The effect of relaxation time and oblique incidences to resonant responses are also investigated. Additionally, we find an optical analogue of a spring, where the spectral dip vibrates around its equilibrium position at a certain wavelength. Our study suggests that the proposed structure is potentially attractive for realization of tunable double-channel filter, optical switch, and variable optical attenuator based on the graphene metasurface. [ABSTRACT FROM AUTHOR]

Dynamically tunable plasmonic multi-functional is particularly desirable for various nanotechnological applications. In this paper, graphene nano-sheet pair arrays separated by a substrate, which can act as a dynamically tunable plasmonic band stop filter with transmission at resonance wavelength lower than 1%, a high sensitivity refractive index sensor with sensitivity up to 4879 nm/RIU, figure of merit of 40.66 and a two circuit optical switch with the modulation depth up to 0.998, are proposed and numerically investigated. These excellent optical performances are calculated by using FDTD numerical modeling and theoretical deduction. Simulation results show that a slight variation of chemical potential of the graphene nano-sheet can achieve significant resonance wavelength shifts. In additional, the resonance wavelength and transmission of this plasmonic device can be tuned easily by two voltages owing to the simple patterned graphene. These studies may have great potential in fabrication of multi-functional and dynamically tunable optoelectronic integrated devices. [ABSTRACT FROM AUTHOR]

A tunable terahertz filter based on graphene plasmonic all-dielectric metasurfaces is proposed and investigated numerically by using the finite-difference time-domain (FDTD) method. Especially, hybrid all-dielectric metasurfaces are used to make a whole single-sheet graphene forms two different conductivity patterns with the same gate voltage. The simulated results show that resonance wavelength is shifted significantly with the change of gate voltage. Besides, the transmittance spectra are also shifted with the change of the width of SiC, and the filter shows a polarization-dependent modulation property for the length and the width of SiC being 480 and 320 nm, respectively. In addition, the filter can be applied for refractive sensing because the transmittance spectra are shifted with the change of the background refractive index. The study could provide availability for versatile tunable terahertz graphene plasmonic metasurfaces. [ABSTRACT FROM AUTHOR]

We report the observation of an analog of double electromagnetically induced absorption (EIA) in a plasmonic system consisting of two disk resonators side-coupled to a discrete metal-insulator-metal (MIM) waveguide. The finite-difference time-domain (FDTD) simulation calculations show that two absorption windows are obtained and can be easily tuned by adjusting the parameters of the two resonance cavities. The consistence between the coupled-model theory and FDTD simulation results verify the feasibility of the proposed system. Since the scheme is easy to be fabricated, our proposed configuration may thus be applied to narrow-band filtering, absorptive switching, and absorber applications. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrated a low-loss and high-transmission analogy of electromagnetically induced transparency based on all-dieletric metasurface. The metamaterial unit cell structure is composed of two mutually perpendicular silicon nanoscale bars. Under the joint effects of the neighboring meta-atoms' coherent interaction and significant low absorption loss, the transmission and the Q-factor can reach up to 93 % and 139, respectively. Moreover, we use the coupled harmonic oscillator model to analyze the near field interaction between the two elements in the electromagnetically induced transparency (EIT) metamaterial unit cell qualitatively and the effects of parameters on EIT. The figure-of-merit of 42 and the group delay of 0.65 ps are obtained. These characteristics make the metamaterial structure with potential to apply for ultrafast switches, sensor, and slow-light devices. [ABSTRACT FROM AUTHOR]

Visual detection of tumor markers with accuracy and selectivity exhibits significant advantages for cancer early diagnosis due to its low-cost and simple analytical instruments. Herein, a highly photosensitive colorimetric immunoassay for carcino embryonie antigen (CEA, as a model) detection based on Cu 2+ doped Ag-AgI nanocomposite was constructed. First, Cu 2+ doped Ag-AgI nanocomposite (Cu 2+ /Ag-AgI) owned the ability of oxidization of TMB was synthesized by impregnation method, which was characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). Second, based on sandwich-type immunoassay, the immunocomplex was built on the surface of magnetic bead by utilizing Cu 2+ /Ag-AgI as labels. The blue color of TMB ox was obtained under visible irradiation and ultraviolet spectrum scanning was carried out in ABS buffer solution. Under optimal conditions, the absorbance values increased with the increasing of CEA concentrations in sample with the linearity range of 1.0 pg mL −1 −5.0 ng mL −1 . The detection limit was 0.13 pg mL −1 . More importantly, the developed colorimetric immunoassay exhibited good selectivity, repeatability, stability and possible applications in the real serum sample analysis. [ABSTRACT FROM AUTHOR]

We firstly investigate plasmon induced transparency (PIT) effect in a metal–dielectric–metal (MDM) waveguide coupled to a single loop stub resonator by finite difference time domain method (FDTD). Compared with previous PIT sup based on MDM waveguide, PIT phenomena can be realized in a single plasmonic composite nanocavity without employment of additional optical elements. Plasmon induced transparency windows can be controlled by adjusting the geometrical parameters of the vertical branches or the horizontal branch in the plasmonic structure. The red-shift of PIT peak is almost linearly proportional to the refractive index of the horizontal branch. This plasmonic system takes the advantages of easy fabrication and compactness. The results may pave a way for the dynamic control of light in highly integrated optical circuits, which can realize ultrafast switching, light storage and nanosensor devices. [ABSTRACT FROM AUTHOR]

A novel optical fiber sensor for the detection of Fe3+ based on AIEgens was reported for the first time. A new anti-B 18 H 22 derivative ((5-NH 2 C 9 H 6 N) 2 B 18 H 20 , Referred as to S1) bearing 5-aminoisoquinoline was synthesized via a one-pot and its structure was verified by 1H NMR and HRMS, photophysical properties were characterized by UV–Vis, fluorescence spectrum and theoretical calculation. The fluorophore exhibits obvious aggregation-induced emission enhancement (AIEE) characteristics in THF/H 2 O solution by increasing the aqueous concentration from 70% to 90%. The aggregation-induced emission (AIE) molecule in THF/H 2 O (ƒw = 90%) solution shows high selectivity for detecting Fe3+ over other metal ions by forming a 1:1 metal-to-ligand complex, and the detection limit is 5.25 × 10−5 M. The optical fiber sensor based on S1 for the detection of Fe3+ was fabricated, and the detection limit of Fe3+ can reach to be 0.137 nM. The sensor can be used to detect Fe3+ in chemical, environmental and biological fields. 1. The amino-containing anti-B 18 H 22 derivative with AIE characteristics was synthesized for the first time. 2. A novel optical fiber sensor for the detection of Fe3+ based on AIEgens was reported for the first time. 3. The optical fiber sensor based on this AIEgen for the detection of Fe3+ was fabricated, and the detection limit of Fe3+ can reach 0.137 nM. Compared with other fluorescence methods for detecting iron ions, the detection limit of our technique has obvious advantage. [ABSTRACT FROM AUTHOR]

• The dew point sensor based on the thermal effect of humidity sensitive film is reported for the first time. • The sensor has the advantages of simple device and strong anti-interference ability. • The response time of the sensor can be shorten by the software settings. A novel dew point measurement method has been developed by using a temperature sensor covered by humidity sensitive thin film (referred as HSTF). The measurement mechanism is that the mutation of the temperature-time curve caused by the thermal effect of the HSTF can be used to detect dew points. The automatic measurement system of dew point and relative humidity (RH) based on LabVIEW is built. Compared with the existing dew point detection methods, the technique has the advantages of simple device and anti-interference. The experimental data were compared with the reference values with the satisfactory results, relative humidity deviations are less than 1%, the working range is 0–30 °C within 25–85% humidity environment and the maximum response time are less than 65 s which can be further shortened by software. The research provides an effective way for the construction of a simple and automatic dew point measurement system. [ABSTRACT FROM AUTHOR]

A relative humidity (RH) sensor based on a seven-core fiber (SCF) coated with graphene oxide (GO) is proposed. The sensing structure consists of a part of the SCF sandwiched between two parts of no-core fibers (NCFs). The SCF was corroded by hydrofluoric acid until the six outer cores were exposed to air and then coated with a layer of GO. The two NCFs play splitting and coupling roles because of the core diameter mismatch. The center core of the SCF acts as the reference arm, and the outer six cores of the SCF act as the sensing arm to construct a Mach–Zehnder interferometer. When GO absorbs water molecules, its refractive index changes. Consequently, the phase difference between the center core and outer core modes varies, and the resonant dip moves. The experimental results indicate that the RH sensitivity can reach 0.165 nm/%RH in the range of 30% to 100%, and the corresponding linear fitting coefficient is 99.9%. [ABSTRACT FROM AUTHOR]

Quasi-bound states in the continuum provide an effective and observable way to improve metasurface performance, usually with an ultra-high-quality factor. Dielectric metasurfaces dependent on Mie resonances have the characteristic of significantly low loss, and the polarization can be affected by the parameter tuning of the structure. Based on the theory of quasi-bound states in the continuum, we propose and simulate a bifunctional resonant metasurface, whose periodic unit structure consists of four antiparallel and symmetrical amorphous silicon columns embedded in a poly(methyl methacrylate) layer. The metasurface can exhibit an extreme Huygens' regime in the case of an incident plane wave with linear polarization, while exhibiting chirality in the case of incident circular polarized light. Our structure provides ideas for promoting the multifunctional development of flat optical devices, as well as presenting potential in polarization-dependent fields. [ABSTRACT FROM AUTHOR]

The multifocal metalens with an adjustable intensity has great potential in many applications such as the multi-imaging system, but it is less studied. In this paper, by combining the electro-optic material barium titanate (BTO) with the Pancharatnam-Berry phase, an electrically modulated bifocal metalens in a visible light band is innovatively proposed. Due to the electro-optic effect, we can control the refractive index of the BTO nanofins to vary between 2.4 and 3.07 by applying different voltages (0–60 V). Thus, the method of modulating the intensity ratio of the two focal points is applying an electric field. It is different from using phase change materials or changing the ellipticity of incident light, the strategies proposed in previous studies. Moreover, when the applied voltage is 0 V or 60 V, the bifocal metalens becomes a single focal metalens with different focal lengths, and the full width at half maximum of each focal point is close to the diffraction limit. It has great potential in applications of optical storage, communication and imaging systems. [ABSTRACT FROM AUTHOR]

With the presence of a driving field applied to double quantum dots and a control field applied on the cavity, the transmission performance and group delay effect of a probe field have been theoretically studied in a hybrid optomechanical system (HOMS). Due to the interaction between the mechanical mode and the double quantum dots system, double optomechanically induced transparency (OMIT) arises in the HOMS. With the assistance of a driving field, the system can be tuned to switch on any one of the two OMIT windows, switch on both of the two OMIT windows or switch off both of the two OMIT windows by dynamically adjusting control of the optical field and the driving field. Furthermore, the transmitted probe fields of the two OMIT windows can be tuned to be absorbed or amplified with proper parameters of the driving field and control field. Moreover, the transmission properties of the two OMIT windows are asymmetrical. One can obtain the maximum group delay time of the probe field by optimizing the amplitude and phase of the driving field. These results provide a new way for constructing optically controlled nanostructured photonic switch and storage devices. [ABSTRACT FROM AUTHOR]