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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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

• Synthesis of anti-B 18 H 22 -isoquinoline hybrid for the first time. • Fluorescence modulation of anti-B 18 H 22 by introducing isoquinoline group. • Anti-B 18 H 22 -isoquinoline hybrid displays aggregation-induced emission characteristic. • The potential application of the polystyrene hybrid film. A novel compound (B 18 H 20 (NC9H 7) 2) was synthesized by connecting isoquinoline moieties to the anti-B 18 H 22. The fluorescence emission performance in tetrahydrofuran/water mixtures showed that the compound had obvious aggregation-induced emission characteristic. Upon addition of water in tetrahydrofuran (90:10, v/v) solution, the quantum yield is increased by 0.04–1.41%. The photophysics properties of B 18 H 20 (NC 9 H 7) 2 /polystyrene and B 18 H 20 (NC 9 H 7) 2 /anti-B 18 H 22 /polystyrene film were also studied, and the testing results show that these two films have a wide range of absorption in the visible region. Our work broadens the structure types of anti-B 18 H 22 derivatives and provides a new way to develop new anti-B 18 H 22 fluorescent materials containing isoquinoline units. [ABSTRACT FROM AUTHOR]