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A high-sensitivity and fast-response fiber-optic plasmonic temperature sensor is developed by coating graphene and polydimethylsiloxane (PDMS) onto an optical-fiber based plasmonic interface. The sensor is composed of a side-polished-fiber for light excitation and readout, a gold layer to excite surface plasmon resonance (SPR), graphene layers to enhance the SPR effect and accelerate the sensing response, and a PDMS layer acting as a thermo-optical responsive material. It is found that the number of graphene layers exhibits positive enhancement on the sensitivity toward the refractive index (RI) until 4 layers, and further increasing the number of layers leads to a decreased sensitivity. The four-layered graphene could improve the sensitivity of the RI sensor by 33% and the temperature sensitivity by 21.9% after overcoating the PDMS layer, increasing the temperature sensitivity from 1.28 nm °C−1 for the SPR sensor with a PDMS layer to only 1.56 nm °C−1 for the graphene–PDMS based sensor. Furthermore, the graphene layers shorten the response time of the temperature sensor by more than one order of magnitude, i.e., from 65 to 6 s. It is believed that the multilayer graphene/PDMS structure can be further exploited for optimizing other temperature sensors in terms of sensitivity and response time.

Molybdenum disulfide (MoS2), as a representative layered transition metal dichalcogenide material, possesses great potential applications in highly sensitive detection. In this paper, a sensitivity...

A long-range surface plasmon resonance (LRSPR) sensor with enhanced performance has been theoretically calculated and experimentally investigated for biosensing applications. The LRSPR-based sensor is fabricated by employing a side-polished multimode fiber as a waveguide and MgF2 as a buffer layer beneath a thin silver film for supporting LRSPR excitation. Theoretical optimization based on transfer matrix method and the corresponding validation experiments were carried out in detail. The theoretical and experimental results consistently indicate that the sensing performance parameters of the LRSPR-based sensor are improved with varying degrees in comparison to conventional SPR (CSPR) sensors. It was experimentally achieved that the maximal figure of merit of the LRSPR-based sensor exceeds that of the CSPR sensor by a factor of 1.14. At last the bovine serum albumin (BSA) concentration detection was performed to further confirm the sensitivity enhancement of the optimized sensor in biosensing. This SPR sensor design and development is expected to exert a positive influence on real-time and label-free.

It has long been a challenge to develop strain sensors with large gauge factor (GF) and high transparency for a broad strain range, to which field silver nanowires (AgNWs) have recently been applied. A dense nanowire (NW) network benefits achieving large stretchability, while a sparse NW network favors realizing high transparency and sensitive response to small strains. Herein, a patterned AgNW-acrylate composite-based strain sensor is developed to circumvent the above trade-off issue via a novel ultrasonication-based patterning technique, where a water-soluble, UV-curable acrylate composite was blended with AgNWs as both a tackifier and a photoresist for finely patterning dense AgNWs to achieve high transparency, while maintaining good stretchability. Moreover, the UV-cured AgNW-acrylate patterns are brittle and capable of forming parallel cracks which effectively evade the Poisson effect and thus increase the GF by more than 200-fold compared to that of the bulk AgNW film-based strain sensor. As a result, the AgNW-based strain sensor possesses a GF of ∼10,486 at a large strain (8%), a high transparency of 90.3%, and a maximum stretchability of 20% strain. The precise monitoring of human radial pulse and throat movements proves the great potential of this sensor as a measurement module for wearable healthcare systems.

A highly sensitive surface plasmon resonance fiber sensor for a vector magnetic field is proposed. The sensor is composed of a half-side gold-coated multimode-single-mode-multimode hetero-core fiber structure encapsulated with ferrofluids. The half-side gold film on the fiber not only produces the surface plasmon resonance, but also breaks the centrosymmetry of the light field in the fiber. Moreover, the magnetic-field-dependent anisotropy of the surrounding ferrofluids makes the sensor sensitive to both the intensity and direction of the magnetic field. Owing to the unique half-side coating configuration and the resulting enhancement of the evanescent field, the sensor can achieve a sensitivity as high as 1008 pm/Oe to the magnetic field intensity. The proposed sensor, possessing advantages such as high sensitivity, ease of fabrication, and low cost, has potential in the detection of a weak vector magnetic field.

A novel magnetic field sensing system based on a ferrofluid-coated multimode interferometer (MI) integrated into a fiber-loop ring-down cavity is proposed and demonstrated. The MI is composed of a piece of no-core fiber (NCF) sandwiched by two sections of single-mode fiber. Through appropriately designing the length of the NCF, the ferrofluid-coated MI not only works as the sensing unit but also can help to filter the unwanted amplified spontaneous emission arising from the erbium-doped fiber amplifier in the fiber loop. The proper length of NCF can be determined by simulations. Corresponding experiments are conducted, and the experimental results demonstrate the feasibility of the sensing system. A sensitivity of $- 0.83\,\,\mu \text{s}$ /Oe in the linear region is achieved in experiments.

Sm3+ doped SrWO4 was synthesized by the high temperature solid-state reaction method to explore its possible application in optical thermometry. Under a 404 nm excitation, the fluorescence intensity ratios (FIRs) between the down conversion emissions of the Sm3+:4G5/2 → 6H5/2 (564 nm) to the Sm3+:4G5/2 → 6H7/2 (600 nm) and Sm3+:4G5/2 → 6H9/2 (647 nm), respectively, were measured as a function of temperature in the range of 300–573 K. A maximum temperature sensitivity of 0.016 K−1 at 300 K is achieved. The results indicate that the SrWO4:Sm3+ is a promising candidate for optical thermometry.

In this paper, Tm3+/Yb3+ codoped SrWO4 materials for optical thermometry is synthetized and characterized. Under a 980 nm diode laser excitation, the upconversion emission spectra of the material under different temperature were measured in the temperature range of 308 K–573 K. The fluorescence intensity ratios (FIRs) of the Tm3+:3F2 → 3H6 (684 nm) and Tm3+:3F3 → 3H6 (696 nm) emissions to the Tm3+:3H4 → 3H6 (814 nm) emission were respectively calculated. The results show that the natural logarithm of both FIRs change linearly with the reciprocal of temperature. The maximum absolute sensitivities are 0.00544 K−1 and 0.00617 K−1 at 323 K, respectively, which are about one order higher than that of most of the previously reported Tm3+/Yb3+ doped materials with other hosts. The results indicate that SrWO4:Tm3+/Yb3+ is a very promising material for highly sensitive optical thermometry.

In this paper, a fiber-loop ring-down interrogated refractive index sensor based on a single-mode-no-core-single-mode (SNS) fiber structure is reported. The influence of the wavelength and pulsewidth on the performance of the sensor are systematically investigated. Results show that the performance of the sensing system is strongly dependent on the interrogation wavelength and a narrower pulsewidth is helpful to avoid the disturbance of the relaxation oscillation. A method to determine the optimal interrogation wavelength was proposed. After determining the interrogation wavelength and pulsewidth, refractive index (RI) measurement was experimentally performed in the RI range of 1.3330–1.3539. And a cubic polynomial fitting was established between RI and ring-down time. In the linear region, a sensitivity of −3271 μs/RIU was achieved.

Aiming at the problem of Unmanned Combat Air Vehicle (UCAV) air combat decision-making and maneuver optimization, an UCAV optimal decision method based on dynamic Bayesian network (DBN) is proposed. Firstly, The DBN maneuver recognition model is established based on the causal relationship between flight characteristic parameters and maneuver actions, and the target flight path is predicted according to the acquired attitude information and trajectory prediction model. Secondly, combined with the comprehensive analysis of other information, the air combat occupation decision is established, and the decision result is the functional index of maneuver optimization to be adopted by UCAV. Finally, used optimal control algorithm to calculate the optimal boot quantity iteratively. The simulation results prove the convergence and real-time performance of the control algorithm, it can meet the requirements of engineering application.

In this paper, a fiber-optic temperature sensing system, based on surface plasmon resonance (SPR) and integrated with a smart-phone platform, is proposed and demonstrated. The sensing system is composed of a side-polished-fiber-based SPR sensor, which is illuminated by the LED flash from one end, and the output signals are recorded and processed by the camera and a designed application in the smart-phone. The sensing performance is evaluated by immersing the sensor in distilled water under different temperatures. Experimental results show that the measurement resolution of the proposed temperature sensor can reach 0.83°C in the range from 30 to 70°C, corresponding to a linear correlation coefficient of 0.9798. The low-cost and portable fiber optic SPR sensor based on a smart-phone platform has wide application potentials in the fields of health-care, environmental monitoring, etc.

In-plane photonic spin splitting effect is investigated in tunneling terahertz waves through an epsilon-near-zero metamaterial sandwiched between monolayer black phosphorus (BP). The strong in-plane anisotropy of BP layers will induce in-plane asymmetric spin splitting. The asymmetric spin splitting can be flexibly tuned by the angles between the incident plane and the armchair crystalline directions of the top and bottom BP layers, i.e., ϕ1 and ϕ2. Based on this, an angle-resolved barcode-encryption scheme is discussed. For the special case of ϕ1 = ϕ2 = 0 or 90°, the transmitted beam undergoes Goos-Hanchen shift, which varies with the carrier density of BP. We believe these findings can facilitate the development of novel optoelectronic devices in the Terahertz region.

In this work, we demonstrate a highly-sensitive vector magnetometer based on a few-mode-fiber-based surface plasmon resonance (SPR) sensor functionalized by magnetic nanoparticles (MNPs) in liquid. To fabricate the sensor, a few-mode fiber is side-polished and coated with a gold film, forming an SPR sensor that is highly sensitive to the surrounding refractive index. The vector magnetometer operates based on the mechanism whereby the intensity and orientation of an external magnetic field alters the anisotropic aggregation of the MNPs and thus the refractive index around the fiber SPR device. This, in turn, shifts the resonance wavelength of the surface plasmon. Experimental results show the proposed sensor is very sensitive to magnetic-field intensity and orientation (0.692 nm/Oe and &minus, 11.917 nm/&deg, respectively). These remarkable sensitivities to both magnetic-field intensity and orientation mean that the proposed sensor can be used in applications to detect weak magnetic-field vectors.

A surface plasmon resonance (SPR) biosensor, which contains an overlayer of titanium dioxide nanoparticles (TDNPs) to modify the plasmonic interface, has been developed and investigated. Owing to its large surface area and high refractive index, the TDNP overlayer significantly enhances the probing electric field intensity and detection sensitivity. This sensitivity is related to the TDNP overlayer thickness, which can be engineered by changing the TiO2–ethanol dispersion’s spin-coating concentration. The highest refractive index sensitivity for ethylene glycol measurement is 2567.3 nm/RIU, which is 38% higher than that of a conventional SPR sensor with an uncoated gold film. The proposed TDNP-SPR sensor also exhibits a 1.59-fold sensitivity enhancement in fetal bovine serum detection. Moreover, the proposed interface modification approach that is applied without additional biochemical amplification steps is chemical-free and contamination-free; therefore this TDNP-SPR sensor could be integrated into a sensitive, cost-effective, and biocompatible platform for rapid and label-free biochemical detection.

A novel optical fiber sensor for simultaneous measurement of magnetic field and temperature is proposed and demonstrated. The sensor consists of a cascaded photonic crystal fiber (PCF) interferometer and fiber Bragg grating (FBG). The interferometer and the FBG are sealed in a capillary tube filled with magnetic fluid. The transmission spectrum of the sensor contains both the information of the interferometer and the FBG. The FBG is only sensitive to the temperature but the PCF interferometer is also sensitive to the magnetic field, which in turn can be used for the simultaneous measurement of magnetic field and temperature. A sensor was fabricated and investigated experimentally.

In this paper, an optical fiber sensor for simultaneous measurement of magnetic field and temperature is proposed and demonstrated. The sensor consists of a macro-bending single-mode-fiber structure (MSS) and a closely concatenated fiber Bragg grating (FBG), both of which are coated with magnetic fluid. The MSS and FBG induce two types of dips in the transmission spectrum of the sensor, and they have the different sensitivities to magnetic field and temperature. Consequently, the simultaneous measurement for the dual-parameter can be realized by monitoring the wavelength shifts of the two types of dips. A sensor was fabricated and experimentally characterized. The results show that the proposed sensor is simple and effective in the simultaneous measurement of temperature and magnetic field.

A kind of intensity-interrogated magnetic field sensor composed of ferrofluid and photonic crystal fiber (PCF) with a lateral-offset fusion splicing is proposed and investigated. The sensing principles are mainly based on the tunable absorption coefficient of ferrofluid and mode interference in the PCF section. Theoretical analyses show that the sensitivity depends on the allocation condition of the light intensity of the core and cladding modes in the PCF, which in turn depends on the amount of the lateral offset between the lead-in fiber and the PCF. Several sensors with different offset amounts are fabricated and tested. The experimental results show that a lateral-offset fusion splicing can significantly enhance the sensitivity of the sensor. In addition, the sensitivity as high as -0.0303 dB/Oe in the range of 20-160 Oe is achieved when setting the offset as 20 μm.

A novel all-fiber sensor based on cascaded singlemode-no-core-singlemode (SNS) and siglemode-multimode-singlemode (SMS) fiber structure is proposed and investigated. Simulation results show that for the given fibers, by appropriately choosing the lengths of no-core fiber and multimode fiber, the transmission spectrum will exhibit two distinguishable dips corresponding to SNS and SMS, respectively. The simultaneous measurement of liquids’ refractive index (RI) and temperature can be realized by monitoring the two dips’ central wavelength shifts. According to the simulations, a corresponding sensor is fabricated and tested. The experimental results demonstrate the feasibility of the sensor and show that the sensor has the RI and temperature sensitivities of 113.66 nm/RIU and 9.2 pm/°C, respectively.

Hyperbolic metamaterials (HMMs) have attracted increasing attentions because of their unique dispersion properties and the flexibility to control the dispersion by changing the components and fractions of the composed materials. In this work, for the first time, we demonstrate a plasmonic sensor based on a side-polished few-mode-fiber coated with a layered of HMM, which is composed of alternating layers of Ag and TiO2. To optimize the sensor performance, the effects of the metal filling fraction (ρ) and the number of bilayers (Nbi) on the HMM dispersion are thoroughly engineered with the effective medium theory and the finite element method. It is found that the HMM with ρ=0.7 and Nbi = 3 can provide the average sensitivity of 5114.3 nm/RIU (RIU: refractive index unit), and the highest sensitivity 9000 nm/RIU in the surrounding refractive index (SRI) ranging from 1.33 to 1.40 RIU. The corresponding figure of merit (FOM) reaches a maximum of 230.8 RIU-1 which is much higher than that of the conventional silver film based SPR sensor. The influence of ρ and Nbi on the sensitivity are well explained from the aspects of the electrical field distribution and the dispersion relationship. This work opens a gate to significantly improve fiber plasmonic sensors performance by engineering the HMM dispersion, which is expected to meet the emergent demand in the biological, medical and clinical applications.

Polarization-sensitive Tamm plasmons are investigated in a multi-layer photonic configuration where a monolayer black phosphorus (BP) is coated on a Bragg mirror separated by a dielectric. Owing to the in-plane anisotropy of BP, the Tamm plasmon can be excited selectively by tuning the BP carrier density. Cross-polarization conversion occurs when the armchair direction of BP makes an angle with the incident plan, i.e., ϕ≠0 or 90°. The BP-based Tamm device can be used as an intensity modulator with a modulation depth up to ∼100% and an insertion loss smaller than -0.55 dB. By analyzing the polarization evolution carefully, a multichannel polarization division multiplexing scheme is proposed and discussed. These findings open a new avenue for exploiting versatile tunable THz devices based on the monolayer of BP.

Herein we propose a novel strategy to enhance surface plasmon resonance (SPR) by introducing a photonic cavity into a total-internal-reflection architecture. The photonic cavity, which is comprised of a highly reflective photonic crystal (PC), defect layers, and a gold (Au) film, enables Fabry–Perot (FP) resonances in the defect layers and therefore narrows the SPR resonance width in the metallic surface as well as increases the electric field intensity and penetration depth in the evanescent region. The fabricated sensor exhibits a 5.7-fold increase in the figure of merit and a higher linear coefficient as compared with the conventional Au-SPR sensor. The demonstrated PC/FP cavity/metal structure presents a new design philosophy for SPR performance enhancement.

A high-sensitivity vector magnetic field is proposed and demonstrated. The sensor consists of a side-polished-fiber (SPF)-based surface plasmon resonance (SPR) structure integrated with ferrofluid. Because of the high refractive index sensitivity of the SPR scheme and the outstanding magneto optical properties of ferrofluid, the sensor shows a high sensitivity (up to 598.7 pm/Oe) to magnetic field intensity. Moreover, owing to the non-circular-symmetric geometry of the SPF and non-uniform distribution of the ferrofluid around the SPF, the sensor exhibits a sensitivity of -5.63 nm/deg to the orientation of the magnetic field. The proposed vector magnetic field sensor, integrating over magnetic, plasmonic, and fiber-optic schemes, is highly sensitive to both the intensity and orientation of the magnetic field simultaneously, and holds potential in applications in many fields, such as medicine, industry, and the military.

A novel strategy to modify the plasmonic interface by spin-coating an overlayer of graphene oxide sheets (GOSs) on top of the surface plasmon resonance (SPR) sensor is proposed and demonstrated. Thanks to the excellent electrical conductivity, large surface area, and high-refractive index of the GOSs layer, the GOSs-modified SPR (GOSs-SPR) sensor achieves an improved sensitivity in the detection of bulky refractive index solutions and bovine serum albumin (BSA) solutions. The maximum sensitivity of 2715.1 nm/RIU achieved by three spin-coatings shows an enhancement of 20.2% than the case without the modification of the GOSs overlayer. Benefiting from the large surface area and abundant surface functional groups, the GOSs-SPR sensor has a greater sensitivity enhancement (up to 39.35%) in the detection of the BSA molecules. Most importantly, we have firstly experimentally demonstrated that the GOSs overlayer with thickness over hundreds nanometers can still lead to a great enhancement of sensitivity of SPR sensors. Additionally, the proposed modification method for the plasmonic interface is a simple and effective strategy to boost the sensitivity in a chemical-free and environment-friendly manner, without additional chemical or biological amplification steps. These unique features make the proposed GOSs-SPR biosensor a low-cost and biocompatible platform in the fields of biochemical sensing, drug screening, and environmental monitoring.

Thermal effects are critical constraints for developing high-power Er/Yb-codoped fiber amplifiers (EYDFAs), especially those with an auxiliary Yb-band cavity. In this paper, we developed a numerical model to investigate the temperature-dependent effects on EYDFAs with an Yb-band cavity with consideration of thermal-induced cross-section changes. Our results show that the quantum-defect-induced heat affects the performance of the EYDFA, and its effect varies with the resonant wavelength of the Yb-band cavity. There is a finite applicable resonant wavelength range limited by thermal damage. So, it is important to take into account the thermal effect during the design of such EYDFAs in order to optimize their performance and determine the heat dissipation systems.

In this paper, a new efficient pumping scheme was proposed for high-power rare-earth co-doped fiber lasers and amplifiers. We show by numerical simulations that by introducing a resonant cavity oscillating in the sensitizer's emission band can effectively convert the cladding-pump to a more efficient core-pump. This method greatly helps to suppress the amplified spontaneous emission in the sensitizer's band, increase the efficiency, and reduce the gain fiber length.

The fiber geometry, fiber parameters and mode-guiding properties are crucial for realizing high-performance fiber-based sensors. In this work, we propose and demonstrate a few-mode fiber (FMF)-based surface plasmon resonance (SPR) biosensor. The FMF-SPR sensor was fabricated via side-polishing a few-mode fiber and coating a thin layer of gold film, on the basis of the optimization of fiber geometry, thickness of the gold film and mode selection, which were performed with the finite element method. The refractive index (RI) sensing performance of three such sensors with different residual fiber thicknesses were investigated. In the RI range from 1.333 to 1.404, the highest sensitivity up to 4903 nm/RIU and a figure of merit of 46.1 RIU-1 are achieved. For testing the bovine serum albumin (BSA) solution, an averaged BSA RI sensitivity of 6328 nm/RIU and an averaged BSA concentration sensitivity of 1.17 nm/(mg/ml) are realized. Benefiting from only a few modes supported in the FMF, a smaller line-width of the SPR spectrum is obtained, which further results in a higher figure of merit (FOM). Moreover, when combined with the superiority of the mode-multiplexing technology brought by the FMF, the FMF-SPR sensors may find applications in biochemical analysis with high performance and high throughputs.

In this work, a sensitivity-enhanced surface plasmon resonance (SPR) sensor, which is integrated with MoSe2 as modification overlayer, is proposed and investigated. The sensor is constructed by physically depositing MoSe2 onto the surface of a conventional SPR sensor based on Krestchman configuration. Thanks to the commendable properties of MoSe2 including high carrier mobility, high refractive index (RI), large surface area, and so forth, adding an overlayer within a certain thickness can effectively improve the RI sensitivity. Experimental results show that, with the increased number of deposition cycles—which positively correlates with the duty ratio and the MoSe2 overlayer’s thickness—the sensitivity at first increases, and then declines. The highest sensitivity of 2524.8 nm/RIU is achieved experimentally, which corresponds to the 2 deposition cycles. This shows an improvement of 36.3%, compared with the case without the MoSe2 modification. The ease of fabrication, efficiency of performance enhancement, and great potentials (such as the large surface area of MoSe2 for linking abundant functional groups) allow the method presented in this paper to contribute to the development of performance-enhanced SPR sensors for the biological, chemical, and medical fields.

A novel magnetic field sensing system based on the fiber loop ring-down technique is proposed in this paper. In the fiber loop, a U-bent single-mode-fiber structure coated with magnetic fluid (MF) serves as the sensing head, and an erbium-doped fiber amplifier (EDFA) is introduced to compensate for the intrinsic loss of the cavity. The ring-down time of the system varies with the change of applied magnetic field due to the tunable absorption coefficient and refractive index of the MF. Therefore, measurement of the magnetic field can be realized by monitoring the ring-down time. The experimental results show that the performance of the system is extremely dependent on the interrogation wavelength, because both the gain of the EDFA and the loss of the sensing head are wavelength dependent. We found that at the optimal wavelength, the ratio of the gain to loss attained its maximum. The sensing system was experimentally demonstrated and a sensitivity of −0.5951 μs/Oe was achieved.

In this paper, Er/Yb co-doped fiber amplifiers (EYDFAs) with an Yb-band fiber Bragg grating (FBG) at the pump end to improve the performance of the amplifier is systematically studied. The influence of the reflectivity and center wavelength of the FBG along with the gain-fiber length on the performance of an EYDFA are numerically analyzed. The results show that the wavelength of the FBG has critical influence on the efficiency of the EYDFA, whereas the requirement to its reflectivity is relaxed. It is an effective and promising way to improve the efficiency of a high-power pumped EYDFA by introducing a suitable Yb-band FBG at the pump end. Based on the analysis of the underlying principles, suggestions for the practical design and possible further improvement strategies are also proposed.

A novel and compact all-fiber sensor based on a macrobent fiber Bragg grating (FBG) structure for simultaneous measurement of refractive index (RI) and temperature is proposed and experimentally investigated. The sensor can be easily fabricated by properly bending an FBG. The bending causes interference between the core mode and the whispering gallery mode, which induces another kind of dip in the transmission spectra of the sensor besides the sharp one of the FBG. Because the two kinds of dips respond differently to the surrounding RI and temperature, these two parameters can be unambiguously measured by the sensor. A sample sensor was fabricated and experimentally investigated, and RI sensitivity of 165.9276 nm/RIU in the range from 1.3330 to 1.3785 and temperature sensitivity of 31.7 pm/°C were achieved. This sensor provides a convenient and economical way for applications where temperature and RI have to be simultaneously measured.