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Glutathione (GSH) plays vital role in human biological systems, so its rapid and sensitive detection is necessary for health condition monitoring. In this work, a simple structure for dual channel GSH and refractive index (RI) detection is proposed. By introducing Au-MnO 2 thin film coating on the fiber surface for the first time, GSH solution would lead to the dissolution of MnO 2 , the change in GSH levels could be monitored over a short period in channel 2. For channel 1, ITO-Ag thin film is applied for RI change detection. After optimization, the GSH detection sensitivity reached about -2.361 nm/mM in the range of 0.005-50 mM, and the RI sensitivity reached 1704.252 nm/RIU in the range of 1.331-1.3895 RIU. Channel 1 could also put into GSH detection in the high concentration scale to enlarge the sensor's range and 0.095 nm/mM of sensitivity is acquired within the range of 50-600 mM. With the presence of MnO 2 film, the detection sensitivity increased 25.663 times. Neither channel interferes with the operation of the other. Proposed sensor provides stability, high selectivity and elevation in GSH detection sensitivity, which shows great potential for environmental and biological detection field and their applications.

In this paper, we fabricate a transmissive fluorescent temperature sensor (TFTS) that based on Er 3+ /Yb 3+ /Mo 6+ tri-doped tellurite fiber, which has the advantages of compactness and simplicity, corrosion resistance, high stability and anti-electromagnetic interference. The doping of Mo 6+ ions will enhance the up-conversion (UC) fluorescence emission efficiency of Er 3+ ions, thus improving the signal-to-noise ratio of TFTS. Using the fluorescence intensity ratio (FIR) technique, the real-time thermal monitoring performance of TFTS is evaluated experimentally. Apart from good stability, its maximum relative sensitivity is 0.01068 K -1 at 274 K in the measured temperature range. In addition, it is successfully used to monitor the temperature variation of the stator core and stator winding of the motor in actual operation. The results show that the maximum error between the FIR-demodulated temperature and the reference temperature is less than 1.2 K, which fully confirms the effectiveness of the TFTS for temperature monitoring. Finally, the FIR-based TFTS in this work is expected to provide a new solution for accurate and real-time thermal monitoring of motors and the like.

A surface plasmon resonance (SPR) temperature sensor based on a hollow core fiber (HCF) is designed in this paper. The sensor is composed of a multi-mode fiber (MMF)-HCF-MMF structure, and the self-made HCF is deposited successively with a thin layer of Au film (50 nm in thickness), gold nanoparticles (10 nm in diameter) and polydimethylsiloxane (PDMS). A series of theoretical and experimental investiagtions are conducted, and the results are as follows: the proposed sensing structure only with Au film can effectively excite the SPR effect, with a sensitivity of (2200 ± 100) nm / RIU in the refractive index (RI) range of 1.3334-1.3811; after adding AuNPS, the sensitivity of the sensor is effectively improved, the sensitivity can be increased to (3100 ± 100) nm / RIU, and after the PDMS coating, temperature sensing can be realized due to its unique temperature-sensitive characteristics, a linear sensitivity of (-2.1 ± 0.1) nm / °C is realized in the temperature range of 25 °C to 100 °C. The sensor has the advantages of simple structure, wide application, large measurement range, high sensitivity, good stability and repeatability. Meanwhile, the internal air hole of HCF leaves a preparation channel for dual-parameter measurement. It has broad application prospect in medical treatment, environmental monitoring and manufacturing industry.

Multi-core fiber based on space division multiplexing technology provides a practical solution to achieve multi-channel and high-capacity signal transmission. However, long-distance and error-free transmission remains challenging due to the presence of inter-core crosstalk within the multi-core fiber. Here, we propose and prepare a novel trapezoid-index thirteen-core single-mode fiber to solve the problems that MCF has large inter-core crosstalk and the transmission capacity of single-mode fiber approaches the upper limit. The optical properties of thirteen-core single-mode fiber are measured and characterized by experimental setups. The inter-core crosstalk of the thirteen-core single-mode fiber is less than -62.50 dB/km at 1550 nm. At the same time, each core can transmit signals at a data rate of 10 Gb/s and achieve error-free signal transmission. The prepared optical fiber with a trapezoid-index core provides a new and feasible solution for reducing inter-core crosstalk, which can be loaded into current communication systems and applied in large data centers.

We propose a novel heterogeneous nineteen-core four-mode fiber. The heterogeneous core arrangement and trench-assisted structure can significantly suppress inter-core crosstalk (XT). In order to control the number of modes in the core, a low refractive index area is introduced in the core. The number of LP modes and the effective refractive index difference (Δn eff ) of adjacent modes in the core are controlled by changing the refractive index distribution of the core and the parameters of the low refractive index area in the core. And the mode state of low intra-core crosstalk is successfully realized in the graded index core. After the optimization of fiber parameters, each core can stably transmit four LP modes under the optimal fiber parameters, and the inter-core crosstalk of LP 02 mode is less than -60 dB/km. Finally, the effective mode area (A eff ) and dispersion (D) of nineteen-core four-mode fiber in C+L band are described. The results show that the nineteen-core four-mode fiber is suitable for terrestrial and undersea communication systems, data centers, optical sensors and other fields.

In this paper, a no-core tellurite optical fiber (NCTOF)-based sensor was proposed for cryogenic temperature detection in refrigeration process. The ultraviolet adhesive (UVA) dual-curing method was operated to stablish a sandwich-like composite structure, in which a section of NCTOF was compactly sandwiched between two segments of silica fiber to form multimode interference. The temperature sensing characteristics in cryogenic range were experimentally investigated by monitoring the transmission spectral movement, where a high sensitivity of 105.6 pm/°C was achieved in the range of -20-0 °C and 51.6 pm/°C in the range of -20-25 °C. The excellent performance was consistent with the simulation analysis. The maximum repeatability standard deviation and stability wavelength error of the sensor are 0.9799 pm/°C and 0.1676 nm, respectively. To the best of our knowledge, this is the first report on using tellurite optical fibers for cryogenic temperature detection, and the UVA dual-curing method provides a reliable solution for the integration and practical application of tellurite optical fiber. The proposed sensor is simple in structure, easy in fabrication, low in cost and excellent in performance. It can be expected to be used in food refrigeration, air-conditioning engineering, medical and health, industrial production, etc.

Energy transfer between Tm 3+ and Tb 3+ dependent on the power density of pump laser was investigated in NaYF 4 : Tb 3+ ,Tm 3+ ,Yb 3+ microcrystals. Under the excitation of a 976-nm near-infrared laser at various power densities, Tb 3+ -Tm 3+ -Yb 3+ doped samples exhibited intense visible emissions with tunable color between green and blue. The ratio of blue and green emission were determined by energy transfer between Tm 3+ and Tb 3+ . When the power density of pump laser was low, the energy transfer process from Tm 3+ ( 3 F 4 ) to Tb 3+ ( 7 F 0 ) occurred efficiently. Upconversion processes in Tm 3+ were inhibited, only visible emissions from Tb 3+ with green color were observed. When the power density increased, energy transfer from the 3 F 4 (Tm 3+ ) to 7 F 0 level (Tb 3+ ) was restrained and population on high energy levels of Tm 3+ was increased. Contribution of upconversion emissions from Tm 3+ gradually became dominant. The emission color was tuned from green to blue with increasing the power density. Energy transfer processes between low-lying levels of activators, such as Tm 3+ will greatly reduce the population on certain levels for further high-order upconversion processes. The Tb 3+ -Tm 3+ -Yb 3+ doped phosphors are promising materials for detecting the condition of power density of the invisible near-infrared laser.