Abstract:A Mach-Zehnder interferometer (MZI) for simultaneously measuring refractive index (RI) and temperature is proposed and verified in this paper. The sensor head is composed of thin core fiber (TCF) S-taper structure and spherical structure. By monitoring two interference dips, experimental results show that the RI sensitivities are −70.392 nm/RIU and −60.08 nm/RIU in the RI range of 1.338 4—1.350 0, respectively. And the temperature sensitivities are 0.050 72 nm/°C and 0.071 7 nm/°C in the temperature range of 30—70 °C, respectively. The simultaneous measurement of the temperature and external RI is demonstrated based on the sensitive matrix. The sensor also has the advantages of low cost, simple structure and high sensitivity.

Abstract:In this paper, an optical fiber fluid sensing system based on optoelectronic oscillator (OEO) was proposed and studied numerically. The fluid sensor head is constructed by splicing two sections of side-polished fiber (SPF) to one section of photonic crystal fiber (PCF). Fluid sample can flow continuously through the holes of PCF. The refractive index (RI) change of the fluid sample can lead to the effective RI change of the fiber, resulting in frequency change of microwave signal generated by OEO. By monitoring the oscillation frequency using an electronic spectrum analyzer (ESA), the RI of fluid sample can be measured. Thanks to the fast interrogation speed of ESAs, the measuring speed can be increased significantly compared to traditional optical fiber RI sensing systems using optical spectrometers. The sensing principle of the system was studied. The sensitivity of the proposed system was evaluated by simulation, and an RI sensitivity of −14.20 MHz/RIU can be achieved. The results show that with proper system design, real-time RI measurement with high sensitivity can be achieved. Increasing the length of the PCF while under the premise of the fluid parameters will be the most reasonable way to improve the sensitivity. The proposed design and simulation results can provide suggestions for the fabrication and optimization of fluid sensing systems used for real-time detection and measurement of biological elements and heavy metal ions in liquid environment.

Abstract:In this letter, a fiber Bragg grating (FBG) dynamic strain sensing system using a semiconductor optical amplifier (SOA)-fiber ring laser (FRL) and an arrayed waveguide grating (AWG) demodulator is proposed. Due to the characteristics of SOA, it can act as the gain medium as well as light source. The AWG module is used as the wavelength demodulator. It is shown that SOA-based FRL sensors can accurately respond to 1.5 με dynamic strain signal with high frequency up to 120 kHz and almost no distortion in the waveforms. Experimental results show that the system can be used for acoustic testing, such as underwater ultrasonic detection and external impact monitoring. In addition, the simultaneous dual-channel demodulated system is investigated in detail to verify the multiplexing. This dynamic strain sensing system can be widely utilized in structural health monitoring because of its high stability, low cost and good multiplexability.

Abstract:Inorganic perovskite solar cells (IPSCs) have attained attention due to their excellent thermal and phase stability. In this work, we demonstrate a novel approach for fabricating IPSCs, using the strategies of interface passivation and anti-solvent before spin-coating perovskite. Poly(methyl methacrylate) (PMMA) and chlorobenzene (CB) are used as passivator and anti-solvent, respectively. The CB improves the perovskite crystal morphology. Meanwhile, PMMA passivates the defects between poly(3, 4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and perovskite layer, thus increasing the short-circuit current. Excitingly, we find that PMMA benefits the grain boundaries (GBs) of perovskite, which makes it more humidity-resistant, increasing the stability of perovskite film. Especially, PMMA mitigates interfacial charge losses, and the devices based on CsPbI3-xBrx passivated by PMMA exhibit the power conversion efficiency (PCE) much higher than those based on pure CsPbI3-xBrx.

Abstract:A simple and inexpensive sensing structure, single mode fiber (SMF) alignment fusion to 62.5 μm stepped index-multimode fiber (SI-MMF), combined with Brillouin optical time domain reflectometry (BOTDR) system, is used as a distributed sensor in the field of structural safety and health monitoring (SSHM) of large infrastructures in terms of its prominent bending resistance. The bend loss principle and influencing factors of the fiber are analyzed, and the bending resistances of different fibers are discussed on the basis of theoretical and experimental comparisons. The bend-tolerant capacity and temperature sensing characteristics of the 5 km sensing structure are measured by using the self-developed frequency-shifted local heterodyne BOTDR system. The results show that the proposed sensing structure has excellent bend-tolerant capacity with a minimum bend radius and temperature measurement error of 1.25 mm and 0.69 °C, respectively, which indicates that the proposed sensing structure has huge potential in the field of SSHM of large infrastructures.

Abstract:We demonstrate a multi-wavelength Brillouin-erbium fiber laser (BEFL) with narrow linewidth and tunable wavelength interval using dual-wavelength Brillouin pumping. The generation of multi-wavelength output in BEFL is based on the combination of stimulated Brillouin scattering (SBS) and four-wave mixing (FWM) effect in a fiber cavity. The tunable wavelength interval is determined by the artificially controlled wavelength interval of the pumping lasers. The BEFL could compress a 1 MHz pump laser to a 340 Hz Brillouin Stokes laser, which proves the BEFL has excellent capability of linewidth compression. An erbium-doped fiber pumped by 980 nm laser is inserted into the cavity to further amplify the Brillouin laser. The wideband multi-wavelength BEFL covering over 50 nm is successfully generated when the 980 nm pump power is 400 mW. These features of multi-wavelength BEFL provide an effective method for optical communication systems and optical fiber sensing.

Abstract:Air lasing emission by launching intense ultrafast laser pulses in atmosphere has recently attracted increasing interest in the ultrafast laser science and atmospheric science fields, especially for remote sensing techniques. We demonstrated the fluorescence emissions at 337 nm, 357 nm and 391 nm induced by multiple filaments using four kinds of step phase plates. Our results have indicated that the fluorescence signal has been amplified as it propagates along the filament through amplified spontaneous emission (ASE), and the fluorescence intensity is also enhanced in the backward direction via multiple filaments. Furthermore, the gain coefficient through ASE is increased with the number of filaments.

Abstract:In this paper, an optically transparent broadband absorbing metamaterial is designed for electromagnetic protection and stealth for visible parts of ships. Based on the coupling resonance loss of double-lay metamaterial structure, the new absorbing material realizes broadband characteristics. Based on the photoelectric compatibility characteristics of graphene thin films, the new absorbing material realizes high transmittance characteristics. The measured results show that when the absorbing rate is higher than 90%, the bandwidth of the absorbing metamaterial is 7.95—18.65 GHz, covering X-band (7.95—12 GHz) and Ku-band (12—18.65 GHz), and the visible light transmittance is 85%. The design and preparation of new absorbing material can solve electromagnetic compatibility (EMC) design problems of high transmittance and broadband. It can be widely used in observation windows of ships, aircraft and reconnaissance control vehicle, display terminal of the information system.

Abstract:For the PANDA ring-core polarization-maintaining few-mode fiber (RC-PM-FMF) with the given supported eigenmodes, the minimum effective refractive index difference min(Dneff) between the adjacent eigenmodes decreases with the RC size. Consequently, we propose a PANDA RC-PM-FMF assisted by a ring-sector (RS) structure, which can be used to mainly increase the Dneff values between the adjacent even and odd eigenmodes with the same polarization. The RS-RC-PM-FMF with an appropriate choice of the parameters can support 10 linearly polarized (LP) eigenmodes, which have min(Dneff) values higher than 1.9´10-4 for the adjacent eigenmodes over the whole C + L band. Furthermore, the fiber is characterized by the low group velocity dispersion (GVD) (−40—20 ps.nm-1.km-1) and effective mode areas (63—104 mm2), while the total losses are within the range of 0.19—0.23 dB/km over the whole band.

Abstract: Ceramic sanitary products with complex curved surfaces are generally fragile and difficult to clamp. If the industrial robot is utilized to realize the automatic grinding of such products, the precise positioning of the product is required firstly. In this paper, an accurate pose measurement system for complex curved surface parts is designed by point cloud registration algorithm. In order to improve the stability of the system, this paper combines the advantages of normal vector features and fast point feature histogram (FPFH) features, and proposes a point cloud registration algorithm based on the rapid extraction of local feature points. Experimental results verify that the improved algorithm has improved both efficiency and accuracy, and the system can effectively achieve accurate positioning of products.

Abstract:Cell confluence is an important metric to determine the growth and the best harvest time of adherent cells. At present, the evaluation of cell confluence mainly relies on experienced labor, and thus it is not conducive to the automated cell culture. In this paper, we proposed an improved U-Net algorithm (called DU-Net) for the segmentation of adherent cells. First, the general convolution was replaced by the dilated convolution to expand the receptive fields for feature extraction. Then, the convolutional layers were combined with the batch normalization layers to reduce the dependence of the network on initialization. As a result, the segmentation accuracy and F1-score of the proposed DU-Net for adherent cells with low confluence (<50%) reached 96.94% and 93.87%, respectively, and for those with high confluence (≥50%), they reached 98.63% and 98.98%, respectively. Further, the paired t-test results showed that the proposed DU-Net was statistically superior to the traditional U-Net algorithm.