High-Sensitivity Temperature Sensor Based on Fiber Fabry-Pérot Interferometer with UV Glue-Filled Hollow Capillary Fiber.

Optical fiber Fabry-Pérot (FP) interferometer sensors have long been the focus of researchers in sensing applications because of their simple light path, low cost, compact size and convenient manufacturing methods. A miniature and highly sensitive optic fiber temperature sensor using an ultraviolet glue-filled FP cavity in a hollow capillary fiber is proposed. The sensor is fabricated by fusion splicing a single-mode fiber with a hollow capillary fiber, which is filled with ultraviolet glue to form a FP cavity. The sensor has a good linear response in the temperature testing and high-temperature sensitivity, which can be increased with the length of the FP cavity. The experimental results show that the temperature sensitivity reaches 1.174 nm/°C with a high linear response in the range of 30-60 °C. In addition, this sensor is insensitive to pressure and can be highly suitable for real-time water temperature monitoring for ocean research. The proposed ultraviolet glue-filled structure has the advantages of easy fabrication, high-temperature sensitivity, low cost and an arbitrary length of capillary, which has broad application prospects for marine survey technology, biological diagnostics and environmental monitoring.

Optical Fiber Probe Microcantilever Sensor Based on Fabry-Perot Interferometer.

Optical fiber Fabry-Perot sensors have long been the focus of researchers in sensing applications because of their unique advantages, including highly effective, simple light path, low cost, compact size, and easy fabrication. Microcantilever-based devices have been extensively explored in chemical and biological fields while the interrogation methods are still a challenge. The optical fiber probe microcantilever sensor is constructed with a microcantilever beam on an optical fiber, which opens the door for highly sensitive, as well as convenient readout. In this review, we summarize a wide variety of optical fiber probe microcantilever sensors based on Fabry-Perot interferometer. The operation principle of the optical fiber probe microcantilever sensor is introduced. The fabrication methods, materials, and sensing applications of an optical fiber probe microcantilever sensor with different structures are discussed in detail. The performances of different kinds of fiber probe microcantilever sensors are compared. We also prospect the possible development direction of optical fiber microcantilever sensors.

High-Temperature Measurement of a Fiber Probe Sensor Based on the Michelson Interferometer.

In this paper, a fiber probe high-temperature sensor based on the Michelson Interferometer (MI) is proposed and experimentally verified. We used a fiber splicing machine to fabricate a taper of the single-mode fiber (SMF) end. The high order modes were excited at the taper, so that different modes were transmitted forward in the fiber and reflected by the end face of the fiber and then recoupled back to the fiber core to form MI. For comparison, we also coated a thin gold film on the fiber end to improve the reflectivity, and the reflection intensity was improved by 16 dB. The experimental results showed that the temperature sensitivity at 1506 nm was 80 pm/°C (100 °C~450 °C) and 109 pm/°C (450 °C~900 °C). The repeated heating and cooling processes showed that the MI structure had good stability at a temperature up to 900 °C. This fiber probe sensor has the advantages of a small size, simple structure, easy manufacturing, good stability, and broad application prospects in industrial and other environments.

Tin diselenide-based saturable absorbers for eye-safe pulse lasers.

Eye-safe pulse lasers have attracted increasing attention due to their potential wide application in many fields. However, optical modulators with excellent nonlinear optical absorption properties in the range of 1.4-2.1 µm are still very scarce. In this study, tin diselenide (SnSe2), a newly-developed 2D layered semiconductor material with facile processability and low cost, was investigated. The nonlinear optical response of SnSe2 was investigated using the open aperture Z-scan method at 1500 and 1800 nm. Using SnSe2 as the saturable absorber, a passive Q-switched solid-state laser was realized at 1.3 and 1.9 µm for the first time. This study proved SnSe2 to be an effective optical modulating material for the eye-safe waveband.

Micro-bending vector sensor based on six-air-hole grapefruit microstructure fiber using lateral offset splicing.

A one-dimensional micro-bending vector sensor based on two-mode interference has been introduced. This device was fabricated by lateral offset splicing a piece of six-air-hole grapefruit microstructure fiber (GMF) with single mode fiber (SMF). Variation of effective mode index occurred by micro-bending was investigated in simulation and experiment. This device exhibits micro-bending sensitivities of 0.441 nm/m(-1) and -0.754 nm/m(-1) at 0° and 180° bending orientations, respectively. Moreover, this sensor is immune to surrounding refractive index (SRI) and presents a low crosstalk of temperature.

Characterization of kidneys in patients with systemic sclerosis by multi-parametric magnetic resonance quantitative imaging.

PURPOSE: To determine the usefulness of multiparametric magnetic resonance (MR) quantitative imaging in characterizing the kidneys in systemic sclerosis (SSc) patients. MATERIAL AND METHODS: Forty-six SSc patients (47.9 ± 12.8 years, 40 females) and 22 age- and sex- matched healthy volunteers (46.1 ± 13.8 years, 20 females) were recruited and underwent renal MR imaging by acquiring blood oxygen level dependent and saturated multi-delay renal arterial spin labeling (SAMURAI) sequences. The T2* value, T1 value, renal blood flow (RBF), arterial bolus arrival time (aBAT), and tissue bolus arrival time (tBAT) of renal cortex were measured and compared among diffuse cutaneous SSc (dcSSc) and limited cutaneous SSc (lcSSc) groups and healthy controls using One-way ANOVA and analyzed by logistic regression. RESULTS: Compared to healthy volunteers, SSc patients with normal estimated glomerular filtration rate (n = 40) had significantly lower T2* value (P = 0.026) in the left renal cortex, longer T1 value (right: P = 0.015; left: P = 0.023), lower RBF (right: P < 0.001; left: P < 0.001), and shorter tBAT (right: P < 0.001; left: P = 0.005) in both right and left renal cortex after adjusting for demographics. The dcSSc patients (n = 23) had significantly lower RBF in both right (226.7 ± 65.2 mL/100 g/min vs. 278.2 ± 73.5 mL/100 g/min, P = 0.022) and left (194.5 ± 71.5 mL/100 g/min vs. 252.7 ± 84.4 mL/100 g/min, P = 0.020) renal cortex compared to the lcSSc patients (n = 23) after adjusting for demographics, but the significance of the difference was attenuated after further adjusting for modified Rodnan skin score and digital ulcers. CONCLUSION: Multi-parametric MR quantitative imaging, particularly multi-delay ASL perfusion imaging, is a useful technique for characterizing the kidneys and classification of SSc patients.

Diode-pumped simultaneously Q-switched and mode-locked YVO4/Nd:YVO4/YVO4 crystal self-Raman first-Stokes laser.

A diode-end-pumped simultaneously Q-switched and modelocked self-Raman YVO(4)/Nd:YVO(4)/YVO(4) laser at first-Stokes wavelength of 1175.9 nm was demonstrated. The shortest mode-locked pulse width of the laser was obtained to be ~23.57 ps, with the corresponding timebandwidth product of ~0.51. The maximum average output power, the highest pulse energy and the highest peak power were obtained to be 1.83 W, 6.1 µJ and 220 kW, respectively. The nonlinear Raman process improved the Q-switched mode-locking performance of the Stokes pulses.

Ambient refractive index-independent bending vector sensor based on seven-core photonic crystal fiber using lateral offset splicing.

A novel, simple, and compact optical fiber directional bending vector sensor based on Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The device consists of a piece of seven-core photonic crystal fiber (PCF) sandwiched between two single mode fibers (SMFs) with a lateral offset splicing joint that covering two cores of PCF. Bending sensitivity of the seven-core PCF based MZI is changed by an axial rotation angle, which shows its capacity for recognizing positive and negative directions. Within a curvature range of -7.05 m-1 to 7.05 m-1, the calculated bending sensitivities of two resonant central wavelengths with opposite fiber orientations are 1.232 nm/m-1 and 1.174 nm/m-1, respectively. This novel MZI is formed by invoking interference between the LP01-like supermode and other higher order supermodes in the core, which leads to insensitive to ambient refractive index (ARI). We have also investigated the transmission characteristics of the sensor with the temperature change.

A Real-Time Non-Implantation Bi-Directional Brain-Computer Interface Solution Without Stimulation Artifacts.

The non-implantation bi-directional brain-computer interface (BCI) is a neural interface technology that enables direct two-way communication between the brain and the external world by both "reading" neural signals and "writing" stimulation patterns to the brain. This technology has vast potential applications, such as improving the quality of life for individuals with neurological and mental illnesses and even expanding the boundaries of human capabilities. Nonetheless, non-implantation bi-directional BCIs face challenges in generating real-time feedback and achieving compatibility between stimulation and recording. These issues arise due to the considerable overlap between electrical stimulation frequencies and electrophysiological recording frequencies, as well as the impediment caused by the skull to the interaction of external and internal currents. To address those challenges, this work proposes a novel solution that combines the temporal interference stimulation paradigm and minimally invasive skull modification. A longitudinal animal experiment has preliminarily validated the feasibility of the proposed method. In signal recording experiments, the average impedance of our scheme decreased by 4.59 kΩ , about 67%, compared to the conventional technique at 18 points. The peak-to-peak value of the Somatosensory Evoked Potential increased by 8%. Meanwhile, the signal-to-noise ratio of Steady-State Visual Evoked Potential increased by 5.13 dB, and its classification accuracy increased by 44%. The maximum bandwidth of the resting state rose by 63%. In electrical stimulation experiments, the signal-to-noise ratio of the low-frequency response evoked by our scheme rose by 8.04 dB, and no stimulation artifacts were generated. The experimental results show that signal quality in acquisition has significantly improved, and frequency-band isolation eliminates stimulation artifacts at the source. The acquisition and stimulation pathways are real-time compatible in this non-implantation bi-directional BCI solution, which can provide technical support and theoretical guidance for creating closed-loop adaptive systems coupled with particular application scenarios in the future.

Diffusing capacity of lungs for carbon monoxide associated with subclinical myocardial impairment in systemic sclerosis: A cardiac MR study.

BACKGROUND: Systemic sclerosis (SSc) is characterised by microvascular and fibrotic lesions, which are located not only in skin but also in lungs and heart. OBJECTIVE: This study aimed to investigate the association between lung function and myocardial T1 values using cardiac MR (CMR) imaging in patients with SSc without cardiovascular symptoms. METHODS: The SSc patients and age- and sex-matched healthy subjects underwent CMR. The cardiac function and native T1 values of myocardium and lung function were measured. Spearman's rank correlations and linear regression analyses were performed to determine the association between lung function and myocardial T1. RESULTS: Forty-five SSc patients (aged 47.7±13.2 years, 40 females) and 23 (aged 46.0±14.4 years, 20 females) healthy subjects were enrolled. SSc patients exhibited considerably higher native T1 values compared with healthy subjects (1305.9±49.8 ms vs 1272.6±37.6 ms, p=0.006). Linear regression analysis revealed that decrease of diffusing capacity of lungs for carbon monoxide (DLCO) in SSc patients was notably associated with myocardial native T1 value before (ß -1.017; 95% CI -1.883 to -0.151; p=0.022) and after adjusting for confounding factors (ß -1.108; 95% CI -2.053 to -0.164; p=0.023). Moderate-to-severe decrease of DLCO was found to be significantly associated with myocardial native T1 value (ß 48.006; 95% CI 17.822 to 78.190; p=0.003) after adjusting for confounding factors. CONCLUSION: DLCO inversely correlates with myocardial native T1 values in SSc patients, particularly moderate-to-severely decreased DLCO, suggesting that DLCO might be a potential indicator for subclinical myocardial impairment in SSc patients.

Minimally Invasive Local-Skull Electrophysiological Modification With Piezoelectric Drill.

The research on non-invasive BCI is nowadays hitting the bottleneck due to the humble quality of scalp EEG signals. Whereas invasive solutions that offer higher signal quality in contrast are suffocated in their spreading because of the potential surgical complication and health risks caused by electrode implantation. Therefore, it puts forward a necessity to explore a scheme that could both collect high-quality EEG signals and guarantee high-level operation safety.This study proposed a Minimally Invasive Local-skull Electrophysiological Modification method to improve scalp EEG signals qualities at specific brain regions. Six eight-month-old SD rats were used for in vivo verification experiment. A hole with a diameter of about 500 micrometers was drilled in the skull above the visual cortex of rats. Significant changes in rsEEG and SSVEP signals before and after modification were observed. After modification, the skull impedance of rats decreases by about 84 %, the average maximum bandwidth of rsEEG increase by 57 %, and the broadband SNR of SSVEP is increased by 5.13 dB. The time of piezoelectric drilling operation is strictly controlled under 30 seconds for each rat to prevent possible brain damage from overheating. Compared with traditional invasive procedures such as ECoG, Minimally Invasive Local-skull Electrophysiological Modification operation time is shorter and no electrode implantation is needed while it remarkably boosts the scalp EEG signal quality. This technical solution has the potential to replace the use of ECoG in certain application scenarios and further invigorate studies in the field of scalp EEG in the future.

Slice-based and time-specific hemodynamic measurements discriminate carotid artery vulnerable atherosclerotic plaques.

BACKGROUND AND OBJECTIVE: Hemodynamic patterns play key roles in progression of carotid vulnerable plaques. However, most of previous studies utilized maximum or averaged value of hemodynamic measurements which is not an ideal representative of hemodynamic patterns. This study aimed to investigate the association of slice-based and time-specific hemodynamic measurements with carotid vulnerable plaque using magnetic resonance (MR) vessel wall imaging and histology. METHODS: Thirty-two patients (mean age: 63.9±8.1 years; 25 males) with carotid atherosclerotic stenosis (≥50% stenosis) referred to carotid endarterectomy were recruited and underwent MR vessel wall imaging. Carotid plaque burden was evaluated on MR images and vulnerable plaque features including calcification, lipid-rich necrotic core, and intra-plaque hemorrhage (IPH) were identified by histology. The slice-based and time-specific hemodynamic measurements were extracted from computational fluid dynamics simulation of 3D carotid arterial model. Correlation coefficients between hemodynamic measurements and carotid plaque features were calculated and the logistic regressions with generalized estimating equation (GEE) were conducted. The value in discriminating carotid vulnerable plaque features was determined by receiver-operating-characteristic analysis. RESULTS: Of 102 MR-histology matched slices from 32 patients, time-averaged wall shear stress (TAWSS) (r=0.263, p=0.008), oscillatory shear index (OSI) (r=-0.374, p<0.001), and peakWSS (r=0.232, p=0.019) were significantly associated with carotid IPH. The logistic regression with GEE revealed that peakWSS (OR, 1.206; 95% CI, 1.026-1.418; p, 0.023) and TAWSS (OR, 0.364, 95% CI, 0.138-0.959; p, 0.041) were significantly associated with presence of IPH after adjusting for age and BMI. In discriminating carotid IPH, the AUC of TAWSS, OSI, combined TAWSS with maximum wall thickness (MWT) and combined OSI with MWT was 0.656, 0.722, 0.761, and 0.764, respectively. CONCLUSIONS: Slice-based and time-specific hemodynamic characteristics could effectively discriminate carotid IPH. Combination of hemodynamic measurements with carotid plaque burden might be a stronger indicator for carotid vulnerable plaque features than each measurement alone.

Polarization dependent visible supercontinuum generation in the nanoweb fiber.

We have fabricated a novel nanoweb fiber with web-like bundle of the fused-silica membranes with different thickness in its cross section. We pumped the 0.55-µm-thick membrane with 200-fs laser pulse at 800-nm just adjacent to its second-zero-dispersion wavelength, and demonstrated the polarization dependent visible supercontinuum (SC). The mode patterns were recorded in detail and analyzed at different polarization angles of incident pulse. The broadband spectrum range from ~350 nm to 950 nm is achieved for TM mode excitation. The tunable visible SC in the nanoweb fiber may be used in the substrate integrated waveguide for sensing.

10.2-W Q-switched intracavity frequency-doubled Nd:YVO(4)/LBO red laser double-end-pumped by laser-diode-arrays.

We report a high-power diode-double-end-pumped Q-switched Nd:YVO4 red laser through intracavity frequency-doubling with a type-I critical phase-matched LBO crystal. At a repetition frequency of 21.72 kHz, a maximum average output power of 10.2 W at 671 nm was measured to while the incident pump power was 78.4 W, the corresponding optical conversion efficiency was 13.0%, with a pulse width of about 94 ns and a pulse energy of 469.6 muJ, the peak power was 5.0 kW. At an average output power around 9.6 W a power stability better than 2.3% was maintained for half an hour.

6-W diode-end-pumped Nd:GdVO4/LBO quasi-continuous-wave red laser at 671 nm.

We report a high-power diode-end-pumped Q-switched Nd:GdVO4 red laser through intracavity frequency-doubling with a type-I critical phase-matched LBO crystal. The maximum average output power at 671 nm was obtained to be 6 W at the repetition frequency of 47 kHz, with the corresponding optical conversion efficiency of 12.8% and the pulse width of about 97 ns. At the average output power around 5 W, the power stability was better than 5.8% for one hour.

High-power intracavity second-harmonic generation of 1.34 microm in BiB3O6 crystal.

The phase-matching curve and effective nonlinear optical coefficient distribution for the second-harmonic generation of 1342 nm in BiB3O6 crystal were calculated. High-power intracavity second-harmonic generation of 1.34 microm in BiB3O6 crystals, at a type-I phase-matching direction of (theta, ø)=(9.07 degrees , 0 degrees ), was performed with a LD-end-pumped Nd:YVO4 laser. The maximum continuous-wave (CW) and quasi-CW output powers at 671 nm were obtained to be 1.22 W and 4.38 W, with the corresponding optical conversion efficiency of 4.9% and 9.5%, respectively.

Pulsed laser output of LD-end-pumped 1.34 mum Nd: GdVO4 laser with Co: LaMgAl11O19 crystal as saturable absorber.

The absorption spectra of the 0.5at.% and 1at.% Co: LaMgAl11O19 (LaMg1-xCoxAl11O19, x=0.005 and 0.01, abbreviated as Co:LMA) crystals were measured at room temperature, and the results show that the Co: LMA crystals have two absorption bands, and the absorption band located at 1030-1660 nm can be used for a passive saturable absorber Q switch of 1.3-1.6mum laser. The passive pulsed laser output of LD-end-pumped Nd:GdVO4 1.34mum laser was demonstrated for the first time by using the 0.5 at.% Co:LMA crystal as a saturable absorber Q switch. The maximum average output power of 500 mW was obtained under the pumping power of 25 W. The shortest pulse width, the largest pulse energy and the highest peak power were obtained to be 160 ns, 25.5muJ and 150 W, respectively.