Fabrication of elliptical-silica microfiber for ultrasound detection.

Elliptical shape microfiber enables many higher order modes compared with a circular microfiber. The small difference in the optical path length among many modes enabled multi-resonance peaks with high contrast in Mach-Zehnder (MZI) interferometers, which allows a large dynamic range and minimum detection sensitivity for broadband ultrasound sensing. In this paper, we present the design and fabrication of an ultra-compact elliptical-silica microfiber utilizing off-axis flame-drawing for ultrasound detection. The narrow transmission peak showed high contrast for ultrasensitive ultrasound wave detection. With a major-axis diameter of 6.25 µm, the elliptical-silica microfiber sensor exhibits a broadband ultrasound frequency response spanning from 20 kHz to 38.5 MHz. Furthermore, it achieves a signal-to-noise ratio (SNR) of up to 80 dB at 1 MHz, which is the resonance frequency of the microfiber and the linear response under driving voltages of 3-10 V for the PZT ultrasound generator. This low-cost microfiber sensor offers exceptional sensitivity across a broad ultrasonic bandwidth response, making it an ideal choice for nondestructive testing (NDT) and medical imaging applications. Its compact size and immunity to electric and magnetic fields further enhance its utility in various environments.

Estrogen deficiency accelerates postmenopausal atherosclerosis by inducing endothelial cell ferroptosis through inhibiting NRF2/GPX4 pathway.

Oxidative stress and lipid metabolism disorder caused by estrogen deficiency are regarded as the main causes of postmenopausal atherosclerosis, but the underlying mechanisms remain still unclear. In this study, ovariectomized (OVX) female ApoE-/- mice fed with high-fat diet were used to imitate postmenopausal atherosclerosis. The atherosclerosis progression was significantly accelerated in OVX mice, accompanied by the upregulation of ferroptosis indicators, including increased lipid peroxidation and iron deposition in the plaque and the plasma. While both estradiol (E2) and ferroptosis inhibitor ferrostatin-1 alleviated atherosclerosis in OVX mice, with the inhibition of lipid peroxidation and iron deposition, as well as the upregulation of xCT and GPX4, especially in endothelial cells. We further investigated the effects of E2 on ferroptosis in endothelial cells induced by oxidized-low-density lipoprotein or ferroptosis inducer Erastin. It was found that E2 exhibited anti-ferroptosis effect through antioxidative functions, including improving mitochondrial dysfunction and upregulating GPX4 expression. Mechanistically, NRF2 inhibition attenuated the effect of E2 against ferroptosis as well as the upregulation of GPX4. Our findings revealed that endothelial cell ferroptosis played a pivotal role in postmenopausal atherosclerosis progression, and the NRF2/GPX4 pathway activation contributed to the protection of E2 against endothelial cell ferroptosis.

Cigarette tar accelerates atherosclerosis progression via RIPK3-dependent necroptosis mediated by endoplasmic reticulum stress in vascular smooth muscle cells.

BACKGROUND: Tar is the main toxic of cigarettes, and its effect on atherosclerosis progression and the underlying mechanisms remain largely unknown. Vascular smooth muscle cells (VSMCs) play a key role in atherogenesis and plaque vulnerability. The present study sought to investigate the mechanism of atherosclerosis progression through tar-induced VSMC necroptosis, a recently described form of necrosis. METHODS: The effect of tar on atherosclerosis progression and VSMC necroptosis was examined in ApoE-/- mice and cultured VSMCs. The role of necroptosis in tar-induced plaque development was evaluated in RIPK3-deletion mice (ApoE-/-RIPK3-/-). The key proteins of necroptosis in carotid plaques of smokers and non-smokers were also examined. Quantitative proteomics of mice aortas was conducted to further investigate the underlying mechanism. Pharmacological approaches were then applied to modulate the expression of targets to verify the regulatory process of tar-induced necroptosis. RESULTS: Tar administration led to increased atherosclerotic plaque area and reduced collagen and VSMCs in ApoE-/- mice. The expression of RIPK1、RIPK3、and MLKL in VSMCs of plaques were all increased in tar-exposed mice and smokers. RIPK3 deletion protected against VSMC loss and plaque progression stimulated by tar. In mechanistic studies, quantitative proteomics analysis of ApoE-/- mice aortas suggested that tar triggered endoplasmic reticulum (ER) stress. PERK-eIF2α-CHOP axis was activated in tar-treated VSMCs and atherosclerotic plaque. Inhibition of ER stress using 4PBA significantly reduced plaque progression and VSMC necroptosis. Further study revealed that ER stress resulted in calcium (Ca2+) release into mitochondria and cytoplasm. Elevated Ca2+ levels lead to mitochondrial dysfunction and excessive reactive oxygen species (ROS) production, which consequently promote RIPK3-dependent necroptosis. In addition, Ca2+/calmodulin-dependent protein kinase II (CaMKII) activated by cytosolic Ca2+ overload binds to RIPK3, accounting for necroptosis. CONCLUSION: The findings revealed that cigarette tar promoted atherosclerosis progression by inducing RIPK3-dependent VSMC necroptosis and identified novel avenues of ER stress and Ca2+ overload.

Homocysteine promotes atherosclerosis through macrophage pyroptosis via endoplasmic reticulum stress and calcium disorder.

BACKGROUND: Elevated plasma homocysteine levels, known as hyperhomocysteinemia, have been identified as an independent risk factor for atherosclerosis and related cardiovascular diseases. Macrophage pyroptosis-mediated inflammation is crucial in the development of atherosclerosis, but the underlying mechanisms remain unclear. METHODS: A hyperhomocysteinemia atherosclerotic model with ApoE-/- mice fed with a high-methionine diet was constructed to investigate the role of plasma homocysteine in atherosclerosis. THP-1-derived macrophages were used to investigate the mechanisms by which Hcy regulates pyroptosis. RESULTS: We found that hyperhomocysteinemia resulted in larger atherosclerotic plaques and more secretion of inflammatory cytokines, while these effects were attenuated in Caspase-1 knockdown mice. Likewise, in vitro experiments demonstrated that treatment of macrophages with homocysteine resulted in NLRP3 inflammasome activation and pyroptosis, as evidenced by cleavage of Caspase-1, production of downstream IL-1ß, elevation of lactate dehydrogenase activity, and extensive propidium iodide-positive staining of cells. These were all inhibited by Caspase-1 inhibitor. In addition, excessive generation of reactive oxygen species was associated with mitochondrial dysfunction, characterized by loss of mitochondrial membrane potential and ATP synthesis. Moreover, further experiments revealed that homocysteine induced endoplasmic reticulum stress, enhanced communication between the endoplasmic reticulum and mitochondria, and consequently contributed to calcium disorder. Furthermore, the endoplasmic reticulum stress inhibitor, 4PBA, the calcium chelator, BAPTA, and calcium channel inhibitor, 2-APB significantly improved macrophage pyroptosis. CONCLUSION: Homocysteine accelerates atherosclerosis progression by enhancing macrophages pyroptosis via promoting endoplasmic reticulum stress, endoplasmic reticulum-mitochondria coupling, and disturbing of calcium disorder.

Self-injection locking of a low-noise erbium-doped random fiber laser by a random fiber grating ring.

We demonstrate a self-injection locking (SIL) in an Er-doped random fiber laser by a high quality factor (high-Q) random fiber grating ring (RFGR) resonator, which enables a single-mode narrow-linewidth lasing with ultra-low intensity and frequency noise. The RFGR resonator includes a fiber ring with a random fiber grating to provide random feedback modes and noise suppression filters with self-adjusted peak frequency adaptable to small perturbations allowing single longitudinal mode over 7000 s with frequency jitter below 3.0 kHz. Single-mode operation is accomplished by carefully controlling phase delays and mode coupling of resonant modes between main ring and RFGR with a side-mode suppression ratio of 70 dB and narrow linewidth of 1.23 kHz. The relative intensity noise is -140 dB/Hz above 100 kHz and the frequency noise is 1 Hz/Hz1/2 above 10 kHz.

Orthogonal polarization multi-wavelength Brillouin random fiber laser with triple Brillouin frequency shift space.

A novel multi-wavelength Brillouin random fiber laser with the channel space of triple Brillouin frequency shift and high polarization orthogonality between adjacent wavelengths (TOP-MWBRFL), to the best of our knowledge, is experimentally demonstrated. The TOP-MWBRFL is structured in a ring form by cascading two Brillouin random cavities of single-mode fiber (SMF) and one Brillouin random cavity of polarization-maintaining fiber (PMF). Based on polarization pulling properties of stimulated Brillouin scattering in long-distance SMFs and PMFs, the states of polarization (SOPs) of lasing light from SMF random cavities are linearly bounded to the SOPs of local pump light, whereas the SOP of lasing light from the PMF random cavity is strictly clamped on one of the principal axes of the PMF. Thus, the TOP-MWBRFL can stably emit multi-wavelength light with high polarization extinction ratio (>35d B) between adjacent wavelengths without precise polarization feedback. In addition, the TOP-MWBRFL can also work in one polarization mode to stably lase multi-wavelength light with SOP uniformity as high as 37 dB.

Apigenin inhibits macrophage pyroptosis through regulation of oxidative stress and the NF-κB pathway and ameliorates atherosclerosis.

Pyroptosis plays an important role in inflammatory diseases such as viral hepatitis and atherosclerosis. Apigenin exhibits various bioactivities, particularly anti-inflammation, but its effect on pyroptosis remains unclear. The aim of this study is to investigate the effect of apigenin on pyroptosis and explore its potential against inflammatory diseases. THP-1 macrophages treated by lipopolysaccharides/adenosine 5'-triphosphate were used as the in vitro pyroptosis model. Western blot was used to detect the expression of NLRP3 inflammasome components and key regulators. Immunofluorescence was used to observe ROS production and intracellular location of p65. The potential of apigenin against inflammatory diseases was evaluated using atherosclerotic mice. Plaque progression was observed by pathological staining. Immunofluorescence was used to observe the expression of NLRP3 inflammasome components in plaques. The results showed that apigenin inhibited NLRP3 inflammasome activation. Apigenin reduced ROS overproduction and inhibited p65 nuclear translocation. Additionally, apigenin decreased the expression of NLRP3 inflammasome components in the plaque. Plaque progression was inhibited by apigenin. In conclusion, apigenin exhibited a preventive effect on macrophage pyroptosis by reducing oxidative stress and inhibiting the NF-κB pathway. Apigenin may alleviate atherosclerosis at least partially by inhibiting macrophage pyroptosis. These findings suggest apigenin to be a promising therapeutic agent for inflammatory diseases.

Distributed Impact Wave Detection in Steel I-Beam with a Weak Fiber Bragg Gratings Array.

In this paper, acoustic, dynamic and static strain variations along a steel I-beam generated by an impact load are reconstructed simultaneously within a single measurement. Based on the chirped pulse φ-OTDR system with the single-shot measurement technique, both a higher strain-sensing resolution and a higher measurable vibration frequency are achieved. In addition, a weak fiber Bragg gratings array (WFBGA) with enhanced Rayleigh reflection is employed as a sensor, providing high signal-to-noise ratio Rayleigh traces, resulting in lower measurement uncertainty. In the experiments, the damping constant and fundamental frequency of the damped harmonic oscillator could then be measured based on the recovered strain variation profile for further structural health analysis. Compared with commercial strain gauges, linear potentiometers, and OFDR systems, the proposed sensing system ensures a distributed, quantitative, and high-frequency sensing ability, with an extensive range of potential applications.

Sensitivity enhancement of fiber optical polarimetric sensors using self-induced nonlinear phase modulation via the Kerr effect.

This work presents an analytical model accounting for the impact of optical polarization on the generation of frequency sidebands by the Kerr effect in a highly nonlinear fiber. Theoretical analysis shows that for a relative polarization angle, α, between two input lasers expressed on the Poincaré sphere, the optical power of the nth order sideband is proportional to cos 2n(α/2). This theoretical result enables a novel all-optical technique for interrogating changes in polarization with higher sensitivity than conventional measurement schemes using linear polarizers. The predicted theoretical relationship between the sideband power and the relative polarization angle is verified experimentally and sensitivity enhancement by a factor of 1.45 compared to a conventional polarimetric sensor is demonstrated for the 3rd order sideband. This novel nonlinear approach, which allows dynamic range to be traded for an enhanced ability to detect small polarization variations, has potential applications in fusion reactor monitoring, instrumentation and material characterization.

Distributed birefringence sensing at 10-9 accuracy over ultra-long PMF by optical frequency comb and distributed Brillouin amplifier.

Brillouin dynamic gratings (BDG) can measure the distributed birefringence of polarization-maintaining fibers (PMF), however, its sensing range is limited by both stimulated Brillouin scattering depletion and fiber losses in PMF, which are significantly higher than those in standard single-mode fibers. In this work, we theoretically and experimentally verify that BDG can be sustained over ultra-long distances when assisted by distributed Brillouin amplification, significantly extending the distributed birefringence measurement distance. Using an optical frequency comb pumped by a narrow linewidth laser to both generate and interrogate the amplified BDG, a birefringence measurement accuracy of 7.5 × 10-9 was achieved over 7 km sensing length, more than double the longest range reported. This opens a new opportunity to investigate small birefringence changes due to nonlinear optics effects and monitoring fiber network security from eavesdropping.

Generation of high performance optical chirped pulse for distributed strain sensing application with high strain accuracy and larger measurement range.

A photonic approach for generating low frequency drifting noise, arbitrary and large frequency chirping rate (FCR) optical pulses based on the Kerr effect in the nonlinear optical fiber is theoretically analyzed and experimentally demonstrated. Due to the Kerr effect-induced sinusoidal phase modulation in the nonlinear fiber, high order Kerr pulse with a large chirping rate is generated. In the concept-proof experiments, the FCR of the mth Kerr pulse has been significantly improved by a factor of 2m+1. In addition, dynamic strain measurement along with a random fiber grating array (RFGA) sensor by using different order Kerr pulse is carried out for demonstrating a large strain measurement range with lower uncertainty sensing capability. Benefiting from the use of a single laser source and large FCR Kerr pulse, the system exhibits a 3.9 µÉ› static strain measurable range, 0.24 µÉ› measurement uncertainty by using -4th order Kerr pulse that has an FCR up to 0.8 GHz/ns. Note that the FCR of the chirped pulse could be further enhanced by using larger FCR chirped pulse seed or choosing higher order Kerr pulses.

Distributed temperature profile in hydrogen flame measured by telecom fiber and its durability under flame by OFDR.

The distributed temperature profile of hydrogen flame based on optical frequency-domain reflectometry (OFDR) was experimentally demonstrated for the first time. Spatial temperature field at different flow rate of H2 flame was monitored by OFDR via a telecom fiber (Corning SMF-28, CPC6) inside the flame over seconds, and the highest temperature is on the sides of center flame separated by ∼1.4mm with difference of 140∼190°C over the flame dimension of 2.5 mm above 900°C. Uniformity level of temperature is studied by varying the distance between fiber and tube entrance, and the largest uniform region over 1-millimeter length of fiber is obtained. Rayleigh scatters correlation coefficient decreases with temperature to 90% around 400°C, further reduces to 70% about 800°C, and 50% roughly at 1000°C. It indicates that a nonlinear thermal sensitivity of SMF is expected for temperature higher than 400°C with OFDR measurement. The durability of single-mode fiber under H2 flame is studied via decorrelation time at various temperature. It maintains 20s at 880°C with correlation coefficient around 68% and drops to 50% decorrelation at 1000°C over 20s. This information is important for high temperature measurement using telecom fiber over 800°C based on OFDR. A maximum temperature of 1100°C was measured by OFDR, and it is possible for higher temperature measurement beyond of 1100°C with quicker system response time (<1s).

All-optical polarimeter for laser Stokes vector measurement using self-induced nonlinear phase modulation.

This paper utilizes an analytical model of polarization dependent frequency sideband generation via the Kerr effect in a highly nonlinear fiber to determine the state of polarization (SOP) of a laser by all-optical means. Theoretical analysis shows that the power of the nth order sideband generated by the propagation of two lasers with distinct frequencies in the nonlinear medium is proportional to cos 2n(α/2), where α is the angle between the normalized Stokes vectors representing the SOPs of the lasers on the Poincaré sphere. By tailoring the SOP of one laser acting as a reference and experimentally measuring the power of the first order sideband, the SOP of the laser under test is recovered with an error smaller than 10.22° on the Poincaré sphere corresponding to 0.8% the sphere's total area. Comparing the SOPs of two lasers without referencing them to fixed polarizers enables potential applications in remote environmental sensing, novel polarization division multiplexing schemes for enhanced telecommunication data rates, and scientific instrumentation.

Broadband ultrasound sensing based on fused dual-core chalcogenide-PMMA microfibers.

High-frequency ultrasound sensors are essential for high-resolution medical ultrasonic imaging and industrial ultrasonic non-destructive monitoring. In this paper, we propose highly sensitive broadband ultrasound sensors based on fused dual-core chalcogenide-polymethyl methacrylate (As2Se3-PMMA) microfibers. We demonstrate that ultrasound response is determined by the differential slope of transmission spectra in the dual-core microfiber, which is verified by detecting the acoustic response in various microfibers of different tapering parameters. A broadband ultrasound frequency range with a high signal-to-noise ratio (SNR) is achieved in the fused dual-core microfiber (DCM) with a sub-micron core diameter and a close core separation due to the large spectral slope at the quadrature points of the transmission spectrum. In addition, we experimentally demonstrate the sensing of ultrasound waves propagating with and without an aluminum plate in the DCM sensor. An ultrasound sensor with a broadband frequency range from 20 kHz to 80 MHz and an average SNR of 31 dB is achieved in a compact fused dual-core As2Se3-PMMA microfiber when it is directly placed on a piezoelectric transducer (PZT).

Stabilizing Brillouin random laser with photon localization by feedback of distributed random fiber grating array.

Strong scattering random media can localize light and extend photon lifetime through multiple scattering, which offers opportunities for stabilizing random lasers. Here, we demonstrate a frequency stabilized Brillouin random laser with high coherence enabled by photon localization in random fiber grating array (RFGA). Photon trapping is realized due to wave interference in multi-scattering Fabry-Pérot (FP) cavities between random fiber gratings enabling light localization to prolong photon lifetime. The formation of the high finesse peaks of RFGA suppresses multi-longitudinal modes, which offers single-mode operation at high pump power. The RFGA distributed feedback-based Brillouin random fiber laser (BRFL) maintains a small frequency drift with the pump laser (a phase-locked laser with a linewidth of 100 Hz) at 51 kHz/s for a total change of 620 kHz over 12 s. Note there is no locking between the two lasers, and the beat frequency is measured by the optical heterodyne method. The correlation coefficient change of the measured optical beat frequency is maintained at 4.5%. This indicates that the BRFL is capable of maintaining a small optical frequency difference with the phase-locked pump laser over 12 s thanks to the RFGA capable of trapping photons in the same path, which is a remarkable feature for a random fiber laser. Furthermore, we confirm the single-mode lasing with a long lifetime in the stabilizing BRFL by the replica symmetry behavior and ultralow intensity noise at high pump power. Our findings explore a new approach to stabilize the frequency of Brillouin random lasers passively without commonly used active phase locking laser themes, which makes a simple and cost-effective system.

Monitoring local temperature and longitudinal strain along a nonuniform As2Se3-PMMA tapered fiber by Brillouin gain-profile tracing.

The local temperature and longitudinal strain at spatial resolution of 0.5% of the pulse-width equivalent length along a nonuniform As2Se3-PMMA tapered fiber is investigated by a Brillouin gain-profile tracing method. This scheme uses a 20 ns pump pulse with the pulse-width equivalent length longer than the fiber under test (FUT) of 50 cm nonuniform As2Se3-PMMA tapered fiber. The whole interaction process of long pump pulse is investigated including pump pulse entering the FUT, overlapping completely with FUT and leaving the FUT. The evolution of Brillouin gain spectrum (BGS) along the nonuniform fiber is formed by the subtraction of frequency-domain BGS of two adjacent sensing points in the trailing edge (where the pump pulse leaves the FUT) of the BOTDA spectrum. The trailing part is preferred due to the pre-amplified acoustic field by the long pumping pulse. Then the local responses of temperature and wide-range longitudinal strain with high spatial resolution of 1.1 cm along the nonuniform As2Se3-PMMA tapered fibers are investigated. The change of the local temperature and strain shifts the BGS that is different along the nonuniform fibers, which forms the distributed measurement. The spatial resolution, the fiber length of the detected section in the proposed method, is 1.1 cm for the local temperature and longitudinal strain measurement, which is 0.5% of the pulse-width equivalent length and is limited by the sampling rate of data acquisition and the fall-time of the pump pulse.

Reducing frequency fluctuation in a Brillouin random fiber laser by a random fiber grating ring resonator.

Frequency fluctuation is a major problem in high-precision metrology as real-time optical frequency measurement is not available with commercial photodetectors; alternatively, frequency-stabilized lasers as a reference are also not accessible in most laboratories. In this study, we propose and demonstrate a polarization-maintaining random fiber grating ring (PM-RFGR) resonator in a PM Brillouin random fiber laser (BRFL) to achieve sub-MHz frequency drift, which is measured by the optical beat of the random laser and the pump laser. Experimental results show that longitudinal modes are suppressed in the BRFL owing to the feedback of the RFGR resonating with one longitudinal mode of the random laser. The BRFL shows mode-hopping-free operation over 14.9 s due to the self-adjustment of random modes with small frequency difference to thermal and acoustic variations and self-injection locking through RFGR. As a result, a small frequency drift of ∼340 kHz with single-longitudinal mode is achieved in the BRFL enabled by the RFGR, which offers an all optical locking mechanism for optical frequency stabilization.

Frequency-stabilized Brillouin random fiber laser enabled by self-inscribed transient population grating.

A frequency-stabilized Brillouin random fiber laser (BRFL) realized by a self-inscribed transient population grating (TPG) is proposed and demonstrated for the first time, to the best of our knowledge. The TPG is formed via the redistribution of the population in erbium-doped fibers (EDFs) by bidirectionally injected phonon-controlled random laser beams. Long-lifetime metastable ion states in EDFs basically prolonged the time dynamics of a stimulated Brillouin scattering (SBS) laser up to milliseconds. Consequently, significant random modes are suppressed with low relative intensity noise, owing to reduced mode hopping in a Stokes random laser, hence one dominating lasing mode at milliseconds of lifetime is established from the competition of numerous random modes, which is proved theoretically and experimentally via TPG.

Oxidative Stress-Mediated Programmed Cell Death: a Potential Therapy Target for Atherosclerosis.

Nowadays, as a type of orderly and active death determined by genes, programmed cell death (PCD), including apoptosis, pyroptosis, ferroptosis, and necroptosis, has attracted much attention owing to its participation in numerous chronic cardiovascular diseases, especially atherosclerosis (AS), a canonical chronic inflammatory disease featured by lipid metabolism disturbance. Abundant researches have reported that PCD under distinct internal conditions fulfills different roles of atherosclerotic pathological processes, including lipid core expansion, leukocyte adhesion, and infiltration. Noteworthy, emerging evidence recently has also suggested that oxidative stress (OS), an imbalance of antioxidants and oxygen free radicals, has the potential to mediate PCD occurrence via multiple ways, including oxidization and deubiquitination. Interestingly, more recently, several studies have proposed that the mediating mechanisms could effect on the atherosclerotic initiation and progression significantly from variable aspects, so it is of great clinical importance to clarify how OS-mediated PCD and AS interact. Herein, with the aim of summarizing potential and sufficient atherosclerotic therapy targets, we seek to provide extensive analysis of the specific regulatory mechanisms of PCD mediated by OS and their multifaceted effects on the entire pathological atherosclerotic progression.

U-shape core-offset fiber sensor with submicrostrain resolution over a 35 millistrain range.

Large strain with submicro resolution is essential for steel structural monitoring; however, the fiber base sensors are limited by the glass extension to be less than 1%. Here, we propose a U-shape core-offset fiber sensor including four fiber segments to realize a large strain sensor. Four fiber segments with slight length differences in between are core-offset fused together to achieve U-shape spring-like microstructure fiber for large transverse bending radius. The reflected high-order modes at three silica/air interfaces interfere to give a broad spectrum due to unequal segment length, which enables continuous strain detection over 35 mɛ. The air and glass hybrid structure of the device enables the large bending, and hence compression and tension measurement can be achieved simultaneously. The strain sensitivity is up to 20.75 pm/µÉ› with the strain accuracy of 0.5 µÉ›. This novel, to the best of our knowledge, core-offset fiber has high strain sensitivity and large strain range for compression and tension strain measurement. Furthermore, the proposed strain sensor can be fabricated easily for practical applications where large strain with high strain accuracy is needed.