Formation of E-band luminescence-active centers in bismuth-doped silica fiber via atomic layer deposition.

In this study, a Si defect structure was added into the silica network in order to activate the bismuth and silica structure active center. TD-DFT theoretical simulations show that the Bi and Si ODC(I) models can excite the active center of the E-band at 1408 nm. Additionally, the Bi-doped silica fiber (BDSF) with improved fluorescence was fabricated using atomic layer deposition (ALD) combined with the modified chemical vapor deposition (MCVD) technique. Some tests were used to investigate the structural and optical properties of BDSF. The UV-VIS spectral peak of the BDSF preform is 424 cm-1, and the binding energy of XPS is 439.3 eV, indicating the presence of Bi° atom in BDSF. The Raman peak near 811 cm-1 corresponds to the Bi-O bond. The Si POL defect lacks a Bi-O structure, and the reason for the absence of simulated active center from the E-band is explained. A fluorescence spectrometer was used to analyze the emission peak of a BDSF at 1420 nm. The gain of the BDSF based optical amplifier was measured 28.8 dB at 1420 nm and confirmed the effective stimulation of the bismuth active center in the E-band.

Modeling and calibration of micro/nano FBG temperature probe for scanning probe microscopy.

To accurately measure the local temperatures of the micro-nano area, we propose an optical method using a tapered fiber Bragg grating (FBG) probe with a nano tip for scanning probe microscopy (SPM). When the tapered FBG probe senses local temperature through near-field heat transfer, the intensity of the reflected spectrum decreases, along with a broadening bandwidth and a shift in the central peak position. Modeling the heat transfer between the probe and the sample shows that the tapered FBG probe is in a non-uniform temperature field when approaching the sample surface. Simulation of the probe's reflection spectrum reveals that the central peak position shifts nonlinearly with increasing local temperature. In addition, the near-field temperature calibration experiments show that the temperature sensitivity of the FBG probe increases nonlinearly from 6.2 pm/°C to 9.4 pm/°C as the sample surface temperature increases from 25.3°C to 160.4°C. The agreement of the experimental results with the theory and the reproducibility demonstrate that this method offers a promising approach for exploring micro-nano temperature.

Near 0.5†dB gain per unit length in O-band based on a Bi/P co-doped silica fiber via atomic layer deposition.

In this work, bismuth doped fiber (BDF) and bismuth/phosphosilicate co-doped fiber (BPDF) were fabricated by atomic layer deposition (ALD) combined with the modified chemical vapor deposition (MCVD). The spectral characteristics are studied experimentally and the BPDF has good excitation effect covering the O band. A diode pumped BPDF amplifier with the gain over 20 dB from 1298-1348 nm (50 nm) has been demonstrated. The maximum gain of 30 dB was measured at 1320 nm with a gain coefficient of around 0.5 dB/m. Furthermore, we constructed different local structures through simulation and found that compared with the BDF, BPDF has a stronger excited state and a greater significance in O-band. This is mainly because phosphorus (P) doping changes the associated electron distribution and forms the bismuth-phosphorus active center. The fiber has a high gain coefficient, which is of great significance for the industrialization of O-band fiber amplifier.

Improved Fluorescence and Gain Characteristics of Er-Doped Optical Fiber with PbS Nanomaterials Co-Doping.

Er-doped optical fiber (EDF) with ultra-broad gain bandwidth is urgently needed given the rapid advancement of optical communication. However, the weak crystal field of the host silica glass severely restricts the bandwidth of traditional EDF at 1.5 µm. In this study, we theoretically explored the introduction of PbS nanomaterials in the silica network assisted with the non-bridging oxygen. This can significantly increase the crystal field strength of Er3+ ions in the local structure, leading to their energy level splitting and expanding the fluorescence bandwidth. Additionally, the PbS/Er co-doped optical fiber (PEDF) with improved fluorescence and gain characteristics was fabricated using modified chemical vapor deposition combined with the atomic layer deposition technique. The presence of PbS nanomaterials in the fiber core region, which had an average size of 4 nm, causes the 4I13/2 energy level of Er3+ ions to divide, increasing the fluorescence bandwidth from 32 to 39 nm. Notably, the gain bandwidth of PEDF greater than 20 dB increased by approximately 12 nm compared to that of EDF. The obtained PEDF would play an important role in the optical fiber amplifier and laser applications.

Effects of multi-mode physical stimulation on APP/PS1 Alzheimer's disease model mice.

Some researchers and clinics have reported that non-drug treatments for Alzheimer disease (AD) such as electrical stimulation, light stimulation, music stimulation, laser stimulation, and transcranial magnetic stimulation may have beneficial treatment effects. Following these findings, in this study, we performed multimodel physical stimulation on APP/PS1 mice using visible light, music with a γ rhythm, and an infrared laser. And the effects of physical stimulation on APP/PS1 mice were evaluated by behavioral analysis, the content of amyloid (Aß40 and Aß42), and NISSL staining of hippocampal tissue slices. The results of subsequent behavioral and tissue analyses showed that the multi-model physical stimulations could relieve APP/PS1 mice's dementia symptoms, such as the behavior ability, the content of Aß40 and Aß42 in the hippocampal tissue suspension, and Nissl staining for hippocampal tissue analyses.

Magneto-refractive properties and measurement of an erbium-doped fiber.

The magneto-refractive properties of an erbium-doped fiber (EDF) are investigated by theoretically analyzing the change in mode characteristics with a magnetic field and experimentally measuring it based on a fiber-optic Mach-Zehnder interferometer (MZI). The numerical results indicate that the mode effective refractive index (RI) increases as the magnetic field increases, and the mode field intensity distribution tends to be more concentrated in the core region with an increasing magnetic field. The variation in the mode effective RI of the fundamental mode with the magnetic field is greater than that of the higher-order modes. A magneto-refractive measurement system based on a fiber-optic MZI is set up to analyze the magneto-refractive effect of the EDF. The changes in the mode effective RI measured with a direct-current (DC) magnetic field and with a 100 Hz alternating-current (AC) magnetic field are 4.838×10-6 and 4.245×10-6 RIU/mT, respectively. The experimental results are in reasonable agreement with the theoretical analysis. Furthermore, the error between the experimental and numerical results is discussed. The magneto-refractive properties of the EDF exhibit potential in all-fiber magnetic field or current sensing area.

Simultaneous measurement of magnetic field and temperature based on two anti-resonant modes in hollow core Bragg fiber.

A simple and compact magnetic field and temperature dual-parameter sensor is proposed, which is based on a sandwich structure consisting of a section of hollow core Bragg fiber (HCBF) filled with magnetic fluid (MF) and two sections of single-mode fiber (SMF). The corresponding relationship between the resonant dip with different periods in the transmission spectrum and specific anti-resonant (AR) mode in the HCBF is determined. The resonant dips based on different AR modes shift differently when the magnetic field intensity and temperature change. Then, the simultaneous measurement of the magnetic field intensity and temperature can be achieved by utilizing a cross matrix. The experimental results show that the maximum magnetic field sensitivity in the range of 0-12 mT is 86.43 pm/mT, and the maximum temperature sensitivity in the range of 20-60 ℃ is 17.8 pm/℃. The proposed sensor has the advantages of compact structure, easy fabrication and low cost, thus, it has great potential applications in the field of simultaneous sensing of magnetic field intensity and temperature in complex environments.

Segmenting nailfold capillaries using an improved U-net network.

To assess the microcirculation in a patient's capillaries, clinicians often use the valuable and non-invasive diagnostic tool of nailfold capillaroscopy (NC). In particular, evaluating the images that result from NC is particularly important for diagnosing diseases in which the capillary morphology is altered. However, NC images are generally of poor quality, such that analyzing them is difficult and time consuming. Thus, the purpose of this work was to determine a way to segment the capillaries in poor-quality NC images accurately. To do this, we proposed using a deep neural network with a Res-Unet structure. The network combines the residual network (ResNet) and the U-Net to establish an encoding-decoding network and to deepen the layers in the network to preserve the features of the deep layer. The network was trained on 30 nailfold capillary images to discriminate the pixels belonging to capillaries, and it was then tested on a dataset consisting of 20 images to achieve a binarized map. The mean accuracy was 91.72% and the mean Dice score was 97.66% compared to the ground truth, which indicates that using Res-Unet to perform capillary segmentation in NC images had good performance.

Ultra-wideband and flat-gain optical properties of the PbS quantum dots-doped silica fiber.

We investigate the microstructural characteristics and optical properties of PbS quantum dots-doped silica fiber (PQDF), prepared by atomic layer deposition (ALD) doping technique. The fiber exhibits ultra-wideband luminescence and flat-gain with 3 dB bandwidth of 300 nm. The on-off gain and net gain can reach to 7.1-15.0 dB and 6.0-9.2 dB at 1050-1350 nm, respectively. The results of high-resolution transmission electron microscopy (HRTEM) further reveal the effects of PbS QDs doping in PQDF. The broadband luminescence spectrum originating from three active centers (1086, 1179, and 1304 nm), can be attributed to the dimension effect of PbS QDs (3.7, 4.0, and 4.3 nm, respectively). Moreover, the calculation results indicate that the multi-sized PbS QDs concentrated at 3.65-4.45 nm make the 3 dB gain bandwidth increase, which is six times wider than that of traditional erbium-doped fiber (EDF). Therefore, this type of PQDF is a promising gain medium for optical amplifiers and broadband light sources.

Continuous variable entanglement enhancement and manipulation by a subthreshold Type II optical parametric amplifier.

We experimentally demonstrate that the quantum entanglement between amplitude and phase quadratures of optical modes produced from a nondegenerate optical parametric amplifier (NOPA) can be enhanced and manipulated phase sensitively by means of another NOPA. When both NOPAs operate at deamplification, the entanglement degree is increased at the cavity resonance of the second NOPA. When the first NOPA operates at deamplification and the second one at amplification, the spectral features of the correlation variances are significantly changed. The experimental results are in good agreement with the theoretical expectation.