Effects of system parameters on a single-beam synthetic gradiometer with a dual-cell structure.

We report a single-beam synthetic gradiometer operated in the spin-exchange-relaxation free (SERF) regime, using the structure of two separate atomic vapor cells spaced 2 cm apart. To improve the capability of the gradiometer in suppressing the common-mode magnetic field noise, we are aiming at investigating the effects of the system parameters on the gradiometer common-mode rejection ratio (CMRR). The mathematical expression for the relationship between the gradiometer CMRR and the two variables including the linewidth ratio and the pumping factor ratio is constructed for the first time, to our knowledge. This means that the CMRR can be optimized by controlling the linewidth and the pumping factor, which is easy to implement in the operation process. As a result, a CMRR of 246 is achieved and a gradiometer sensitivity of 4.5 fT/cm/Hz1/2 is also measured. This method provides a theoretical and experimental basis for the automated operation of gradiometers, and the gradiometer system performance can be tuned to a desired state by simply controlling the linewidth and the incident light intensity.

Ultra-narrow linewidth and a low-noise cascading Brillouin random fiber laser with a dual pump.

A cascading Brillouin random fiber laser with a dual pump (DP-CBRFL) is proposed and demonstrated. The DP-CBRFL can improve the Brillouin gain significantly to achieve an ultra-narrow linewidth (95.5 Hz) with 200 mW pump power, due to two cascading Brillouin gain fibers with an identical Brillouin frequency shift. Compared with the general Brillouin random fiber laser, the proposed random fiber laser has a more stable Brillouin gain spectrum and a lower mode density, which makes it have a lower intensity noise and frequency noise, especially in the low-frequency range. Meanwhile, it exhibits a high slope efficiency of 28% even if the pump power has reached 1.1 W due to the strong suppression ability of the high-order Stokes light.

A high-sensitivity single-light-source triaxial atomic magnetometer with double-cell and orthogonally pumped structure.

We first report a single-light-source orthogonally pumped triaxial atomic magnetometer with a double-cell structure. By using a beam splitter to equally allocate the pump beam, the proposed triaxial atomic magnetometer is responsive to magnetic fields in all three directions, and without sacrificing system sensitivity. The experimental results indicate that, the magnetometer achieves a sensitivity of 22 fT/Hz1/2 in x-direction with a 3-dB bandwidth of 22 Hz, a sensitivity of 23 fT/Hz1/2 in y-direction with a 3-dB bandwidth of 23 Hz, and a sensitivity of 21 fT/Hz1/2 in z-direction with a 3-dB bandwidth of 25 Hz. This magnetometer is useful for the applications that require the measurements of the three components of the magnetic field.

Effect of spectrum broadening on photon-counting fiber Bragg grating sensing.

In a photon-counting fiber Bragg grating (FBG) sensing system, a shorter probe pulse width reaches a higher spatial resolution, which inevitably causes a spectrum broadening according to the Fourier transform theory, thus affecting the sensitivity of the sensing system. In this work, we investigate the effect of spectrum broadening on a photon-counting FBG sensing system with a dual-wavelength differential detection method. A theoretical model is developed, and a proof-of-principle experimental demonstration is realized. Our results give a numerical relationship between the sensitivity and spatial resolution at the different spectral widths of FBG. In our experiment, for a commercial FBG with a spectral width of 0.6 nm, an optimal spatial resolution of 3 mm and a corresponding sensitivity of 2.03 nm-1 can be achieved.

Hybrid Fine-Tuning Strategy for Few-Shot Classification.

Few-shot classification aims to enable the network to acquire the ability of feature extraction and label prediction for the target categories given a few numbers of labeled samples. Current few-shot classification methods focus on the pretraining stage while fine-tuning by experience or not at all. No fine-tuning or insufficient fine-tuning may get low accuracy for the given tasks, while excessive fine-tuning will lead to poor generalization for unseen samples. To solve the above problems, this study proposes a hybrid fine-tuning strategy (HFT), including a few-shot linear discriminant analysis module (FSLDA) and an adaptive fine-tuning module (AFT). FSLDA constructs the optimal linear classification function under the few-shot conditions to initialize the last fully connected layer parameters, which fully excavates the professional knowledge of the given tasks and guarantees the lower bound of the model accuracy. AFT adopts an adaptive fine-tuning termination rule to obtain the optimal training epochs to prevent the model from overfitting. AFT is also built on FSLDA and outputs the final optimum hybrid fine-tuning strategy for a given sample size and layer frozen policy. We conducted extensive experiments on mini-ImageNet and tiered-ImageNet to prove the effectiveness of our proposed method. It achieves consistent performance improvements compared to existing fine-tuning methods under different sample sizes, layer frozen policies, and few-shot classification frameworks.

Dual Wavelength Differential Detection of Fiber Bragg Grating Sensors with a Pulsed DFB Laser.

We show how dual wavelength differential detection can be used to measure fiber Bragg grating sensors using nanosecond pulses from a single DFB laser diode, by taking advantage of its dynamic chirp. This can be performed in two ways: by measuring the reflected power from two separate pulses driven by two different currents, or by taking two delayed digitized samples within a single pulse. A prototype instrument using fast digitizing and processing with an FPGA is used to characterize the chirp, from which the performance can be optimized for both measurement schemes.

High-resolution interrogation of tilted fiber Bragg gratings using an extended range dual wavelength differential detection.

An extended range dual wavelength differential detection technique for interrogating fiber Bragg grating sensors is implemented for the measurement of tilted fiber Bragg gratings. The dynamic chirp of a single DFB laser diode modulated with a square wave is used to generate two pairs of wavelengths, in the high and low modulation states, with a separation approximately equal to the bandwidth of the TFBG, resulting in a doubling of the range of the DWDD measurement. A spectral resolution of 0.08 pm and a refractive index resolution of 9.9 × 10-6 are obtained over a range of refractive index of 3.7 × 10-2, corresponding to 11.9 bits of resolution.

Dispersion independent long-haul photon-counting optical time-domain reflectometry.

Photon-counting optical time-domain reflectometry (PC-OTDR) based on single photon detection is an effective scheme to attain the high spatial resolution for optical fiber fault monitoring. Currently, due to the spatial resolution of PC-OTDR being proportional to the pulse width of a laser beam, short laser pulses are essential for a high spatial resolution. However, short laser pulses have a large bandwidth, which would be widened by the dispersion of fiber, causing inevitable deterioration in the spatial resolution, especially for long-haul fiber links. In this Letter, we propose a scheme of dispersion independent PC-OTDR based on an infinite backscatter technique. Our experimental results-with more than 45 km long fiber-show that the spatial resolution of the PC-OTDR system is independent with the total dispersion of the fiber under test. Our method provides an avenue for developing long-haul PC-OTDR with high performance.

Random Fabry-Perot resonator-based sub-kHz Brillouin fiber laser to improve spectral resolution in linewidth measurement.

For the first time, we propose a novel Brillouin random fiber laser with a narrow linewidth of ∼860 Hz based on the bi-directionally pumped stimulated Brillouin scattering (SBS) in a 10-km-long optical fiber. A random fiber Fabry-Perot (FP) resonator is built up through the pump depletion effects of SBS at both ends of the fiber. A theoretical model is developed to reveal the physics behind the unique random FP resonator that enables narrow random lasing emission. The novel laser is successfully applied for linewidth characterization beyond 860 Hz of light source under test.

Random spaced index modulation for a narrow linewidth tunable fiber laser with low intensity noise.

A tunable random feedback fiber laser with low intensity noise is proposed and experimentally demonstrated. The random feedback is effectively achieved by multiple reflections from 100 randomly spaced refractive index modulation regions over 10 cm SMF in both longitudinal and transverse directions. A tunable erbium-doped fiber ring laser with narrow linewidth of 2.4 kHz and a high side-mode suppression ratio of 59 dB is achieved over a 0.5 nm tuning range. The proposed fiber laser exhibits low relative intensity noise (<-120 dB/Hz) and low frequency fluctuation of ∼3.41×10(-11) over 5 s.

Putative signal peptides of two BURP proteins can direct proteins to their destinations in tobacco cell system.

Plant-specific BURP family proteins have a diverse subcellular localization with different functions. However, only limited studies have investigated the functions of their different domains. In the present study, the role of the N-terminal putative signal peptide in protein subcellular localization was investigated using a tobacco cell system. The results showed that SALI3-2 was present in vacuoles, whereas AtRD22 was directed to the apoplast. The N-terminal putative signal peptides of both proteins were confirmed to be the essential and critical domains for targeting the proteins to their destinations. We also demonstrate that the expression and accumulation of mGFP in tobacco cells was increased when mGFP was fused to the putative signal peptide of SALI3-2. The findings offer the potential application of this short peptide in protein production in plants.

Expression of a vacuole-localized BURP-domain protein from soybean (SALI3-2) enhances tolerance to cadmium and copper stresses.

The plant-specific BURP family proteins play diverse roles in plant development and stress responses, but the function mechanism of these proteins is still poorly understood. Proteins in this family are characterized by a highly conserved BURP domain with four conserved Cys-His repeats and two other Cys, indicating that these proteins potentially interacts with metal ions. In this paper, an immobilized metal affinity chromatography (IMAC) assay showed that the soybean BURP protein SALI3-2 could bind soft transition metal ions (Cd(2+), Co(2+), Ni(2+), Zn(2+) and Cu(2+)) but not hard metal ions (Ca(2+) and Mg(2+)) in vitro. A subcellular localization analysis by confocal laser scanning microscopy revealed that the SALI3-2-GFP fusion protein was localized to the vacuoles. Physiological indexes assay showed that Sali3-2-transgenic Arabidopsis thaliana seedlings were more tolerant to Cu(2+) or Cd(2+) stresses than the wild type. An inductively coupled plasma optical emission spectrometry (ICP-OES) analysis illustrated that, compared to the wild type seedlings the Sali3-2-transgenic seedlings accumulated more cadmium or copper in the roots but less in the upper ground tissues when the seedlings were exposed to excessive CuCl2 or CdCl2 stress. Therefore, our findings suggest that the SALI3-2 protein may confer cadmium (Cd(2+)) and copper (Cu(2+)) tolerance to plants by helping plants to sequester Cd(2+) or Cu(2+) in the root and reduce the amount of heavy metals transported to the shoots.

A carrier removal method in phase measuring deflectometry based on the analytical carrier phase description.

In phase measuring deflectometry (PMD), a camera observes a sinusoidal fringe pattern via the surface of a specular object under test. Any slope variations of the surface lead to distortions of the observed pattern. Without height-angle ambiguity, carrier removal process is adopted to evaluate the variation of surface slope from phase distribution when a quasi-plane is measured. However, in the usual measurement system, the carrier phase will be nonlinear due to the restrictions of system geometries. In this paper, based on the analytical carrier phase description in PMD, a carrier removal method is proposed to remove the nonlinear carrier phase. Both the theoretical analysis and the experiment results are presented. By comparison with reference-subtraction method and series-expansion method, this proposed method can achieve carrier removal process with only the measurement of one single object, as well as high accuracy and time-saving.