Tunable single frequency Hz-magnitude narrow linewidth Brillouin fiber laser based on parity-time symmetry.

An Hz-magnitude ultra-narrow linewidth single-frequency Brillouin fiber laser (BFL) is proposed and experimentally demonstrated. The single frequency of the laser is selected by parity-time (PT) symmetry, which consists of a stimulated Brillouin scatter (SBS) gain path excited by a 24 km single-mode fiber (SMF) and an approximately equal length loss path tuned with a variable optical attenuator (VOA). These paths are coupled through a fiber Bragg grating (FBG) into a wavelength space. Accomplishing single-frequency oscillation involves the precise adjustment of polarization control (PC) and VOA to attain the PT broken phase. In the experiment, the linewidth of the proposed BFL is 9.58 Hz. The optical signal-to-noise ratio (OSNR) reached 78.89 dB, with wavelength and power fluctuations of less than 1pm and 0.02 dB within one hour. Furthermore, the wavelength can be tuned from 1549.9321 nm to 1550.2575 nm, with a linewidth fluctuation of 1.81 Hz. The relative intensity noise (RIN) is below -74 dB/Hz. The proposed ultra-narrow single-frequency BFL offers advantages such as cost-effectiveness, ease of control, high stability and excellent output characteristics, making it highly promising for the applications in the coherent detection.

Dual wavelength laser Doppler anemometer for simultaneous velocity and particulate size distribution measurements in submarine environments.

An in-situ laser Doppler current probe (LDCP) for the simultaneous measurements of the micro-scale subsurface current speed and the characterizations of micron particles is dedicated in this paper. The LDCP performs as an extension sensor for the state-of-the-art laser Doppler anemometry (LDA). The all-fiber LDCP utilized a compact dual wavelength (491 nm and 532 nm) diode pumped solid state laser as the light source to achieve the simultaneous measurements of the two components of the current speed. Besides its ability for the measurements of the current speed, the LDCP is also capable of obtaining the equivalent spherical size distribution of the suspended particles within small size range. The micro-scale measurement volume formed by two intersecting coherent laser beams makes it possible to accurately estimate the size distribution of the micron suspended particles with high temporal and spatial resolution. With its deployment during the field campaign at Yellow Sea, the LDCP has been experimentally demonstrated as an effective instrument to capture the micro-scale subsurface ocean current speed. The algorithm for retrieving the size distribution of the small suspended particles (2∼7.5µm) has been developed and validated. The combined LDCP system could be applied to the continuous long-term observations of plankton community structure, ocean water optical parameter over a wide range, and useful to elucidate the processes and interactions of the carbon cycles in the upper ocean.

Neutralization of Typhoid Toxin by Alpaca-Derived, Single-Domain Antibodies Targeting the PltB and CdtB Subunits.

Typhoid toxin is secreted by the typhoid fever-causing bacterial pathogen Salmonella enterica serovar Typhi and has tropism for immune cells and brain endothelial cells. Here, we generated a camelid single-domain antibody (VHH) library from typhoid toxoid-immunized alpacas and identified 41 VHHs selected on the glycan receptor-binding PltB and nuclease CdtB. VHHs exhibiting potent in vitro neutralizing activities from each sequence-based family were epitope binned via competition enzyme-linked immunosorbent assays (ELISAs), leading to 6 distinct VHHs, 2 anti-PltBs (T2E7 and T2G9), and 4 anti-CdtB VHHs (T4C4, T4C12, T4E5, and T4E8), whose in vivo neutralizing activities and associated toxin-neutralizing mechanisms were investigated. We found that T2E7, T2G9, and T4E5 effectively neutralized typhoid toxin in vivo, as demonstrated by 100% survival of mice administered a lethal dose of typhoid toxin and with little to no typhoid toxin-mediated upper motor function defect. Cumulatively, these results highlight the potential of the compact antibodies to neutralize typhoid toxin by targeting the glycan-binding and/or nuclease subunits.

Coherent high-spectral-resolution lidar for the measurement of the atmospheric Mie-Rayleigh-Brillouin backscatter spectrum.

In this study, a 1550 nm coherent high-spectral-resolution lidar (CHSRL) is developed to measure the optical properties of aerosols and atmospheric wind profiles in the atmospheric boundary layer. To determine the optical properties, a coherent frequency discriminator based on the fast Fourier transform is designed in the CHSRL to separate the Mie and the Rayleigh-Brillouin backscatter spectra to fulfill the needs of high-spectral measurements. The atmospheric wind velocity is retrieved using the simultaneously measured Doppler shift. This non-optical frequency discriminator is a feasible and low-cost solution compared to a narrow-bandwidth optical filter, such as a Fabry-Perot interferometer or an atomic filter. However, shot, amplifier spontaneous emission, and detector noise interfere with the Rayleigh-Brillouin spectrum. Therefore, a spectrum correction algorithm is proposed to recover the interfered Rayleigh-Brillouin spectrum, and the measurement results of the spectral line agree well with those modeled with Tenti S6 at different central frequencies. Finally, field observations for comparison are conducted with the co-located CHSRL, Raman lidar, and coherent Doppler wind lidar. The comparison results indicate that the correlation coefficient of the aerosol backscatter coefficient is 0.84. The correlation coefficient and standard deviation of wind velocity are 0.98 and 0.13 m · s-1, respectively.

Improved spatial-shifting two-wavelength algorithm for 3D shape measurement with a look-up table.

Conventional two-wavelength algorithms have been broadly used for three-dimensional shape measurement. However, the maximum unambiguous range of phase unwrapping depends on the least-common multiple of two wavelengths, and thus coprime wavelengths are commonly selected. The recently proposed spatial-shifting two-wavelength (SSTW) algorithm can achieve the maximum unambiguous range with two non-coprime wavelengths, but this algorithm tends to fail for some wavelength selections. To address this problem, this paper presents a general look-up-table-based SSTW (LUT-SSTW) algorithm with arbitrary wavelength selection. The paper also analyzes the phase unwrapping robustness in terms of phase errors and provides guidance for wavelength selection. In addition, an improved LUT-SSTW algorithm is developed to enhance the phase unwrapping robustness, and further relax wavelength selection. Some experiments have been conducted, and their results verify the efficiency of the proposed method.

Spatial binary coding method for stripe-wise phase unwrapping.

Binary coding methods have been widely used for phase unwrapping. However, traditional temporal binary coding methods require a sequence of binary patterns to encode the fringe order information. This paper presents a spatial binary coding (SBC) method that encodes the fringe order into only one binary pattern. Each stripe of the sinusoidal phase-shifting patterns is corresponding to an N-bit codeword of the binary pattern. A robust stripe-wise decoding scheme is also developed to extract the N-bit codeword, then fringe order can be determined, and stripe-wise phase unwrapping can be performed. Experiment results confirm that the SBC method can correctly recover the absolute phase of measured objects with only one additional binary pattern.

Depth range enhancement of binary defocusing technique based on multi-frequency phase merging.

Binary defocusing technique has demonstrated various merits for high-speed and high-accuracy three-dimensional measurement. However, the existence of excessive defocusing zone (EDZ) limits the depth range of binary defocusing system. To overcome this problem, this paper proposes a multi-frequency phase merging (MFPM) approach, which makes it possible to measure the object surface in large depth range (LDR). The method is based on our finding that for different fringe frequencies, the associated EDZs of binary defocusing system are different and not totally overlapped. Thus by merging the phase maps of multiple binary fringes, we could effectively enhance the measurement depth range. Meanwhile, a strategy to determine the optimal combination of fringe frequencies is also proposed by analyzing the phase error distribution under different defocusing degrees. Both simulations and experiments verify the effectiveness and robustness of the proposed method.

Stereo calibration with absolute phase target.

Stereo cameras have been widely used for three-dimensional (3D) photogrammetry, and stereo calibration is a crucial process to estimate the intrinsic and extrinsic parameters. This paper proposes a stereo calibration method with absolute phase target by using horizontal and vertical phase-shifting fringes. The one-to-one mapping from the world points to the image points that can be recovered by referring to the absolute phase and then used to calibrate the stereo cameras. Compared with traditional methods that only use feature points within the overlapping field-of-view (FOV), the proposed method can use all feature points within the overlapping and non-overlapping FOVs. Besides, since phase is more robust against camera defocusing than intensity, the target images can be captured regardless of the depth-of-field (DOF). With the advantages of whole-field capability and defocusing tolerability, the target placement becomes very flexible. Both simulations and experiment results demonstrate the robustness and accuracy of the proposed method.

Defocused camera calibration with a conventional periodic target based on Fourier transform.

State-of-art camera calibration methods always require sharp target images for accurate feature detection. This Letter presents a novel calibration method for a defocused camera with a conventional periodic target. Two crossed phase maps are recovered from the periodic target image by Fourier transform. Instead of intensity, feature points are extracted from the phase domain, which is robust against camera defocusing. Simulations and experiments confirm that the proposed method can realize accurate camera calibration using both focused and defocused images.

Enhanced phase-coding method for three-dimensional shape measurement with half-period codeword.

The phase-coding method has been widely used for 3D shape measurement, which uses sinusoidal phase-shifting patterns to recover the wrapped phase and the stair phase-coding patterns to determine the fringe order. However, due to random noises and image blurring, the fringe order is always misaligned with the wrapped phase, which will lead to fringe order errors. This paper presents an enhanced phase-coding method to address this misalignment problem by using half-period codewords, in which each codeword is aligned to the half-period of the sinusoidal patterns. Then, two complementary fringe orders with half-period dislocation can be calculated, which can effectively eliminate the fringe order errors. To extend the coding range of stair phase, this paper further develops a computational scheme based on the geometric constraint method. Simulations and experiments have been carried out, and their results confirm that the enhanced method can reliably recover the 3D shape of the measured objects.

Camera Calibration Robust to Defocus Using Phase-Shifting Patterns.

Camera parameters can't be estimated accurately using traditional calibration methods if the camera is substantially defocused. To tackle this problem, an improved approach based on three phase-shifting circular grating (PCG) arrays is proposed in this paper. Rather than encoding the feature points into the intensity, the proposed method encodes the feature points into the phase distribution, which can be recovered precisely using phase-shifting methods. The PCG centers are extracted as feature points, which can be located accurately even if the images are severely blurred. Unlike the previous method which just uses a single circle, the proposed method uses a concentric circle to estimate the PCG center, such that the center can be located precisely. This paper also presents a sorting algorithm for the detected feature points automatically. Experiments with both synthetic and real images were carried out to validate the performance of the method. And the results show that the superiority of PCG arrays compared with the concentric circle array even under severe defocus.

Modified Gray-Level Coding Method for Absolute Phase Retrieval.

Fringe projection systems have been widely applied in three-dimensional (3D) shape measurements. One of the important issues is how to retrieve the absolute phase. This paper presents a modified gray-level coding method for absolute phase retrieval. Specifically, two groups of fringe patterns are projected onto the measured objects, including three phase-shift patterns for the wrapped phase, and three n-ary gray-level (nGL) patterns for the fringe order. Compared with the binary gray-level (bGL) method which just uses two intensity values, the nGL method can generate many more unique codewords with multiple intensity values. With assistance from the average intensity and modulation of phase-shift patterns, the intensities of nGL patterns are normalized to deal with ambient light and surface contrast. To reduce the codeword detection errors caused by camera/projector defocus, nGL patterns are designed as n-ary gray-code (nGC) patterns to ensure that at most, one code changes at each point. Experiments verify the robustness and effectiveness of the proposed method to measure isolated objects with complex surfaces.

Quantized phase coding and connected region labeling for absolute phase retrieval.

This paper proposes an absolute phase retrieval method for complex object measurement based on quantized phase-coding and connected region labeling. A specific code sequence is embedded into quantized phase of three coded fringes. Connected regions of different codes are labeled and assigned with 3-digit-codes combining the current period and its neighbors. Wrapped phase, more than 36 periods, can be restored with reference to the code sequence. Experimental results verify the capability of the proposed method to measure multiple isolated objects.

Accurate feature detection for out-of-focus camera calibration.

For conventional camera calibration methods, well-focused images are necessary to detect features accurately. However, this requirement causes practical inconveniences to image acquisition for long- and short-distance photogrammetry. In this study, three active phase-shift circular grating (PCG) arrays are used as calibration patterns. The PCGs' centers are regarded as feature points that can be accurately extracted by ellipse fitting of 2π-phase points even though patterns are substantially blurred. In the experiments, Gaussian filters are utilized to blur pattern images, and different standard deviations are set for different fuzzy degrees. Pattern images with different defocusing degrees are also captured. The period and number of PCGs and noise are considered. Experimental results indicate that our method is accurate, reliable, and insensitive to image defocusing.

A Framework for Applying Point Clouds Grabbed by Multi-Beam LIDAR in Perceiving the Driving Environment.

The quick and accurate understanding of the ambient environment, which is composed of road curbs, vehicles, pedestrians, etc., is critical for developing intelligent vehicles. The road elements included in this work are road curbs and dynamic road obstacles that directly affect the drivable area. A framework for the online modeling of the driving environment using a multi-beam LIDAR, i.e., a Velodyne HDL-64E LIDAR, which describes the 3D environment in the form of a point cloud, is reported in this article. First, ground segmentation is performed via multi-feature extraction of the raw data grabbed by the Velodyne LIDAR to satisfy the requirement of online environment modeling. Curbs and dynamic road obstacles are detected and tracked in different manners. Curves are fitted for curb points, and points are clustered into bundles whose form and kinematics parameters are calculated. The Kalman filter is used to track dynamic obstacles, whereas the snake model is employed for curbs. Results indicate that the proposed framework is robust under various environments and satisfies the requirements for online processing.

Bi-soliton generation and its properties in stretched pulse fiber ring laser.

We studied the formation of bi-soliton pairs in Kerr-type stretched pulse fiber ring laser (SPFRL). By solving the modified Ginzburg-Landau (GL) equaition, which models the SPFRL, we show that anti-phase bi-soliton can be generated robustly if a low level Gaussian pulse is injected into the ring laser in the initial set-up stage. With the help of properly selected high order nonlinear gain coefficient, the observation of anti-phase bi-soliton pairs is expected to become feasible in experiments.

Development of liquid biopsy in detection and screening of pancreatic cancer.

Pancreatic cancer is a highly lethal malignant tumor, which has the characteristics of occult onset, low early diagnosis rate, rapid development and poor prognosis. The reason for the high mortality is partly that pancreatic cancer is usually found in the late stage and missed the best opportunity for surgical resection. As a promising detection technology, liquid biopsy has the advantages of non-invasive, real-time and repeatable. In recent years, the continuous development of liquid biopsy has provided a new way for the detection and screening of pancreatic cancer. The update of biomarkers and detection tools has promoted the development of liquid biopsy. Circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), circulating tumor RNA (ctRNA) and extracellular vesicles (EVs) provide many biomarkers for liquid biopsy of pancreatic cancer, and screening tools around them have also been developed. This review aims to report the application of liquid biopsy technology in the detection of pancreatic cancer patients, mainly introduces the biomarkers and some newly developed tools and platforms. We have also considered whether liquid biopsy technology can replace traditional tissue biopsy and the challenges it faces.

Modulating the Activity of Enzyme in Metal-Organic Frameworks Using the Photothermal Effect of Ti3C2 Nanosheets.

Enzymes are versatile catalysts with high potential in various applications, and much attention has been paid to the stability improvement of native enzymes and activity modulation. Encapsulation in metal-organic frameworks (MOFs) as an efficient strategy for protecting fragile native enzymes while modulating the activity of enzymes remotely, which is practically demanded, has rarely been explored in MOF-encapsulated enzymes. Herein, Ti3C2 nanosheets exhibiting photothermal effect and biocompatibility were encapsulated in Cyt c-embedded ZIF-8 to tailor the enzymatic activity remotely by near-infrared (NIR) irradiation for the first time. By exposure to NIR light, the temperature of an aqueous solution containing Ti3C2/Cyt c@ZIF-8 increases obviously (up to 15 °C), while that of Cyt c@ZIF-8 shows no change. The enzymatic activity in the composites with a certain amount of nanosheets increases, which is attributed to the created defect and transformed microenvironment caused by the introduction of nanosheets. Importantly, the enzymatic activity in ZIF-8 can be further enhanced up to 150% under NIR light irradiation, and this enhancement can be modulated flexibly by varying laser power density. Our investigations indicate that Ti3C2 nanosheets are promising candidates for modulating the activity of encapsulated enzymes remotely.

Frequency-selective harmonic retrieval for Schottky mass spectrometry.

Nuclear mass measurements by means of Schottky mass spectrometry critically rely on an accurate determination of revolution frequencies of the circulating ions in a storage ring. Such a harmonic retrieval problem is conventionally tackled via the periodogram of the Schottky data, where the ion peaks are identified and their spectral locations are obtained by fittings. However, the discrete frequency grid of the periodogram has unfortunately hampered a fine resolution of two closely spaced harmonics. We thereby propose a method based on the state space representation in the frequency domain to overcome this limit. Moreover, its frequency-selective merit has allowed the method to focus only on a narrow band and thus greatly reduced the computational cost while still retaining superb accuracy. With the real Schottky data from an isochronous-Schottky beam time at the experimental cooler-storage ring in Lanzhou, the accuracy of the retrieved harmonics is demonstrated to be around 1 ppm, as limited by the anisochronism effect of the ion optics.

Absolute phase measurement with four patterns based on variant shifting phases.

Fringe projection profilometry has been proverbially utilized for measuring the shapes of objects. A common challenge in those systems is to accurately obtain a smooth absolute phase. Many new methods have been proposed to address this challenge. In this paper, we discuss a technique based on variant shifting phases. This approach embeds codewords into the shifting phase and only needs four patterns. However, reliable measurement results are difficult to achieve with a large number of codewords because of the phase errors. To address this shortcoming, we present a robust coding method that embeds a specific code sequence into the shifting phase and can generate more than 36 periods. The fringe order is determined using unique three-adjacent-codes combining the current period and its neighbors. An error correction algorithm is also proposed to optimize the codewords. The proposed method is experimentally verified using an established measurement system. The result shows that the proposed method is robust and efficient.