All-fiber normal-dispersion single-polarization passively mode-locked laser based on a 45°-tilted fiber grating

An all-fiber normal-dispersion Yb-doped fiber laser with 45- tilted fiber grating (TFG) isto the best of our knowledgeexperimentally demonstrated for the first time. Stable linearly-chirped pulses with the duration of 4 ps and the bandwidth of 9 nm can be directly generated from the laser cavity. By employing the 45 TFG with the polarization-dependent loss of 33 dBoutput pulses with high polarization extinction ratio of 26 dB are implemented in the experiment. Our result shows that the 45 TFG can work effectively as a polarizerwhich could be exploited to singlepolarization all-fiber lasers

Joint denoising method of seismic velocity signal and acceleration signals based on independent component analysis

The signal-to-noise ratio (SNR) of seismic data is the key to seismic data processing, and it also directly affects interpretation of seismic data results. The conventional denoising method, independent variable analysis, uses adjacent traces for processing. However, this method has problems, such as the destruction of effective signals. The widespread use of velocity and acceleration geophones in seismic exploration makes it possible to obtain different types of signals from the same geological target, which is fundamental to the joint denoising of these two types of signals. In this study, we propose a joint denoising method using seismic velocity and acceleration signals. This method selects the same trace of velocity and acceleration signal for Independent Component Analysis (ICA) to obtain the independent initial effective signal and separation noise. Subsequently, the obtained effective signal and noise are used as the prior information for a Kalman filter, and the final joint denoising results are obtained. This method combines the advantages of low-frequency seismic velocity signals and high-frequency and high-resolution acceleration signals. Simultaneously, this method overcomes the problem of inconsistent stratigraphic reflection caused by the large spacing between adjacent traces, and improves the SNR of the seismic data. In a model data test and in field data from a work area in the Shengli Oilfield, the method increases the dominate frequency of the signal from 20 to 40 Hz. The time resolution was increased from 8.5 to 6.8 ms. The test results showed that the joint denoising method based on seismic velocity and acceleration signals can better improve the dominate frequency and time resolution of actual seismic data

Orientational Epitaxy of van der Waals Molecular Heterostructures

The shape of individual building blocks is an important parameter in bottom-up self-assembly of nanostructured materials. A simple shape change from sphere to spheroid can significantly affect the assembly process due to the modification to the orientational degrees of freedom. When a layer of spheres is placed upon a layer of spheroids, the strain at the interface can be minimized by the spheroid taking a special orientation. C70 fullerenes represent the smallest spheroids, and their interaction with a sphere-like C60 is investigated. We find that the orientation of the C70 within a close-packed C70 layer can be steered by contacting a layer of C60. This orientational steering phenomenon is potentially useful for epitaxial growth of multilayer van der Waals molecular heterostructures

Comparison between two device structures of SPR enhanced UV detectors based on ZnO

Surface plasmon resonance can be exploited to greatly enhance the photo response of photo detectors. The enhancement is highly dependent on the device structure of the detector. In this paper, we compared two types of SPR enhanced UV detectors based on ZnO in terms of fabrication process, absorption, I–V curves, and spectral response. The peak responsivity is enlarged by 22–100 times due to SPR enhancement. The embedding type detector has an advantage in dark current controlling. However, the surface type detector has a simpler fabrication process and more importantly a more prominent responsivity enhancement. Therefore, the surface type is a more favourable structure to incorporate SPR with ZnO UV detectors to realize large enhancement of responsivity

An Efficient Polarimetric SAR Calibration Algorithm Using Corner Reflectors

Fully polarimetric synthetic aperture radar (SAR) has been widely used in applications, such as ground parameter inversion and classification. However, to accurately decipher the information contained in the polarimetric characteristics of an illuminated scene, the cross talks in cross-polarimetric channels and imbalances among co-pol channels must be removed from the measured polarimetric responses. Therefore, it is important to improve the polarimetric SAR calibration technique to reduce the distortions between various channels and calibrate the polarimetric data. In this article, we propose an efficient polarimetric SAR calibration method that uses known calibration point targets to remove the uncertainties among observed polarized responses. We first construct a common scattering model of natural targets organized by matrix products. Next, we reorder the square matrices in vector form. Finally, we construct a set of analytical equations based on the relations between theoretical and measured scattering matrices and derive the full elements of the distortion matrix by solving these equations. This algorithm determines the calibration matrix from corner reflectors with known scattering matrices, and it is efficient and easy to understand. Finally, we validate the algorithm with airborne C-band polarimetric SAR data