基于DP-QPSK调制器的光域微波矢量信号发生器

利用DP-QPSK调制器设计了一种光域微波矢量信号发生器。DP-QPSK调制器的一路QPSK输入单频微波信号,双偏振正交的另一路QPSK输入I/Q数据信号,设置合适的偏置电压和工作点,分别得到光域SSB-CS信号和基带矢量信号,再通过起偏器进行拍频,最终得到光域微波矢量信号。经过实验验证,工作在10.5GHz的DP-QPSK调制器可产生速率为1.25Gbaud的矢量信号。

星上微波光子技术应用研究进展

未来宽带、可靠的卫星通信系统是微波与激光链路混合通信系统,微波光子技术集成了微波通信的灵活性和激光传输的低损耗、大带宽优势,可以解决星上微波与激光通信两种体制并存带来的信息融合问题。文章解析了星上微波光子技术的基本内涵,对星上微波信号光学生成、星上微波光子转发与高吞吐量背板间光学互联、星内光无线链路与光域微波放大等星上微波光子关键技术应用研究的国内外最新研究进展进行了全面评述,并指出了一些值得继续关注的研究方向。

基于小波域HMM模型的自适应图像水印算法

An adaptive image watermarking algorithm based on HMM in wavelet domain is proposed. The algorithm is abstracted as follows: 1) the vector HMM model is employed to describe the statistical characteristic of image wavelet coefficients and the resulting HMM based detector achieves significant improvements in performance compared to the conventional correlation detector;2) adaptive watermark embedding based on HVS analysis; 3) a novel embedding strategy which is optimized for the HMM tree structure is adopted; 4) the strategy of dynamical threshold is applied in watermark detection. High robust results are achieved against Stirmark attacks, such as JPEG compression, adding noise, median cut and filter.

Enhanced Kerr Nonlinearities Caused by Cross Talk Between Optical and Microwave Transitions

We investigate the enhanced Kerr nonlinearities in four-level atomic vapors driven by a coupling,probe andmicrowave fields.Under the optical one-photon and two-photon resonant conditions,the linear and nonlinear responsesof the weak probe field can be modified by the cross talk among optical and microwave transitions.The enhanced Kerrnonlinearity can form bright optical solitons of the probe field.

New design of 2-D photonic crystal waveguide couplers

Based on couple wave equation and finite-difference time-domain (FDTD) algorithm,the strong couple characteristic of 2-D photonic crystal couplers is calculated.Theoretical analysis and numerical simulated results indicate that the energy in a 2-D photonic crystal coupler can not be totally transferred between two wave-guides.Compared with the result of weak coupling theory,our result is more accurate.

Assessment of wind products obtained from multiple microwave scatterometers over the China Seas

Sea surface winds （SSWs） are vital to many meteorological and oceanographic applications, especially for regional study of short-range forecasting and Numerical Weather Prediction （NWP） assimilation. Spaceborne seatterometers can provide global ocean surface vector wind products at high spatial resolution. However, given the limited spatial coverage and revisit time for an individual sensor, it is valuable to study improvements of multiple microwave scatterometer observations, including the advanced scatterometer onboard parallel satellites MetOp-A （ASCAT-A） and MetOp-B （ASCAT-B） and microwave scatterometers aboard Oceansat-2 （OSCAT） and HY-2A （HY2-SCAT）. These four scatterometer-derived wind products over the China Seas （0°-40°N, 105°-135°E） were evaluated in terms of spatial coverage, revisit time, bias of wind speed and direction, after comparison with ERA-Interim forecast winds from the European Centre for Medium-Range Weather Forecasts （ECMWF） and spectral analysis of wind components along the satellite track. The results show that spatial coverage of wind data observed by combination of the four sensors over the China Seas is about 92.8% for a 12-h interval at 12：00 and 90.7% at 24：00, respectively. The analysis of revisit time shows that two periods, from 5：30-8：30 UTC and 17：00-21：00 UTC each day, had no observations in the study area. Wind data observed by the four sensors along satellite orbits in one month were compared with ERA-Interim data, indicating that bias of both wind speed and direction varies with wind speed, especially for speeds less than 7 m/s. The bias depends on characteristics of each satellite sensor and its retrieval algorithm for wind vector data. All these results will be important as guidance in choosing the most suitable wind product for applications and for constructing blended SSW products.

First observations of the water masers with the Urumqi 25m radio telescope

A new radio spectral receiving system has been installed on the 25 m radio telescope of the Urumqi Astronomical Observatory. The back end is a surface acoustic wave chirp transform spectrometer (SAW CZT), used for the first time in radio astronomy. The calibration of the line observations has carefully been investigated for the new-type spectrometer. In order to test the feasibility of the prototype spectrometer, we observed water maser emission from a number of known Galactic sources. We describe the observed spectra of W49N, W3(OH), 2248+600 and 1909+090. We found that W49N spectrum showed high-velocity features ranging from -330 to 146 km s-1. In comparison with the spectra observed by Medicina, the feature at the LSR velocity -52 km s-1 in the W3(OH) presented the rapid variation in flux density.

Tunable nonlinear optical responses based on host-guest MOF hybrid materials

The realization of tunable nonlinear optical(NLO)responses in a single nano-/micro-structure is extremely important.However,in lack of effective ways to integrate multiple performances,it still faces severe limitations during applications.Herein,we demonstrate a wavelength-dependent NLO micro-structure based on host-guest metal-organic framework(MOF)materials through encapsulating linear dye molecules into periodic one-dimensional(1D)channels.The confinement to non-centrosymmetric polar dye molecules enhances the second-/third-order NLO responses of the hybrid crystals,causing obvious two-photon luminescence(TPL),second harmonic generation(SHG)and third harmonic generation(THG)responses in the as-prepared composites.The highly ordered structures of MOFs impart spatial regulation on the linear dye molecules to realize orientation alignment,resulting in the polarized anisotropy emission.NIR-to-NIR(NIR,near-infrared region)two-photon pumped lasing is realized with the natural whispering gallery mode resonance cavities of MOFs under the excitation of a 1200-nm fs laser.Furthermore,tunable NLO properties such as TPL,SHG and THG are achieved through switching the incident excitation wavelength from 800 to 1500 nm.Such hybrid materials with tunable NLO responses may open a new avenue toward designing multifunctional NLO devices in the future.