超分辨率重建在视频监控、高清晰度电视、遥感图像、医学图像处理等领域具有广阔的应用前景.最大后验估计(maximum a posteriori,MAP)法是普遍采用的一种超分辨率重建方法.针对传统MAP法存在的局限性,本文提出了一种基于MAP框架的时空联合自适应视频序列超分辨率重建算法.时空联合自适应机制的引入使得算法在保持边缘的同时可减小错误运动估计矢量对重建图像质量的影响.实验结果表明,算法具有重建质量好、边缘保持能力强、收敛速度快等特点.
The dynamic behavior of an optical micro ring resonator (OMRR) with an amplitude modulator positioned in the micro ring is investigated quantitatively by adopting a recently introduced quantifier, the permutation entropy (PE). The effects of modulation depth are focused on, and the roles of input power are considered. The two-dimensional (2D) maps of PE showing dependence on both modulation depth and input power are presented as well. PE values nearly increase with modulation depth. On the other hand, the optimal value of input power is achieved when the PE reaches its maximum. Thus, PE can successfully quantify the dynamics of modulated OMRR. Selecting the parameters in the region with high PE values would contribute to the complexity-enhanced OMRR-based chaotic communication systems.
This paper gives a detailed theoretical investigation on phase conjugation induced by nearly degenerate four- wave mixing in single mode vertical-cavity surface-emitting lasers (VCSELs) with weak optical injection. Considering VCSELs that can work in linearly polarized or elliptically polarized states, it derives the theoretical expression of the conjugated field by small signal analysis based on the vectoral rate equations—the spin-flip model. For linearly polarized state, VCSELs show similar conjugate spectra to edge-emitting semiconductor lasers. For the elliptically polarized state, dichroism and birefringence parameters as well as the spin-flip rate can change the conjugate spectra. Especially, when frequency detuning of the probe and pump waves is between the positive and negative relaxation oscillation frequency, changes are evident. For specific values of parameters, conjugate efficiency between 20 dB to 40 dB are obtained.
We perform a theoretical study on the polarization-resolved compound lasing mode (CLM) of two mutually coupled vertical-cavity surface-emitting lasers (VCSELs). Different solutions of CLMs are derived though stability analysis of the spin-flip model. The dynamical evolvements of CLMs with the existence of polarization degrees of freedom are also charactered. The most stable CLM with the smallest carrier density tend to be excited, since the gain needed for this mode to emit is the lowest. In the given system, varying values of injection rate or birefringence, etc., will change the generation of the preferred CLMs in the two polarization directions, and thus influence the polarization switching (PS) characteristics. Thus, hoppings between CLMs are also companied by PSs. Through mapping of average power in the parameter space, the influences of coupling rate and anisotropy parameters (linear dichroism and linear birefringence) on PS and hopping between CLMs are discussed.
ZHANG WeiLi PAN Wei LUO Bin WANG MengYao ZOU XiHua
