Two-dimensional shift-orthogonal random-interleaving phase-code multiplexing for holographic data storage

A novel phase encoding technology for phase-code multiplexing in holographic data storage (HDS) system called two-dimensional shift-orthogonal random-interleaving (2-D SORI) phase encoding is proposed. Compared with the traditional one-dimensional orthogonal phase-code multiplexing methods, the 2-D method is less sensitive to the variations of the diffraction amplitude and to the phase error of the phase mask. Phase masks for the 2-D SORI phase-code multiplexing can be generated by shifting an elaborately designed phase plate at a certain step, which can avoid the use of a high-cost phase spatial light modulator for the generation of multiple orthogonal phase masks. The cross-talk arising from the systematic phase defects of the static phase modulator is eliminated by the shift operation of the phase plate. Phase codes are interleaved under a predetermined random mapping rule to prevent unauthorized users from accessing the data and eliminate the Bragg degeneration cross-talk. A 2-D SORI phase plate with the size of 5.12 mm × 10.24 mm is designed and fabricated, from which 128 orthogonal phase patterns are generated. The feasibility of the 2-D SORI phase-code multiplexing method for HDS is experimentally demonstrated.     

只需一个解调器的偏分复用差分相移键控系统实验实现

偏分复用技术是提高系统传输速率的有效方法之一.搭建了被称为双偏振态差分相移键控(Dual-Pol.DPSK)码的新型偏分复用实验系统,它与具有相同的比特波特比的差分正交相移键控(DQPSK)调制方式相比,接收机要简单很多.与传统的偏振分解复用(POLMUX)技术相比,它无需偏振控制或偏振跟踪,只需一个解调器和一个平衡探...     

Retrospectively gated cardiac cine imaging with temporal and spatial acceleration

Parallel imaging methods are routinely used to accelerate the image acquisition process in cardiac cine imaging. The addition of a temporal acceleration method, whereby k-space is sampled differently for different time frames, has been shown in prior work to improve image quality as compared to parallel imaging by itself. However, such temporal acceleration strategies prove difficult to combine with retrospectively gated cine imaging. The only currently published method to feature such combination, by Hansen et al. [Magn Reson Med 55 (2006) 85-91] tends to be associated with prohibitively long reconstruction times. The goal of the present work was to develop a retrospectively gated cardiac cine method that features both parallel imaging and temporal acceleration, capable of achieving significant acceleration factors on commonly available hardware and associated with reconstruction times short enough for practical use in a clinical context.Seven cardiac patients and a healthy volunteer were recruited and imaged, with acceleration factors of 3.5 or 4.5, using an eight-channel product cardiac array on a 1.5-T system. The prescribed FOV value proved slightly too small in three patients, and one of the patients had a bigemini condition. Despite these additional challenges, good-quality results were obtained for all slices and all patients, with a reconstruction time of 0.98±0.07 s per frame, or about 20 s for a 20-frame slice, using a single processor on a single PC. As compared to using parallel imaging by itself, the addition of a temporal acceleration strategy provided much resistance to artifacts.     

WDM网状网中动态域间流量疏导策略

对波分复用(Wavelength Division Multiplexing,WDM)网状网中的动态域间流量疏导问题进行了深入研究.在源路由模式下,提出了一种基于固定备选路由方式的动态域间流量疏导算法,并在其基础上提出了只考虑波长均衡和同时考虑波长均衡与业务均衡的改进方法.该算法可以有效地避免路由环,得到较低的阻塞率,节省全网的收发器数目和波长资源.仿真结果表明,这种算法可以有效地改善网络性能.     

激光器非线性失真对SCM光波系统的影响

对于宽带副载波复用(SCM)的光波系统,研究并设法减小光源的非线性所引起的谐波失真和交调失真,是一个重要的理论课题。本文分析激光器的P—I曲线的非线性以及谐振腔里光子和电子相互耦合所引起的固有非线性及其对复用信道的影响。     

THE NONLINEAR SCHR?DINGER EQUATION AND THE CROSS-PHASE MODULATION IN ERBIUM-DOPED FIBER AMPLIFIERS

The nonlinear Schr$\ddot{o}$dinger equation(NLSE) in erbium-doped fiber(EDF) was obtained. The cross-phase modulation (XPM) in the erbium-doped fiber amplifiers (EDFA) was studied based on this NLSE and the rate equations. A more generalized form of the propagation equation in EDFA was obtained which included the phase shifts the EDFA induced. An analytical expression was given to the XPM in the EDFA. It was found that the XPM in the EDFA dose not change very much with the wavelength except at the neighboring wavelengths (around 1531 nm) where the absorption and emission cross-sections of the erbium ions reach their maxima, and the XPMs have opposite signs on the two sides around 1531 nm. Furthermore, it was found that the XPM increases with the increase of the length of EDF.     

外控弱周期电流约束下电极B-Z反应体系中的时间自组织

以经典BZ化学反应体系的三变量Oregonator模型及电极过程动力学为基础,提出了外控弱周期电极电流约束下电极BZ反应体系与体相BZ反应体系相互耦合的动力学模型.在体相处于稳定定态参数条件下,系统地研究了外控弱周期电流约束下电极BZ反应体系中的动力学行为,定量分析了电流慢变流型上的准定态稳定性及有利于出现极限环振荡区域.研究表明,与以前所报道的外控弱周期电位约束情况类似,在外控弱周期电流约束下电极BZ反应体系中的极限环振荡区域亦发生了蜕变,但体系对外控电流约束中的这种持续性之周期扰动的响应表现在两个方面:有利于出现极限环振荡区域的缩变及原非振荡区胁迫振荡的出现.     

Modes conversion due to plasmons induced transparency

We investigate simulated and theoretically the optical properties of the metamaterial, composed of two bigger split ring resonators and one smaller split ring resonator in unit cell. We observe the magic phenomena that one mode B is inhibited from strong to weak then disappears while another mode A appears and becomes stronger and stronger as asymmetric degree increases. The results show the mode A originates from the destructive interference between the dipole mode and the quadrapole mode, and its strength is proportional to the cross coupling coefficient of near-field. The disappearance of the mode B is due to the competition between the mode B and the mode A, and the variation of strength is proportional to the frequency shift of the dark mode. That is, with asymmetric degree increasing, the mode B converts into the mode A. These phenomena are explained very well by the temporal coupled-mode theory. Our metamaterial provides a kind of new design for understanding the interaction between light and matter.     

Securing multiplexed information by in-plane rotation of random phase diffusers constituting a sandwich diffuser placed in the Fourier plane of a double random phase encoding system

We propose the encryption and multiplexing of two-dimensional input images by rotating the constituent diffusers of a sandwich random phase diffuser kept in the Fourier plane of a double random phase encoding system. Successive recording of encrypted images is done by taking the input images one by one. The results of multiplexing in encryption and decryption due to different sets of rotation of one or both of the random constituent phase masks have been presented. The use of an aperture system in addition to the rotation of one or both of the random phase masks enhances the multiplexing capability and security of the system avoiding the generation of cross-talk images at the time of decryption. Simulation results are presented in support of the proposed techniques. The decrypted images obtained from a multiplexed encrypted image have been recorded successfully. Mean square-error (MSE) and signal-to-noise ratio (SNR) values as a function of the number of multiplexed images have been calculated.     

Multimode optical fiber demultiplexer-star coupler using a single gradient-index-rod lens and a multi-facet grating

An optical fiber multi-function device consisting of a single gradient-index-rod lens and a multi-facet blazed reflection grating is proposed to simultaneously realize functions of wavelength demultiplexing and optical signal distribution in a multimode optical fiber transmission system. We analyzed the demultiplexing characteristics and the tolerance of optical components using the ray trace method. This device can realize not only low loss optical signal distribution but also offers improved demultiplexing characteristics in comparison with the previously proposed demultiplexer-multiposition switch. The following characteristics are expected from the design using commercially available optical components: a working band of 0.64–0.88 μm, channel separation of 34–36 nm, 3 dB bandwidth of 27–28 nm, channel cross-talk of less than - 40 dB and minimum excess insertion loss of 0.9–2.1 dB.