Polarization storage by two-photon-induced anisotropy in bisazobenzene copolymer film

A copolymer containing bisazobenzene chromophores, poly[(methylmethacrylate)-co-4-{(2-methacryloyloxyethyl)oxy}-4′-(4-nitro-phenylazo)azobenzene)] (poly(MMA-co-M2BAN)), was synthesized and used for two-photon-induced polarization storage. Based on two-photon-induced optical anisotropy resulting from photoselective isomerization of bisazochromophores, the data have been recorded by linearly polarized Ti:Sapphire laser (wavelength: 800 nm, pulse duration: 80 fs, and repetition rate: 80 MHz) and read by reflection confocal laser scanning microscope. The recorded bits are dark dots when the polarization of the reading beam is parallel to the recording beam, but the recorded bits become bright dots when the polarization of the reading beam is perpendicular to the recording beam. Two letters can be encoded in the same region of a given layer by separating the two polarization directions of recording beams at an angle of 45°. The relationships between the readout intensity of the recorded bits and the recording power under two different readout modes were investigated and the results showed that there are two opposite change trends for parallel readout and perpendicular readout, respectively, and the readout threshold value is around 12 mW.     

利用菌紫质薄膜进行角度复用和偏振复用全息存储实验研究

全息光存储以其高密度、大容量、高速并行数据存取而成为光存储领域的一个重要研究方向。生物光致变色材料———菌紫质是一种新型可擦重写全息记录介质。实验证明了使用菌紫质薄膜进行角度复用和偏振复用全息存储的可行性。利用菌紫质的光致变色特性,采用90°角度复用全息存储光路,在BR-D96N薄膜样品同一位置上实现了6幅全息图存储,并分别读出了无串扰的再现像。利用菌紫质薄膜的光致各向异性进行了偏振复用全息存储,在BR-D96N薄膜样品的同一位置上存储了两幅正交偏振光记录的图像,用原参考光再现和偏振片选择,可分别读出这两幅图像。     

Land/groove optical recording with GeTe/Sb2Te3 superlattice-like structure

A superlattice-like (SLL) structure was applied to phase-change optical recording. The recording layer consisting of alternating thin layers of two different phase-change materials, GeTe and Sb2Tes, were grown by magnetron sputtering on polycarbonate substrates. Land/groove optical recording was adopted to suppress crosstalk and obtain a large track density. Dynamic properties of the SLL disc were investigated with the shortest 1T pulse duration of 8 ns. Clear eye pattern was observed after 10000 direct overwrite cycles. Erasability above 20 dB was achieved at a constant linear velocity of 19 m/s. Carrier-noise ratio (CNR) kept above 46 dB when the recording frequency reaches 21 MHz. The SLL phase change optical disc demonstrates a better recording performance than the Ge1Sb2Te4 and Ge1Sb4Te7 discs in terms of CNR, erasability, and overwrite jitter.     

Evaluation of polycarbonate substrate hologram recording medium regarding implication of birefringence and thermal expansion

In this paper, we evaluate photopolymer media using a polycarbonate (PC) substrate. In holographic data storage medium, substrates that sandwich the photopolymer material are needed to protect the photopolymer material against exogenous shock and open air. An optical glass such as BK-7 is normally used as a substrate, but a PC substrate has a cost advantage and is easy to fabricate compared with optical glass. For holographic recording and reading, however, the high birefringence and high thermal expansion of a PC substrate are significant problems. First, we analyze the degree of degradation of output power by the polarization change and estimate the threshold value of birefringence to record hologram normally. Next, we estimate the temperature tolerance of hologram readout with polycarbonate substrate hologram medium. These analyses results indicate the possible usage of the PC substrate as holographic recording media.     

菌紫质高密度偏振全息光数据存储实验研究

实验研究了基因改性菌紫质BR_D96N薄膜在不同偏振光记录下的全息存储特性，比较了不同 偏振态记录光和读出光对衍射像光强及信噪比的影响. 实验结果表明，与其他偏振全息记录 相比，正交圆偏振光记录可实现衍射光偏振状态与散射噪声偏振状态的分离，得到高信噪比 的衍射像，同时还具有高的衍射效率. 以 He_Ne 激光器（633nm，3mW）为记录和读出光源 ，用空间光调制器作为数据输入元件，CCD作为数据读出器件，采用傅里叶变换全息记录的 方法，在 BR_D96N 薄膜样品60μm×42μm的面积上进行了正交圆偏振全息数据存储，达到 了2×10⁸bit/cm²的存储面密度，并实现了编码数据的无误读出与 还原. 关键词： 菌紫质 偏振全息 光致变色 光致各向异性 高密度光存储     

Reflection-type polarization holograms in bacteriorhodopsin films for low-light recording

Reflection-type polarization holograms with phase-conjugated readout are very useful for low-light recording with bacteriorhodopsin (BR) films. The dependence of reflection-type holograms with parallel and orthogonal recording beams on their intensity ratio (1:1-1:20) was investigated. It was found that for orthogonally polarized beams the phase-conjugated signal depends significantly less on the beam intensity ratio than predicted by coupled-wave theory. This finding is of particular relevance for recording of very low object-beam intensities with BR films, e.g., in interferometry, where signals with a high signal-to-noise ratio, owing to the different polarizations of the scattered light and the signal, and with low dependence of the diffraction efficiency on the ratio between the reference and object-beam intensities are obtained. With this asymmetric recording process, holograms were recorded successfully in BR films with a good signal-to-noise ratio at exposures (from the object side) as low as 50muJ/cm(2) . These exposures are in the range of those typically used for silver halide films.     

Thermal effect of Ge_2Sb_2Te_5 in phase change memory device

The properties of Raman phonons are very important due to the fact that they can availably reflect some important physical information. An abnormal Raman peak is observed at about 558 cm-1in In film composed of In/InOx core–shell structured nanoparticles, and the phonon mode stays very stable when the temperature changes. Our results indicate that this Raman scattering is attributed to the existence of incomplete indium oxide in the oxide shell.     

AgInSbTe薄膜的短波长记录性能分析

采用自制的装置研究了Ag5In5Sb47Te33薄膜的静态记录性能与记录激光的功率和脉冲宽度的关系，并对其记录畴形貌特点进行了直接观察。结果表明只有记录激光的功率和脉冲宽度在一定范围之内才能起到信息记录的作用，所得的记录畴形貌十分清晰，基本为非晶态Ag5In5Sb47Te33；小于该范围的激光能量不能使材料结构发生较大的变化，所得的记录畴形貌模糊，反射率对比度低于2％；大于该范围所得的记录畴由烧蚀区和其周围的非晶态Ag5In5Sb47Te33组成。另外，得到了记录激光功率为12mW、脉冲宽度为90ns的Ag5In5Sb47Te33薄膜的短波长最佳记录条件，其记录畴的反射率对比度为22％，直径为380nm-400nm。     

激光致晶态Ag11In12Te26Sb51相变介质光学常数的研究

研究了结晶度对Ag11In12 Te2 6Sb51相变薄膜光学常数的影响。用初始化仪使相变薄膜晶化 ,改变晶化参量得到不同的结晶度 ,当转速固定时 ,随激光功率的增加 ,折射率基本随之减小 ,消光系数先是增大 ,而后减小 ;当激光功率固定时 ,随转速的增大 ,折射率也随之增大 ,消光系数也是先增大后减小。非晶态与晶态间的变换、薄膜微结构的变化 (包括晶型的转变和原子间键合状态的变化 )以及薄膜内残余应力是影响Ag11In12 Te2 6Sb51相变薄膜复数折射率的主要原因。测量了单层膜的透过率和CD RW相变光盘中Ag11In12 Te2 6Sb51薄膜非晶态和晶态的反射率     

Autler–Townes spectroscopy of high-lying state by phase conjugate six-wave mixing

An Autler-Townes(AT) spectroscopy based on phase conjugate six-wave mixing(SWM) is proposed to detect AT doublet of high-lying state in a Doppler-broadened cascade four-level system.It is found that the SWM spectrum is dependent strongly on the ratios between the magnitudes of the wave vectors.We discuss how the Doppler broadening affects the SWM spectrum from a time-domain viewpoint and find that,due the atomic motion,the atomic polarizations acquire different phases for atoms with different velocities as time evolves.The Doppler free SWM spectrum can be obtained only when the atomic polarization can be rephasing again at certain time after the interactions of all the incident fields.     

吲哚俘精酰胺的偏振全息图像光存储实验研究

在吲哚俘精酰胺/PMMA薄膜上记录了同偏振全息和正交偏振全息图，获得了它们的再现衍射像.实验结果表明：吲哚俘精酰胺具有光致各向异性，可以进行正交偏振全息记录.在偏振全息中，衍射光的偏振方向依赖于物光和再现光的偏振方向，衍射像的噪声主要来源于再现光照射到样品上引起的散射.正交偏振全息可以得到比同偏振全息更高信噪比的衍射像.存储于样品上的全息图在室温下黑暗处至少可以保存五个月而衍射效率无明显下降.结果表明，吲哚俘精酰胺是一种可用于偏振全息的可擦重写记录介质. 关键词： 偏振全息 光致各向异性 俘精酸酐 光致变色     

Thermal phase change and activation energy of crystallization of Ge-Sb-Te-Sn thin films

To improve the optical storage performance, Sn was doped into Ge2Sb2Te5 phase change thin films. The optical and thermal properties of Sn-doped Ge2Sb2Te5 film were investigated. The crystal structures of the as-sputtered and the annealed films were identified by the X-ray diffraction (XRD) method. The differential scanning calorimeter (DSC) method is used to get the crystallization temperature and crystallization energy (Ea). It was found that proper Sn-doping could highly improve storage performance of the Ge2Sb2Te5 media.     

Real-time holographic reflection gratings in volume media of azo-dye-doped poly(methyl methacrylate)

Real-time formation of holographic reflection gratings is experimentally demonstrated in thick media of Disperse Red 1- (DR-1) doped poly(methyl methacrylate) at a nonresonant wavelength (647 nm). Our diffraction efficiencies of 30% and 23% are achieved for reflection gratings inscribed by spatial modulation of intensity and polarization, respectively, and are believed to be the highest achieved for a dye-doped polymer. In addition to the recording of amplitude and phase, the polarization state is also recorded and reconstructed.     

双光束磁光存贮中信号读出的偏振态分析

利用琼斯矩阵分析了双光束磁光存贮中信号读出系统偏振态的传输情况，推导了读出信号的表达式，分析了偏振分束镜与光盘盘基的相位延迟对读出信号的影响。     

榕树型互连网络及光学实现

讨论了一种用扭曲向列相液晶器件和偏振分光棱镜实现光学榕树上互连网络的结构，这种结构具有直线式传输、无错位、无缩放，并能够实现模块化和集成化的优点。     

Holographic simultaneous readout polarization multiplexing based on photoinduced anisotropy in bacteriorhodopsin

Bacteriorhodopsin (bR) is a reversible photochromic protein that can be used as a holographic medium. The dichroic absorption of the bR molecule is polarization dependent, thereby allowing for the recording of polarization holograms. The properties of polarization holograms can be used to multiplex two independent images in a single bR film. A new technique and associated polarization-multiplexing scheme are demonstrated that allow for simultaneous readout of two orthogonally polarized images while achieving a high normalized diffraction efficiency for each of the individual images.     

Coherent control and polarization readout of individual excitonic states

We present measurements and simulations of coherent control and readout of the polarization in individual exciton states. The readout is accomplished by transient four-wave mixing detected by heterodyne spectral interferometry. We observe Rabi oscillations in the polarization, which show half the period of the Rabi oscillations in the population. A decrease of the oscillation amplitude with pulse area is observed, which is not accompanied by a change in the dephasing time. This suggests the transfer of the excitation to other states as the origin of the Rabi-oscillation damping. Detuning of the excitation enables the control of the polarization in phase and amplitude and is in qualitative agreement with simulations for a two-level system. Additionally, simultaneous Rabi flopping of several spatially and energetically close exciton states is demonstrated.     

双中心全息记录的矢量分析与记录方向优化

对描述双掺杂晶体非挥发性全息记录动力学过程的Kukhtarev方程进行了矢量分析,分析中考虑了体光生伏特效应和外加电场的作用。在小信号近似的基础上给出了双中心全息记录中记录与固定阶段空间电荷场的矢量解析解。在综合考虑空间电荷场的各向异性以及晶体有效电光系数的各向异性后,给出了双中心全息记录的优化记录方向。结果表明,对(Fe,Mn)∶LiNbO3晶体633nm寻常光记录,优化记录方向主要由有效电光系数决定,光栅波矢与光轴夹角为22°,方位角为30°;对(Fe,Mn)∶LiNbO3晶体633nm非寻常光记录,优化记录方向主要由固定空间电荷场决定,光栅波矢与光轴夹角为44°,方位角为90°。     

低功率近红外光的偏振方向对光致折射率变化影响的实验研究

研究了利用低功率近红外光辐照In:Fe:LiNbO3晶体时写入光束的偏振方向对光致折射率变化(Δn)的影响.分别采用正常偏振(o光)和非常偏振(e光)的近红外细激光束,在In:Fe:LiNbO3晶体中进行了光折变实验.研究表明,两种偏振方向引起晶体的Δn实测曲线相似,但变化规律恰好相反,o光引起的折射率变化量约是e光的3倍左右.近红外光写入下两种偏振光束引起晶体的Δn分布规律都不同于可见光,尤其是e光辐照区域中心晶体的折射率升高.因此,通过选择不同偏振方向的近红外光可以在光折变晶体中制作不同折射率分布的非线性光学器件.     

Zero and first-order phase shift correction for field map estimation with dual-echo GRE using bipolar gradients

A simple phase error correction technique used for field map estimation with a generally available dual-echo gradient-echo (GRE) sequence is presented. Magnetic field inhomogeneity maps estimated using two separate GRE volume acquisitions at different echo times are prone to dynamic motion errors between acquisitions. By using the dual-echo sequence, the data are collected during two back-to-back readout gradients in opposite polarity after a single radio frequency pulse, and interecho motion artifacts and alignment errors in field map estimation can be factored out. Residual phase error from the asymmetric readout pulses is modeled as an affine term in the readout direction. Results from phantom and human data suggest that the first-order phase correction term stays constant over time and, hence, can be applied to different data acquired with the same protocol over time. The zero-order phase correction term may change with time and is estimated empirically for different scans.