基于级联MZMs倍频系数可调的相位编码信号光产生方法

提出了一种基于级联马赫-曾德尔调制器(MZMs)倍频系数可调的相位编码信号光产生方法。该方法的系统核心器件为级联MZMs,通过合理选择两个MZMs的直流偏置电压和调制指数等参数,可任意选取±k(k=1,2,…,5)阶边带中的一组边带。通过可编程光滤波器滤除5阶以上的高阶边带,再结合相位调制,可产生载波2、4、6、8和10倍频的相位编码信号。该方法是通过改变施加在级联MZMs上的射频驱动信号幅度实现倍频系数调节,方案简洁灵活。通过仿真实验验证了利用4GHz的微波信号源分别产生载频32GHz和40GHz的相位编码信号,从而实现了8和10倍频信号输出,且所生成的相位编码信号具有很好的脉冲压缩性能。     

谐振式微光学陀螺偏置频率调制技术研究

谐振式微光学陀螺(RMOG)是一种基于光学Sagnac效应的新型角速度传感器.提出了基于模拟波形连续线性相位调制技术的偏置频率调制.与传统的双频率锯齿波调制以及数字调制方法相比,偏置频率调制消除了由于锯齿波回扫或数字波形中的台阶效应引入的脉冲噪声.从理论上推导了连续线性相位调制波形参数与陀螺的动态范围和灵敏度的关系,得...     

频率可调的双路相位编码微波信号系统

提出一种在单输入情况下同时产生两路任意相位编码微波信号的方法,不仅可以保证编码信号180°的相移,还可实现编码信号的频率大范围调谐.建立由一个双平行马赫曾德调制器和一个保偏布拉格光栅组成的系统,激光输入双平行马赫曾德调制器调制后,通过保偏布拉格光栅与偏振分束器的共同作用产生两路偏振正交的±2阶边带.其中一对边带经过相位调制器调制后与另一对耦合,最后输出两个光电探测器拍频得到高频率、低噪声的相位编码微波信号.仿真结果表明,通过调节驱动信号的频率,可得到5～100 GHz的一系列四倍频相位编码微波信号.还原的相位信息与脉冲压缩比均和理论值吻合,证明了所提方法具有良好的脉冲压缩性能.     

集总式放大波分复用链路中交叉相位调制的边带不稳定性

集总式放大链路中，放大器的周期分布，等效于形成一折射率光栅，它为四波混频提供了相位匹配的条件，产生边带不稳定性．本文通过解析和数值模拟的方法，研究了周期集总式放 大链路中，交叉相位调制边带不稳定性．解析研究中，根据耦合方程的稳态解，计算了反常 色散与正常色散光纤链路中由于扰动而产生的边带不稳定性的增益；数值模拟中，利用分裂 步长傅里叶变换法与Monte_Carlo方法，得出了输出光脉冲的频谱，说明输出光脉冲频谱中 产生新的边带．两种方法的计算结果表明，在周期集总式放大光通信链路中，存在交叉相位 调制边带不稳定性，两种方法得到的结论基本一致． 关键词： 交叉相位调制 边带不稳定性 集总式放大     

非均匀相互作用MAS边带的抑制

在本文中,我们用Bessel函数展开法从理论上分析了非均匀相互作用产生的MAS旋转边带以及消除这些旋转边带的各种方法,从而指出当相互作用强度与转速的比值大于2时,对于最常用的TOSS方法来说会产生严重的谱失真。本文还对现存的各种抑制边带的方法作了实验比较。     

基于相位调制器与Fabry-Perot干涉仪的激光多普勒频移测量方法

提出了一种激光多普勒频移测量方法, 此方法利用正弦相位调制使信号光在原频率成分基础上产生正负一阶边带, 再由Fabry-Perot干涉仪对调制光振幅和相位进行调整, 使其产生固定频率的拍频信号, 利用此拍频信号的振幅随频率变化而变化的性质来进行多普勒频移测量. 通过理论分析证明该方法具有很高的测量精度, 加工装调难度不大, 兼顾了普通相干与非相干探测方法的优势. 另外通过实验证明该方法的正确性与可行性, 并通过与普通非相干方式比较发现该方法在测量精度上可以提高 约1个数量级. 关键词： 多普勒频移 相位调制 Fabry-Perot干涉仪 拍频     

基于偏振模干涉的可变系数微波光子滤波器

基于偏振调制和光的干涉原理,设计了同时具有正系数和负系数特性的微波光子滤波器,并通过搭建实验模型证实了方案的可行性。利用偏振调制及光的偏振特性实现载波和一阶边带的正交偏振,并通过改变偏振调制器的偏置电压分别对载波和一阶边带引入相移。当载波和一阶边带的相位差为0或90时,利用保偏光纤快慢轴上两正交偏振光在同一偏振态上的干涉效应,分别对应实现具有负系数或正系数特性的微波光子滤波器。最后,测量并验证了0~15 GHz频率范围内滤波器的频率响应。     

基于双通道马赫曾德尔调制器调制边带滤波的微波光子移相器

提出了一种基于双通道马赫曾德尔调制器(DPMZM)调制边带滤波的微波光子移相器。在双通道马赫曾德尔调制器的结构中,在一路马赫曾德尔干涉仪上实现抑制光载波的双边带调制输出,而在另一路马赫曾德尔的相位调节臂上通过调节偏置电压实现光载波信号的光学移相,两路光信号经过干涉合路后由光纤布拉格光栅(FBG)滤除其中一个一阶边带,最后输入到光电探测器(PD)进行光电转换得到移相的微波信号。实验结果表明,基于DPMZM调制边带滤波的微波光子移相器具有传输特性稳定、输出幅度波动小的优点。该结构还具有相移调节响应速度快、应用频带宽以及移相范围大于360°等特点。     

主动相位偏置折叠型萨尼亚克光纤传感阵列时分复用技术

针对折叠结构萨尼亚克(Sagnac)光纤传感阵列存在噪声光与信号光混叠的问题,提出了一种主动相位偏置时分复用方案.在传统梯形结构传感阵列的基础上,通过调整总线光纤的长度关系和附加延迟光纤的方法,使噪声光和信号光依次交替返回而不会发生混叠.进一步分析表明,通过调整延迟光纤环的长度,可以使输入光脉冲的重复频率达到标准时分复用系统重复频率的二分之一.整个阵列的相位偏置由一个与输入光脉冲同步的相位调制信号驱动集成光学芯片实现.实验演示了一个两基元的传感阵列,最小时间间隔为331.25 ns,输入光脉冲重复频率可达754.727 kHz,在5 kHz处相位灵敏度为7.3μrad√(Hz),探头间串扰约为-51.75 dB.     

魔角旋转情形下固体的非均匀相互作用

各向异性非均匀相互作用的慢旋转MAS-NMR谱是一系列的旋转边带,这些边带的强度包含了该相互作用张量的全部信息,只要计算和分析少数几条边带就可以得到这些有用的结构信息,本文用不可约球谐张量算符表示非均匀相互作用,采用Bessel函数展开法分析计算非均匀相互作用产生的旋转边带,这种分析计算方法适用于各种非均匀相互作用。以化学位移和四极相互作用为例的实验与理论符合很好。 关键词：     

利用法布里-珀罗腔抑制电光相位调制中的剩余幅度调制

激光经电光相位调制后,由于剩余幅度调制的存在造成调制边带幅度不相等。利用法布里-珀罗腔的透射特性和Pound-Drever-Hall技术对通过法布里-珀罗腔的调制光正、负一级边带的幅度产生不同的衰减,使得调制边带的幅度相等,从而实现对电光相位调制中剩余幅度调制的抑制。采用该方法,理论上计算了调制光经法布里-珀罗腔后的光外差光谱信号,获得锁定法布里-珀罗腔后调制边带幅度的不对称度较腔锁定前减小四个数量级。实验研究了调制光经法布里-珀罗腔透射的光外差光谱,结果表明将法布里-珀罗腔锁定于该透射光外差光谱中心零位时,对剩余幅度调制的抑制程度可达45 dB。     

A two-dimensional experiment that separates decoupling sidebands from the main peaks.

Broadband decoupling techniques generate undesirable cycling sidebands. The new two-dimensional technique described here allows separation of these sidebands from the main peaks by spreading the sideband responses in the indirectly detected dimension (F(1)) according to their frequency separations from the parent peaks, leaving the main resonances at zero frequency in F(1). This trace at zero frequency shows a thousandfold suppression of the residual sidebands, making possible the detection of very weak signals from dilute constituents of the sample. The experimental results can be displayed as one-dimensional "quiet decoupling" spectra without any significant loss of sensitivity. The new technique (DESIRE-decoupling sideband resolved spectroscopy) is simple, robust, and straightforward to implement.     

Resonance fluorescence of a two-level atom in a feedback loop

The resonance fluorescence spectrum of a two-level atom in a classical light field, whose phase is changed by a feedback system by π after the detection of each spontaneous photon, has been calculated. The spectrum resembles the well-known Rautian-Mollow triplet. However, the sidebands become sharply asymmetric at a nonzero frequency detuning of the light field from the atomic resonance transition. In addition, the spectrum retains the pronounced triplet shape even beyond the secular approximation, when the sidebands of the Rautian-Mollow structure become unresolved in the absence of the feedback.     

A two-dimensional artifact from asynchronous decoupling

Many heteronuclear NMR experiments employ decoupling to collapse the heteronuclear multiplet, using decoupling schemes with a periodic phase modulation like WALTZ, MLEV, or GARP. Because of the periodic nature of these schemes, cycling sidebands are generated, whose intensity can be strongly reduced by decoupling asynchronously. We show that the most common implementation of asynchronous decoupling on modern spectrometers is such that the cycling sidebands are subjected to a periodic modulation. For multidimensional experiments, this results in ridges that can seriously compromise the quality of the spectrum. Based on our model, the artifact in a 2D [(1)H]-(15)N NOE equilibrium experiment is simulated and it is shown that the artifact can be prevented by using synchronous decoupling.     

Investigations of polymer dynamics in nanoporous media by field cycling NMR relaxometry and the dipolar correlation effect

The chain dynamics of short-chain perfluoropolyether melts confined in Vycor nanoporous media has been characterized by field cycling nuclear magnetic resonance relaxometry and the dipolar correlation effect. The slowdown of motions under confinement, leading to larger residual dipolar couplings, has been probed by looking at the quotient of stimulated and primary echoes. Using field cycling relaxometry, it has been shown that there is strong evidence of reptation-like motion, even for such short-chain polymers as shown by the frequency and molecular weight dependences of the spin-lattice relaxation time.     

"BEST" homonuclear adiabatic decoupling for 13C- and 15N-double-labeled proteins.

The cyclic irradiation sidebands appearing in homonuclear adiabatic decoupling are calculated in detail, which reveals the origin of the antisymmetric sidebands. The sidebands can be inverted by inserting an initial decoupling with a different period, but the same f1rms as the main decoupling that is required for Bloch-Siegert shift compensation. The sidebands can be eliminated in a broad decoupling range by adding spectra of opposite sidebands. Based on this scheme, an offset-independent double-adiabatic decoupling, named Bloch-Siegert Shift Eliminated and Cyclic Sideband Trimmed Double-Adiabatic Decoupling, or "BEST" decoupling for short, is constructed, which not only compensates the Bloch-Siegert shift as shown earlier by Zhang and Gorenstein (1998) but also eliminates residual sidebands effectively.     

“BEST” Homonuclear Adiabatic Decoupling for C- and N-Double-Labeled Proteins

The cyclic irradiation sidebands appearing in homonuclear adiabatic decoupling are calculated in detail, which reveals the origin of the antisymmetric sidebands. The sidebands can be inverted by inserting an initial decoupling with a different period, but the same f_1rms as the main decoupling that is required for Bloch–Siegert shift compensation. The sidebands can be eliminated in a broad decoupling range by adding spectra of opposite sidebands. Based on this scheme, an offset-independent double-adiabatic decoupling, named Bloch–Siegert Shift Eliminated and Cyclic Sideband Trimmed Double-Adiabatic Decoupling, or “BEST” decoupling for short, is constructed, which not only compensates the Bloch–Siegert shift as shown earlier by Zhang and Gorenstein (1998) but also eliminates residual sidebands effectively.     

Localized proton spectroscopy without water suppression: removal of gradient induced frequency modulations by modulus signal selection

Most Magnetic Resonance Spectroscopy (MRS) localization methods can generate gradient vibrations at acoustic frequencies and/or magnetic field oscillation, which can cause a time-varying magnetic field superimposed onto the static one. This effect can produce frequency modulations of the spectral resonances. When localized MRS data are acquired without water suppression, the associated frequency modulations are manifested as a manifold of spurious peaks, called sidebands, which occur symmetrically around the water resonance. These sidebands can be larger than the small metabolite resonances and can present a problem for the quantitation of the spectra, especially at short echo times. Furthermore, the resonance lineshapes may be distorted if any low frequency modulations are present. A simple solution is presented which consists of selecting the modulus of the acquired Free Induction Decay (FID) signal. Since the frequency modulations affect only the phase of the FID signal, the obtained real spectrum of the modulus is free from the spurious peaks where quantitative results may be directly obtained. Using this method, the distortions caused by the sidebands are removed. This is demonstrated by processing proton MRS spectra acquired without water suppression collected from a phantom containing metabolites at concentrations comparable to those in human brain and from a human subject using two different localization methods (PRESS and Chemical Shift Imaging PRESS-(CSI)). The results obtained illustrate the ability of this approach to remove the spurious peaks. The corrected spectra can then be fit accurately. This is confirmed by the results obtained from both the relative and the absolute metabolites concentrations in phantoms and in vivo.     

Quasi-phase-matched modulation instability in birefringent fibers

The phase-sensitive nature of polarization modulation instability has been demonstrated in optical fibers whose birefringence has been manipulated to generate phase mismatches. Quasi-phase-matched modulation instability has been demonstrated, and the gain of the quasi-phase-matched sidebands has been investigated. The results are in good agreement with experiment.     

Sideband entanglement in collective resonance fluorescence

We examine the quantum correlation between the Mollow sidebands in the collective resonance fluorescence from a strongly driven ensemble of two-level atoms. By using the criterion proposed by Shchukin and Vogel, we show that non-Gaussian entanglement exists between the two separated sidebands. The responsible mechanism is traced to the spontaneous parametric process, in which the nonclassical correlation is established. This suggests that the collective resonance fluorescence provides a continuous source for the non-Gaussian entangled light and thus has great potentials for various applications in quantum information and quantum computation.