Soliton propagation optimization and dynamic modulation in photonic crystal waveguide with polystyrene background

Bright optical soliton propagation properties near the left band edge of photonic crystal waveguide (PCW) are numerically investigated. Compared with the normal PCW with air background, by employing polystyrene as PCW background and adjusting the structure parameters simultaneously, the required soliton peak power sharply decreases from 8.63 × 10⁶ W/m to 9.98 × 10² W/m. The influence of optical loss on soliton propagation is numerically investigated. The dynamic modulation of the soliton propagation in PCW is realized, and a modulation range of 459 nm wavelength for the soliton transmission has been achieved. Simulation results show that the transmission wavelength, required soliton peak power and delay time decrease almost linearly as the external modulated voltage increases; the modulation sensitivities are 8.316 nm/V, 3.416 W/m/V and 16.6 ps/V, respectively.     

High-bandwidth and low-loss photonic crystal power-splitter with parallel output based on the integration of Y-junction and waveguide bends

A 1×2 power-splitter with parallel output that exhibits high-bandwidth and low-loss splitting for TE-polarized light is designed based on a photonic crystal slab in a silicon-on-insulator (SOI) material. The high performance is achieved by the integration of a Y-junction and 60° waveguide bends, which is designed to ensure single-mode operation, and keep the output channels of the power-splitter be parallel to the input channel. With a three-dimensional finite-difference time-domain (3D-FDTD) technique, ultralow-loss output of the optimized power-splitter with normalized transmission above 45% (in the range 3.216±0.18 dB) is obtained in the high-bandwidth range 1472–1634 nm, which covers the entire C-band of optical communication. In addition, the simulation results demonstrate that when the manufacture error of the lattice shift (dx) is in the range of ±10 nm, the disturbance of the transmission and the bandwidth are 1.52% and 6.79%, respectively. Both the specific result and the general idea of integration design are promising in the optical integrated circuit (OIC) and integrated optical devices in the future.     

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by using a frequency shifter

We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation (PA) spectra are recorded with two laser beam induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the PA spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is (34.84 ± 0.22) MHz. By analyzing other broadening mechanisms, a value of (32.02 ± 0.70) MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.     

Study on the relations of sensitivity with energy properties for HMX and HMX-based PBXs by molecular dynamics simulation

Molecular dynamics simulation was applied to study the structure and energy properties of β-HMX (β-cyclotetramethylene tetranitramine) crystal and its composite PBXs (polymer-bonded explosives) with F₂₃₁₁ as a polymer binder under different temperatures and F₂₃₁₁ concentrations. The interface interaction energy of HMX and F₂₃₁₁, the interaction energy E_N–N between N atoms in N–NO₂ trigger bond in HMX molecules, and the cohesive energy density (CED) are presented and analyzed. A meaningful finding is that there exists correlation between E_N–N and the sensitivity of β-HMX and its composites, i.e. the less the E_N–N is, the larger the sensitivity is. Additionally, molecular interactions are inherently disclosed by using pair correlation function (PCF) to analyze the interfacial structure between (1 0 0)HMX crystal surface and F₂₃₁₁ molecular chain.     

Influence of switchable magnetic field on the modulation property of nanostructured magnetic fluids

Magnetic fluid is a kind of colloidal material with tunable microstructure and unique optical properties. The tunable magneto-optical modulation property of magnetic fluid under externally switchable magnetic field with various modulation periods is investigated theoretically and experimentally. The transitional modulation period (lower limit of the working frequency) between the square-like and oscillation-like modulation is achieved and found to be magnetic-field- and sample-concentration-dependent. The modulation mechanism is analyzed and ascribed to the dynamic microstructure of magnetic fluid under different modulation periods of external magnetic fields. The result of this work may be helpful for the pragmatic applications of magnetic fluid based on the square-like modulation.     

Analysis of spectral properties of acoustic noise produced during magnetic resonance imaging

Magnetic resonance imaging (MRI) technique enables non-invasive analysis of the human vocal tract during phonation. Creation of MR images of the vocal tract is accompanied by simultaneous recording of the produced speech. The paper analyzes and compares spectral properties of an acoustical noise produced by mechanical vibration of the gradient coils during scanning in the open-air MRI equipment working in a weak magnetic field with low B₀ up to 0.2 T. This noise exhibits harmonic character, so it is suitable to analyze its properties in the spectral domain. Obtained results of spectral analysis will be used to devise a new cepstral-based filtering method for noise suppression of recorded speech.     

点缺陷对硼掺杂直拉硅单晶p/p~+外延片中铜沉淀的影响

系统研究了点缺陷对晶体硅中氧沉淀生成的影响,及点缺陷和氧沉淀对重掺硼直拉硅单晶p/p⁺外延片中铜沉淀的影响.样品先在不同的气氛下进行1250℃/60 s快速热处理,随后在750℃/8 h+1050℃/16 h常规热处理过程中引入铜沾污.通过腐蚀结合光学显微镜研究发现,以O₂作为保护气氛时,p⁺衬底中的沉淀密度较小,以Ar和N₂作为保护气氛时,重掺硼p⁺衬底中生成了高密度的沉淀,且在上述所有样品的外延层中均无缺陷生成.研究认为,以O₂作为保护气时引入的自间隙硅原子（Si_I）可以抑制沉淀的形成,而以Ar和N₂作为保护气氛时引入的空位则会促进沉淀的生成,这是导致此差异的主要原因.另外,研究还发现,p/p⁺外延结构能很好地吸除硅片中的铜杂质,从而保持了外延层的洁净.     

微波场中Josephson结的微波发射与吸收研究

采用数值仿真方法,研究微波场中约瑟夫森结微波感应台阶处的功率特性。发现微波场中约瑟夫森结不止吸收辐射,也发射辐射的情况。得到微波辐照和结电阻对功率吸收和发射的影响规律。结果表明,处于发射功率的状态对应的偏置电流范围占整个台阶总电流范围的比例可以趋于50%。这一发现对约瑟夫森结理论和应用研究具有重要的意义。     

红外偏振成像对伪装目标的探测识别研究

针对目前普通光电成像系统对伪装目标的探测和识别概率较低的状况,提出伪装目标的探测识别新技术研究。介绍了红外偏振成像系统的原理、组成和特点,研制的中波/长波红外偏振成像装置,其波段范围为3 m ~5 m和8 m~12 m,线偏振度95%,消光比大于100∶1,给出了试验分析数据和偏振融合效果图。研究表明,采用红外偏振成像技术可以有效地实现对地面伪装目标的探测和识别。研究结果还可以扩展到对人工假目标、空中隐身目标等的探测和识别。     

Temperature-insensitive Mach-Zehnder interferometric strain sensor based on concatenating two waist-enlarged fiber tapers

A novel temperature-insensitive strain sensor,based on an in-line Mach-Zehnder interferometer,is fabricated by concatenating two waist-enlarged fiber tapers separated by a short piece of photonic crystal fiber. The interference spectrum of the proposed sensor is analyzed in detail.Experimental results demonstrate that this sensor has a strain sensitivity of.3.02 pm/μεand maintains the temperature insensitivity feature. The proposed sensor has great potential in diverse sensing applications due to its advantages,such as its compact size,low cost,and simple fabrication process.