Browsing by Author "Dong, Bin"

Now showing 1 - 4 of 4
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    Decoding The Spectra Of Low-Finesse Extrinsic Optical Fiber Fabry-Perot Interferometers
    Ma, Cheng; Dong, Bin; Gong, Jianmin; Wang, Anbo (Optical Society of America, 2011)
    A theoretical model is developed to address the fringe visibility and additional phase in the interference spectra of low-finesse extrinsic optical fiber excited Fabry-Perot interferometers. The model described in the paper applies to both single-mode and multimode fiber excitations; according to the theory, the fringe visibility and additional phase term are primarily determined by the working wavelength and angular power density distribution outputting from the excitation fiber, rather than based on spatial and temporal degree of coherence. Under certain approximations, the output interference intensity and the spatial power density distribution projected onto the fiber axis form a Fourier-transform pair, which potentially provides a tool for spatial density distribution analysis of fiber output. With excellent agreement with experiments, the theory presented in this paper leads to design guidelines for Fabry-Perot interferometric sensors and insightful physical understanding of such devices. (C) 2011 Optical Society of America
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    Implementation Of A Loss-Compensated Recirculating Delayed Self-Heterodyne Interferometer For Ultranarrow Laser Linewidth Measurement
    Chen, X. P.; Han, M.; Zhu, Y. Z.; Dong, Bin; Wang, Anbo (Optical Society of America, 2006-12-01)
    Ultranarrow laser linewidth measurement using an optimized loss-compensated recirculating delayed self-heterodyne interferometer is described. An experimental setup is constructed to measure subkilohertz laser linewidths. The system parameters are optimized to obtain the best beat signals. The experimental results agree well with the theoretical analysis. Two methods of linewidth interpretation are presented and analyzed based on the experimental results. It is proved that a loss-compensated recirculating delayed self-heterodyne interferometer is an effective tool for measuring an ultranarrow laser linewidth. (c) 2006 Optical Society of America.
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    Modal Analysis of General Cyclically Symmetric Systems with Applications to Multi-Stage Structures
    Dong, Bin (Virginia Tech, 2019-10-10)
    This work investigates the modal properties of general cyclically symmetric systems and the multi-stage systems with cyclically symmetric stages. The work generalizes the modal properties of engineering applications, such as planetary gears, centrifugal pendulum vibration absorber (CPVA) systems, multi-stage planetary gears, etc., and provides methods to improve the computational efficiency to numerically solve the system modes when cyclically symmetric structures exist. Modal properties of cyclically symmetric systems with vibrating central components as three-dimensional rigid bodies are studied without any assumptions on the system matrix symmetries: asymmetric inertia matrix, damping, gyroscopic, and circulatory terms can be present. In the equation of motion of such a cyclically symmetric system, the matrix operators are proved to have properties related to the cyclic symmetry. These symmetry-related properties are used to prove the modal properties of general cyclically symmetric systems. Only three types of modes can exist: substructure modes, translational-tilting modes, and rotational-axial modes. Each mode type is characterized by specific central component modal deflections and substructure phase relations. Instead of solving the full eigenvalue problem,all vibration modes and natural frequencies can be obtained by solving smaller eigenvalue problems associated with each mode type. This computational advantage is dramatic for systems with many substructures or many degrees of freedom per substructure. Group theory is applied to further generalize the modal properties of cyclically symmetric systems when both rigid-body and compliant central components exist, such as planetary gears with an elastic continuum ring gear. The group theory for symmetry groups is introduced, and the group-theory-based modal analysis does not rely on any knowledge of the properties of system matrices in system equations of motion. The three types of modes (substructure modes, translational-tilting modes, and rotational-axial modes) are characterized by specific rigid-body central component modal defections, substructure phase relations, and nodal diameter components of compliant central components. The general formulation of reduced eigenvalue problems for each mode type is obtained through group-theory-based method, and it applies to discrete, continuous, or hybrid discrete-continuous cyclically symmetric systems. The group-theory-based modal analysis also applies to systems with other symmetry types. The group-theory-based modal analysis is generalized to analyze the multi-stage systems that are composed of symmetric stages coupled through the motions of rigid-body central components. The proposed group-theory-based modal analysis applies to multi-stage systems with cyclically symmetric stages, such as multi-stage planetary gears and CPVA systems with multiple groups of absorbers. The method also applies to multi-stage systems with component stages that have different types of symmetry. For a multi-stage system with symmetric stages, a unitary transformation matrix can be built through an algorithmic and computationally inexpensive procedure. The obtained unitary transformation matrix provides the foundation to analyze the modal properties based on the principles of group-theory-based modal analysis. For general multi-stage systems with symmetric component stages, the vibration modes are classified into two general types, single-stage substructure modes and overall modes, according to the non-zero modal deflections in each component stage. Reduced eigenvalue problems for each mode type are formulated to reduce the computational cost for eigensolutions. Finite element models of multi-stage bladed disk assemblies consist of multiple cyclically symmetric bladed disks that are coupled through the boundary nodes at the inter-stage interface. To improve the computational efficiency of calculating the full system modes, a numerical method is proposed by combination of the multi-stage cyclic symmetry reduction method and the subspace iteration method. Compared to the multi-stage cyclic symmetry reduction method, the proposed method improves the accuracy of obtained eigensolutions through an iterative process that is derived from the subspace iteration method. Based on the cyclic symmetry in each component stage of bladed disk, the proposed iterative method that can be performed using single stage sector models only, instead of using matrix operators for the full multi-stage bladed disks. Parallel computations can be performed in the proposed iterative method, and the computational speed for eigensolutions can be increased significantly.
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    Temperature effects on the energy bandgap and conductivity effective masses of charge carriers in lead telluride from first-principles calculations
    Venkatapathi, Sarankumar; Dong, Bin; Hin, Celine (American Institute of Physics, 2014-07-07)
    We determined the temperature effects on the electronic properties of lead telluride (PbTe) such as the energy bandgap and the effective masses of charge carriers by incorporating the structural changes of the material with temperature using ab-initio density functional theory (DFT) calculations. Though the first-principles DFT calculations are done at absolute zero temperatures, by incorporating the lattice thermal expansion and the distortion of Pb2+ ions from the equilibrium positions, we could determine the stable structural configuration of the PbTe system at different temperatures. (C) 2014 AIP Publishing LLC.