Results 1 - 10 of 1020
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[en] We investigate the three-dimensional (3D) scattering problem of an incident plane shear horizontal wave by a partly through-thickness hole in an isotropic plate, in which the Lamb wave modes are also included due to the mode conversions by the scattering obstacle in the 3D problem. An analytical model is presented such that the wave fields are expanded in all of propagating and evanescent SH modes and Lamb modes, and the scattered far-fields of three fundamental guided wave modes are analyzed numerically for different sizes of the holes and frequencies. The numerical results are verified by comparing with those obtained by using the approximate Poisson/Mindlin plate model for small hole radius and low frequency. It is also found that the scattering patterns are different from those of the S0 wave incidence. Our work is useful for quantitative evaluation of the plate-like structure by ultrasonic guided waves. (paper)
[en] A new approach for the design of a quasi-optical gyrotron mode converter is proposed. It is based on the synthesis of quasi-optical mirrors using diffraction (Helmholtz-Kirchhoff) integrals. First application of such a method was already described. Now a more powerful technic is used to provide optimal distributions of the wave beam field. It is shown that by means of specially shaped mirrors, parameters of the main converter are enhanced strongly. In this paper the authors review the search for the optimal scheme of the converter, present and compare results of calculations and measurements of the gyrotron wave beam
[en] A brief review is presented of the contributions of Allan Kaufman to the theory of plasma waves. These contributions have been rich and various, characterized by high quality and a sense of what makes a problem both interesting and important. We include a brief summary of work prior to the mid-1980's, but the primary emphasis will be on more recent work concerning the use of phase space methods in the theory of linear plasma waves and mode conversion. One goal of the paper is to place Allan's contributions in the wider context of semi-classical methods. We will emphasize the underlying intuitions rather than providing a detailed mathematical exposition which can be found in the literature cited.
[en] A C-band polarization rotator-splitter based on a mode-evolution structure and an asymmetric directional coupler is proposed. The mode-evolution structure is designed in a bi-level taper through which the TM0 mode can evolve into the TE1 mode. Then the TE1 mode is coupled to the TE0 mode at the cross port using the asymmetric directional coupler. The input TE0 mode propagates along the waveguide without mode conversion and output at the through port. From the experimental results, the extinction ratio is lower than 30 dB and the excess loss is less than 1 dB for input TE0 mode at the whole C-band. For input TM0 mode, the ER and the EL are, respectively, lower than −10 and 1.5 dB. (paper)
[en] Optomechanical dark mode plays a central role in effective mechanically-mediated conversion of two different cavity fields. In this paper, we present a more efficient method to utilize the dark mode to transfer a coherent signal. When an auxiliary cavity mode is exploited, two approaches are proposed to effectively eliminate the optomechanical bright mode, and only the optomechanical dark mode is left to facilitate state transfer. Even with small cooperativity and different losses for the two target modes, the internal cavity mode-conversion efficiency can also reach unity. - Highlights: • Reservoir-engineering is used for state conversion. • The optomechanical bright mode can be absolutely eliminated. • Small cooperativity and different losses are feasible for ideal conversion efficiency.
[en] We propose a novel embedded long-period waveguide grating (LPWG) for the implementation of a broadband mode conversion. The proposed LPWG is formed in the inner of waveguide where the two coupled modes have the largest field overlap and, hence, features an ultra-short length and a wide bandwidth. Besides, the bandwidth of the proposed LPWG is further increased by manipulating its phase-matching curve. Our proof-of-principle device, fabricated with polymer for the conversion between the E11 and E21 modes, contains only two periods and achieves a mode conversion efficiency larger than 98.2% (99.2%) for the x (y) polarization over the C + L band. The proposed LPWG could find applications as an ultra-compact and broadband mode converter in mode-division-multiplexing system.
[en] The mode-conversion characteristics of a few-mode optical waveguide based on adiabatic mode evolution are investigated. The mode-conversion efficiency and cross talks of the configuration are found dependent on the position and angle between the assistant waveguide and the main waveguide, and also the size of the assistant waveguide. By setting the bottoms of the two waveguides at the same plane, the symmetry of the configuration can be broken. The configuration is able to convert each mode to a higher order or lower order mode by launching light from different ports. In particular, mode conversion between the two degenerated LP11 modes can be achieved with wide bandwidth.