Mode transformation due to curvature and diameter variations in smooth-wall circular waveguides

2004 ◽  
Author(s):  
V.V. Zemlyakov ◽  
G.F. Zargano ◽  
G.P. Sinyavskiy
Keyword(s):  
Smooth Wall ◽  
Mode Transformation ◽  
Circular Waveguides

Mode transformation in very oversized circular waveguides

1987 ◽  
Vol 8 (9) ◽  
pp. 1129-1143 ◽  
Author(s):  
D. Pasquet ◽  
J. L. Gautier ◽  
P. Pouvil
Keyword(s):  
Mode Transformation ◽  
Circular Waveguides

scholarly journals Adiabatic mode transformation in width-graded nano-gratings enabling multiwavelength light localization

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Moein Shayegannia ◽  
Arthur O. Montazeri ◽  
Katelyn Dixon ◽  
Rajiv Prinja ◽  
Nastaran Kazemi-Zanjani ◽  
...  
Keyword(s):  
Multispectral Imaging ◽  
Groove Depth ◽  
Surface Enhanced Raman Spectroscopy ◽  
Fine Tuning ◽  
Mode Transformation ◽  
Resonance Modes ◽  
Light Localization ◽  
Metal Insulator Metal ◽  
Surface Enhanced Raman ◽  
Adiabatic Mode

AbstractWe delineate the four principal surface plasmon polariton coupling and interaction mechanisms in subwavelength gratings, and demonstrate their significant roles in shaping the optical response of plasmonic gratings. Within the framework of width-graded metal–insulator-metal nano-gratings, electromagnetic field confinement and wave guiding result in multiwavelength light localization provided conditions of adiabatic mode transformation are satisfied. The field is enhanced further through fine tuning of the groove-width (w), groove-depth (L) and groove-to-groove-separation (d). By juxtaposing the resonance modes of width-graded and non-graded gratings and defining the adiabaticity condition, we demonstrate the criticality of w and d in achieving adiabatic mode transformation among the grooves. We observe that the resonant wavelength of a graded grating corresponds to the properties of a single groove when the grooves are adiabatically coupled. We show that L plays an important function in defining the span of localized wavelengths. Specifically, we show that multiwavelength resonant modes with intensity enhancement exceeding three orders of magnitude are possible with w < 30 nm and 300 nm < d < 900 nm for a range of fixed values of L. This study presents a novel paradigm of deep-subwavelength adiabatically-coupled width-graded gratings—illustrating its versatility in design, hence its viability for applications ranging from surface enhanced Raman spectroscopy to multispectral imaging.

Mode transformation properties in the integrated bimodal resonance structure

2021 ◽  
pp. 127187
Author(s):  
Junxue Chen ◽  
Liu Wang ◽  
Xiongping Xia ◽  
Qiuqun Liang ◽  
Runmei Gao
Keyword(s):  
Resonance Structure ◽  
Mode Transformation

Applicability of Taylor’s hypothesis in rough- and smooth-wall boundary layers

2016 ◽  
Vol 812 ◽  
pp. 398-417 ◽  
Author(s):  
D. T. Squire ◽  
N. Hutchins ◽  
C. Morrill-Winter ◽  
M. P. Schultz ◽  
J. C. Klewicki ◽  
...  
Keyword(s):  
Boundary Layers ◽  
Outer Region ◽  
Rough Wall ◽  
Turbulent Shear ◽  
Normal Velocity ◽  
Turbulent Shear Flow ◽  
Smooth Wall ◽  
Wall Boundary ◽  
Taylor’S Hypothesis ◽  
Velocity Spectra

The spatial structure of smooth- and rough-wall boundary layers is examined spectrally at approximately matched friction Reynolds number ($\unicode[STIX]{x1D6FF}^{+}\approx 12\,000$). For each wall condition, temporal and true spatial descriptions of the same flow are available from hot-wire anemometry and high-spatial-range particle image velocimetry, respectively. The results show that over the resolved flow domain, which is limited to a streamwise length of twice the boundary layer thickness, true spatial spectra of smooth-wall streamwise and wall-normal velocity fluctuations agree, to within experimental uncertainty, with those obtained from time series using Taylor’s frozen turbulence hypothesis (Proc. R. Soc. Lond. A, vol. 164, 1938, pp. 476–490). The same applies for the streamwise velocity spectra on rough walls. For the wall-normal velocity spectra, however, clear differences are observed between the true spatial and temporally convected spectra. For the rough-wall spectra, a correction is derived to enable accurate prediction of wall-normal velocity length scales from measurements of their time scales, and the implications of this correction are considered. Potential violations to Taylor’s hypothesis in flows above perturbed walls may help to explain conflicting conclusions in the literature regarding the effect of near-wall modifications on outer-region flow. In this regard, all true spatial and corrected spectra presented here indicate structural similarity in the outer region of smooth- and rough-wall flows, providing evidence for Townsend’s wall-similarity hypothesis (The Structure of Turbulent Shear Flow, vol. 1, 1956).

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