Defocusing in an optical system is a common practical issue that affects the quality and shape of the beam and is hence important in the light-matter interaction. A detailed investigation is carried out on the interaction of the tightly focused beam with a spherical nanoparticle under defocusing. Tightly focused beams with linear and radial polarization are considered for the investigation and the influence of such beams on plasmonic characteristics of a nanoparticle is analyzed. The effect of defocusing is observed on intensity enhancement in near-field in different surrounding media.
We present a detailed analysis and recipe for designing a channel Bragg-plasmon coupled waveguide where the
intermodal coupling between a bandgap-guided mode and surface plasmon mode substantially modifies the phase-velocity
dispersion slope of supermodes. This leads to appreciably large group-velocity-dispersion with peak value of ≈4.33x104 ps/km-nm close to the optical communication band as well as interaction bandwidth of about 765 pm for 1 cm
long waveguide. We also found that bandgap guided Bragg modes exhibit stronger dispersive features than the plasmon
modes around ~ 1.50 μm which is exactly opposite to what is usually observed in visible region. The impact of
waveguide parameters such as channel width etc. on mode-coupling mechanism is also studied with significant
emphasis on the propagation loss suffered by the supermodes of the structure.
A fiber-optic surface plasmon resonance (SPR) sensor for the detection of human blood groups is proposed. Previous experimental results describing the wavelength-dependent refractive index variation of multiple samples of different blood groups are considered for theoretical calculations. The spectral interrogation method, along with silica fiber and silver layer, is considered. The sensor's performance is closely analyzed in terms of shift in SPR wavelength and SPR curve width in order to optimize the design parameters for a reliable and accurate blood-group identifier. The sensor design parameters include silver layer thickness, fiber core diameter, sensing region length, and temperature variation. The results are explained in terms of light coupling and plasmon resonance condition. The proposed sensing probe is able to provide high sensitivity and accuracy of blood-group detection, thereby opening an easy and reliable window for medical applications.
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