Search

The paper studies plasmonics modeling issues and examines the reasons behind the failure of the field-based methods relying on Padé approximations widely used in the analysis of photonic devices based on dielectric materials. Through a study of evanescent, radiation, guided, and surface modes of a plasmonic structure where the failure appears clearly, we demonstrate the physical explanation of this failure and suggest some remedies. We developed a Bidirectional Beam Propagation Method (BiBPM) by adopting a Blocked Schur (BS) algorithm to introduce an unconditionally stable method for plasmonic structures with strong discontinuities. Central to BiBPMs is the accurate calculation of the square root operators that is very widely performed using Padé approximations. However, recent reports demonstrate convergence of Padé that is too slow to lend itself a stable solver in plasmonics. Moreover, Padé approximations completely fail in handling such a strong discontinuity between dielectric and plasmonic waveguides, where a very-wide spectrum of modes could be excited. Alternatively, we propose calculating these operators by the twice faster BS algorithm. Beyond the computational speed, our suggested approach overbears the Padé-based BiBPMs instability and accuracy problems, thanks to the proper physical treatment of surface and evanescent waves: the notorious sources of instability. Through the plasmonic discontinuity problems, the superiority of BS approach has been determined numerically and explained physically.

A novel design of a highly sensitive self-calibration biosensor based on a surface plasmon photonic crystal fiber is presented and analyzed using a full-vectorial finite-element method. In this paper, the sensor geometrical parameters are optimized to achieve high sensitivity for the two polarized modes. The numerical results reveal that the resonant peaks corresponding to the two polarized beams are highly sensitive to the variation of the analyte refractive index. Therefore, high refractive index sensitivity of about 6700 nm/refractive index unit (RIU) and 10000 nm/RIU with the corresponding resolution of 1.49 × 10-5 and 1.0 × 10-5 RIU can be obtained according to the quasi-transverse magnetic (TM) and quasi-transverse electric (TE) modes, respectively. Additionally, the reported self-calibration biosensor has high linearity and high accuracy. Furthermore, the suggested biosensor has great potential for biological and biochemical analytes detection.

A novel design of polarization-independent surface plasmon multiplexer- demultiplexer (MUX/DEMUX) based on dual-core photonic crystal fiber with a central gold wire is proposed and analyzed. The cladding air holes are infiltrated with a nematic liquid crystal of type E7 with rotation angle φ, and the background material is a soft glass of type SF57 (lead silica). The simulation results are obtained using full-vectorial finite-difference method and coupled mode theory. At φ = 900, the suggested MUX/DEMUX has a short device length of 953.254 μm for x-polarized modes with broad bandwidths of 235 and 175 nm around wavelengths of 1.3 and 1.55 μm, respectively, with low cross-talk better than -20 dB. For y-polarized modes, the reported MUX/DEMUX has short device length of 1322.86 μm with broad bandwidths of 193 and 170 nm around 1.3 and 1.55 μm, respectively. Moreover, the polarization independence is achieved with short device lengths of 1138.06 and 1180 μm at φ = 90° and 0°, respectively.

A novel design of a polarization splitter based on index-guiding soft glass nematic liquid crystal (NLC) photonic crystal fiber is proposed and analyzed. The simulation results are obtained using the full-vectorial finite-difference modal solution along with the full-vectorial finite-difference beam propagation method. The numerical results reveal that the suggested splitter of length 8.227 mm can provide low crosstalk of better than -20 dB with great bandwidths of 30 nm and 75 nm for the quasi TE and TM modes, respectively. In addition, the reported splitter has a tolerance of ±3% in its length, which makes the design less sensitive to the perturbation introduced during the fabrication process.