As shown in Figure 4a, when the height of mismatch varies from 0 to 100 nm, the normalized modal area changes a little in the range of 0.06 to 0.08, which is far below the diffraction limit [25].
The normalized modal area is defined as A m /A0 to quantitatively evaluate the mode confinement, where A0 represents the diffraction-limited area in free space, A0 = λ2/4.
As a consequence, the normalized modal area decreases and the metal nanowire dissipates less energy, leading to a longer propagation length.
A modified hexagonal index guiding photonic crystal fiber made of pure silica with high birefringence and a low effective modal area is proposed, and properties, including birefringence and effective modal area, are numerically analyzed using the multipole method.
Therefore, in this section, we investigate the geometric dependence of the propagation length and normalized modal area of the SHP waveguide on a substrate.
Numerical results show that high birefringence of 1.362 × 10−2 and a low effective modal area of 3.435 μm2 are achieved at 1.55 μm, simultaneously.
Compared to an SHP waveguide with the same structure embedded in air cladding, the propagation length of the AHP waveguide is approximately the same along with a comparable normalized modal area.
Compared to the ideal condition of the SHP in air cladding, the propagation length of the AHP waveguide is approximately equal to that of the SHP waveguide in air (2.38 × 103 μm) with a comparable normalized modal area.
Propagation length and normalized modal area are important parameters describing the mode features in a plasmonic waveguide.
Using the finite elements method (FEM), the guiding properties including mode effective index, propagation length, normalized modal area, and figure of merit (FoM) are intensively investigated at a wavelength of 1,550 nm to target potential applications in telecommunications.
