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Sub-wavelength slot waveguides
Published in Ching Eng Png, Yuriy Akimov, Nanophotonics and Plasmonics, 2017
We studied the effective index and power confinement of the first-order modes as a function of the Si-slab or Cu-slab widths w ranging from 10 nm to 2000 nm for three different waveguides (Si-slot, Cu-slot, and hybrid-slot based) at a fixed SiO2 slot width (gap) of 50 nm and a wavelength of λ = 1.55μm. Figure 11.11 shows the variation of effective indices neff of the three waveguides as a function of w. It demonstrates that neff of the Cu-slot waveguide decreases rapidly as the Cu-slab width increases from 10 nm to 80 nm. For a value w larger than 80 nm, this variation stabilizes, as the SPs become fully confined inside the SiO2-slot. The results also reveal a cut-off of w for the Si-slot waveguide. In particular, if the Si-slab width is smaller than 100 nm, the effective index is close to the SiO2 refractive index. The hybrid Si-Cu slot waveguide is a best trade-off between truly confined Cu-slots and extremely-low-loss Si-slot waveguides. As observed, if the slab width is equal to or greater than 250 nm, the bounded slab polariton is dominant. This is the case when the effective index is the same for both Si-slot and hybrid-slot waveguides.
Silicon Subwavelength Grating Slot Waveguide based Optical Sensor for Label Free Detection of Fluoride Ion in Water
Published in IETE Technical Review, 2023
Kritika Awasthi, Nishit Malviya, Amitesh Kumar
In Figure 5, the effect of the slot gap on transmission resonances is investigated, while other parameters are constant to Λ = 450 nm, ns = 1.33, d = 0.4, g = 30. With the increase in slot gap, the resonance wavelength shifts to shorter wavelengths and the peak transmission changes. There is a trade-off between propagation loss and light confinement of a slot waveguide, the propagation loss of a slot waveguide decreases with the increase in slot gap but its light confinement decreases with the increase in slot gap [36]. For s = 75 nm, the first-order resonance occurs at the wavelength of 1562 nm with a transmission peak of 66.124% and high propagation loss. When the slot gap increases to 80 nm, the first-order resonance occurs at the wavelength of 1556 nm with a transmission peak of 68.274%. For s = 85 nm, the first-order resonance wavelength shifts to 1552 nm and its transmission peak is at 68.211% with lower light confinement. Thus, considering the trade-off between the propagation loss and light confinement we choose s = 80 nm with better light confinement and lower propagation loss.
Silicon on silicon dioxide slot waveguide evanescent field gas absorption sensor
Published in Journal of Modern Optics, 2018
M. A. Butt, S. N. Khonina, N. L. Kazanskiy
In our previous work (10), we proposed an evanescent field gas sensor based on strip waveguide with an EFR > 55%. However, in this paper, we explore the slot waveguide geometry to study the evanescent field absorption CH4 gas sensor in mid-IR absorption wavelength. Methane gas is a colourless and odourless gas which can be toxic and/or explosive in unsafe quantities. Slot waveguides are a recently established class of waveguides that have received noteworthy consideration and promised various applications in recent years (11–14). Unlike conventional waveguides, a slot waveguide is a high index contrast waveguide for the high confinement of mode field in the low-index slot region (14–16). However, slot waveguide-based devices are strictly polarization sensitive. The working principle of a slot waveguide is based on the discontinuity of the electric field at the high index contrast interface. When the electromagnetic wave travels through the low-index slot region, most of the energy is confined within the slot, though there is a part of light known as evanescent field extending to the substrate and cladding region as shown in Figure 1.
Transverse electric modes in planar slot waveguides
Published in Journal of Modern Optics, 2018
Yi Jiang, Mei Kong, Can Liu, Yao Liu, Yu Wang
A slot waveguide is a micro-nano structure consisted of two high-index dielectric strips and a low-index slot between them. It can efficiently confine light in the low-index slot (12). Till now a variety of functional devices have been designed or realized based on slot waveguides, such as microring resonators (345), electro-optic modulators (67), optical switches (89), biochemical sensors (101112) and polarization splitters (1314). The modal characteristics of a waveguide are the grounding of waveguide devices’ design and optimization. Planar waveguides can be solved analytically, and their rigorous mode solutions can provide a valuable reference to recognize the corresponding three-dimensional waveguides. In practice, horizontal slot waveguides can be regarded as planar waveguides because of the large waveguide width, and the modal behaviours of three-dimensional vertical slot waveguides are similar to those of the planar slot waveguides as well. Therefore, mastering the modal characteristics of the planar slot waveguides will benefit the design and utilization of three-dimensional slot waveguides greatly.