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Sub-wavelength slot waveguides
Published in Ching Eng Png, Yuriy Akimov, Nanophotonics and Plasmonics, 2017
In order to overcome these challenges, a silicon slot waveguide platform was pro- posed and demonstrated. It allows for a large portion of the optical mode to propagate through a low index region of the waveguide. By definition a slot waveguide is an op- tical waveguide that guides strongly confined light at a sub-wavelength scale in low refractive index regions [6,10,11]. A slot waveguide consists of two strips or slabs of high refractive-index (nH) materials separated by a sub-wavelength scale low refrac- tive index (nS) slot and surrounded by low refractive-index (nC) cladding materials, as sketched in Fig. 11.2(b). Alternatively, we can use photonic crystals [12], which are periodic structures with high index contrast. An example consisting of air holes etched into a silicon layer is illustrated in Fig. 11.2(c). Because of their wavelength- scale periodicity, photonic crystals can have a photonic band gap, i.e., a wavelength region where no light can penetrate the crystal. A defect in such a photonic crys- tal made by changing or removing a row of holes can sustain a guided mode in the photonic crystal. Light in the photonic band gap is bound to the waveguide defect because it is not allowed to propagate through the areas of photonic crystal on both sides of the waveguide [13,14].
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.
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.
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
Usually, the loss of a slot waveguide fabricated with regular electron beam lithography and plasma etching have loss is in the range of 10–20 dB/cm and the side wall roughness can go up to about 10–20 nm (21). The loss in slot waveguides is absolutely connected with the EFR which means that stronger evanescent field results in stronger electric field at the sidewalls, which will be scattered. However, in this work, we have assumed that there are no scattering points along the waveguide structures and high confinement modes in the slot region are part of the true Eigen modes of the waveguide and are theoretically lossless. Therefore, we are considering the total losses of the waveguide depending on the geometry of the waveguide.