This paper presents a single-mode waveguide based in cross-sectional antiresonant confinement. The confinement in the vertical direction is obtained placing a Fabry-PeΣrot tuned at its antiresonant condition underneath the core [defining the antiresonant reflecting optical waveguides (ARROW) structure]. Small weightings are placed on both sides of the core to achieve a local increase in the effective refractive index, obtaining the so-called lateral antiresonant structures (LASs). They assure both the cross-sectional confinement and the single-mode behavior of the global structure. Simulations predict the transition of the symmetrical mode of the LAS to a bidimensional ARROW mode below the cutoff condition of the former, while at the cutoff condition of the asymmetrical LAS mode power is directly transferred to a radiative mode. Experimental results have shown that losses decrease as the lateral core width increases, which is in agreement with a minor confinement in the structure. Near-field images from a 3-mm-thick, 16 mm-wide ARROW-two-dimensional structure have shown that when a misalignment between the input optical fiber and the waveguide is produced, no higher order modes are excited, confirming the single-mode behavior of these structures.