We present a weakly coupled bow-tie rectangular dual-step few-mode fiber supporting 20 eigenmodes for short-haul communication systems across the O band. The rectangular dual-step core and bow-tie stress-applying area are introduced to effectively split adjacent eigenmodes. We evaluate the impact of parameters on modal mode effective refractive index difference (MERID) Δn_eff, min Δn_eff, min A_eff, B_m, and bending loss at a wavelength of 1310 nm. Broadband performance of the entire O band, including n_eff, MERID Δn_eff, differential mode delay, and dispersion, is also analyzed. Results indicate that the 20 eigenmodes supported by the designed fiber are completely separated with MERID Δn_eff between adjacent modes larger than 2.319  ×  ^{10  −  4} over the whole O band. The designed fiber can be used for short-haul multiple-input multiple-output-free eigenmode-division multiplexing systems to improve transmission capacity and expand bandwidth.