We study periodic waveguides of silicon cylinders for an optical isolator in the configuration of a Mach–Zehnder interferometer, as one of the possible applications in silicon photonics. Magneto-optical effect in silicon is considered under application of external magnetic field normal to the waveguide in the on-chip configuration that is Voight geometry. External magnetic field remains perpendicular to the direction of propagation of the electromagnetic wave for any direction of the waveguide on the surface, which allows us using a serpentine folding of waveguides. The nonzero integral electric field rotation in the plane of the waveguide is demonstrated. Our results uncover the possibility of using bare silicon as a magneto-optical material for optical isolators.