Our structured illumination microscopy (SIM) is based on a spatial light modulator (SLM) instead of an illumination mask, which does not need to be attached to a linear stage. This SIM can easily design the period of the one-dimensional grid related to the optical sectioning strength and can rapidly acquire three-dimensional data. The optimization of SIM with an SLM is proposed. Previous studies primarily varied magnification with a high numerical aperture objective to optimize the axial response. It is feasible to obtain the maximum optical sectioning strength by designing a grid pattern that has an appropriately high spatial frequency and to uniformly cover the entire frequency spectrum of the sample by rotating a grid pattern. We have successfully optimized SIM with such a grid and covered the frequency spectrum by rotating a grid pattern in multiple orientations.