<p>Reaching mode, which guides system states toward the sliding mode surface, is a crucial aspect of sliding mode control. This paper proposes an optimal reaching filter designed to achieve an optimal reaching mode while accounting for control input constraints. The optimal reaching law is formulated as an optimization problem to ensure efficient and constrained control execution. Using a double integrator system with a linear sliding mode surface as a representative example, the effectiveness and superiority of the proposed approach are validated through rigorous theoretical analysis and simulation. Additionally, an experimental setup is developed for further verification, with comparative results demonstrating that the proposed method significantly enhances the speed at which system states converge to the sliding mode surface.</p>