<p>In this article, an all-optical half-subtractor is proposed using the self-collimation phenomenon of optical beams inside photonic crystals. The overall structure is composed of six optical power splitters. Five of the mentioned splitters are 50:50, and one of them is a 60:40 splitter. The working mechanism is based on constructive and destructive interference of optical beams. Numerical methods, such as the finite difference time domain and the plane wave expansion, were employed to perform the required simulations and calculations. In the proposed structure, high power intensities are not necessary, as the switching task is accomplished through the constructive and destructive interference of the self-collimated beams. In this paper, we propose and design an optical half subtractor utilizing the self-collimation effect. The novelty of the designed structure lies in its independence from high power intensities. In other words, the action of the structure is not dependent on the power intensity in the waveguides. The final structure has a width of 39√2a in the x-direction and a length of 39√2a in the z-direction, where a is equal to 1 µm. The self-collimation phenomenon occurs when the polarized light with the frequencies around 0.194 (a/λ) propagates along the Γ-M direction. According to the time analysis of the structure at output ports, the time duration to reach a steady-state response is 0.5 psec and 0.7 psec, respectively.</p>