Using optical beam interference inside photonic-crystal-based waveguides is a promising method for designing and realizing all-optical logic gates and other digital devices. In this paper we design and propose an all-optical 1-bit comparator using optical beam interference. In the proposed structure, the logic states of input ports are determined based on their initial phases. The 180 deg and 0 deg phases are used as logic 0 and 1. However, the logic states of the output ports are determined based on the amplitude of the optical signal at the output ports. For the proposed structure, the maximum rise and fall times are about 0.6 ps and 0.3 ps, respectively.