This paper presents the results of simulation of a compact all-optical logical comparator based on a GaAs photonic crystal. The influence of geometric parameters of structural elements of the photonic crystal on characteristics of the  comparator was studied in order to establish the optimal diameter of GaAs columns and the distance between them (period) for operation at a wavelength of 1.3 μm. Simulations of the dependences of the ratio of signal intensities at the input and output of the comparator show that it decreases with increasing diameter, both with one and both open channels. Calculating the difference between these ratios, we reveal that an optimal diameter of the  photonic crystal columns is equal to 155 nm. After a similar study for the distance between the GaAs columns, we determine its optimal value as 600 nm.