In this paper, we used photonic crystal resonant cavity structure for designing a 2-channel optical wavelength demultiplexer. It has been shown that by using photonic crystal resonant cavity, wavelength separation is possible. In order to select 2 channels with different central wavelengths we employed 2 resonant cavities with different structural parameters. The platform used for designing the proposed demultiplexer is a hexagonal lattice of dielectric rods immersed in air. The demultiplexer has 2 channels with central wavelengths equal to l1=1549.4 nm and l2=1551.2 nm. The transmission efficiency of the demultiplexer is more than 92%. The quality factors for first and second channels are 1936 and 3021 respectively. Manuscript profile