We proposed a three-wavelength multiplexer/demultiplexer based on the characteristics of resonant coupling between
photonic crystal ring resonator (PCRR) and cavity. The structure composed of one PCRR and three cavities. The
numerical results obtained by the finite-different time-domain (FTDT) method show that it can realize the
demultiplexing of three wavelengths, i.e. 1430nm, 1490nm and 1550nm only by modulating the radius of the cavities.
The designed device not only has a compact size with 12μm×11μm but also a high efficiency, may have potential
applications in the integrated optics fields.