A two-dimensional photonic crystal in which are inserted four waveguides and a resonant cavity. Owing to the existence of the photonic band gap, an electromagnetic signal propagating through the device is confined within the guides and the cavity and, through the adjustment of the orientation of a dipole mode generated within the cavity, is able to function in three distinct regimes. In regime 1, subjected to an external DC magnetic field +H0, it functions as a two-way divider, with isolation of the input relative to the two outputs, and, upon reversal of the field signal, it functions as an optical key. In regime 2, with the use of a DC magnetic field −H0, it functions as a waveguide bender, with the input isolated from the output, and, upon reversal of the field signal, functions as an optical key. In regime 3, subject to the application of an external DC magnetic field +H1, the device functions as a three-way divider.