A multiport free-space wavelength division multiplexing (“WDM”) device is capable of handling multiple optical signals carried in multiple wavelengths (“λn”) using a prism. The WDM device includes an input collimator, prism, and optical filter. The input collimator receives an optical beam containing multiple wavelengths λn traveling through free-space. The prism uses at least two (2) surfaces to generate a first optical beam which travels in opposite direction of the optical beam. The optical filter is situated at a predefined angle with respect to the interface surface of the prism for facilitating frequency separation as well as extracts a first wavelength (“λ1”) from λn to form a first light signal with λ1 and form a second optical beam with the remaining wavelengths of λn. A collimator is used to guide the first light signal to a port.