It works like this Input signal 4IIIIIIID Selected NON. Sooted Wavelengh wawdengshs resonant wavelengths are reflected back toward the source non-resonant wavelengths are transmitted through the device without loss The centre wavelength is given by =2n effIt works like this • resonant wavelengths are reflected back toward the source • non-resonant wavelengths are transmitted through the device without loss. • The centre wavelength is given by:  = 2neff 