A demultiplexer should give rise to minimum cross talk , i.e., the amount of input power associated with a particular wavelength (say, ) which reaches a channel for a different wavelength ( ) should be minimum.
Arrayed Waveguide Grating:
Arrayed waveguide gratings (AWG) are used for demultiplexing. These are based on diffraction principle. The input consists of several channels carrying different wavelengths.
Light propagating in the input waveguides are coupled to the arrayed waveguides after propagating through a free space region (FPR). The AWG consists of an array of curved waveguides. Each curved waveguide has a length which is more than the array element immediately below it, where is the central operating wavelength, is the effective refractive index and is an integer. Thus at the central wavelength, the light will focus at the centre of the image plane. Different wavelengths have different phase differences and the focal point for each will be shifted. A second coupler will deliver different wavelengths to different waveguides.
) which reaches a channel for a different wavelength ( 
) should be minimum. 
more than the array element immediately below it, where 
is the central operating wavelength, 
is the effective refractive index and 
is an integer. Thus at the central wavelength, the light will focus at the centre of the image plane. Different wavelengths have different phase differences and the focal point for each will be shifted. A second coupler will deliver different wavelengths to different waveguides. 
