A new method for characterizing the amplitude and phase distributions of
the light propagating through arrayed-waveguide gratings is presented.
The new method is based on the IFT. A very good agreement of the results
obtained from the IFT method in comparison with OLC method has been
achieved. The new method has been applied to an AWG with a small .DELTA.L
of 22 .mu.m where the other methods fail. The precision of this
measurement is demonstrated by a good agreement between the transmittance
obtained from direct measurement and from calculation using the amplitude
and phase distributions. Finally we want to point out, that although the
results are based on a FTS measurement, the method can be applied to any
experimental technique that provides a measurement of the complex
transmittance of the AWG.