Figure 13.22 shows a more modular OADM architecture . Here the N incoming light channels are spilt into several bands of wavelengths. This function can be achieved using either a set of thin-film filter or an AWG. The band to be dropped can be sent through a second demultipelxer followed by processing of the individual wavelengths. As an example, if N= 12 and three wavelengths need to be dropped, the incoming wavelengths