Optical Add Drop Multiplexers

Optical add-drop multiplexer can be made using accousto-optic effect or interferometeric effect [6]. In an add-drop multiplexer there are three ports: input port, add-drop port and output port. Assuming that there are $\lambda_1 \ldots \lambda_{n-1}, \lambda_n$ wavelength at the input and $\lambda_i$ is dropped, then at the add-drop port $\lambda_i$ is diverted. At the output port all the other wavelengths ( $\lambda_1 \ldots \lambda_{i-1} \lambda_{i+1} \ldots \lambda_{n-1} \lambda_n$) will be there (Fig.3). When wavelength $\lambda_i$ is added then at the input port $\lambda_i$ should not be there (i.e., input has $\lambda_1 \ldots \lambda_{i-1} \lambda_{i+1} \ldots \lambda_{n-1} \lambda_n$). At the output port all the wavelengths ( $\lambda_1 \ldots \lambda_{n-1} \lambda_n$) will be there (Fig.4)

  

Figure 3: drop function in OADM

  

Figure 4: add function in OADM