Question

Why is the wavelength-selective ROADM architecture colorles even though it uses AWGs for the multiplexers/demultiplexers rather than WSSs?

Answer 1

the colorless function is that the optical sign wavelength isn't fixed by the physical port of ouptu and input of the TPA and can be set byutilizing programming control.

the optical ways of the WDM flag between the output and input fibers of every degree and the transponders at the nodes of ROADM , for every wavelength channel the TPA must choose the way of signal  to the ideal transponder . Since a TPA comprises of a arrayed-waveguide grating (AWG) where the port of output task which is dictated by the optical signal wavelength, the signal wavelength of the transponder is likewise controlled by the port associated with the TPA. This switch structure makes certain issues with deference activity. For instance, if the transponder wavelength signal should be changed from λ1 to λ2 to manage a traffic change, the association port of the TPA should likewise be changed. This association port change which includes tasks that must be performed physically in the field at the site where the equipment node is found, and this diminishes the adaptability of the system operation network.

This confinement can be lifted by utilizing a wavelength-selective switch (WSS) rather than an AWG at the TPA. For every wavelength channel, the WSS can convey the information WDM signal to any port ouput . In addition, these port of output assignments can be changed under programming control. In this way, by utilizing the WSS, we can change the wavelength way setting without doing any work in the field. This additional capacity is called colorless that the way between the transponders and the output and input fiber isn't fixed by the color wavelength of the optical signal.

Answer 2

Use of AWGs implies a fixed wavelength allocation and direction in ROADM. For this purpose the wavelengths are assigned and fixed with particular transceivers used.

But,a colorless ROADM enables the flexible allocation of wavelengths . Here, any wavelength or color can be assigned to any port. And the complete setup is software controller hence no truck rolls are required. Only thing is that filter modules must be implemented for realizing colorless features.