The fierce battle Bell vs Gray over the patent for the revolutionary telephone stemmed from their parallel quests to invent a device that could transmit speech electronically.
At the heart of all commercial ROADM systems is the wavelength selective switch (WSS). As the name suggests, a WSS can switch selected wavelengths or spectrum slices from an input fiber to desired output fibers. The recent progress in WSS devices, outlined in this paper, has been a crucial factor enabling the growth of modern optical networks.