From today's perspective, the photonic future is out of reach, not because of technology but because of network economics. A purely photonic network (one in which wavelengths are created at the edge then networked throughout the core without ever being electronically regenerated) is in fact an analog network that gives the appearance of ultimate scalability and protocol flexibility, while driving up overall network operation and capital costs, and reducing reliability .
It has become common wisdom that carriers have spent too much on their core networks for too little revenue. On the data side, Internet protocol (IP) revenues could not pay for core router ports, while in the transport network, wholesale bandwidth sales could not keep up with the cost of deploying 160-channel dense wavelength division multiplexing (DWDM) systems .
The answer from many carriers has been to place the blame on the immaturity of the optical equipment. All the optical-electrical-optical (OEO) conversions among synchronous optical networking (SONET) add/drop multiplexers (ADMs), metro DWDM systems, optical switching systems, and long-haul DWDM line systems cost too much. Scaling a network in this old-fashioned way will always be too costly, and yet another generation of optical equipment would be required to bring carriers back to profitability .
The answer, many have argued, is to eliminate those OEO conversions by making them optical—simple passive connections ...