Multi-degree ROADM based on wavelength selective switches: Architectures and scalability

Multi-degree implementations of the reconfigurable optical add–drop multiplexer (ROADM) are analyzed in terms of in-band crosstalk performance with an emphasis on the reduction in the number of wavelength selective switches used in the module. It is shown experimentally that an 8-degree ROADM using the wavelength selective switches for channel adding and optical splitters for channel dropping performs closely to one that uses switches for both operations. A new modular architecture based on the wavelength selective switches is proposed for implementations applicable to large degree nodes. Performance analysis of this architecture indicates node scalability to 256 degree with crosstalk-induced power penalties below 0.5 dB.