a versatile , wavelength - slicing methodology , referred to herein as spectrum division multiplexing , provides new avenues and technologies for optical communication applications . specifically , sdm separates a composed optical signal into a group of output spectra . each output spectrum carries a multiple of optical communication signal channels . the bandwidth of each channel and spacing between adjacent channels may differ from one output spectrum to another . a critical building block of sdm technology is a spectrum filter with periodic passbands , referred to herein as an optical spectrum synthesizer . the cascade of oss devices , the combinations of oss with prior art components and modules , and other new devices to be used in conjunction with oss , lead to new spectrum devices that add new dimensions to existing and new optical network architectures . the invention of oss leads to new spectrum division multiplexing and management devices based on cascading oss devices . examples of these devices include spectrum exchanger , spectrum multiplexer , spectrum demultiplexer and spectrum add drop module . the combinations of oss and other prior art devices also lead to several new spectrum devices and modules . examples of these include , spectrum switch , spectrum cross - connect and spectrum long haul transport modules . other devices designed to be used in conjunction with oss , e . g ., 1 / n multiplexer and 1 / n demultiplexer , can also be used to form new devices and modules . in sdm methodology , spectra , instead of single channels , are managed collectively thereby offering both flexibility and efficiency for next generation high channel count optical networks .