Experimental demonstration and performance evaluation of flexible add/drop operations of DSP-switched ROADMs for cloud access networks

Making use of Hilbert-pair-based digital filtering, intensity modulation and passive optical coupling, optical filter- and O-E-O conversion-free flexible ROADMs are, for the first time, experimentally demonstrated to perform DSP-enabled dynamic add/drop operations at wavelength, sub-wavelength and spectrally overlapped sub-band levels. Extensive experimental explorations of physical-layer add/drop operation performances and their robustness to variations in both differential optical power dynamic range and drop RF signal power are also undertaken in IMDD-based optical network nodes. It is shown that the ROADM add/drop operation performances are independent of the sub-band spectral location, and that the add/drop operations introduce optical power penalties of ≤ 1.8 dB. In addition, for a total optical power as low as −12 dBm, the add operation still can tolerate a differential optical power dynamic range of > 2 dB. Whilst for the drop operation, an optical power penalty of < 2 dB is observed over a drop RF signal power variation range of 7.1 dB. Experimental results indicate that the add/drop operations of DSP-switched ROADMs have excellent performance robustness to considerably relax stringent requirements on network components.