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Utilizing Hilbert-pair-based digital filtering, intensity modulation and passive optical coupling, optical filterand O-E-O conversion-free ROADMs with excellent flexibility, colorlessness, gridlessness, contentionlessness, adaptability, and transparency to physical-layer network characteristics are proposed and evaluated, for the first time, which offer DSP-enabled dynamic add/drop operations at wavelength, subwavelength, and orthogonal subband levels. Extensive numerical simulations are undertaken to explore the operation characteristics of the proposed ROADMs in IMDD-based optical network nodes. It is shown that the add/drop operation performance is independent of the signal's location in the digital filtering space. In addition, the results also indicate that the drop operation introduces negligible optical power penalties, while for the worst-case scenarios, optical power penalties induced by the add operation can be 3.5 dB. Furthermore, the impacts of key digital filter parameters and intensity modulation-associated drop RF signals on the ROADM add/drop performance are also investigated, based on which optimum ROADM design criteria are identified not only for effectively reducing the digital filter DSP complexity but also simultaneously improving the ROADM performance.Index Terms-Digital filtering, digital signal processing (DSP), intensity modulation, reconfigurable optical add/drop multiplexer (ROADM).

The generation of dissipative cavity solitons is one of the most intriguing features of microresonator-based Kerr frequency combs, enabling effective mode locking of comb modes and synthesis of ultrafast pulses. With the Lugiato-Lefever model, here, we conduct detailed theoretical investigations on the transient dynamics of dissipative cavity solitons and describe how several intrinsic effects of the Kerr comb disturb the stability of cavity solitons, including soliton breathing, higher order dispersion, dispersive wave emission, and cavity mode coupling. Our results and analysis agree well with recent measurements and provide insight into some as yet unexplained observations.

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