“…Unlike AFC [30], the GFC comb teeth are distributed along the incoming photon propagation direction rather than being together uniformly everywhere in the medium. The mechanism of GFC scheme is the same as AFC, and the singlephoton storage and processing techniques developed in AFC, such as on-demand retrieval [30,37,39,82], temporal sequencing [83], time-bin qubit measurement [84], etc, are all applicable in GFC scheme. Beyond this, by assigning different comb teeth to different positions, the preparation of the frequency comb is simplified, leading to various ways for the implementation of this scheme.…”