“…However, fundamental modelocking is more reliable for some certain applications owing to its high spectral purity and stability. During the last two decades, candidates of active media providing optical gain for gigahertz fundamental repetition rates have been restricted to semiconductors [15][16][17] , rare-earth-(RE) doped ceramic/crystals [18][19][20] , Ti:sapphire crystals [21,22] , and glass fibers [23][24][25][26] . In contrast, the laser setup constructed with active fibers, i.e., fiber lasers, stands out for its compactness, lack of susceptibility to misalignment, and efficient thermal dissipation.…”