Ultrashort pulses at 920 nm are a highly desired light source in two-photon microscopy for the efficient excitation of green fluorescence protein. Although Nd3 + -doped fibers have been utilized for 920-nm ultrashort pulse generation, the competitive amplified spontaneous emission (ASE) at 1.06 μm remains a significant challenge in improving their performance. Here, we demonstrate a coordination engineering strategy to tailor the properties of Nd3 + -doped silica glass and fiber. By elevating the covalency between Nd3 + and bonded anions via sulfur incorporation, the fiber gain performance at 920 nm is enhanced, and 1.06-μm ASE intensity is suppressed simultaneously. As a result, the continuous-wave laser efficiencies and signal-to-noise ratio at 920 nm by this fiber are significantly enhanced. Importantly, the stable picosecond pulses at 920 nm are produced by a passive mode-locking technique with a fundamental repetition rate up to 207 MHz, which, to the best of our knowledge, is the highest reported repetition rate realized by Nd3 + -doped silica fibers. The presented strategy enriches the capacity of Nd3 + -doped silica fiber in generating 920-nm ultrashort pulses for application in biophotonics, and it also provides a promising way to tune the properties of rare-earth ion-doped silica glasses and fibers toward ultrafast lasers.
Yb-Al co-doped rod glass introducing with F- as the large core of photonic crystal fiber (PCF) was prepared by solgel method combined with high temperature sintering, and the rod without F- was fabricated as the comparison. The refractive index and homogeneity of the rods, and the attenuation, laser properties of the fibers have been investigated to confirm the effects of F- in the fibers. The results show that introducing F- in the fiber core can obviously decrease the refractive index of Yb3+ doped silica glass, and the beam quality of the PCF has been greatly improved by the lower NA of core.