Amplified spontaneous emission generation of wavelength upconversion in a Er³⁺-doped silicate single-mode optical fiber pumped at 1.313 μm

The observation of amplified spontaneous emission (ASE) in the visible light range in silica-base single-mode optical fibers doped with Er³⁺ was reported. Frequency-upconverted emissions were observed simultaneously in a number of visible wavelengths around 463 nm (463 nm, 475nm, 485nm, 494nm, 501nm and 510nm), 525nm and 540nm (525nm, 540nm, 547nm, 552nm and 565nm), around the second harmonic signal wavelength 656nm (656nm, 663nm, 669nm and 675nm) and near-infrared line (782nm, 802nm 809nm, and 823nm) when the fibers were pumped by a mode-locked, Q-switched Nd³⁺: YLF laser operating at 1.313 μm. An interesting phenomenon has been observed that the emission spectrum around 463nm band likely has a cascade amplification enhancement characteristic when the fiber is pumped with more than 100mW average power. The nonpolarization-preserving Er³⁺-doped single mode fiber used in the experiment has a 6 μm diameter core and a 0.979 μm cutoff wavelength. The NA is 0.235. The Er³⁺ dopping level is about 500×10^-6. The fiber lengths used are 4.5m and 3m separately. The laser power coupled into the fiber is about several hundred milliwatts.