Development of Ultrafast Laser Oscillators Based on Thulium-Doped ZBLAN Fibers

Fluoride glass known as ZBLAN is well known for high transparency in the infrared region and is a promising candidate for the host material for infrared lasers. Furthermore, low material dispersion of ZBLAN glasses around 2-μm wavelength region suggests the usefulness of ZBLAN fibers for developing ultrafast fiber lasers. Based on these considerations, we have conducted a detailed study of ultrashort fiber laser oscillators based on thulium-doped ZBLAN fibers. Two types of diode-pumped, mode-locked oscillators are demonstrated using single-mode ZBLAN fibers and double-clad ZBLAN fibers. The oscillator with single-mode ZBLAN fibers generate stable output pulses at 67.5-MHz repetition rate with the average output power of 19 mW. The broad spectra spreading over 300 nm enabled the generation of pulses as short as 45 fs in 2-μm region. The oscillator with double-clad ZBLAN fibers was built with a multimode laser diode as the pump source and was successfully mode-locked at the pump power of 1.04 W. The output pulses with the spectrum extending over 150 nm are compressed to 90 fs.