Generation and amplification of ultrashort pulses in erbium, neodymium, and thulium fibers

The motivation for this work is to develop a compact, high energy, and ultrashort pulses in a rare earth doped fiber-based laser system. A passively mode-locked femtosecond fiber laser based on the nonlinear polarization evolution technique has the stability problem due to thermal and mechanical perturbations. We demonstrate an environmentally stable mode-locked fiber laser by adding a Faraday rotator mirror and wave plates to compensate the linear phase delay and control the polarization state. The basic mode-locking operation of the environmentally stable laser is analyzed by Jones matrix representations. Experimental results show that the environmentally stable mode-locked 1.56 {dollar}mu{dollar}m erbium doped silica fiber laser generates a near transform limited pulse of 125 fs with a repetition rate of 44 MHz.; The absorption at 1.06 {dollar}mu{dollar}m is very weak in thulium doped ZBLAN/fluoride fiber by measuring the absorption spectrum. However, a strong emission at 0.8 {dollar}mu{dollar}m is observed by pumping at 1.06 {dollar}mu{dollar}m in thulium doped ZBLAN/fluoride fiber. A threshold behavior is observed when plotting the transmission versus the input pump power. This threshold of the input pump power is the characteristic of the avalanche upconversion. Therefore, a five-level model including an excited state absorption and cross-relaxations is proposed and this model can well explain the weak absorption of 1.06 {dollar}mu{dollar}m and the strong emission at 0.8 {dollar}mu{dollar}m. Experimentally, we demonstrate a thulium doped ZBLAN multimode fiber amplifier with a single pass gain of 31 dB based on the chirped pulse amplification technique. The output pulse energy is greater than 14 {dollar}mu{dollar}J before the damage occurs in the fiber. We also demonstrate a high conversion efficiency of 26% upconversion mode-locked laser in a thulium doped ZBLAN multimode fiber and the output pulse width is 380 ps at a repetition rate of 80 MHz.