Effect of steady-state conditions on self-pulsing characteristics of Yb-doped cw fiber lasers

Self-pulsing Dynamics in Yb-doped Fiber Lasers

“…Study of three different Fabry-Perot resonator configurations as shown in Figures 1(a), 1(b), and 1(c) was carried out. [15] Figure 1(a) shows the forward-pumping configuration with high finesse in which a dichroic mirror with ~100% reflectivity at signal wavelength and high transmission at pump wavelength is kept in between the two lenses used for coupling pump light in to the Yb-doped fiber and the cleaved end with 4% Fresnel reflection at the farther fiber end of the doped fiber acts as the output coupler. Figure 1(b) shows the backward-pumping configuration with high finesse in which two dichroic mirrors have been used, one for ~ 100% feedback of the signal and another at an angle of 45° for taking laser output from pump input end of fiber.…”

“…(a) High-finesse forward-pumping configuration with output power taken from the farther end of Yb-doped fiber, (b) high-finesse backward-pumping configuration with output power taken from the pumping end of the Ybdoped fiber using the 45° tilted dichroic mirror, and (c) low-finesse resonator configuration with laser output from both the ends. [15] Fiber Laser of the population inversion in the gain medium and the gain increases gradually. However, CW lasing is completely inhibited due to the suppression of feedback by the imposed angle at the fiber ends and feedback into the cavity is provided mainly by the distributed RS and SBS that leads to generation of gigantic irregular random self-pulses.…”

“…Several possible origins have been suggested for self-pulsing in the literature. These include re-absorption of laser signal in the weakly pumped or un-pumped section of the rare-earth-doped fiber, [11][12][13][14] ion-pairing acting as a saturable absorber, [8][9][10] relaxation oscillations due to inversion in the gain medium and population of photons in the cavity, [10] resonator steady-state conditions and Q-factor of the cavity, [5,15] interaction between laser signal and population inversion, [16] pump noise as the source of self-pulsing. [17,18] Further, cascaded stimulated Brillouin scattering (SBS), distributed Rayleigh scattering, and the set of other nonlinear effects (SRS (stimulated Raman scattering); SPM (self-phase modulation); XPM (cross-phase modulation); and FWM (four wave mixing)) [19][20][21][22] have also been suggested as the sources of self-modulation and selfpulsing in different rare-earth-doped fiber lasers.…”

“…(a) Output of the fiber laser, showing random self-pulses in the case of low-finesse cavity ofFigure 1(c), for an input pump power of 8 W, and (b) an expanded oscilloscope trace of one of the random self-pulses from Yb-doped fiber laser [15]. …”

“…Output spectrum in case of low-finesse cavity ofFigure 1(c); the lower trace shows spectrum before onset of random self-pulsing at 2.5 W of input pump power, and the upper trace shows output spectrum after onset of strong random self-pulsing at 8 W of input pump power [15]. …”