Spectral dynamics of square pulses in passively mode-locked fiber lasers

We investigate experimentally and numerically the spectral dynamics of square pulses generated in passively mode-locked fiber lasers under the dissipative soliton resonance. The features of the transition from the single-peak spectral profile to the doublet spectrum with increasing pump power are studied. The used master equation takes into account the gain saturation, the quadratic frequency dispersion of the gain and the refractive index, and the cubic-quintic nonlinearity of the losses and refractive index. Experimental data are obtained for an Er:Yb-doped fiber ring laser. The theoretical and experimental results are in good agreement with each other.

Figure 1

Experimental setup of the nonlinear polarization evolution: PI-ISO (polarization-insensitive isolator), PC (polarization controller), and OC (output coupler).

Figure 2

Temporal profile of the laser emission registered at 633 mW of pump power.

Figure 3

The rf spectrum registered with 100 Hz BW at 633 mW of pump power.

Figure 4

Pulse width (black squares) and pulse energy (blue triangles) as a function of pump power.

Figure 5

Spectral profile of the square pulse for various values of the pump power.

Figure 6

Temporal profile of the square pulse as a function of the pump power.

Figure 7

Spectral spacing evolution as a function of pump power.

Figure 8

Spectral $I_{\omega }\left(\omega \right)$ profile of a steady-state pulse as a function of the pump power $a$. $b=0.02$, $D=0.5$, $D_i=0$, $q=0.4$, ${\sigma }_0=1$, $p=1$, and $p_2=1.$

Figure 9

Temporal $I\left(\tau \right)$ profile of a steady-state pulse as a function of the pump power $a$. $b=0.02$, $D=0.5$, $D_i=0$, $q=0.4$, ${\sigma }_0=1$, $p=1$, and $p_2=1.$

Figure 10

Dependences of the duration D (black circles) and energy J (black squares) of the steady-state pulse on the pump power $a$.

Figure 11

Distance $D_{\omega }$ between the spectral peaks in a spectral doublet of a steady-state pulse as a function of the pump power $a$.