Cavity Solitons in Two-Level Lasers with Dense Amplifying Medium

Local-field effects are known to induce bistability in dense optical media. We examine theoretically whether this property is preserved in broad-area cavities, and show that bistability between the homogeneous lasing and nonlasing states of the system persists provided a Fourier filtering technique is used to prevent off-axis emission. The resulting bistability gives rise to spatial light localization in the form of cavity solitons, which exhibit a particularly large degree of plasticity as a function of the characteristics of the addressing beam. This is the simplest laser able to sustain cavity solitons.

Figure 1

(a) Intensity of the generated field as a function of the cavity detuning for $p=250$, $\sigma =0.5$, $b=0.5$, $r=0.1$, $a=0$, and different values of the LFC parameter: $L=0$ (dotted line) and $150$ (solid line for the stable part, dashed line for the unstable one). The vertical dot-dashed lines indicate the limits of the bistability region for the last case. (b) Corresponding limits ${\Delta }_{c1}$ and ${\Delta }_{c2}$ of the bistability region (grey area) as a function of the LFC parameter.

Figure 2

Neutral stability curves for $p=250$, $\sigma =0.5$, ${\Delta }_c=-1.5$, $a=0.01$, and $L=150$. In the white region only the nonlasing solution exists, in the gray region that solution is unstable versus perturbations of wave number $k$, and in the striped region the nonlasing and off-axis solutions coexist. The wide horizontal lines represent the Fourier filter to be discussed later in the text.

Figure 3

(a) Horizontal cross section of a cavity soliton, in terms of the intensity (solid line, left $y$ axis) and the refraction index shift (dashed line, right $y$ axis). Parameters are those of Fig. 2, plus $b=0.5$ and $r=0.1$. The Fourier filter has a cutoff wave number $|k{|}_{\mathrm{m}\mathrm{a}\mathrm{x}}=10$. The seed is a 10-pixel-wide, sixth-order super-Gaussian placed at the center of the lattice. (b) Dependence of the peak intensity of the soliton on the pump rate $r$.

Figure 4

Intensity (left) and phase (right) profiles of three coexisting localized structures. Parameters are $p=250$, $\sigma =b=0.5$, ${\Delta }_c=-1.5$, $a=0.01$, $L=50$, $r=0.8$, and $|k{|}_{\mathrm{m}\mathrm{a}\mathrm{x}}=14$.