the plot of a 1st order soliton. It's the 2D plot of the modulus of the following function:

${\displaystyle a(\xi ,\zeta )=\operatorname {sech} (\xi )e^{i\zeta /2}}$

I made it with the following Gnuplot code:

set terminal svg
set output "Soliton_1nd_order.svg"

# choose quality
set samples 50, 50
set isosamples 70

# change the angle the plot is shown
set view 55, 45, 1, 2

# output of the surface
set pm3d at bs
set hidden3d offset 1 trianglepattern 3 undefined 1 altdiagonal bentover
set style data lines

# remove the box with the meaning of the color
unset colorbox

# set ranges
set xrange [-1.5:1.5]
set yrange [0:pi]
set zrange [0:1]


set grid
set key off

# remove tics on the z-axis
unset ztics


set xlabel "xi"
set ylabel "zeta"

#set xzeroaxis linetype -1 linewidth 0.5
#set yzeroaxis linetype -1 linewidth 0.5
set xtics axis
set ytics axis

splot 1/cosh(x)