The spatial spectrum is obtained by using a lens to !l&lb]V cz
do Fourier transform and the far-field spectrum is recorded <>R7G)w
F
by a CCD camera positioned in its focal plane.
U]P;X~$!
First, we summarize our results of on-axis excitation of a 4gZN~_AI<
single 2D gap soliton in Fig. 1. Different from previous _,'UP>Si
experimental observations in which either the probe beam 9#agI|d~
was launched off-axis to match the edge of the first BZ [6] (Hs frc
or its input phase or spectrum was engineered [11], we EuAa
demonstrate on-axis excitation of a 2D gap soliton without 7Jqp 2\
a priori phase or spectral engineering. In fact, we show
D?E5p.!A
