The spatial spectrum is obtained by using a lens to e+#k\x
do Fourier transform and the far-field spectrum is recorded ^(T~ Q p
by a CCD camera positioned in its focal plane. :>ca).cjac
First, we summarize our results of on-axis excitation of a A[fTpS ~~%
single 2D gap soliton in Fig. 1. Different from previous /9SoVU8
experimental observations in which either the probe beam l%0-W
was launched off-axis to match the edge of the first BZ [6] /i_FA]Go
or its input phase or spectrum was engineered [11], we ZjY?T)WE9
demonstrate on-axis excitation of a 2D gap soliton without T_wh)B4xW
a priori phase or spectral engineering. In fact, we show EcytNY n
