The spatial spectrum is obtained by using a lens to wKH ::!
do Fourier transform and the far-field spectrum is recorded /cZ-tSC)o
by a CCD camera positioned in its focal plane. #Oha(mRY
First, we summarize our results of on-axis excitation of a %0Y=WYUH>
single 2D gap soliton in Fig. 1. Different from previous ]x&u`$F
experimental observations in which either the probe beam 2r%lA\,h$
was launched off-axis to match the edge of the first BZ [6] <94_ @3
or its input phase or spectrum was engineered [11], we %?e( hnM
demonstrate on-axis excitation of a 2D gap soliton without c/ 5W4_J
a priori phase or spectral engineering. In fact, we show Iyo@r%I
