The spatial spectrum is obtained by using a lens to b+yoD
do Fourier transform and the far-field spectrum is recorded .]0B=w* Z
by a CCD camera positioned in its focal plane. zI8Q "b
First, we summarize our results of on-axis excitation of a HT)b3Ws~M8
single 2D gap soliton in Fig. 1. Different from previous Ox.&tW%@
experimental observations in which either the probe beam RN238]K
was launched off-axis to match the edge of the first BZ [6] iJIPH>UMX
or its input phase or spectrum was engineered [11], we xcwyn\93)
demonstrate on-axis excitation of a 2D gap soliton without EMzJJe{Cv
a priori phase or spectral engineering. In fact, we show RzQ1Wq