The spatial spectrum is obtained by using a lens to *R] Ob9X
do Fourier transform and the far-field spectrum is recorded pmm?Fq!s=
by a CCD camera positioned in its focal plane. V$y6=Q <c
First, we summarize our results of on-axis excitation of a d~bZOy
single 2D gap soliton in Fig. 1. Different from previous cL 31g_u
experimental observations in which either the probe beam w! J|KM
was launched off-axis to match the edge of the first BZ [6] VMry$
or its input phase or spectrum was engineered [11], we tUS)1*{_
demonstrate on-axis excitation of a 2D gap soliton without (G:A^z
a priori phase or spectral engineering. In fact, we show qPh
@Bl3
