The spatial spectrum is obtained by using a lens to i:#R
U^ R
do Fourier transform and the far-field spectrum is recorded :Puv8[1i
by a CCD camera positioned in its focal plane. R n{ q/h
First, we summarize our results of on-axis excitation of a )EO/P+&
single 2D gap soliton in Fig. 1. Different from previous 5q]u:
experimental observations in which either the probe beam kyJv,!};
was launched off-axis to match the edge of the first BZ [6] "!)8bTW
or its input phase or spectrum was engineered [11], we 89l_%To
demonstrate on-axis excitation of a 2D gap soliton without F dv&kK!
a priori phase or spectral engineering. In fact, we show c7\bA7 .
