The spatial spectrum is obtained by using a lens to '' S&e
do Fourier transform and the far-field spectrum is recorded %j E Y 3q
by a CCD camera positioned in its focal plane. |y"jZT6R}t
First, we summarize our results of on-axis excitation of a EA|k5W*b
single 2D gap soliton in Fig. 1. Different from previous K) S;:MLG=
experimental observations in which either the probe beam ? } ( =
was launched off-axis to match the edge of the first BZ [6] TJae Qqob
or its input phase or spectrum was engineered [11], we s t/n"HQ
demonstrate on-axis excitation of a 2D gap soliton without e"R m_t
a priori phase or spectral engineering. In fact, we show @ u)
'yS
