The spatial spectrum is obtained by using a lens to BT&rp%NO6l
do Fourier transform and the far-field spectrum is recorded Ngn\nkf
by a CCD camera positioned in its focal plane. t^`<*H
First, we summarize our results of on-axis excitation of a 2qt=jz\s
single 2D gap soliton in Fig. 1. Different from previous 8W(<q|t
experimental observations in which either the probe beam sx<}
tbG
was launched off-axis to match the edge of the first BZ [6] c jC E3V9X
or its input phase or spectrum was engineered [11], we Kh>?!` lL
demonstrate on-axis excitation of a 2D gap soliton without Vww@eK%5Q
a priori phase or spectral engineering. In fact, we show bv .EM
