  All-optical switching of 77 fs pulses centered at 1560 nm, driven by 270 fs,
1030 nm pulses in a dual-core optical fiber exhibiting high index contrast is
presented. The fiber is made of a thermally matched pair of lead silicate and
borosilicate glasses used as core and cladding material, respectively. The
novel switching approach is based on nonlinear balancing of dual-core
asymmetry, by control pulse intensity induced group velocity reduction of the
fast fiber channel. Due to the fiber core made of soft glass with high
nonlinearity high switching contrast exceeding 20 dB is attained under
application of control pulses of only few nanojoule energy. The optimization of
the fiber length brought the best results at 14 mm, which is in good
correspondence with the calculated coupling length at the signal wavelength.
The results express significant progress in comparison to similar studies based
on self-switching of solitonic pulses in dual-core fibers and represent high
application potential.
