  Temporal cloaks have inspired the innovation of research on security and
efficiency of quantum and fiber communications for concealing temporal events.
The existing temporal cloaking approaches possessing ps ~ns cloaking windows
employed the third-order nonlinearity mostly. Here we explore a temporal cloak
for perpetually concealing pulse events using high efficiency second-order
nonlinearity. A temporal pulse event was cloaked as a continuous wave with
constant intensity and restored by polarization dependent sum frequency
generation processes between the continuous wave and probe. The variety of
quasi phase-matching second-order nonlinear processes in periodically poled
lithium niobate make sure the pulse event cannot be filched during
transmission. The proposed temporal cloak predicts hopeful applications in
information security of photonic integrated circuit on lithium niobite thin
film.
