  Breaking the symmetry between forward and backward propagating optical modes
is of fundamental scientific interest and enables crucial functionalities, such
as isolators, circulators, and duplex communication systems. Whereas there has
been progress in achieving optical isolation on-chip, integrated broadband
non-reciprocal signal processing functionalities that enable transmitting and
receiving via the same low-loss planar waveguide, without altering the
frequency or mode of the signal, remain elusive. Here, we demonstrate a
non-reciprocal delay scheme based on the uni-directional transfer of optical
data pulses to acoustic waves in a chip-based integration platform. We
experimentally demonstrate that this scheme is not impacted by simultaneously
counter-propagating optical signals. Furthermore, we achieve a bandwidth more
than an order of magnitude broader than the intrinsic opto-acoustic linewidth,
linear operation for a wide range of signal powers, and importantly, show that
this scheme is wavelength preserving and avoids complicated multi-mode
structures..
