  Cavity-free optical nonreciprocity components, which have an inherent strong
asymmetric interaction between the forward- and backward-propagation direction
of the probe field, are key to produce such as optical isolators and
circulators. According to the proposal presented by Xia et al., [Phys. Rev.
Lett. 121, 203602 (2018)], we experimentally build a device that uses
cross-Kerr nonlinearity to achieve a cavity-free optical isolator and
circulator. Its nonreciprocal behavior arises from the thermal motion of N-type
configuration atoms, which induces a strong chiral cross-Kerr nonlinear
response for the weak probe beam. We obtain a two-port optical isolator for up
to 20 dB of isolation ratio in a specially designed Sagnac interferometer. The
distinct propagation directions of the weak probe field determine its
cross-phase shift and transmission, by which we demonstrate the accessibility
of a four-port optical circulator.
