Abstract
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.
Highlights
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
Nonreciprocity optical devices that break the time-reversal symmetry are very difficult to achieve without magnetic fields, such as optical isolators and circulators [1]
The transmission for the probe field is further given by the imaginary part of optical susceptibility Im[χ2±3], which strongly depends on the propagation direction of the probe field regarding the coupling and the switch field, leading to the chiral cross-Kerr nonlinearity
Summary
Nonreciprocity optical devices that break the time-reversal symmetry are very difficult to achieve without magnetic fields, such as optical isolators and circulators [1]. The traditional method is to guide light through a medium with a powerful magneto-optical Faraday effect [2,3,4]. Systems with this nature often have serious conflicts with miniaturization due to the surrounding environmental interference from their strong magnetic fields. The reported cross-Kerr optical isolator and optical circulator could work under high isolation, low loss, and weak field, which holds potential applications for quantum communication [34], 2643-1564/2020/2(3)/033517(6)
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