In a non-reciprocal optical amplifier, gain depends on whether the light propagates forwards or backwards through the device. Typically, one requires either the magneto-optical effect, temporal modulation or optical nonlinearity to break reciprocity. By contrast, here we demonstrate non-reciprocal amplification of fibre-guided light using Raman gain provided by spin-polarized atoms that are coupled to the nanofibre waist of a tapered fibre section. The non-reciprocal response originates from the propagation-direction-dependent local polarization of the nanofibre-guided mode in conjunction with polarization-dependent atom–light coupling. We show that this novel mechanism can also be implemented without an external magnetic field and that it allows us to fully control the direction of amplification via the atomic spin state. Our results may simplify the construction of complex optical networks. Moreover, by using other suitable quantum emitters, our scheme could be implemented in photonic integrated circuits and circuit quantum electrodynamics.

在单向光放大器中，增益取决于光在器件中是向前传播还是向后传播。通常，需要磁光效应、时间调制或光学非线性来打破互易性。相比之下，这里我们展示了使用由耦合到锥形光纤部分的纳米纤维腰部的自旋极化原子提供的拉曼增益来进行光纤引导光的非互易放大。非互易响应源于纳米纤维引导模式的传播方向相关的局部偏振以及偏振相关的原子 - 光耦合。我们表明，这种新颖的机制也可以在没有外部磁场的情况下实现，并且它允许我们通过原子自旋态完全控制放大的方向。我们的结果可以简化复杂光网络的构建。此外，通过使用其他合适的量子发射器，我们的方案可以在光子集成电路和电路量子电动力学中实现。