Liang Chao, Liu Bei, Xu An-Ning, Wen Xin, Lu Cuicui, Xia Keyu, Tey Meng Khoon, Liu Yong-Chun, You Li
State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China.
Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurements of Ministry of Education, Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Physics, Beijing Institute of Technology, Beijing 100081, China.
Phys Rev Lett. 2020 Sep 18;125(12):123901. doi: 10.1103/PhysRevLett.125.123901.
Optical nonreciprocity is an essential property for a wide range of applications, such as building nonreciprocal optical devices that include isolators and circulators. The realization of optical nonreciprocity relies on breaking the symmetry associated with Lorentz reciprocity, which typically requires stringent conditions such as introducing a strong magnetic field or a high-finesse cavity with nonreciprocal coupling geometry. Here we discover that the collision effect of thermal atoms, which is undesirable for most studies, can induce broadband optical nonreciprocity. By exploiting the thermal atomic collision, we experimentally observe magnet-free and cavity-free optical nonreciprocity, which possesses a high isolation ratio, ultrabroad bandwidth, and low insertion loss simultaneously. The maximum isolation ratio is close to 40 dB, while the insertion loss is less than 1 dB. The bandwidth for an isolation ratio exceeding 20 dB is over 1.2 GHz, which is 2 orders of magnitude broader than typical resonance-enhanced optical isolators. Our work paves the way for the realization of high-performance optical nonreciprocal devices and provides opportunities for applications in integrated optics and quantum networks.
光学非互易性是广泛应用中的一项基本特性，例如构建包括隔离器和环行器在内的非互易光学器件。光学非互易性的实现依赖于打破与洛伦兹互易性相关的对称性，这通常需要严苛的条件，比如引入强磁场或具有非互易耦合几何结构的高精细度腔。在此我们发现，热原子的碰撞效应，虽然在大多数研究中是不利的，但却能诱导宽带光学非互易性。通过利用热原子碰撞，我们通过实验观测到了无磁且无腔的光学非互易性，其同时具备高隔离比、超宽带宽和低插入损耗。最大隔离比接近40 dB，而插入损耗小于1 dB。隔离比超过20 dB的带宽超过1.2 GHz，比典型的共振增强型光学隔离器宽2个数量级。我们的工作为实现高性能光学非互易器件铺平了道路，并为集成光学和量子网络中的应用提供了机会。
