Isolators, or optical diodes, are devices enabling unidirectional light propagation by using non-reciprocal optical materials, namely materials able to break Lorentz reciprocity. The realization of isolators at terahertz frequencies is a very important open challenge made difficult by the intrinsically lossy propagation of terahertz radiation in current non-reciprocal materials. Here we report the design, fabrication and measurement of a terahertz non-reciprocal isolator for circularly polarized waves based on magnetostatically biased monolayer graphene, operating in reflection. The device exploits the non-reciprocal optical conductivity of graphene and, in spite of its simple design, it exhibits almost 20 dB of isolation and only 7.5 dB of insertion loss at 2.9 THz. Operation with linearly polarized light can be achieved using quarter-wave plates as polarization converters. These results demonstrate the superiority of graphene with respect to currently used terahertz non-reciprocal materials and pave the way to a novel class of optimal non-reciprocal devices.

中文翻译：

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接近最佳石墨烯太赫兹不可逆隔离器。

隔离器或光电二极管是通过使用不可逆的光学材料（即能够破坏洛伦兹可逆性的材料）实现单向光传播的设备。在太赫兹频率下实现隔离器是一个非常重要的公开挑战，由于太赫兹辐射在当前不可逆材料中的固有损耗传播而变得困难。在这里，我们报告了基于静磁偏置单层石墨烯的，用于反射的圆极化波的太赫兹不可逆隔离器的设计，制造和测量。该设备利用了石墨烯的不可逆的光导率，尽管其设计简单，但在2.9 THz的频率下却具有近20 dB的隔离度和仅7.5 dB的插入损耗。使用四分之一波片作为偏振转换器可以实现线性偏振光的工作。这些结果证明了石墨烯相对于目前使用的太赫兹不可逆材料的优越性，并为新型一类最佳不可逆设备铺平了道路。