Optical switching is a fundamental element in all-optical integrated circuits and networks with ultrahigh speed and low energy consumption compared to their electronic counterparts. Switching on/off the waveguiding with another light beam demands large optical nonlinearity to compactify device footprint and decrease energy consumption, which is difficult to achieve in photonic systems. By introducing strong light-matter coupling in an optical cavity, all-optical switching has been realized in ultracold-atom gases[1], and cavity quantum electrodynamics of a single atom and a quantum dot[2, 3], where giant optical nonlinearity stems from the matter part. Exciton polaritons, half-light, half-matter quasiparticles formed by strong coupling of excitons and photons in a semiconductor microcavity[4, 5], represent a promising platform for all-optical logics and computations with considerable nonlinearity and on-chip integratability. Writing in Science Advances (https://doi.org/10.1126/ sciadv.abj6627), Feng et al. reports all-optical switching on the basis of exciton polaritons in self-assembled metal-halide perovskite microwire arrays[6]. In this work, research group led by Prof. Qihua Xiong realized non-local and strongly interacting exciton polaritons in self-assembled halide perovskites at room temperature, which represents an important step towards on-chip integration of polaritonic devices. The concept of optical logics and circuits based on exciton polaritons was firstly proposed by Liew et al. in 2008[7]. Then, experimental demonstration of polariton switching were realized in GaAs quantum wells by using spin-dependent polariton–polariton interactions[8], propagating polariton condensates[9], resonant tunneling of polaritons[10], phase-controlled interferometers[11] and polariton transistors[12]. These polariton switches on the basis of GaAs quantum wells are restricted by their cryogenic operational temperature because of the small exciton binding energy. In 2019, polariton transistors were demonstrated by Lagoudakis and his colleagues in organic semiconductors at room temperature, but the localized exciton polaritons in organics restrict the on-chip integratability[13]. From 2017, Xiong and his colleagues demonstrated exciton–polariton Bose–Einstein condensation[14], propagating polariton condensates[15], and polariton lattices[16, 17] at room temperature in single-crystalline inorganic perovskites grown by chemical vapor deposition. Their recent work also showed that strong and robust optical nonlinearity exist in those devices[18]. These works provide fundamental insights into exciton polaritons on the basis of perovskite materials. The authors developed all-optical switching based on self-assembled CsPbBr3 microwire arrays embedded in distributed Bragg reflector cavity. This optical switching is designed and fabricated based on three advantages. Firstly, single crystallinity of microwires suppresses the defect-induced localization and scattering of exciton polaritons and 1D morphology permits directional waveguiding of polariton fluids. Secondly, Wannier-Mott excitons with binding energy of ca. 40 meV and Bohr radius of ca. 3.5 nm in CsPbBr3 underpin stable and delocalized exciton polaritons with strong interactions at room temperature. Thirdly, the developed self-assembly method provides a platform for direct patterning and integration of polaritonic devices. The configuration of all-optical switching based on exciton polaritons is shown in Fig. 1(a). This optical switching leverages propagating and interacting exciton polaritons in CsPbBr3 microwires. The propagating polariton fluids with a defined momentum of 4.4 μm–1 is realized by an obliquely incident source beam, which is resonant with the lower polariton branch. To switch on/off the polariton propagation, the authors introduce localized polaritons with a zero momentum by a block beam. Because of strong polariton–polariton interactions, the polariton dispersion is blue-shifted in the block beam region, which can serve as an energy barrier to turn off the polariton propagation. The on/off of optical switching can be controlled by tuning the delay time of two beams. In such optical switch, the propagation length and interaction strength of exciton polaritons play important roles. The authors have determined a propagation length of around 25 μm. This propagation distance benefits from the self-assembly method, which can fabricate microwires with single crystallinity and smooth surface to suppress the optical loss (Fig. 1(b)). The exciton-exciton interaction coefficient has been determined as 4.1 ± 0.6 μeV·μm2, which is comparable with ca. 6 μeV·μm2 in GaAs at cryogenic temperature. On the basis of strong interactions and delocalization of exciton polaritons, ultrafast all-optical switching with response time of less than 2 ps has been realized (Figs. 1(c)–1(e)). This study employ waveguide exciton polaritons to construct all-optical switching at room temperature, which highlights its importance for onchip integration. For the practical applications of exciton polaritons in integ-

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基于自组装卤化物钙钛矿微线的全光开关

光交换是全光集成电路和网络中的基本元件，与电子同类产品相比具有超高速和低能耗。用另一束光束打开/关闭波导需要较大的光学非线性，以缩小设备占用空间并降低能耗，这在光子系统中很难实现。通过在光腔中引入强光-物质耦合，实现了超冷原子气体的全光切换[1]，以及单原子和量子点的腔量子电动力学[2, 3]，其中巨大的光学非线性源于事的部分。半导体微腔中激子和光子强耦合形成的激子极化子、半光、半物质准粒子[4, 5], 代表了具有相当大的非线性和片上可集成性的全光逻辑和计算的有前途的平台。撰写科学进展 (https://doi.org/10.1126/sciadv.abj6627)，冯等人。报道了基于自组装金属卤化物钙钛矿微线阵列中激子极化子的全光切换[6]。在这项工作中，熊启华教授领导的研究小组在室温下实现了自组装卤化物钙钛矿中的非局域和强相互作用激子极化子，这是向极化子器件片上集成迈出的重要一步。基于激子极化子的光学逻辑和电路概念最早由 Liew 等人提出。2008 年[7]。然后，通过使用自旋相关的极化子-极化子相互作用[8]、传播极化子凝聚体[9]、极化子谐振隧道效应[10]、相位控制干涉仪[11]和极化子晶体管[10]，在GaAs量子阱中实现极化子切换的实验演示12]。由于激子结合能小，这些基于 GaAs 量子阱的极化子开关受到低温工作温度的限制。2019 年，Lagoudakis 及其同事在室温下在有机半导体中展示了极化子晶体管，但有机物中的局域激子极化子限制了片上可集成性[13]。从 2017 年开始，熊和他的同事们展示了激子-极化子 Bose-Einstein 凝聚[14]、传播极化子凝聚物[15] 和极化子晶格[16，17]在室温下通过化学气相沉积生长的单晶无机钙钛矿。他们最近的工作还表明，这些设备中存在强大而稳健的光学非线性[18]。这些工作为基于钙钛矿材料的激子极化子提供了基本的见解。作者开发了基于嵌入分布式布拉格反射腔的自组装 CsPbBr3 微线阵列的全光开关。这种光开关是基于三个优点设计和制造的。首先，微线的单结晶度抑制了缺陷引起的激子极化子的定位和散射，并且一维形态允许极化子流体的定向波导。其次，具有约结合能的Wannier-Mott激子。40 meV 和 ca 的玻尔半径。3. CsPbBr3 中的 5 nm 支持在室温下具有强相互作用的稳定和离域激子极化子。第三，开发的自组装方法为极化器件的直接图案化和集成提供了平台。基于激子极化子的全光开关配置如图1（a）所示。这种光学切换利用 CsPbBr3 微线中的传播和相互作用激子极化子。具有 4.4 μm–1 ​​定义动量的传播极化子流体是通过与下极化子分支共振的倾斜入射源光束实现的。为了打开/关闭极化子传播，作者通过块束引入了具有零动量的局部极化子。由于强极化子 - 极化子相互作用，极化子色散在阻挡光束区域蓝移，它可以作为关闭极化子传播的能量屏障。可以通过调节两束光的延迟时间来控制光开关的开/关。在这种光开关中，激子极化子的传播长度和相互作用强度起着重要作用。作者已确定传播长度约为 25 μm。这种传播距离得益于自组装方法，该方法可以制造具有单晶和光滑表面的微线以抑制光学损耗（图 1（b））。激子-激子相互作用系数已确定为 4.1 ± 0.6 μeV·μm2，与 ca. 6 μeV·μm2 在 GaAs 中在低温下。基于激子极化子的强相互作用和离域，已经实现了响应时间小于 2 ps 的超快全光切换（图 1（c）-1（e））。本研究采用波导激子极化子在室温下构建全光开关，这突出了其对片上集成的重要性。对于激子极化子在积分中的实际应用