Suk Sang Ho, Nah Sanghee, Sajjad Muhammad, Seo Sung Bok, Chen Jianxiang, Sim Sangwan
School of Electrical Engineering, Hanyang University, Ansan, South Korea.
Seoul Center, Korea Basic Science Institute, Seoul, South Korea.
Light Sci Appl. 2024 Sep 6;13(1):240. doi: 10.1038/s41377-024-01585-0.
In cutting-edge optical technologies, polarization is a key for encoding and transmitting vast information, highlighting the importance of selectively switching and modulating polarized light. Recently, anisotropic two-dimensional materials have emerged for ultrafast switching of polarization-multiplexed optical signals, but face challenges with low polarization ratios and limited spectral ranges. Here, we apply strain to quasi-one-dimensional layered ZrSe to enhance polarization selectivity and tune operational energies in ultrafast all-optical switching. Initially, transient absorption on unstrained ZrSe reveals a sub-picosecond switching response in polarization along a specific crystal axis, attributed to shifting-recovery dynamics of an anisotropic exciton. However, its polarization selectivity is weakened by a slow non-excitonic response in the perpendicular polarization. To overcome this limitation, we apply strain to ZrSe by bending its flexible substrate. The compressive strain spectrally decouples the excitonic and non-excitonic components, doubling the polarization selectivity of the sub-picosecond switching and tripling it compared to that in the tensile-strained ZrSe. It also effectively tunes the switching energy at a shift rate of ~93 meV %. This strain-tunable switching is repeatable, reversible, and robustly maintains the sub-picosecond operation. First-principles calculations reveal that the strain control is enabled by momentum- and band-dependent modulations of the electronic band structure, causing opposite shifts in the excitonic and non-excitonic transitions. Our findings offer a novel approach for high-performance, wavelength-tunable, polarization-selective ultrafast optical switching.
在前沿光学技术中，偏振是编码和传输大量信息的关键，凸显了选择性切换和调制偏振光的重要性。最近，各向异性二维材料已出现用于偏振复用光信号的超快切换，但面临偏振比低和光谱范围有限的挑战。在此，我们对准一维层状ZrSe施加应变，以增强偏振选择性并在超快全光切换中调节操作能量。最初，未受应变的ZrSe上的瞬态吸收揭示了沿特定晶轴的偏振中的亚皮秒切换响应，这归因于各向异性激子的移动 - 恢复动力学。然而，其垂直偏振中的非激子慢响应削弱了其偏振选择性。为克服这一限制，我们通过弯曲其柔性衬底对ZrSe施加应变。压缩应变在光谱上使激子和非激子成分解耦，使亚皮秒切换的偏振选择性加倍，与拉伸应变的ZrSe相比增加了两倍。它还以约93 meV %的移动速率有效调节切换能量。这种应变可调切换是可重复的、可逆的，并且稳健地保持亚皮秒操作。第一性原理计算表明，应变控制是通过电子能带结构的动量和能带依赖性调制实现的，导致激子和非激子跃迁发生相反的移动。我们的发现为高性能、波长可调、偏振选择性超快光切换提供了一种新方法。
