反射式光限幅器的实验实现
Experimental Realization of a Reflective Optical Limiter
摘要：
光学限制器传输低强度的光，同时阻挡具有过高强度或通量的激光辐射。典型的无源光限幅器吸收大部分高水平辐射，这可能导致不可逆的损害。在这篇文章中，我们报告了第一个实验实现的反射式光学限幅器，它不吸收高水平的激光辐射，而是将其反射回太空。该设计是基于一个周期性的层状结构组成的交替SiO2和Si3N4层与单一的GaAs缺陷层在中间。在低强度下，层状结构通过局域缺陷模显示出强的共振透射。在高强度下，GaAs层中的双光子吸收抑制了局域模以及共振透射，整个层状结构在覆盖周期性层状结构的整个光子带隙的宽频率范围内变得高度反射。相比之下，独立的GaAs层将吸收大部分的高水平辐射，从而充当基本的吸收性光限制器。所提出的设计只能在短波红外，其中GaAs显示出可忽略的线性吸收和非常强的非线性双光子吸收。通过明智地选择光学材料，相同的原理可以复制到任何其他频率范围。
英文摘要：
Optical limiters transmit low-intensity light, while blocking laser radiation with excessively high intensity or fluence. A typical passive optical limiter absorbs most of the high level radiation, which can cause irreversible damage. In this communication we report the first experimental realization of a reflective optical limiter, which does not absorb the high-level laser radiation, but rather reflects it back to space. The design is based on a periodic layered structure composed of alternating SiO2 and Si3N4 layers with a single GaAs defect layer in the middle. At low intensities, the layered structure displays a strong resonant transmission via the localized defect mode. At high intensities, the two-photon absorption in the GaAs layer suppresses the localized mode along with the resonant transmission, the entire layered structure turns highly reflective within a broad frequency range covering the entire photonic band gap of the periodic layered structure. By contrast, a stand-alone GaAs layer would absorb most of the high-level radiation, thus acting as a basic absorptive optical limiter. The proposed design can only perform at shortwave IR, where GaAs displays negligible linear absorption and very strong nonlinear two-photon absorption. With judicious choice of optical materials, the same principle can be replicated for any other frequency range.
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