Infrared phototransistors with very high performance show great potential in optoelectronic application, attributable to the intrinsic high transconductive gain of the transistor structure and therefore very large photo-responsivity. To distinguish multispectral information with phototransistors, however, the coincident spectral light has to been laterally dispersed and thereby coupled to the individual photo-gates sensing different target bands. Here, the dual-frequency plasmonic photo-coupler based on a single perforated metallic layer is numerically designed in the infrared region to improve photon absorption efficiency at two target wavelengths. The geometric parameters of the plasmonic grating composed of large and small cross-shaped holes are independently tuned to control the resonance frequencies under different incident (x- and y-) polarization conditions. While the dual-frequency resonant modes are induced by the hybridization between localized surface plasmons (LSPs) and propagating surface plasmons (PSPs), it is found that LSPs play the dominant role and can be effectively adjusted to achieve the target dual-frequency response. More importantly, the spectral response with low- (high-) frequency resonance corresponding to large (small) cross-hole region matches the spatially distributed photogates of the phototransistor structure and therefore realizes near-field enhancement and hence large photoresponsivity at target dual frequencies. In addition, the spectral response for x- and y-polarizations can be unified despite of the apparently broken symmetry between these two polarizations. Our work provides a general strategy to realize sensitive multiband-infrared phototransistors which require only state-of-the-art planar technology and are applicable for highly sensitive infrared photodetection.

具有非常高性能的红外光电晶体管在光电应用中显示出巨大的潜力，这归因于晶体管结构固有的高跨导增益，因此具有非常大的光响应性。然而，为了用光电晶体管区分多光谱信息，重合的光谱光必须横向分散，从而耦合到感测不同目标波段的各个光电门。在这里，基于单个穿孔金属层的双频等离子体光耦合器在红外区域进行数值设计，以提高两个目标波长下的光子吸收效率。由大小十字形孔组成的等离子体光栅的几何参数独立调谐，以控制不同入射光下的共振频率（x - 和y -) 极化条件。虽然双频共振模式是由局部表面等离子体 (LSP) 和传播表面等离子体 (PSP) 之间的杂交引起的，但发现 LSP 起主导作用并且可以有效地调整以实现目标双频响应。更重要的是，与大（小）跨孔区域对应的低（高）频率共振光谱响应与光电晶体管结构的空间分布光电门相匹配，因此实现了近场增强，从而实现了目标双频下的大光响应。此外，x - 和y的光谱响应尽管这两种极化之间明显破坏了对称性，但可以统一极化。我们的工作提供了一种实现灵敏的多波段红外光电晶体管的通用策略，该晶体管只需要最先进的平面技术并适用于高灵敏度的红外光电检测。