Gubbin Christopher R, De Liberato Simone
School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK.
Nanophotonics. 2023 May 15;12(14):2849-2864. doi: 10.1515/nanoph-2022-0765. eCollection 2023 Jul.
Efficient electrical generation of mid-infrared light is challenging because of the dearth of materials with natural dipole-active electronic transitions in this spectral region. One approach to solve this problem is through quantum-engineering of the electron dispersion to create artificial transitions, as in quantum cascade devices. In this work we propose an alternative method to generate mid-infrared light, utilizing the coupling between longitudinal and transverse degrees of freedom due to the nonlocal optical response of nanoscopic polar dielectric crystals. Polar crystals support sub-diffraction photonic modes in the mid-infrared. They also support longitudinal phonons, which couple efficiently with electrical currents through the Fröhlich interaction. As we have shown in previous theoretical and experimental works, these two degrees of freedom can hybridize forming longitudinal-transverse polaritons. Here we theoretically demonstrate that longitudinal-transverse polaritons can be efficiently generated by electrical currents, leading to resonant narrowband photonic emission. This approach can therefore be utilised to electrically generate far-field mid-infrared photons in the absence of dipole-active electronic transitions, potentially underpinning a novel generation of mid-infrared optoelectronic devices.
由于在该光谱区域缺乏具有自然偶极活性电子跃迁的材料，高效地电产生中红外光是一项具有挑战性的任务。解决这个问题的一种方法是通过对电子色散进行量子工程来创建人工跃迁，就像在量子级联器件中那样。在这项工作中，我们提出了一种产生中红外光的替代方法，利用纳米级极性介电晶体的非局域光学响应所导致的纵向和横向自由度之间的耦合。极性晶体在中红外区域支持亚衍射光子模式。它们还支持纵向声子，这些纵向声子通过弗罗利希相互作用与电流有效地耦合。正如我们在之前的理论和实验工作中所表明的，这两个自由度可以杂交形成纵向 - 横向极化激元。在这里，我们从理论上证明纵向 -横向极化激元可以由电流有效地产生，从而导致共振窄带光子发射。因此，在没有偶极活性电子跃迁的情况下，这种方法可用于电产生远场中红外光子，这有可能为新一代中红外光电器件奠定基础。
