Foroutan-Barenji Sina, Shabani Farzan, Isik Ahmet Tarik, Dikmen Zeynep, Demir Hilmi Volkan
Department of Electrical and Electronics Engineering, Department of Physics, UNAM - Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800, Turkey.
Faculty of Engineering, Department of Biomedical Engineering, Osmangazi University, Eskisehir 26040, Turkey.
Nanoscale. 2022 Sep 29;14(37):13755-13762. doi: 10.1039/d2nr02146c.
Lasers based on semiconductor colloidal quantum wells (CQWs) have attracted wide attention, thanks to their facile solution-processability, low threshold and wide range spectral tunability. Colloidal microlasers based on whispering-gallery-mode (WGM) resonators have already been widely demonstrated. However, due to their microscale size typically supporting multiple modes, they suffer from multimode competition and higher threshold. The ability to control the multiplicity of modes oscillating within colloidal laser resonators and achieving single-mode lasers is of fundamental importance in many photonic applications. Here we show that as a unique, simple and versatile architecture of all-colloidal lasers intrinsically enabled by balanced gain/loss segments, the lasing threshold reduction and spectral purification can be readily achieved in a system of a WGM-supported microfiber cavity by harnessing the notions of parity-time symmetry (PT). In particular, we demonstrate a proof-of-concept PT-symmetric microfiber laser employing CQWs as the colloidal gain medium along with a carefully tuned nanocomposite of Ag nanoparticles (Ag NPs) incorporated into a PMMA matrix altogether and conveniently coated around a coreless microfiber as a rigorously tailored colloidal loss medium to balance the gain. The realization of gain/loss segments in our PT-symmetric all-colloidal arrangement is independent of selected pumping, reducing the complexity of the system and making compact device applications feasible, where control over the pumping is not possible. We observed a reduction in the number of modes, resulting in a reduced threshold and enhanced output power of the PT-symmetric laser. The PT-symmetric CQW-WGM microcavity architecture offers new opportunities towards simple implementation of high-performance optical resonators for colloidal lasers.
基于半导体胶体量子阱（CQW）的激光器因其易于溶液加工、低阈值和宽光谱可调性而备受关注。基于回音壁模式（WGM）谐振器的胶体微激光器已得到广泛证明。然而，由于其微尺度尺寸通常支持多种模式，它们存在多模竞争和较高阈值的问题。在许多光子应用中，控制胶体激光谐振器内振荡模式的多重性并实现单模激光器的能力至关重要。在这里，我们表明，作为一种独特、简单且通用的全胶体激光器架构，通过利用宇称 - 时间对称（PT）的概念，在WGM支持的微光纤腔系统中可以轻松实现激光阈值降低和光谱纯化。特别是，我们展示了一个概念验证的PT对称微光纤激光器，它采用CQW作为胶体增益介质，以及一种精心调谐的纳米复合材料，该复合材料由银纳米颗粒（Ag NPs）掺入PMMA基质中，并方便地涂覆在无芯微光纤周围，作为经过严格定制的胶体损耗介质以平衡增益。在我们的PT对称全胶体装置中实现增益/损耗段与所选泵浦无关，降低了系统的复杂性，并使紧凑器件应用成为可能，在这种应用中无法控制泵浦。我们观察到模式数量减少，导致PT对称激光器的阈值降低和输出功率增强。PT对称的CQW - WGM微腔架构为胶体激光器高性能光学谐振器的简单实现提供了新的机会。
