Optical properties and applications of anisotropic low-dimensional nanomaterials

This thesis focuses on the optical properties and applications of low dimensional anisotropic nanomaterials, such as carbon nanotubes (CNTs), nanowires (NWs), black phosphorus (BP). The whole thesis can be divided by three main parts. The first part introduces the fabrication methods of various anisotropic nanomaterials. For instance, as-grown CNTs are synthesized and aligned as an array by a mechanical drawing method. As-grown NWs are aligned by a combing method, and our results show that >95% of the NWs are well aligned. Different from CNTs and NWs, BP has the intrinsic anisotropic optical response due to its anisotropic atomic structure. The mechanical exfoliation method for preparation of few-layer BP is presented, which is also applicable for other two-dimensional layered materials. The second part introduces the optical characterization methods of the nanomaterials studied in this thesis. Various polarization-dependent microscopes are introduced to characterize their anisotropic properties, such as polarized absorption/transmission spectroscopy, polarized Raman microscopy, polarization-resolved optical microscopy. These microscopes provide useful methods to verify the anisotropic optical response of these nanomaterials. The third part is the most important one in the thesis, which presents the optical applications of these anisotropic nanomaterials. Firstly, aligned CNTs are used in fiber laser systems to modulate the polarization state of the laser output, which shows excellent performance with the degree of polarization of 89.1% at 1 µm (87.5% at 1.5 µm) for linear polarization modulation. We also demonstrate four-wave mixing based photon-pair generation with CNTs. Secondly, photoluminescence of the combed nanowires is examined to be polarization dependent for multifunctional logic gates. We construct all-optical arithmetic devices with NWs, which provide new means for the realization of all-optical logic gates. Lastly, anisotropic two-dimensional nanomaterials (e.g., BP, ReS2, ReSe2) are studied to demonstrate their waveplate performance. Finally, I summarize the whole contents and give my personal outlook on the study of novel anisotropic nanomaterials to explore their applications in both photonic and optoelectronic fields.