Novel optical devices for photonic networks using nonlinearity in carbon nanotubes

本项目旨在实现基于碳纳米管（CNT）的新型光学器件。我们主要集中在三个主题：使用碳纳米管薄膜的锁模光纤激光器，使用倏逝波耦合的碳纳米管波导和光纤，以及基于碳纳米管的光开关。(1)使用碳纳米管薄膜的锁模光纤激光器：我们证明了碳纳米管薄膜可以在1到1.6微米的宽波长范围内锁模光纤激光器。利用碳纳米管薄膜缩小腔体尺寸，实现了高重复率（~ 10GHz）锁模光纤激光器。(2)利用倏逝波耦合的碳纳米管波导和光纤：制备了一种碳纳米管涂层的无包层平面波导，并通过波导模式与碳纳米管之间的倏逝波耦合观察到可饱和吸收。我们成功地将其应用于光纤激光器的锁模。基于同样的原理，我们利用侧面抛光的d型纤维和锥形纤维制备了光纤型碳纳米管器件，并将其作为锁模器。(3)基于碳纳米管的光开关：我们研究了使用碳纳米管进行光开关的可能性。在非线性环镜（NOLM）结构中使用碳纳米管涂层的平面波导，耦合比的变化约为20%。我们还在5cm长的碳纳米管涂层的d型光纤中实现了基于非线性偏振旋转（NPL）的光开关，开关功率低至50mW，消光比高达>20dB。结果表明，碳纳米管的非线性系数高达10^6 W^<-1>m^<-1>。

This project aims at realizing novel optical devices based on carbon nanotubes (CNT). We mainly concentrated on three topics, mode-locked fiber lasers using CNT thin films, CNT waveguides and fibers using evanescent wave coupling, and CNT based optical switches.(1)Mode-locked fiber lasers using CNT thin films : We demonstrated that CNT thin film can mode-lock the fiber laser at wide wavelength range from 1 to 1.6 microns. We also demonstrated high-repetition-rate (〜10GHz) mode-locked fiber laser by reducing the cavity size using the CNT thin film.(2)CNT waveguides and fibers using evanescent wave coupling : We prepared a CNT coated over-clad-less planar waveguide, and observed saturable absorption through evanescent wave coupling between the guided mode and the CNT. We successfully applied it for mode-locking the fiber laser. Based on the same principle, we fabricated fiber-type CNT devices using side-polished D-shaped fibers and tapered fibers, and also applied it as the mode locker.(3)CNT-based optical switches : We studied the possibility of optical switching using CNTs. By using the CNT coated planar waveguide in a nonlinear loop mirror (NOLM) configuration, we obtained the change of coupling ratio by about 20%. We also acheived the optical switching based on nonlinear polarization rotation (NPL) in a 5cm-long CNT coated D-shaped fiber with the switching power as low as 50mW and the extinction ratio as high as >20dB. It suggests that the nonlinear coefficient of the CNT is as high as 10^6 W^<-1>m^<-1>.