Novel optical devices for photonic networks using nonlinearity in carbon nanotubes

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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>.