Composite film with anisotropically enhanced optical nonlinearity for a pulse-width tunable fiber laser

One-dimensional nanomaterials usually possess unique anisotropic chemical or physical properties. For practical device applications, one of the biggest challenges is their large-scale assembly with predesigned architecture to render optimized collective properties. Based on our previous studies, here we report an extended investigation on the macroscopically aligned assembly of gold nanorods with tunable aspect ratio (AR) in transparent polymer films based on the electrospinning technique. The optical properties of the composite films were investigated using polarized extinction spectra and the Z-scan technique. Due to the collective longitudinal LSPR of the macroscopically aligned gold nanorods, the transparent composite films exhibited anisotropically enhanced optical nonlinearity. The intensity of the nonlinear optical signal of the films can be tuned by varying the polarization direction of the laser on the films. Moreover, the influence from the AR and the doping concentration of GNRs on the optical properties of the composite films was also investigated. To demonstrate an example of practical applications, the composite film was employed as a saturable absorber to construct a pulsed fiber laser. Inspiringly, the pulsed fiber laser with switchable mode-locking and Q-switching operation modes was realized successfully. The switching of the operation mode of the laser can be triggered simply through variation of the laser's polarization direction. Such a pulse-width tunable fiber laser is potentially useful in various application scenarios.