Wavelength-switchable femtosecond pulse fiber laser mode-locked by silica-encased gold nanorods

A wavelength-switchable femtosecond pulse fiber laser is demonstrated by using a saturable absorber (SA) of silica-encased gold nanorods (GNRs@SiO₂). The GNRs@SiO₂ SA presents a modulation depth of 4.5% and nonsaturable loss of 32.1%. By properly adjusting the cavity parameters, femtosecond mode-locked pulses centered at 1535.6 nm and 1560.5 nm could be achieved alternately. The durations of pulses at the two wavelengths are measured to be ∼403 fs and ∼426 fs, respectively. The achieved results indicated that the GNRs@SiO₂ could indeed be a promising nonlinear material with excellent photothermal stability and saturable absorption, which could satisfy the requirements for different photonic devices and applications. (letter)