Passively mode-locked thulium-doped fiber laser based on saturable absorption of carbon nanofibers.

Abstract

As a new type of carbon-based material, carbon nanofibers (CNFs) have attracted much attention due to their unique physical structure and optical properties. In this paper, we propose the application of CNFs as the saturable absorber (SA) and established a passively mode-locked thulium-doped fiber laser (TDFL) for verification. By mixing sodium carboxymethyl cellulose solution with CNFs, CNF SA was prepared, the nonlinearity of which was tested as follows: the modulation depth was ∼1.3%, and the saturation intensity was 18MW/cm2. By inserting the CNF SA into the TDFL ring cavity, mode-locked laser pulses of a central wavelength of 1954.47 nm and a 3 dB bandwidth of 5.93 nm were obtained. The spectral pulse width was 1.31 ps; the repetition frequency was 32.68 MHz; and the signal-to-noise ratio (SNR) was calculated to be ∼57dB. To our knowledge, this is the first time that CNFs have been reported as SAs for mode-locked lasers in the 2 µm wavelength region. Our work provides a new reference for using carbon-based materials in the realization of ultrafast lasers, and the proposed CNFs are highly advantageous in the development of ultrahigh-speed optical modulators and next-generation high-performance nonlinear photonic devices.