Investigation of nonlinear optical properties of rhenium diselenide and its application as a femtosecond mode-locker

We investigated the nonlinear optical properties of ReSe₂. First, we measured the nonlinear absorption coefficient and the nonlinear refractive index of a ReSe₂ thin film using open-aperture (OA) and closed-aperture (CA) Z-scan techniques. ReSe₂ was shown to possess both saturable absorption and self-defocusing properties. The nonlinear absorption coefficient of ReSe₂ was measured to be −5.67 ± 0.35 × 10³ cm∕GW, and its nonlinear refractive index was −2.81 ± 0.13 × 10⁻² cm²∕GW at 1560 nm. Next, a fiberized saturable absorber (SA) based on ReSe₂ was fabricated with a side-polished fiber platform and was tested as an ultrafast mode-locker capable of producing femtosecond pulses operating at a wavelength of 1560 nm. The estimated modulation depth and saturation power are ∼3.9% and ∼42 W, respectively, for the transverse electric mode, while they are ∼2.4% and ∼53 W for the transverse magnetic mode. Using the prepared SA, stable soliton pulses with a temporal width of ∼862 fs were produced from an erbium-doped fiber ring cavity. To the best of the authors’ knowledge, this is the first demonstration of using a ReSe₂-based SA for femtosecond mode-locked pulse generation.