Investigation into nonlinear optical absorption property of CoSb₃ skutterudite in the 2 μm spectral region

We report our recent investigation results on the nonlinear optical absorption property of CoSb₃ skutterudite at 2-μm wavelengths. First, we conducted an open-aperture (OA) Z-scan measurement to figure out the nonlinear absorption coefficient (β) of CoSb₃ skutterudite. The coefficient was estimated to be around −90.5 × 10⁴ cm/GW at a wavelength of 1900 nm with the measurement. Next, in order to demonstrate the practical applicability of CoSb₃ skutterudite in the 2-μm spectral region, a saturable absorber (SA) was implemented on a side-polished fiber platform by depositing a composite of CoSb₃ and polyvinyl alcohol (PVA). The measured saturation power and modulation depth of the fabricated SA were ~21 W and ~10%, respectively. Using the prepared SA within a fiberized ring cavity, stable soliton pulses with a temporal width of ~838 fs could be produced at 1912.9 nm. The output pulses were almost transform-limited with a time-bandwidth product of ~0.32. The signal-to-noise ratio (SNR) was measured as ~72 dB at the fundamental frequency of ~16.93 MHz.