Nonlinear optical properties of perovskite-type oxide La_0.6Sr_0.4Co_0.2Fe_0.8O_{3−<i>δ</i>} for ultrafast photonic applications

We successfully synthesized a nonlinear optical material of perovskite-type oxide La_0.6Sr_0.4Co_0.2Fe_0.8O_3-<i>δ</i> (LSCF) with the sol-gel method. The nonlinear optical properties and the potential for ultrafast pulse generation are investigated with the LSCF-based saturable absorber (SA). The modulation depths are measured to be 18.4% and 13.3% in 1 <i>μ</i>m and 1.5 <i>μ</i>m wavelength regimes, respectively. The LSCF SAs are integrated into both Yb-doped and Er-doped fiber laser cavities to investigate their performance in the generation of ultrashort pulses. The noise-like pulse (NLP) with a pulse duration of 433 fs and the conventional soliton pulse with a pulse duration of 1.06 ps are realized at the central wavelengths of 1034.3 nm and 1561.8 nm, respectively. Additionally, in the 1.5 <i>μ</i>m regime, the conventional soliton pulse can transform into a bound-state soliton pulse and a harmonic bound-state soliton pulse through the optimization of the pumping power and intracavity polarization state. Our study first demonstrates the nonlinear optical properties and realizes the ultrafast photonic applications based on LSCF SAs, providing a valuable reference for exploring the optical properties of perovskite-type oxide materials.