Widely Tunable OPO Spanning From the Violet to Mid-Infrared Based on Aperiodic QPM Crystal

Femtosecond optical parametric oscillators (OPOs) have numerous fundamental applications due to their high conversion efficiency and extensive spectral availability. As a premium alternative, aperiodic quasi-phase-matching crystal can extend the phase-matching bandwidth with its numerous poling periods. In OPO, it can considerably simplify the schematic design and generate broadband spectral coverage. In this study, using an aperiodically poled lithium niobate, we reported a widely tunable broadband OPO generating signal radiation across 1.4- 1.8 \mu \text{m} and idler radiation across 4.0- 2.4 \mu \text{m} . We also investigated the generated harmonics from the violet to near-infrared region, where up to 4th order harmonics (390 nm) upon cascaded quadratic nonlinearity was observed. This scheme demonstrates the potential of aperiodic QPM crystal for broadband OPO sources and provides a promising method for the future exploitation of broadband quasi-phase-matching phenomenon.