Ultracompact zigzag fiber-feedback multipass optical parametric oscillator

Fiber-feedback OPOs are widely used as broadly tunable ultrashort pulse sources, but their limited parametric single-pass gain at a broad bandwidth often necessitates post-amplification stages. Our recently developed multipass amplification allows us to break this gain-bandwidth limit. The novel, to the best of our knowledge, zigzag implementation presented in this Letter enables five dispersion-engineered passes through a single nonlinear crystal using only two nearby plane mirrors. This compact geometry combines high gain with high bandwidth and is integrated in a fiber-feedback cavity. The resulting zigzag fiber-feedback multipass OPO (FFMOPO) delivers up to 1.2 W of shot-noise-limited 100 fs pulses that are continuously tunable from 1360 nm to 1800 nm at a 76 MHz repetition rate and up to 40% system conversion efficiency. With only a few cubic centimeters in size, the ultracompact zigzag geometry can be seamlessly integrated into existing single-pass OPO designs, eliminating the need for post-amplification and reducing the size and cost of tunable pulse sources for ultrafast spectroscopy and bioimaging.