Ultralow-noise sub-two-cycle pulses at 1600 nm from a compact fiber-feedback optical parametric oscillator system at 76 MHz.

We demonstrate fiber-based self-compression down to sub-two optical cycles (9.5 fs) at 1600 nm with an average power of 620 mW (8.2 nJ) and a repetition rate of 76 MHz. We use an Yb-based pump laser to drive an optical parametric oscillator, which is subsequently amplified to the watt scale using an optical parametric amplifier. The grating-free single stage pulse compression is realized by a 42-mm-long common single mode fiber.  The compact system is furthermore shown to be highly stable, shot-noise-limited, and a broadband mid-infrared source through intra-pulse difference frequency generation.