  We present a 100 MHz repetition rate Yb-fiber-laser-pumped synchronously
pumped optical parametric oscillator (SPOPO) delivering tunable frequency combs
covering almost the entire visible spectral range. By intracavity doubling both
the signal and idler combs and using collinear residual pump light, nearly
continuous tuning over the range of 420-700 nm is achieved with only small gaps
near the OPO degeneracy condition. Output powers range from 10 mW to 200 mW,
depending on wavelength, with pulse durations below 150 fs without external
compression. Frequency locking of all three collinearly outcoupled combs (pump,
doubled signal, and doubled idler) to a femtosecond enhancement cavity
facilitates direct comparison of their optical phase noise and phase modulation
transfer functions. In the singly-resonant OPO, optical phase modulation of the
pump comb is transferred nearly completely to the non-resonant idler comb. This
results in a resonant signal comb with reduced optical phase noise and also
enables high-bandwidth modulation on the idler comb via phase modulation of the
pump.
