High repetition rate mode-locked ytterbium fiber laser using dichroic fiber mirrors and photonic bandgap fiber technology

We demonstrate here an all-fiber passively mode-locked laser using an integrated fiber-end mirror and photonic bandgap fiber-based dispersion compensator. The refined technology of thin-film coatings made with electron beam evaporation on a single-mode fiber facet results in a compact dichroic pump combiner/output coupler. The dichroic mirror made of ZrO2 and SiO2 provides a low reflectivity (0.4 %) for the 980 nm pump and over 40 % reflectivity for the 1040 nm signal wavelength, which enabled us to build a short-length mode-locked ytterbium fiber laser. The laser cavity consisted of 8 cm of highly doped ytterbium fiber, 10 cm. of anomalous dispersion photonic bandgap fiber, a semiconductor saturable absorber mirror (SESAM) and the dichroic mirror. Pump and signal wavelengths were separated by a fiber coupler placed outside the cavity contrary to conventional geometry. A butt-coupled SESAM provided reliable self-starting at a pump power of 150 mW. The all-fiber design using dichroic fiber mirror combined with photonic bandgap fiber dispersion compensator is highly stable and requires virtually no alignment. The mode-locked laser produces 572-fs soliton pulses at 571.03 MHz fundamental repetition rate. To the best of our knowledge, this is the highest fundamental repetition rate fiber laser operating around 1 mu m reported to date.