Ultra-fast fibre laser systems based on SESAM technology: new horizons and applications

A promising route to manufacturing portable (sub-)picosecond fibre lasers is to use a semiconductor saturable absorber mirror (SESAM). With SESAMs, the mode-locked regime can be achieved for different values of cavity dispersion for a broad spectrum ranging from 0.8 to 1.6 mum. The fibre lasers, characterized by a high efficiency and reliability and a small footprint, are very attractive for applications traditionally occupied by solid-state lasers. The broad fluorescence spectrum makes different fibre gain media attractive for tuneable and ultra-short-pulse sources. In this paper, we discuss recent advances in ultra-fast fibre lasers. We study the fundamental properties and technical challenges of mode-locked fibre lasers operating in the 0.9-1.6 mum range, and the methods to achieve high peak-powers from all-fibre devices. The key component is the SESAM, notably, a dilute nitride SESAM. The SESAM supplies a strong mechanism for picosecond pulse generation that is entirely self-starting for a wide range of cavity dispersion and ensures stability against Q-switched mode-locking. In particular, compact mode-locked lasers stabilized by near-resonant SESAMs can be realized in a short fibre cavity free from any dispersion compensator. An appropriate dispersion delay line at the output of the master source may be used for pulse clean-up. The high-quality pulses obtained can then be compressed using traditional methods, when the pulse first undergoes spectral enrichment via self-phase modulation in an auxiliary fibre and then gets compressed in a grating pair. The fibre laser is capable of efficient wavelength conversion via second harmonic generation in non-linear crystals. Using a periodically poled LiNbO3 crystal for frequency doubling, we produce sub-100 fs pulses at 0.8 mum with a 50% conversion efficiency.