Mode-locked fibre laser with e-controlled cavity length in ultra-wide range

We propose for the first time a new method to electronically control the cavity length of mode-locked fibre lasers, allowing different lasing conditions and performance in a single laser configuration. A special cavity design was developed that combines a multi-kilometre fibre resonator boosting pulse energy to hundreds nJ with an all-PM fibre resonator providing nearly 200-m long environmentally-stable cavity round trip. Switching between the cavities is achieved automatically by adjusting modulation frequency of an optical switcher (used for active mode locking) to match the cavity round-trip time of one of the cavities. We discuss details of our method, its possibilities and limitations, in particular related to stability of pulse parameters.