A system and method for generating an optical laser pulse train of constant ultrashort pulse duration and low timing jitter in a fiber ring laser system (resonator) while keeping the laser resonator resilient to environmental conditions like temperature, humidity and pressure. The laser resonator may be actively mode-locked with a periodic electrically driven modulation at a specific frequency that corresponds to the inverse of the transit time inside the resonator. The optical pulse train quality may be monitored in real time, and the frequency of the modulation may be dynamically tuned in real time to compensate for resonator length changes due to changes in the environmental conditions.