Compact all-polarization-maintaining dual femtosecond fiber laser system with large repetition rate tuning ranges based on self-made fiber actuators

We present a dual fiber laser system that comprises two compact all-polarization-maintaining fiber lasers. The main feature of this laser system is that, facilitated by self-made fiber actuators, the repetition rates of the sub lasers can be tuned across wide ranges and phase-locked with high stability and low phase noise. The fiber actuator consists of a PZT coupled with an annular displacement amplifier. Through an optimized design of the displacement amplifier's structure, we achieve not only large tuning ranges of 42 kHz (laser 1) and 49 kHz (laser 2) at a repetition rate of around 100 MHz but also a response bandwidth exceeding 1 kHz when the repetition rates are phase locked. Moreover, the self-made actuator demonstrates a lower insertion loss (0.37 dB) compared to commonly used delay lines (1.5 dB). After locking, the relative instability of the repetition rates remains superior to 2.28 × 10^-12 (1s gate time) even under an external temperature variation of up to 20°C. In the presence of environmental disturbances, including temperature fluctuations, humidity, and vibrations, the repetition rate stability of both lasers is kept within 5.1 × 10^-12. Furthermore, due to an effective suppression of phase noise at offset frequencies below 1 kHz, the integrated timing jitters are both smaller than 217 fs [1 Hz-1 MHz]. As a performance proof, the ability to eliminate the dead zone based on our dual fiber laser system is verified through an absolute distance measurement experiment. Additionally, long optical fiber spools with nominal lengths of 8 m, 50 m, 100 m, and 235 m were precisely measured, achieving standard deviations of less than 166 μm, which improved to 15.1 μm after averaging every 200 data points. This result validates the system's capability for long-distance measurements.