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.

We demonstrate an all-fiber polarization-maintaining (PM) single-cavity dual-comb fiber laser based on intracavity polarization multiplexing. Two pulse trains share a common cavity section while two partially non-common branches provide independent gain, spectral filtering, and cavity-length control. The repetition rates are approximately 37.281 and 37.270 MHz, giving a repetition-rate difference of about 11 kHz. With radio-frequency (RF)-referenced repetition-rate stabilization, the 1 h standard deviations of $f_{\mathrm{rep}1}$, $f_{\mathrm{rep}2}$, and $\Delta f_{\mathrm{rep}}$, measured with a 1 s gate time, are 290, 178, and 342 $\mathsf{\mu }$Hz, respectively, corresponding to fluctuation-suppression factors of $6.3\times {10}^5$, $1.2\times {10}^6$, and $4.4\times {10}^5$ relative to free-running operation. Stable dual-comb operation is also obtained at discrete, fiber-length-customized working points near 4, 11, and 43 kHz. Autocorrelation measurements give pulse durations of 30.02 and 36.39 ps for the two outputs. A free-space ranging demonstration at $\Delta f_{\mathrm{rep}}=4$ kHz yields a precision of 96.3 $\mathsf{\mu }$m at a 250 $\mathsf{\mu }$s update time, which improves to 2.7 $\mathsf{\mu }$m after averaging 400 points (100 ms). The proposed architecture combines all-fiber PM propagation, branch-level controllability, and RF-referenced repetition-rate stabilization in one single-cavity platform.

Previous studies have shown that supercontinuum (SC) coherence degradation induced by shot noise can be quantitatively assessed through the injected soliton order, and the degradation process mainly originates from the noise amplification via the modulation instability effect. However, this still cannot clarify the irregular distribution property of SC coherence when the injected soliton order is between 10 and 30. In this paper, we present both theoretical analyses and numerical simulations of SC coherence degradation under shot noise on the premise of a fixed SC span. Our studies clearly show that the injected pulse duration is the dominant factor of SC coherence under the shot noise. In addition, as an auxiliary mechanism, soliton collision can further degrade the SC coherence, and the collision probability becomes greater with the increase of injected soliton order.