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The fiber single-cavity dual-comb laser (SCDCL) is an emerging light-source architecture that opens up the possibility for low-complexity dual-comb pump-probe measurements. However, the fundamental trade-off between measurement speed and time resolution remains a hurdle for the widespread use of fiber SCDCLs in dual-comb pump-probe measurements. In this paper, we break this fundamental trade-off by devising an all-optical dynamic repetition rate difference (Δf_rep) modulation technique. We demonstrate the dynamic Δf_repmodulation in a modified version of the recently developed counterpropagating all-normal dispersion (CANDi) fiber laser. We verify that our all-optical dynamic Δf_repmodulation technique does not introduce excessive relative timing jitter. In addition, the dynamic modulation mechanism is studied and validated both theoretically and experimentally. As a proof-of-principle experiment, we apply this so-called dynamic CANDi (DCANDi) fiber laser to measure the relaxation time of a semiconductor saturable absorber mirror, achieving a measurement speed and duty cycle enhancement factor of 143. DCANDi fiber laser is a promising light source for low-complexity, high-speed, high-sensitivity ultrafast dual-comb pump-probe measurements. 

Optical frequency combs, which consist of precisely controlled spectral lines covering a wide range, have played a crucial role in enabling numerous scientific advancements. Beyond the conventional approach that relies on mode-locked lasers, microcombs generated from microresonators pumped at a single frequency have arguably given rise to a new field within cavity nonlinear photonics, which has led to a robust exchange of ideas and research between theoretical, experimental, and technological aspects. Microcombs are extremely attractive in applications requiring a compact footprint, low cost, good energy efficiency, large comb spacing, and access to nonconventional spectral regions. The recently arising microcombs based on fiber Fabry–Pérot microresonators provide unique opportunities for ultralow noise and high-dimensional nonlinear optics. In this review, we comprehensively examine the recent progress of fiber Kerr microcombs and discuss how various phenomena in fibers can be utilized to enhance the microcomb performances that benefit a plethora of applications. 

Abstract Dissipative Kerr soliton (DKS) microcomb has emerged as an enabling technology that revolutionizes a wide range of applications in both basic science and technological innovation. Reliable turnkey operation with sub-optical-cycle and sub-femtosecond timing jitter is key to the success of many intriguing microcomb applications at the intersection of ultrafast optics and microwave electronics. Here we propose an approach and demonstrate the first turnkey Brillouin-DKS frequency comb to the best of our knowledge. Our microresonator-filtered laser design offers essential benefits, including phase insensitivity, self-healing capability, deterministic selection of the DKS state, and access to the ultralow noise comb state. The demonstrated turnkey Brillouin-DKS frequency comb achieves a fundamental comb linewidth of 100 mHz and DKS timing jitter of 1 femtosecond for averaging times up to 56 μs. The approach is universal and generalizable to various device platforms for user-friendly and field-deployable comb devices.