Ultrafast Raman fiber laser: a review and prospect

Ultrafast Raman fiber laser has been proved to be an effective method to obtain ultrafast optical pulses at special wavelength. Yet, compared with conventional rare-earth doped counterparts, it is challenging for Raman fiber lasers to generate pulses with high pulse energy and short pulse duration. Here, we review three categories of ultrafast Raman fiber laser technologies and give detailed discussions on the advantages and challenges of each. In regards to mode-locking, different saturable-absorbers-based fiber lasers are compared and their common problem resulting from long cavity length are discussed. In terms of synchronously-pumping, several approaches to match the repetition rate of pulsed pump with the length of Raman fiber cavity are discussed, while the technical complexity of each method is analyzed. Moreover, the recently developed technology termed as nonlinear optical gain modulation (NOGM) is introduced, which turns out to be a simple and quality solution to generate high-energy femtosecond pulses with wavelength agility. Compared with the others, NOGM gathers various advantages including simple structure, long-term stability, high pulse energy and short pulse duration, which may effectively promote application expansion of ultrafast Raman fiber laser in the near future.

Automated summary

Ultrafast Raman fiber lasers are effective for obtaining ultrafast optical pulses at specific wavelengths, but generating pulses with high energy and short duration is challenging compared to conventional rare-earth doped lasers. This review discusses three categories of ultrafast Raman fiber laser technologies and their advantages and challenges. A newly developed technology called nonlinear optical gain modulation (NOGM) is introduced as a simple and high-quality solution for generating high-energy femtosecond pulses with wavelength agility.