Phase-matching-induced near-chirp-free solitons in normal-dispersion fiber lasers

• Published in: Light, science & applications science & applications, 2022-01, Vol.11 (1), p.25-25, Article 25
• Main Authors: Mao, Dong, He, Zhiwen, Zhang, Yusong, Du, Yueqing, Zeng, Chao, Yun, Ling, Luo, Zhichao, Li, Tijian, Sun, Zhipei, Zhao, Jianlin
• Format: Article
• Language: English
• Subjects: 140/125; 639/624/1020/1090; 639/766/400/1118; Applied and Technical Physics; Atomic; Birefringence; Classical and Continuum Physics; Compression; Lasers; Molecular; Optical and Plasma Physics; Optical Devices; Optics; Photonics; Physics; Physics and Astronomy; Polarization
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/s41377-022-00713-y

Direct generation of chirp-free solitons without external compression in normal-dispersion fiber lasers is a long-term challenge in ultrafast optics. We demonstrate near-chirp-free solitons with distinct spectral sidebands in normal-dispersion hybrid-structure fiber lasers containing a few meters of polarization-maintaining fiber. The bandwidth and duration of the typical mode-locked pulse are 0.74 nm and 1.95 ps, respectively, giving the time-bandwidth product of 0.41 and confirming the near-chirp-free property. Numerical results and theoretical analyses fully reproduce and interpret the experimental observations, and show that the fiber birefringence, normal-dispersion, and nonlinear effect follow a phase-matching principle, enabling the formation of the near-chirp-free soliton. Specifically, the phase-matching effect confines the spectrum broadened by self-phase modulation and the saturable absorption effect slims the pulse stretched by normal dispersion. Such pulse is termed as birefringence-managed soliton because its two orthogonal-polarized components propagate in an unsymmetrical “X” manner inside the polarization-maintaining fiber, partially compensating the group delay difference induced by the chromatic dispersion and resulting in the self-consistent evolution. The property and formation mechanism of birefringence-managed soliton fundamentally differ from other types of pulses in mode-locked fiber lasers, which will open new research branches in laser physics, soliton mathematics, and their related applications. The fiber birefringence, chromatic dispersion, and nonlinear effect follow a phase-matching principle, enabling the formation of birefringence-managed solitons in normal-dispersion fiber lasers containing a section of polarization-maintaining fiber.