Hybrid Wavelength Manipulation with Enhanced Ambient-Thermal Adaptability in an All-Polarization-Maintaining Mode-Locked Fiber Laser

Nonreciprocity of traditional filters severely limits their tunability. To tap alternatives, here we propose hybrid wavelength manipulation with enhanced ambient-thermal-drift adaptability in an all-polarization-maintaining fiber laser. A multifunctional 2-in-1 device, which is based on a CNTs-coated tapered panda fiber and a specially designed PMMA (polymethyl methacrylate) package, is fabricated and applied to induce nonlinear saturable absorption and hybrid spectral filtering. In particular, hybrid tuning is enabled by the combination of mechanical and non-mechanical mechanisms, thus greatly prompting flexibility and efficiency. As wide as 40-nm tuning range in C- and short L-band is covered, with coefficients of 0.0116 nm/μϵ and 0.77 nm/°C respectively via stretching and heating the tapered fiber. Meanwhile, twisting induces steady dualwavelength mode-locking. Required amount of adjustment is also cut nearly in half in contrast to previously reported works. Besides, great thermal expansion of PMMA introduces adaptative compensation towards ambient thermal fluctuation, resulting in over 4.7 times improvement. Numerical analysis is also studied for optimal design of filters. This work explores promising solutions for advanced tunable ultrafast lasers.