Efficient Fabrication of Low-Loss Micro-Tapered Long-Period Gratings for Dissipative Soliton Fiber Laser

A polarization-selective element based on a polarization-maintaining fiber micro-tapered long-period fiber grating (PMF-MT-LPFG) has been efficiently fabricated and used in a dissipative soliton mode-locked fiber laser. The PMF-MT-LPFG was fabricated using a double-side <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{CO}_{2}$</tex-math></inline-formula> laser exposure heating and pulling technique, exhibiting a maximum polarization-dependent loss of 34 dB and an insertion loss as low as 2.6 dB. The PMF-MT-LPFG-based dissipative soliton mode-locked fiber laser can support various mode-locked state outputs. A single dissipative soliton mode-locked pulse with a 3 dB bandwidth of 15.2 nm was observed, featuring a threshold power of 39 mW, a repetition rate of 47.92 MHz, and an external cavity compressed pulse width of 378.2 fs. By simply adjusting the polarization state and pump power, multiple dissipative soliton mode-locked pulses, including harmonic and bound-state mode-locked pulses, were generated. Additionally, twin-soliton and triple-soliton bound-state molecular pulses were thoroughly characterized. These results demonstrate that the fabrication technique offers high flexibility for preparing grating-based polarization-selective devices, enabling flexible wavelength selection and low insertion loss. Furthermore, the PM-MT-LPFG serves as a cost-effective alternative to commercial polarization-dependent devices for achieving nonlinear polarization rotation effects and generating ultrashort pulses with different states, providing a valuable platform for studying the generation and evolution of complex nonlinear effects in dissipative solitons.