Research On Multi-wavelength Mode-locked Erbium-doped Fiber Laser

Fiber lasers have been widely used in military,industrial and scientific research fields for their advantages of compact size,ease of operation,free maintenance,excellent beam quality and etc.While,for different applications,different requirements are needed for fiber lasers.In recent years,researches on ultra-short pulse,low noise,multi-wavelength fiber lasers have become a hotspot in the fiber laser community.Among them,multi-wavelength(multi-color)fiber lasers can produce short pulses with different wavelengths,which is promising to be used in application scenarios such as optical sensing,optical metrology,microwave photonics,optical signal processing,terahertz generation and optical transmission.In this thesis,based on single mode-(multi-mode)-single mode fiber structure(SM-MM-SM)and nonlinear polarization rotation effect,we have demonstrated a multi-color erbium doped fiber laser in an all fiber ring cavity.By finely tuning the SM-MM-SM fiber length,total cavity length and polarization states,stable asynchronous three-color pulses are obtained.The three-color pulses are centered at wavelengths of 1533.43 nm,1548.46 nm and 1562.68 nm.The corresponding repetition rates of the threecolor laser are 388.951 k Hz,388.932 k Hz and 388.913 k Hz respectively,matching well with the cavity length of 532 meters.On the other hand,this fiber laser can also work at single-wavelength and twocolor states by tuning the intra-cavity polarization.Under the single-wavelength operation state,the output wavelength can be tuned to 1533.76 nm,1547.66 nm or 1562.46 nm.While under the two-color operation state,the asynchronous mode-locked pulses are tuned at wavelengths of 1533.48 nm &1547.61nm、1549.16 nm &1561.94 nm or 1533.14 nm &1562.68 nm.This fiber laser has a very compact size and stable working states,so it can be used in optical spectroscopy,communication,sensing and other fields.In this thesis,we have also demonstrated synchronized mode-locked erbium and ytterbium doped fiber lasers based on a shared single wall carbon nanotube saturable absorber.The repetition rates of the two lasers are 39.2992 MHz and 19.6496 MHz.By finely tuning the cavity length of the ytterbium fiber laser,the two lasers are synchronized with output wavelengths at 1565.30 nm and 1034.65 nm.To win ultra-short pulses,we optimized the cavity dispersion of the erbium fiber laser by controlling the lengths of positive and negative dispersion fiber.With respect to the ytterbium doped fiber laser,we optimized the cavity dispersion by adjusting the distance of the dispersion-compensating gratings.Therefore,the pulse widths of the two synchronized laser pulses are compressed to be 1.24 ps and 31 ps.Optimizing the laser cavity to has yielded a large mismatch of 0.52 μm between the two laser cavities.It is predictable for us to further compress the pulse widths into femtosecond region during the amplification process outside of the cavity.Such synchronized fiber lasers based on common single wall carbon nanotube saturable absorber can be used in pump-probe,nonlinear optics,coherent combing and other research experiments.