The Study Of Wavelength Switchable And Tunable Erbium-doped Pulsed Fiber Laser

Fiber lasers have been widely used in many fields such as optical fiber communication,high-performance optical sensing,high-precision spectrum analysis,laser processing,laser medical treatment,etc.due to their small size,high output beam quality,high peak power,narrow pulse width and other optical properties.In the field of optical fiber communication,the output laser waveband of erbium-doped fiber laser basically covers the C-band(1530-1565 nm)and L-band(1565-1610 nm)in optical communication.The characteristics of the all-fiber structure make fiber lasers in optical communication systems It has excellent characteristics of good compatibility and high coupling efficiency.Therefore,erbium-doped fiber lasers have important applications in fiber communication.In order to increase channel transmission capacity and improve signal source utilization,multi-wavelength switchable tunable fiber lasers have gradually become research hot spot.Compared with conventional continuous light fiber lasers,pulsed fiber lasers have higher peak power,high repetition frequency,narrow pulse width and other optical characteristics,which have broader application prospects and research value in optical fiber communications.The research content of multi-wavelength switchable tunable pulse fiber laser mainly includes two parts: One is using Q-switching and mode-locked technology to achieve ultrafast pulse output,the other is to construct a switchable and tunable filter,and realize the switchable and tunable output of the output wavelength based on the filtering effect.In this paper,theoretical analysis and numerical simulation of the filtering effect of Sagnac filter and PMF-SMF-PMF(Polarization Maintaining Fiber-Single Mode Fiber-Polarization Maintaining Fiber)filter are carried out respectively,and the results are constructed according to the analysis results.Switchable and tunable erbium-doped pulsed fiber laser based on Sagnac filter and PMF-SMF-PMF filter.The main research contents and innovations of this paper are as follows:1.The transmission equation of the filter is established by using the Jones matrix of the optical element,and the expression of the transmission coefficient of the filter is obtained.In the Sagnac filter embedded with a section of PMF,the transmission spectrum of the filter is analyzed under different PMF length and different coupling ratio of fiber coupler.In the PMF-SMF-PMF filter,the change of the transmission spectrum of the filter with different PMF lengths is analyzed,and finally a stable switchable tunable filter is obtained.2.The stable Q-switched pulse output is generated by SESAM.The optimal structure parameters of Sagnac filter embedded in polarization maintaining fiber are obtained by numerical simulation.A single/double wavelength switched erbium-doped Q-switched fiber laser is built.When the pump power is stable at 300 m W,the laser can achieve a stable single/ double wavelength switchable tunable output in the 1.5 ?m band.In the single wavelength working state,the central wavelength of the output spectrum achieves a tuning range of 3.72 nm.In the dual wavelength state,the tuning range of 1.04 nm is realized under the dual wavelength output state,and the spectral spacing is kept at 5.27 nm under the dual wavelength working state.The pulse repetition frequency varies from 39.47 k Hz to 58.87 k Hz.The corresponding pulse width range is 7.19 ?s-2.91 ?s and the signal-to-noise ratio is 49 d B.3.Since the polarization dependent isolator and polarization controller introduce the nonlinear polarization rotation(NPR)effect into the switchable tunable erbium-doped pulsed fiber laser based on PMF-SMF-PMF filter,the laser produces stable mode-locked pulse output,and the corresponding signal-to-noise ratio is as high as 71.88 d B.By changing the deflection angle and pump power of the polarization controller properly,the laser is switched to Q-switched state.In the Q-switched state,the polarization controller in the filter is adjusted,and the wavelength of the output spectrum is switchable and tunable.The number of single wavelength and double wavelength output spectrum are included.