Research On 1/1.5 ?m Synchronous Pumped Mode-locked Pulsed Fiber Laser

Synchronous pulsed laser(SPFL)has many advantages,such as simple structure,good system stability,harmonic tuning of pulse repetition frequency,without introducing modulator in the cavity.It was used to generate ultrashort pulses in dye lasers in the early stage,but little research has been done in the field of active fiber lasers.If it is used in fiber laser,It can be used as an ideal seed source in laser amplification system and has important application potential in optical fiber communication and optical fiber sensing.Conventional mode-locked pulsed fiber lasers are single-wavelength output.Dual-band mode-locked fiber lasers with synchronous output characteristics will play an important role in the fields of non-linear frequency conversion,Raman scattering spectrum,pump detection spectrum and ultra-wideband supercontinuum spectrum generation.Therefore,the research of synchronously pumped mode-locked single-band and dual-band pulsed fiber lasers is not only of great academic significance,but also of great application.This paper conducts the following research on this topic:1.Several conventional methods of pulse laser generation,synchronously pumped mode-locked fiber lasers and dual-wavelength synchronous pulse fiber lasers are briefly introduced.2.By modulating semiconductor lasers in the driving circuit to obtain repetition frequency and pulse width adjustable 976 nm pulse,Using it to pump Ytterbium-doped and Erbium-doped fibers to achieve 1 ?m and 1.5 ?m synchronous pumped mode-locking.It can be found that the output characteristics of synchronous pump mode-locked pulse deteriorate with the increase of intracavity fundamental frequency,but the repetition limit can be reached far exceeding the maximum repetition frequency determined by the lifetime of doped ion upper level;the pulse width of synchronous pump mode-locked pulse decreases with the increase of pump power,and the signal-to-noise ratio of pulse increases;the pulse width of synchronous pump mode-locked pulse is much smaller than that of pump.The pulse width is broadened with the broadening of the pump pulse width.In addition,when the ratio of modulation frequency to intracavity fundamental frequency is 1/2 and 3/2,we can achieve rational mode-locking.The output pulse repetition frequency is several times of the fundamental frequency.When the ratio is 1,2,3 and other integer times,it can be regarded as a rational number with denominator 1,then the corresponding harmonic digital mode-locking can be obtained.3.A mode-locked 1 ?m linear cavity based on semiconductor saturable absorber mirror(SESAM)and a mode-locked 1.5 ?m ring cavity based on carbon nanotube(CNT)are pumped by 976 nm continuous light and 976 nm pulse respectively.The 1?m linear cavity and a 1.5 ?m ring cavity passively mode-locked and hybrid mode-locked fiber laser are obtained.The results show that,compared with passive mode-locking,hybrid mode-locking has lower threshold(the mode-locking threshold of 1 ?m laser decreases by about 10%,the mode-locking threshold of 1.5 ?m laser decreases by about 7%);better pulse stability(the signal-to-noise ratio of 1 ?m pulse increases by about 13.7 dB,the signal-to-noise ratio of 1.5 ?m pulse increases by about 8.0 dB);larger stable fundamental frequency mode-locking interval and narrow pulse width comparable to passive mode-locking.4.Pulse width is 14.87 ns at 1.18 W pumping power and 945 ps at 1.94 W pumping power.Pulse width compression with the deterioration of stability.This experiment again verifies the effect of repetition frequency on synchronous pump mode-locking effect.It is difficult to output high quality and narrow pulse width pulse only by synchronous pump mode-locking at repetition frequency which is far beyond the repetition limit determined by the lifetime of doped ion upper level.At the same time,the relationship between synchronization effect and pump energy is verified again.5.Based on the EY305 erbium-ytterbium co-doped fiber,a 1/1.5 ?m dual-wavelength synchronously mode-locked pulse fiber laser is realized,and the relationship between 1 ?m bandwidth and pulse width and its influence on 1.5 ?m pulse characteristics are verified.With the increase of bandwidth(from 5.6 nm to17.48 nm),the pulse width of 1 ?m mode-locked pulse decreases from 104.7 ps to78.3 ps,and the corresponding 1.5 ?m mode-locked pulse spectrum width increases from 0.41 nm to 1.57 nm,and the pulse width decreases from 79 ps to 57.6 ps.The results show that 1 ?m laser is a mode-locked pulse based on NPR technology,while1.5 ?m laser is a mode-locked pulse with synchronous pumping effect and NPR effect by the reabsorption by Yb3+.The common end monitors the output of the two pulses in full synchronization,and the repetition frequency is 25.89 MHz.