Pulsed Fiber Lasers Based On The Novel Intermode Beating Mode-locking Mechanism

Pulse fiber laser with its inherent advantages of compact structure,high quality light beam,high peak power,roubust operation and free maintenance has been widely applied in optical sensing,industrial precision processing,optical communication,biomedicine and optical imaging.Mode-locking technique is one of the main approaches to achieve pulse fiber laser,but both the active and passive mode-locking techniques need the special mode-locking elements which usually have the limitions of narrow operation waveband,high cost and laser system complexity.Therefore,laser scientists always attempt to explore self-mode-locking mechanism without requiring any mode-locking element in laser cavity.Our research group firstly proposed a novel self-mode-locking mechanism:Inter-mode beating mode-locking technique.The key point of this new technique is to adjust the resonant cavity frequency to match a intermode beating frequency of the multi-longitudinal-mode pump source,and the pump intermode beating frequency must be the integer multiples of the resonant cavity frequency.Thus,once the cavity frequency matching condition is satisfied,the resonant laser will self-start mode-locking opeation.On the basis of our previous research works,we comprehensively explore about the intermode-beating mode-locking technique for different kinds of pulsed fiber lasers in this thesis.The main work is as follow:1)Giving an introduction about the current market demand of pulse fiber lasers,predicting the future market developing trend,briefly summarizing the develop-ment course of mode-locked pulse fiber lasers,and elaborating the principle of the mode-locked and stimulated Raman scattering.2)We proposed and successfully realized rare-earth-doped mode-locked fiber laser using the novel intermode-beating mode-locking technique for the first time.We used a 1.56 ?m multi-longitudinal-mode laser to pump a Tm3+-doped fiber cavity.By precisely matching the cavity round-trip frequency with the certain intermode beating frequency(34.5 MHz)of the 1.56 ?m pump laser,we obtained the 12th-order harmonic mode-locking of the Tm3+-doped fiber laser at 1.98 ?m.The mode-locked pulses have a pulse duration of 15.2 ns,repetition frequency of3)34.496 MHz,and the stable RF spectrum with a SNR>61 dB.The output characteristics in the optical spectral,RF spectral and time domain are also investigated in details.4)We proposed and demonstrated an intermode-beating mode-locked Raman fiber laser using an intra-cavity pumping scheme.The first-order Raman mode-locked pulse laser in a phosphosilicate Raman fiber is obtained with a center wavelength of 1212 nm.The mode-locked repetition frequency is 57.863 MHz,and fundamental RF signal-to-noise ratio is about 50 dB.The pulse duration is as narrow as 1.58 ns,which is the shortest pulse duration achieved by inter-mode beating mode-locking.The 1212 nm pulse laser is harmonically mode-locked at the 548th order of the Raman resonant cavity,well matching the 551th harmonic longitudinal mode frequency in the 1044 nm pump.In this experiment,the intermode beating frequency of the 1044 nm pump source and the Raman cavity frequency realize self-matching.Such 1212 nm pulsed laser could be used as an efficient pump source for Holmium-doped fiber.