Study On Ultra-narrow Linewidth Brillouin Fiber Laser Based On DFB-FL

Narrow linewidth fiber lasers have great application value in optical fiber sensing,radar imaging,coherent light detection,optical fiber communication and other fields due to their unique advantages such as narrow linewidth,high pump conversion efficiency,and good fiber system compatibility.Distributed feedback(DFB)fiber laser is one of the common narrowlinewidth fiber lasers.The phase-shifting fiber grating is used as the resonator,and the pump light is used to provide energy excitation.By phase-shifting fiber grating’s frequency-selective and mode-locking,finally achieve narrow linewidth laser output.With the continuous progress of society,in some high-precision and cutting-edge fields,such as high-precision optical fiber sensing,high-resolution radar imaging,and long-distance coherent optical communication systems,there are stricter requirements on the linewidth of the laser.The laser’s linewidth directly determines the measurement accuracy and accuracy of the system.Narrow linewidth lasers with linewidth about several k Hz can no longer meet application requirements.New technologies are urgently needed to realize ultra-narrow linewidth fiber lasers with linewidth about hundred Hz.Brillouin scattering phenomenon is easily observed in the optical fiber.In view of the unique linewidth compression mechanism and frequency shift property of Brillouin scattering,it is mostly used in fiber lasers to form Brillouin fiber lasers.However,the Brillouin gain in the BFL is small,and the output laser power is extremely low.Besides,it is difficult to meet the harsh pump resonance coupling conditions.These make it difficult to apply in practice.Generally,BFL and erbium-doped fiber(EDF)are combined to form the Brillouin Er-doped fiber laser(BEFL).BEFL uses erbiumdoped fiber gain and Brillouin gain to simultaneously provide amplification for Brillouin light,which greatly improves the Brillouin light output power.Compared with BFL,BEFL overcomes strict pump resonance coupling conditions and solves the problem of low output power.It can be used as a high-performance light source in high-precision cutting-edge fields.In BEFL,the Brillouin pump light is combined with the ring cavity structure to realize the Brillouin light output.According to the linewidth compression mechanism of Brillouin scattering,the theoretically obtained Brillouin light’s linewidth is 1/10000 of the Brillouin pump light’s linewidth,so if the Brillouin pump light meets the linewidth about k Hz,the Brillouin light with the linewidth about hundred Hz can be achieved.In response to the application of narrow linewidth fiber lasers in related fields and the demand for ultra-narrow linewidth fiber lasers in high-precision and cutting-edge fields.This paper first studied distributed feedback fiber laser,including manufacturing method of phaseshifted fiber grating,output spectrum,power characteristics,noise characteristics,output light’s linewidth,and so on.And then,a distributed feedback fiber laser was used as the Brillouin pump light to construct an ultra-narrow Brillouin fiber laser based on the distributed feedback fiber laser,and its power characteristics and linewidth characteristics were discussed in detail.The main contents of this thesis were as follows:1.This paper summarized the distributed feedback fiber laser and the Brillouin erbiumdoped fiber laser.The basic structures and principles of the two lasers were introduced respectively,and the phase-shifting fiber gratings and their common manufacturing methods were described.2.The working principles of distributed feedback fiber laser and ultra-narrow linewidth Brillouin fiber lasers based on distributed feedback fiber laser were introduced.Phase-shifting fiber gratings were theoretically analyzed and Brillouin scattering phenomena was explained in detail.3.A distributed feedback fiber laser was built,and the method of making phase-shifting fiber gratings was studied in detail.The distributed feedback fiber laser was tested,including its output spectrum,output power characteristics,noise characteristics and linewidth characteristics.And the relationship between the output power of the fully polarization-maintaining distributed feedback fiber laser and the length of the erbium-doped fiber was explored.4.An ultra-narrow linewidth Brillouin fiber laser based on a distributed feedback fiber laser was constructed.Two ring cavity structures were proposed,and the output power characteristics and linewidth characteristics were studied through experiments.