| Tunable fiber laser has attracted much attention in the field of optical communication and optical sensing due to its tunable central wavelength,switchable output wavelength and variable output wavelength interval.Compared with other tunable lasers,fiber lasers have the advantages of simple tuning,reducing the threshold,improving stability of output spectrum and convenient connection with optical fiber system,which has become one of the research hotspots in recent years.In this paper,the ring cavity erbium-doped fiber laser(EDFL)is taken as the research object to study theoretically and experimentally,in which the interference tunable filter is used as the tuning device.The main research contents of this paper are as follows:(1)A tunable multiwavelength fiber laser is proposed and researched,which is based on tapered fiber coupler Sagnac loop embedded single mode fiber-two mode fiber-single mode fiber(STS)structure filter.Because the interference spectrum of the tapered fiber coupler Sagnac loop is sensitive to the change of stress applied in the waist cone region,the multiwavelength output of the fiber laser can be tuned by changing it.The proposed fiber laser has a tuning range of 24.2nm.The device has the advantages of simple structure,low cost and easy tuning.(2)A multiwavelength fiber laser with adjustable wavelength interval,switchable wavelength number and adjustable wavelength range is researched,which is based on cascaded Lyot filter and STS structure filter.The intensity dependent loss(IDL)caused by nonlinear polarization rotation is changed by adjusting the polarization controller(PC)in the ring cavity,which can realize the switchable output of the number of wavelengths from single wavelength to seven wavelengths,and the maximum wavelength tuning range can reach 1530-1561 nm.In addition,by adjusting the PC,it can also obtain the output of non-adjacent dual wavelengths with adjustable spacing,non-adjacent three wavelengths with adjustable spacing,non-adjacent four wavelengths with adjustable spacing,and non-adjacent six wavelengths.The tunable multiwavelength erbium-doped fiber laser has the advantages of simple structure,high cost performance and various functions.(3)A wavelength tunable mode-locked fiber laser based on cascaded single mode fiber-multimode fiber-single mode fiber(CD-SMS)structure is researched.The SMS structure is wound on the three ring polarization controller as a tunable device and saturable absorber in the laser cavity.By adjusting the direction angle of the polarization controller,the filter is adjustable.Furthermore the limitation of SMS structure as a saturable absorber on the length of multimode fiber is eliminated,so as to realize the function of tunable wavelength and mode locking.The device has the advantages of simple structure,good stability and high damage threshold. |
