Research On Tunable And Multiwavelength Erbium-doped Fiber Laser Based On Birefringent Fiber

With the rapid development of high-capacity optical fiber communication,dense wavelength division multiplexing(DWDM)has been paid more and more attention by researchers.The widely used of DWDM technology has led scholars to speed up the research of multiwavelength fiber lasers.The continuously development multiwavelength fiber laser can provide low-cost and effective multiwavelength channel light sources for high-capacity DWDM system.In the application of multiwavelength fiber lasers,multiwavelength need to be generated with fixed and small wavelength space,moreover,the spectral range of multiwavelength output also can be achieved by adjusting some parameters.Therefore,tunable multiwavelength fiber lasers have a wide range of practical applications.Based on the previous researches of tunable multi-wavelength fiber lasers,the new-type tunable multi-wavelength fiber lasers by using birefringent fiber have been fabricated in this paper,and these lasers not only can produce stable multiple wavelengths,but also can be tuned.1.A multiwavelength erbium-doped fiber laser is proposed and experimentally demonstrated by using Mach-Zehnder interferometer(MZI)and Lyot filter.The Lyot filter provides nonlinear polarization rotation(NPR)to suppress the mode competition and generate multiwavelength.Using spherical-shape structures MZI as mode restricting elements.At room temperature,9-wavelength operation with a side-mode suppression ratio(SMSR)of ~40dB is achieved,and the space of wavelength is 0.68 nm.When the stability of proposed structure is observed for 2 hours every 10 minutes,the fluctuation of the central wavelength's output power is less than 0.67 dB.Furthermore,when the two spherical-shape structures MZI is fixed on a furnace,and the temperature is varied from 30 ? to 110 ?,the spectrum of output wavelength can be tuned within the range of 6.69 nm.2.Two types of tunable multiwavelength fiber lasers based on two sections polarization maintaining fiber(PMF)in cascaded/in parallel and a nonlinear Sagnac loop are proposed and experimentally demonstrated.When two sections PMF in cascaded,two-stage Lyot can generate comb spectrum to achieve multiwavelength output.The nonlinear Sagnac loop acts as an intensity-dependent component to maintain stable output of multiwavelength.It can achieve the tune of channel space among 0.44 nm,0.74 nm,and 0.96 nm by adjusting PC1 and PC2.Therefore,the number of lasing wavelengths can be tuned among 14-line,8-line,and6-line accordingly.When two sections PMF in parallel,the change of the polarization angle of PCs in two branches can adjust the loss in the two branches,and suppress the light of one branch passing through the cavity,then the light of the other branch passes through cavity.So multiwavelength with different wavelength space can be achieved.It can achieve the tune of channel space among 0.75 nm and 0.96 nm by adjusting PC1 and PC2.And the number of wavelengths can be tuned among 7-line and 5-line accordingly.When the channel space isfixed as nearly 0.68 nm in two types of fiber lasers,the tuning range of multiwavelength in two lasers are about 2.28 nm and 1.45 nm by adjusting PC3 in the nonlinear Sagnac loop,respectively.