Based On DMD Tunable Passive Mode-locked Ytterbium-doped Fiber Laser

As the ultra-short pulse,high-energy light source,mode-locked lasers have excellent performance in military weapons,medicine,industrial processing,and lidar,and they have an irreplaceable position in fiber optic sensing,measurement,and imaging.Fiber lasers have become a research hotspot due to their compact structure,easy integration,good beam quality,and good heat dissipation.The spontaneous gain spectrum of fiber gain medium has a wide range.Tunable fiber laser,especially tunable mode-locked fiber laser,has very important research significance and application.In this paper,the wavelength tunable mode-locked ytterbium doped fiber laser(YDFL)is realized by using the digital micro mirror device(DMD)as the wavelength tunable device and combining with the nonlinear polarization rotation(NPR)effect.The research work and results of this paper are as follows:1.The principle and types of mode locking are introduced,and the passive mode locking technologies in optical fiber are introduced in detail.The passive mode locking technologies are divided into solid saturable absorber and virtual saturable absorber.The principle of passive mode locking technology is described,and the advantages and disadvantages of different passive mode locking technologies are analyzed.2.By introducing the structure of DMD,analyzing the diffraction characteristics and filtering characteristics of DMD and using the software of ZEMAX to simulate the optical path,the optical path is built to test the filtering characteristics of the DMD filter system.On this basis,DMD filter system is applied in YDFL to realize the continuous tunability of the central wavelength in the range of 1048.8nm～1088.4nm.The tunable range is 39.6nm,the side-mode suppression ratios of each wavelength is more than 40dB.Moreover,fine wavelength tuning can be realized with a tuning precision of about 0.08nm.3.Based on the DMD filter system and the NPR mode-locked structure,a wavelength tunable mode-locked YDFL is constructed.In this experiment,when the DMD works in unfiltered state,the central wavelength of the mode-locked spectrum is 1069 nm,the spectral width is 8.4 nm,the pulse width is 7.16 ps,and the repetition frequency is 1.96 MHz;when the filter bandwidth of DMD is 3nm,the tunable mode-locked pulse with the central wavelength of 1059.83 nm～1078.75 nm is output;when the filter bandwidth of DMD is 4 nm,the tunable mode-locked pulse with the central wavelength of 1056.53 nm～1081.63 nm is output.The mode locking in these three states is dissipative soliton mode locking.It is also observed in the experiment that when the filter bandwidth of DMD is 3 nm,the dissipative soliton mode-locked state is transformed into the dissipative soliton resonance mode-locked state by fine tuning the polarization controller(PC),the autocorrelation trace is transformed from Gauss pulse to flat top pulse,the spectrum becomes smooth,the central wavelength is adjustable in the range of 1056.01 nm～1082.87 nm.The change of the autocorrelation trace is analyzed and is verified by experiment.The innovation of this paper:Based on the spatial filtering characteristics of DMD,the optical DMD-based filtering system at 1μm-band is realized,and it is applied to an YDFL to achieve a wavelength-tunable YDFL.Combined with the NPR effect,the wavelength tunable mode-locked YDFL is realized.