Research On Wavelength Tunable Passive Mode-locked Laser Based On DMD

Laser mode-locking technology can be widely used in optical communication,material processing,spectral analysis,sensing,optical signal processing and other fields.Due to its compact structure and high operational stability,the mode-locked fiber laser has become a research hotspot in the field of mode-locked lasers.On the other hand,Digital micro-mirror device(DMD),as a very mature optical modulator,has the advantages of flexible modulation,polarization-independent,stable performance and so on.And only through the software control,the output wavelength can be continuously,stably and rapidly tuned in a wide range.In this paper,the wavelength tunable passive mode-locked fiber laser based on DMD is studied in detail both theoretically and experimentally.DMD is used for wavelength tuning and nonlinear amplifying loop mirror(NALM)is used for mode-locking.Finally,the pulsed light with flexibly tuned output wavelength is realized,and some innovative results are achieved.The main contents of this paper include:(1)By analyzing the principle of NALM mode-locking,combining the erbium-doped fiber(EDF)rate equation and the pulse non-linear transmission equation,the mathematical model of NALM laser is established and simulated.On this basis,a mode-locked NALM fiber laser with a cavity length of 120 meters is constructed.The stable mode-locked pulse output with a repetition rate of 1.7MHz is realized.The influence of pump power and cavity length on the output characteristics of mode-locked laser is analyzed in the experiment.(2)By analyzing the principle of DMD filtering and the diffraction characteristics,a tunable optical filter based on DMD is constructed,and the filtering performance of DMD is tested.It proves that DMD filter has the performance of tuning both wavelength and bandwidth.(3)On the basis of(1)and(2),a mode-locked laser with tunable wavelength and pulse width based on DMD is constructed.The laser realizes self-starting mode-locking,and the central wavelength can be continuously tuned from 1538nm to 1565nm.The tuning step can be selected by controlling DMD,and the fine tuning can be less than 0.1nm.The pulse width of the mode-locked laser is controlled by adjusting the filter bandwidth of the DMD filter to realize the tuning of the pulse width.The main innovations of this paper are as follows:For the first time,a passive mode-locked fiber laser with tunable wavelength and pulse width based on DMD is proposed.The central wavelength can be continuously tuned at 1538-1565nm.The tuning step can be selected by controlling DMD,and the fine tuning can be less than 0.lnm.At the same time,the tuning of mode-locked pulse width can be realized.