High-precision Wavelength Tunable Fiber Laser Based On DMD And Echelle Grating

With the development of large-capacity optical communication networks and the widespread application of dense wavelength division multiplexing technology,multi-channel high-precision tunable fiber lasers have become a research focus in the field of fiber communication.This kind of laser not only effectively saves the number of wavelength division multiplexing system converters,lasers and other modules,reduces the operation?maintenance and recovery backup cost of the system,but also realizes the remote dynamic optimization configuration of network resources.This feature provides full flexibility and excellent dynamic performance for signal transmission.In addition,tunable lasers have many important potential applications in optical carrier RF transmission systems,all-optical wavelength conversion,wavelength routing,optical packet switching,and wavelength-based personal virtual networks.At present,laser wavelength tuning devices mainly include fiber Bragg gratings,fiber-optic F-P cavities,acousto-optic tunable optical filters and high birefringence Sagnac fiber interferometers.These devices have advantages and disadvantages in terms of wavelength tuning range,polarization sensitivity,wavelength tuning accuracy,and flexibility and stability.For example in wavelength tuning accuracy,the wavelength tuning precision of the Fiber Bragg Grating based on DC modulation is 0.2nm/V,and the tuning precision of the silicon-based liquid crystal processor is achieved 0.05 nm.Based on the previous research of our group,we propose a high-precision multi-wavelength tunable fiber laser based on digital micromirror device(DMD)and echelle grating.As a kind of spatial light modulator,DMD has been widely used in structural light projection,laser holography,spectral imaging,laser beam shaping,3D printing and other fields with its superior light modulation characteristics.The echelle grating is widely used in high-resolution spectrometers in the ultraviolet and visible light bands by means of ultra-high dispersion characteristics.We applied DMD and echelle grating to the fiber laser,and finally realized the characteristic of 16-channel multi-wavelength laser output with tuning accuracy of 0.036nm.Based on the scalar diffraction theory of two-dimensional blazed grating,we use VirtualLab simulation software to analyze the necessary conditions for DMD to achieve high efficiency diffraction and diffraction beam return along the original path.This provides a theoretical basis for flexible mode selection and construction of low insertion loss closed-loop systems for DMD-based tunable lasers.In order to further improve the multi-wavelength tuning accuracy centered on DMD,we introduce a cross-dispersion structure based on the echelle grating and a two-dimensional bifocal collimation optical path.The chromatic dispersion ability of the echelle grating and the diffraction grating at different positions and the tuning precision that can be achieved in the laser system are analyzed and the off-axis angle of the echelle grating under the C-band quasi-Littrow condition is calibrated.The experimental results show that we can use DMD and echelle grating to achieve 16-port laser output without crosstalk through smart optical design.Each port wavelength can be independently and flexibly tuned in C-band.The laser wavelength channel has a 3dB linewidth of less than 0.02 nm and a wavelength tuning resolution of 0.036 nm.The wavelength drift and output power fluctuations were 0.013 nm and 0.07 dB lower,respectively,within 1 hour at temperature.