Research On Fiber Grating Based Narrow Line-Width Thulium-doped Fiber Laser

Narrow linewidth of2μm-band Thulium-doped fiber lasers are commonly used in biomedicine, space communication and fiber sensing, LIDAR and other fields. Research on narrowing the linewidth of Thulium-doped fiber lasers is highly relevant. In this paper, present research on fiber grating based narrow linewidth Thulium-doped fiber lasers. Studied the frequency selective characteristics of thulium-doped fiber laser based on fiber grating F-P cavity structure both in theory and experiment. Narrow linewidth thulium-doped fiber laser can be implemented through reasonable design of resonant cavity structure under the condition of larger cavity length. The main work may be summarized as the follows:1. Based on the narrow linewidth Erbium-doped fiber laser’s research method, studied the transmission spectra characteristics of thulium-doped fiber laser based on F-P dual chamber structure. Analyzed the effects of cavity length, grating length and the refractive index depth of modulation on the transmission spectra. Analyzed the frequency selective characteristics of symmetric and asymmetric structure in comparison. Pointed out the realization of structure design of single longitudinal mode laser output in the center wavelength.2. Studied the transmission spectrum of F-P three-chambered structure which contains a small cavity. Analyzed the effects of cavity length, cavity location, grating length and modulation depth on the transmission spectrum. Analyzed the frequency selective characteristics of F-P dual-chambered structure and F-P three-chambered structure in comparison. Pointed out F-P three-chambered structure has a stronger ability in restraining the sub resonance peaks.3. Studied the transmission spectra characteristics of cascading F-P resonant cavity structure. Analyzed the influence of cavity length, characteristics of fiber Bragg grating to the transmission spectrum.4. Studied single longitudinal mode of Thulium-doped fiber laser based on saturable absorber and F-P filter. Analyzed the stability of output power and central wavelength of fiber laser. Saturable absorber is verified to achieve laser operation of single longitudinal mode.