Research On The Single Frequency Fiber Lasers Based On All-fiber Filtering Techniques

Single frequency fiber lasers have been drawn much attention due to their wide applications in many areas, such as in optical telecommunication, fiber optic sensors, optical spectroscopy for chemical and biomedical analysis. Fiber based single frequency lasers have numerous advantages such as:more compact and reliable, broadband wavelength laser oscillation, high power output and high signal to noise ratio.Effort of this dissertation has been focused on the single frequency fiber lasers at 1.5 μm and 2μm wavelength band. Based on the active fiber saturable absorber and self-feedback light injection techniques, a stable and tunable narrow linewidth dual-wavelength erbium-doped fiber laser is proposed and demonstrated. By using fiber loop filter, after carefully optimizing laser cavity, the tunable dual-wavelength fiber laser has achieved single-longitudinal-mode, single frequency laser oscillation succesfully. Further more, based on polarization maintaining fiber loop filter, a narrow linewidth stable and tunable mulit-wavelength fiber laser is proposed and demonstrated experimentally. In this research, we also demonstrate that by using fiber core-cladding intermode interference filter can improve stability of the laser line, experiments have been done in both of linear fiber laser cavity and ring fiber laser cavity, respectively. Finally, a 2μm narrow linewidth thulium doped fiber laser is designed based on the cascaded Sagnac loops, and a stable and narrow linewidth output at multiple wavelength has been realized. The main works of this dissertation are summerized in the following:(1) The luminescence properties of erbium doped fiber are further studied, and a novel C+L wavelength band erbium doped ASE source is proposed and demonstrated succesfully, the ASE light source has high spectral flatness. The spectral flatness of the built ASE source is ±0.91dB within 1540-1610nm spectrum range, and ± 1.65dB in 1520-1610nm spectrum range.(2) In order to suppressing mode hopping and wavelength drift, a new method based on self-feedback light injection combined with saturable absorber is studied. Using two FBGs, a dual-wavelength switchble narrow linewidth fiber laser is realized, and stability of the output laser line is much improved.(3) Based on fiber ring filter, a dual-wavelength single-longitudinal-mode erbium doped fiber laser was designed and constructed. The stable single frequency laser operation is achieved. The linewidth of the laser output is measured by using heterodyne delay line techniques, and 3dB linewidth of the two laser lines is 2.8kHz and 2.5kHz, respectively.(4) A stable and tunable erbium doped fiber laser based on polarization maintaining fiber ring filter is proposed, and a FBG in PM fiber is employed for confining laser oscillation frequency. The wavelength drift and power fluctuation of laser output has been evaluated. Based on Sagnac loop filter, a tunable multi-wavelength erbium doped fiber laser with linear cavity is demonstrated.(5) A fiber core-cladding intermode interference filter is studied. In an erbium doped fiber laser built with ring cavity configuration, after splicing a section of thin-core fiber in the cavity, wavelength stability of the laser output is improved efficiently. In a fiber laser with linear cavity, a stable and dual-wavelength switchable single-longitudinal-mode laser is realized, and 3dB linewidth of the laser line is 3.4kHz and 3kHz, respectively.(6) Based on cascaded Sagnac loops, a 2μm thulium doped fiber laser is proposed, and experiments demonstrate the capability of generating stable and tunable multi-wavelength output. Three laser lines can be generated simultaneously and constantly. The stability of the laser output is monitored and evaluated.