The Research On 1.5μm Erbium-Doped Narrow Linewidth Fiber Laser

Narrow linewidth fiber laser has great applications for extremely long-range sensors system and high resolution analysis system of optical spectrum. Especial as fiber laser sensor, it has particular characteristics of safety, remote controller, small bulk and anti-electromagnetic disturbance. It has potential application for defence due to its high sensitivity and the feasibility of multiplex transmission using WDM technology. This thesis is mainly concentrated on the devices of mode selection, design of cavity and measurement method of linewidth in the Erbium-doped narrow linewidth fiber laser. Theoretical analysis and the experiments are both studied.The main results are as follows:1. Theory of laser linewidth has been summarized. Analyses of measurement error of self-heterodyne/homodyne methods have been studied. The influence of coherence factor, multiple of coherence length and the length of delay fiber to the result of measurement have been discussed in the self-homodyne method. The influences of multiple of coherence length and the length of delay fiber to the result of measurement have been discussed in the self-heterodyne method also. The influence of least squares curve fitting algorithm to the result of measurement has been analyzed too. The linewidth of a DFB semiconductor laser has been measured by the delayed self-heterodyne method.2. The model of Erbium-doped fiber laser has been analyzed theoretically. The output characteristic has been illustrated and the scheme of the Erbium-doped fiber laser has been designed. The variations of the performance of the fiber Bragg grating Fabry-Perot etalon with the length of the cavity and the reflection coefficient of fiber Bragg grating have been discussed, according to the theory of fiber Bragg grating Fabry-Perot etalon.3. The experiments of single frequency fiber ring laser with mode selection by fiber Bragg grating Fabry-Perot etalon have been performed. About 9.2mW output power and 7% slope efficiency are obtained in the experiment of fiber ring laser using fiber circulator. The 3dB linewidth of fiber laser is less than 0.01nm. In the experiment of fiber ring laser using fiber coupler, single frequency output power is 42 m W and the slope efficiency attain to 33%. The difference in output characteristic of the two fiber ring laser has been analyzed4. The experiment of 1535nm fiber laser with linear cavity has been carried out, in which, the fiber Bragg grating Fabry-Perot etalon with the Bragg wavelength of 1535nm is used as mode-selecting device, and the fiber Faraday rotator is used to restrain the spatial hole burning effect. Stable single frequency 1534.83 nm laser is acquired. The fiber laser exhibits 12 mW threshold. Total 39.5 mW output power and one end 22 mW output power are obtained. Optical-optical efficiency is 27% and slope efficiency is 29.7%. The 3dB linewidth of laser is less than 7.5 kHz, measured by the delayed self-heterodyne method with 15 km monomode fiber.5. A high output power narrow linewidth fiber laser based on fiber Bragg grating Fabry-Perot etalon has been accomplished. The fiber laser is composed of two 1550nm fiber Bragg grating Fabry-Perot etalons and high Er³⁺-doped fiber linear cavity. Stable single frequency 1550nm laser is acquired. Pumped by two 976nm laser Diodes, the fiber laser exhibits 11mW threshold. 73mW output power is obtained. The slope efficiency is 55%. The 3dB linewidth of laser is less than 10 kHz, measured by the delayed self-heterodyne method with 10km monomode fiber.6. The experiment on the stability of laser linewidth has been performed. The fiber laser exhibits 1 lmW threshold. 50 mW output power is obtained upon the 200 mW pump power. The slope efficiency is 27%. The linewidth of laser is less than 10 kHz, measured by the delayed self-heterodyne method with 10 km monomode fiber. SNR is about 56 dB. The lasing wavelength tuning is achieved by varying temperature of gratings. The lasing wavelength is tuned continuously over 1.02nm when its temperature is varied from 25°C to 90°C. That corresponds to a temperature sensitivity of 0.016nm/°C of these gratings. The output power in the tuning range is not flat because of the variation of gain in Erbium-doped fiber. The change of laser linewidth is less than 1 kHz with tuning. At the same time, no mode hopping is observed.7. Linewidth-narrowing mechanism in fiber laser by fiber saturable absorber has been analyzed theoretically. Single frequency Erbium-doped fiber ring laser is demonstrated by introducing fiber saturable absorber and passive fiber Bragg grating Fabry-Perot etalon in laser cavity. Frequency is stabilized by using short and low loss Erbium-doped fiber as saturable absorber. Stable single frequency 1550 nm laser is acquired. Lasing power is 39 mW, and the corresponding slope efficiency is 30%. SNR is larger than 50 dB. The linewidth is less than 10 kHz.