| The 1.5μm single-frequency fiber amplifier in the eye-safe band is one of the hot spots in the research of fiber laser technology.Due to its advantages of simple and compact structure,stable performance and great output spectrum characteristics,it is widely used in space laser communication,lidar,biomedicine and other fields.However,at present,1.5μm single-frequency fiber amplifiers still have the problems of amplification of spontaneous emission(ASE),which leads to low pumping efficiency,low gain and large noise.Therefore,suppressing amplification of spontaneous emission in fiber amplifiers and carrying out the research of high-performance 1.5μm single-frequency fiber amplifiers in a targeted manner will have excellent research significance and application value.Starting from the application requirements of space laser communication and lidar for 1.5μm band single-frequency fiber amplifiers,this paper conducts theoretical and experimental research on1.5μm band single-frequency fiber amplifiers with main oscillation power amplification(MOPA)structure,focuses on the ASE suppression technology in fiber amplifiers,and realizes the highperformance 1.5μm band single-frequency fiber amplifier in both continuous and pulse systems.The main research contents are as follows:1.The development process and application of 1.5μm single-frequency fiber amplifier are reviewed,and the 1.5μm single-frequency fiber amplifier is studied theoretically according to the rate equation and power transfer equation,and the noise measurement and transient effect of pulsed fiber amplifier are systematically analyzed and studied.2.Design and realize a 1550 nm low-noise high-gain single-frequency continuous fiber amplifier based on domestic erbium-doped fiber and related core components.The fiber amplifier adopts a single-pumped all-fiber dual-stage main oscillation power amplification structure.In the power amplification stage,a combination of a band-pass isolator and a polarizing beam splitter is used to replace the conventional Faraday mirror,which effectively reduces the spontaneous radiation amplification and improves the signal-to-noise ratio of the output signal light.When the input optical power is 1μW,a single-frequency output light of more than 10 m W is obtained,and a signal amplification with a gain of more than 40 d B and a noise figure of less than 4.5d B is realized.The developed 1550 nm low-noise high-gain single-frequency continuous fiber amplifier adopts domestic commercial devices and has a compact structure,which provides technical support for the independent controllability of the core device of the miniaturized space communication fiber amplifier.3.Design and realize a 1550 nm microsecond rectangular pulse fiber amplifier with an adjustable repetition rate from 10 Hz to 10 k Hz.The fiber amplifier adopts a two-stage main oscillation power amplification all-fiber structure,uses an acousto-optic modulator(AOM)to modulate the signal light,and realizes the microsecond rectangular pulse amplification laser output with peak power of 30 W,pulse width of 10μs-1ms,and adjustable repetition rate in the range of 10Hz-10 k Hz through the optimization of the pulse waveform and timing of pump drive and signal light modulation.By optimizing the timing of signal light pulse and pump pulse,the amplification of spontaneous emission in the fiber amplification process is effectively suppressed,and a better microsecond rectangular pulse output is obtained by pre-shaping the pulse waveform of the signal light. |
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