The Research Of Low-noise Narrowlinewidth Single Frequency 1.5?m Fiber Laser

Coherent lidar has been widely applied in many fields such as atmospheric wind field measurement,pollution detection,target tracking,laser velocity measurement and laser imaging.The coherence of lasers in coherent laser radar is a key factor,which determines the level of application.Therefore,narrow-line low-noise single-frequency fiber lasers and nanosecond pulsed single-frequency fiber lasers have became a hotspot,which have the high coherence.This paper mainly studied the low-noise narrow-linewidth single-frequency fiber lasers and the gain-modulated nanosecond pulse single-frequency fiber lasers at 1.5?m.Firstly,the complex optical feedback loop(COFL)structure has been presented,which consisted of erbium-doped fiber amplifier(EDFA),un-pumped erbium-doped fiber and self-injection feedback loop.The COFL combined the nonlinear amplification effect of saturating optical amplifiers,the standing wave saturation effect of saturated absorber(SA)and the self-injection locking technology to realize the noise suppression and linewidth compression of the output single frequency laser.Secondly,the hybrid pump method and the gain switch technology have been combined,then the nanosecond pulse single-frequency laser at 1.5 ?m has been achieved.The main research contents were as follows:1.The theory for the single longitude mode(SLM)generation and measurement of the fiber laser has been described in this dissertation.Firstly,the basic principle for longitudinal mode selection has been described.Then,to better comprehend the longitudinal mode characteristics of the single-frequency fiber laser,we introduced the different methods of longitudinal mode selection and measurement detailedly.2.The single frequency fiber laser based on the complex optical feedback loop has been studied.First,we introduced the self-injection locking technology's theory of linewidth compression and noise suppression,and analyzed the principle of lowfrequency noise suppression by EDFA.Second,the COFL was used to reduce the noise and to narrow the linewidth of single frequency fiber laser.The relative intensity noise(RIN)of relaxation oscillation frequency(ROF)was reduced by 24.5dB from-80.3dB/Hz to-104.8dB/Hz,and the peak of the ROF shifts from 219 kHz to 87kHz;the maximum frequency noise suppression was about 28dB;the linewidth was narrowed from 7.47 kHz to 720 Hz.After the second erbium-doped fiber amplifier,the maximum output power was 11.1w,the optical signal noise ratio(OSNR)was more than 55 dB,the linewidth was still less than 1.8kHz,the RIN and frequency noise didn't have significantly increased.3.We researched on the gain switch nanosecond single frequency fiber laser.Firstly,the main methods and theories of nanosecond pulse were described in detail for single frequency fiber lasers.Then,the tunable single-frequency pulsed laser output was realized in the short-cavity distributed Bragg reflection structure by using the hybrid pump mode and the gain switch technique.The tunable frequency range of the output laser was 1kHz~400kHz,the pulse width was 602 ns,the linewidth was about 6MHz.When the repetition frequency of the output laser was 100 kHz and the pulse width was 602 ns,the repetition frequency of amplification was 100 kHz,the pulse width was 596 ns and the average power was 1.117 w.Then,the linear sweeping single frequency fiber laser has also been studied,the maximum sweeping range was about 800 MHz.