Research On The Noise Measurement And Suppression Technology Of Fiber Laser

In recent years,single frequency fiber laser has been widely used in the fields of precise spectrum measurement,lidar and nonlinear frequency conversion due to their narrow linewidth,compact structure,good stability and excellent beam quality.However,in practical applications such as optical fiber hydrophone,coherent optical communication and gravitational wave detection,the noise characteristics is also an important parameter and worth further optimization.This dissertation focuses on the noise measurement and suppression of single frequency fiber laser.The main works and results are as follows:Firstly,the noise theory of single frequency fiber laser is systematically summarized.Based on the rate equation theory,the theoretical model of relaxation oscillation of single frequency fiber laser is established,the transfer function of laser pump and cavity loss is derived,and the change trend is analyzed numerically,the effects of technical noise and shot noise are discussed.Several main frequency noise sources,including spontaneous emission noise,basic thermal noise and self heating noise,are investigated.The influence mechanism is analyzed in detail and the expression of each noise is deduced.In addition,the relationship between frequency noise and linewidth is clarified.Secondly,aiming at the low noise single frequency fiber laser,a high-precision broadband intensity and frequency noise measurement system is designed and developed.With two developed measurement systems,namely,a correlated delay self-heterodyne frequency noise measurement system based on a fiber-type Michelson interferometer and an optical heterodyne beat-note measurement system with calibration function,combined with common analysis instruments,we successfully measured and obtained both the frequency noise and the intensity noise spectral characteristics of single-frequency fiber laser in a Fourier-frequency range of[mHz,MHz].The accuracy of our measurement results has been verified by comparing with the manufacturer's data and through the mutual confirmation of different measurement schemes.In addition,the noise characteristics of Q-switched fiber laser are measured.Thirdly,active and passive techniques are used to suppress the intensity noise and frequency noise of single frequency fiber laser.A low vibration sensitivity package is designed,combined with precise temperature control,achieving the noise suppression preliminarily.A photoelectric feedback scheme is adopted to suppress the intensity noise,the maximum 20 dB suppression level at the relaxation oscillation peak is realized,the RIN is under-120 dB/Hz in frequency range higher than 100 kHz.Using a high stability fiber interferometer as a frequency reference standard to stabilize the fiber laser,finally,the frequency noise is suppressed more than 30 dB in 10 Hz-10 kHz,the frequency noise reaches 10 Hz2/Hz at 10 Hz and is below 100 Hz2/Hz from 10 Hz-10 kHz.These achievements have reached the advanced level in china.The above results have important value for the development of low-noise single frequency fiber laser to meet the needs of applications such as gravitational wave detection,time-frequency transmission,fiber sensing and so on.