Research On Noise Mechanisms And Its Suppression Of DBR Narrow Linewidth Single-frequency Fiber Laser

Distributed Bragg reflector(DBR)narrow-linewidth single-frequency fiber lasers with centimeter-order cavity length has achieved hundreds single-frequency laser output power,and it has become a research hotspot in the fields of fiber sensing,laser radar and coherent combining,because of the advantages such as compact all-fiber structure,narrow spectral linewidth of kHz order,stable single longitudinal mode operation and good beam quality.However,the noise performance of the single-frequency fiber lasers has severely limited its development in the sophisticated applications such as coherent optical communication,high precision frequency transmission,quantum key distribution and gravitational wave detection.Therefore,it is important to develop the research of its noise mechanism and noise suppression for optimizing the performance of the output laser,which can enhance its application value and promote its application range.This paper focuses on the research of the noise in DBR narrow linewidth single-frequency fiber laser,and the research contents and the main results are as follows:(1)Analyzed the mechanism of the frequency noise source in the DBR single-frequency fiber laser,developed the contribution of the energy-transfer upconversion(ETU)to the frequency noise.Meanwhile the theoretical expression of the frequency noise in the DBR single-frequency fiber laser associated with the relative intensity noise(RIN)in cavity is established for the first time,which is verified by the experimental results.These results show that by optimizing the length of the gain fiber,reducing the RIN of the output laser and the adjustment of the pump power can effectively suppress the frequency noise of the fiber laser and improve the stability of the laser frequency.(2)By combining the nonlinear amplification effect of a Semiconductor optical amplifier(SOA)with its optoelectronic feedback loop,a broad-bandwidth near-quantum-noise-limited intensity noise suppression of single-frequency fiber laser is obtained for the first time.In the frequency range from 0.8 kHz to 50 MHz,the RIN of output single-frequency laser is less than-150 dB/Hz,which is higher than the quantum noise limit(-152.9 dB/Hz)only 2.9 dB.And it has broken the intensity noise bottleneck of single-frequency fiber laser in high-end applications.(3)Utilizing the intensity noise suppressing technique of the nonlinear amplification effect with optoelectronic feedback,the RIN of the 1083 nm single-frequency fiber laser is near the quantum noise limit.Furthermore,using the 4He atomic polarization spectroscopy,optimizing the frequency tuning method of the piezoelectric Transducer(PZT),and innovatively introducing the temperature tuning mechanism,the two-stage laser frequency control has achieved in fastly and slowly.Finally the root-mean-square of frequency fluctuation is reduced to 17 kHz in the 500 s range,and the low intensity noise frequency-stabilized 1083 nm single-frequency fiber laser is obtained.