Single-Frequency Random Distributed Bragg Reflector Fiber Laser

We propose and demonstrate a novelsingle-frequency erbium-doped random distributed Bragg reflector fiber laser (RDBR-FL) constructed by a random fiber grating (RFG) and a high-reflection fiber Bragg grating (HR-FBG). Since it is not necessary to precisely control the axial position of the sub-gratings constituting the RFG, the inscription of long RFGs is easy and low-cost. The RFG manufactured by femtosecond laser point-by-point inscription technique has a length of up to 76 mm. The reflection spectrum of the RFG is designed to ensure the stable single-peak emission of the RDBR-FL under the HR-FBG spectral filtering. The bandwidth of the selected reflection peak of the RFG is only 13 pm, which ensures the single frequency operation of the RDBR-FL. The measured linewidth of the RDBR-FL is 3.9 kHz. Experimental measurement shows that the effective cavity length of the RDBR-FL is as long as 109 mm, which is consistent with the theoretical calculation.