Random fiber laser based on femtosecond weak grating array

Grating Random Fiber Laser (RFL) provides feedback by writing some randomly distributed Fiber Bragg Gratings (FBGs) on the single mode fiber. However, because there are many grating pairs that satisfy the feedback condition, the mode competition is fierce, and the center frequency drift and multi-spike problems caused by gain competition are more serious. To alleviate the modes competition to a certain extent, we can reduce the spacing of FBGs and decrease the length of random structure. In this experiment, we write a random weak grating array with a spacing of the order of micrometer by using the micro-nano processing technique of the femtosecond laser, and the array length is as short as 2.5 cm. At the same time, the reflectivity of the FBG is improved by increasing the energy of the femtosecond laser pulse. The random structure length is reduced while ensuring sufficient feedback efficiency, and the mode competition and multi-spike resonance are suppressed. At the same time, we use a FBG acts as a filter, the linewidth of the RFL measured by delayed heterodyne is 377 Hz. The frequency noise of the RFL is 8 Hz/Hz^1/2 at 10 kHz, and the flatness is good when the frequency is larger than 10 kHz, which creates favorable conditions for improving the resolution of the fiber sensor.