Low-threshold Fiber Lasers Based On Random Distributed Feedback

The random laser has unique characteristics in terms of structure and output laser characteristics.It does not require the existence of a traditional optical resonator.Therefore,fabricate of the random laser is simple,and the cost is relatively low,the output light has low temporal / spatial coherence,Multiple non-coherent laser modes are generated simultaneously in the frequency range.Based on the above characteristics,random lasers have many potential applications in the fields of nonlinear optics,optical communications and sensing,in addition,have many applications in medicine.In laser imaging systems,high-brightness,low-coherence random lasers eliminate the interference noise and speckle problems associated with conventional lasers,enabling high-resolution full-field imaging,microscopy and laser projection.In addition,the mode of outputting the laser light is closely related to the characteristics of the scatter and can be used for medical diagnosis of diseases such as cancer.The research of random laser has important value in scientific and application.The research results have been published in the top academic journals such as Science,Nature and Nature Photonics many times in recent years.In this paper,we first propose a random grating which fabricate by a point-and-click method using a femtosecond laser,and compare with ultra-long single-mode optical fiber,the spectrum prove its feedback effect,and the more the random refractive index modulation point,Its stronger random feedback.Then with the random grating as the feedback and the erbium-doped fiber as the gain medium,the random lasers with different structures are studied,and different conclusions are drawn.Experiments show that the random grating can replace the ultra-long single-mode fiber to treat as random feedback,and the grating can be used to realize the low-threshold random feedback laser.