Study On Fabrication Of Fiber Bragg Gratings With Focused Femtosecond Laser Pulses And Its Application In Fiber Lasers

High power near infrared fiber lasers have become a topic of great interest, attribute to the development of high power laser diodes (LD) and optimization design of optical fiber. High slope efficiencies, power scalability, broad wavelength tunability, and diffraction-limited beam quality at high power make fiber lasers useful for a range of applications, such as military, telecommunication, medical and so on.Fiber lasers fall into two main categories: the first one is those use wavelength selective elements, such as dichroic mirrors and bulk gratings, external to the laser fiber. These systems offer the greatest flexibility, but have a complicated structure and high-cost. The other type is those use fiber Bragg gratings (FBG) as wavelength selective elements. FBG plays an important role in frequency selection, so we can realize a very narrow band wavelength output when it is applied to the fiber lasers. Besides, this type of fiber lasers is more compact and easy to be integrated.Recently, FBGs inscribed in several types of fiber point-by-point with a focused femtosecond laser pulses and its application in fiber lasers and sensors attracted a lot of researcher's interests. This technique possesses many advantages, such as the needless of photosensitive fibers, simple operation system, flexible selection of the grating period, as well as the good thermal stability of the FBGs. In this article, we obtained a FBG inscribed directly into the core of Corning Hi-1060 fiber with a femtosecond laser made by Co. Coherence, and the FBG was applied in fiber laser as output coupler and wavelength selective element. We realized a FBG based, all fiber double clad fiber laser. The main works of this article are as follows:1,The advantages of the fiber laser and the recent development of FBG fabricated with femtosecond laser for the application in fiber lasers were summarized.2,The couple mode theory of fiber Bragg gratings was analyzed in detail. The reflective spectrum was calculated. The variation of the resonation wavelength as well as the bandwidth with the change of writing condition was discussed.3,Physical mechanism of the femtosecond laser interactions with quartz material was analyzed, then the spot shape and the refractive index modulation profile of the femtosecond laser induced FBGs were studied.4,On the basis of rate equation theory, gain,threshold and output characteristics of the fiber laser were analyzed. Optimum fiber length and reflectivity of the output mirror were simulated with the MATLAB software. And then the influence of different parameters on laser characteristics was discussed.5,FBG of 8mm length with a period of 2.9 ? m was inscribed into the Hi1060 fiber by a 800nm femtosecond laser. This is the eight-order grating at 1042nm. As the output mirror, this FBG was applied in the fiber laser and we realized laser output.