| Fiber communication has various advantages, it has archived rapiddevelopment since been put into business applications in 1970s. Till 1990s, it hasbeen the main method of telecommunication.Fiber laser, as a kind of excellent laser source, never stopped getting higherperformance and reducing the cubage. To use Er Yb codoped fiber cansignificantly enhance the performance and efficiency, and to user linearity cavitycan reduce the cubage which helps to save the space and reduce the cost.Narrow band, single frequency laser source and be widely used incommunication, sensor and spectroscopy. By now, semiconductor laser is mainlyused in fiber communication. But semiconductor laser will cost much and hard tocoupling into the transfer fiber. This is now hardly holding back the fibercommunication system. Fiber laser, compares to the semiconductor laser, hasadvantages in the below fields: (1) Using the cheaper diode laser to pump thedoped fiber can reduce the cost of the system. (2) Fiber laser just easily coupleinto transfer fiber for the same size. (3) Fiber laser can be more cooler for the higharea-cubage ratio. (4) Fiber laser is easy to out put different wavelength between380nm-3.9μm and the wavelength can turning either. (5) Fiber laser and fiberamplifier is compatible with now days fiber item, so it is possible to setup aall-fiber system.Recent years, Er3+/Yb3+ codoped fiber laser has drawn widely interesting forit has high pump efficiency, widely ampliate wavelength, and it can work at 1.55μm wave band which is the third window of fiber communication. The fiber laserof this type can archive narrow linewidth, high conversion efficiency and lownoise. It is easy to produce. By outside modulate, it is likely to replace the DBRand DFB semiconductor laser. So fiber laser is the idea laser source of the futurelong distance high speed communication system.Syntony cavity is one part of the fiber laser, there are different ways to makeit. Fiber grating has become is popular to setup a syntony cavity for the agility andthe low cost. For the UV write fiber grating is reliable, many kind fiber laser isachieved using various pump source and out put lasers with differentcharacteristics. For the difficulty to write grating directly into doped fiber, we canfuse the fibers together.DBR fiber laser takes two high reflected fiber grating to enhance moduleselect. One of the difficulties to make DBR fiber laser is to produce high reflected,narrow band fiber grating with the same wavelength. To reduce the difficulty, wecan replace one fiber grating with fiber ring.At the mean time, DBR/DFB fiber laser has some problems.(1) For the short cavity, the fiber laser has a low pump efficiency and low conversion efficiency, the spectrum is not so narrow as ring fiber laser.(2) There is module jump in the fiber laser as well for the three level system's reason.To solve the problems, one of the best ways is to use Er3+/Yb3+ codoped fiber.The team of Davidn.Payne found that Erbium has ampliative effect to 1.55μmwavelength. Yb3+ of Er3+/Yb3+ codoped fiber can be high strength doped and it canabsorb the light of 1μm wavelength. Then it pass the energy to the Er3+ to ensurethe ampliative of the 1.5μm wavelength. So the absorb ability of Er3+/Yb3+codoped fiber is as thousands of times strong as that of Er3+. Yb3+ absorb the lightfrom 0.98 to 1.06μm, and can produce laser in at any point of ASE spectrum.Syntony cavity can only reflect some of the wavelength, so the fiber laser canoutput narrow band, high power, low noise laser.We have the Er doped and ErYb codoped fiber laser experiment, and getstable laser output. In the experiment of the Er doped fiber laser, we work on thevariety of various characters of the fiber laser when it length from 96.5 to 9.5cm.We use 980nm LD as the pump source, and the fiber is high doped of Er3+. Thefiber grating we used in the experiment has peak reflectivity 99.5% and 65%.When the high doped Er fiber is 15cm long, we get narrow linewidth, high Sidemode suppression ratio and stable laser out put.
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