Riyadh Khlf Ahmed
Fiber laser has attracted great attentions during the past few decades due to the advantages of high stability, high reliability, low total cost ownership, low jitter and amplitude noise, compact and immune to tough environment changes. Fiber lasers have demonstrated to span of light in range of 400 nm – 300 um. Many different applications used fiber laser technique such as laser cutting, welding of various materials, maximum precision of drilling and medical application in surgery. Low power (p < 30) watt continuous wave fiber lasers were wide use for marking integrated circuits
In the last twenty years, fiber laser become one of the most promising devices which is used in telecommunication system. In general, the construction of laser source is consists of three parts: active material, resonator and pumping. The design of the active material has the advantage of almost no thermally induced problems as lensing or birefringence because cooling of the thin material of only a few 100 μm radius is easily possible. In addition, using new low mode fibers with large core diameter very high average output powers in the kW-range became possible. The resulting beam quality is perfect when single mode fibers are used. Developments in Fiber Optic technology and devices mean that the "fiber laser" need complex system sophisticated technology like Bragg grating for wavelength selection in addition to simple devices. Engineers developed a method to transfer the pump radiation from the larger cladding into the core with high efficiency. For high power, fiber laser is made by techniques of double cladding and use ytterbium amplifier The one disadvantage of ytterbium for fiber-optic communications, the emission wavelength of one micron, versus the desired 1.3 and/or 1.55 microns is also essentially common to both ytterbium and neodym-ium. However, the smaller quantum defect and longer fluorescence lifetime are advantages. The cladding is reflective surface acts as a non absorbing medium in which the light field in the core can die down to negligibly small levels before coupling to the outside world. Double cladding fibers with D-shaped pump cladding were used to instigate fiber laser for high power applications. Because of the high gain, good stability and excellent beam quality, the fiber lasers are also useful for short pulse generation with impressing parameters.
For applications in range of ps and fs pulse trains with repetition rates in the MHz range were generated with average output powers above 100W.Therefore fiber lasers may overtake all applications where good beam quality in combination with good stability and no high pulse energies are required. Average output powers in the kW-range are feasible for these lasers and only the high diode laser price is limiting an even larger distribution in these cw and quasi-cw applications. Only in Q-switched applications the fiber lasers are very limited. The maximum pulse energy is in the range of a few mJ because of the small active volume and the possible damage of the front facets. In these applications the rod (or slab) geometry of the active material is unbeaten. Several Jouls can be generated with these large volume devices with good beam quality, narrow bandwidth and average output powers of several 100 W. In special cases hundreds of kJ are possible. However, simple flash lamp pumped rod lasers may also have a longer future at least as long as diode prices are not decreasing drastically. However, in long term perspectives completely new laser concepts may be developed with even higher efficiencies and very low prices. These fiber lasers are mostly end pumped often from both sides. Side pumped methods are developed. The diode laser radiation can usually not couple into the core directly because of their bad beam quality. Figure .1 shows the basic design of fiber laser.
fiber laser output
Figure 1. Fiber lasr