An analytic computer-oriented model for the Er / Yb co-doped silicate fiber amplifier is presented. The model is based on iterative solving the rate and propagation equations in their recursive forms at uniform discrete points along the fiber. It is capable of handling double-clad multimode-pumped fiber configurations, as well as conventional single-mode-pumped ones (with the signal featuring single-mode propagation in both cases). Arbitrary number of signals and pumps including wavelength-multiplexed ones from any direction can be treated. Amplification-deteriorating physical effects characteristic of the Er / Yb co-doped system, such as Yb amplified spontaneous emission, Er direct pumping, Er ions up-conversion and pairs formation, pump excited-state absorption and Er - Yb back-transfer, have been accounted for, in addition to the direct Yb - Er energy transfer. The relative importance of these effects in the amplification process has been modeled and discussed on the basis of experimentally determined fiber physical parameters.
High power fiber lasers are now mature products and have numerous applications as medical, military, industrial processing and telecommunication. Usually single mode fiber lasers are pumped with single mode pump diode featuring low output power. Double-clad fiber lasers (DCFL) overcome the issue related to low power single mode pump diodes to take fully advantage of large low cost multimode diodes. Improvement in high power multimode diode combined with double-clad fiber technology permit to DCFLs to be very efficient and promising. They are mainly operating in CW regime however Q-switch or mode lock regimes are also achievable. DCFLs in CW regime can feature several watt output power. Up to 30W CW Ytterbium DCFL has been demonstrated indicating that fiber laser is able to handle very high optical power without any optical damage. Also fiber lasers included tens of meters long fiber, improving heat dissipation and leading to a less critical thermal management compare to bulk lasers. For terrestrial telecommunication applications, DCFLs are mainly operating in CW regime and in particular, Ytterbium DCFL is largely used as a pump for Raman Fiber Laser (RFL). The RFLs are used for components testing, pumping EDFAs and Raman amplifiers.
Ytterbium doped double clad fibers (YDCF) are largely used in the telecom field as high power single mode pump lasers. We present a simple model that permits to describe a double clad pumping scheme. The YDCF is modeled by a sequence of N doped sections. Each section is described by an equation and leads to a set of N coupled equations. It permits to work out the mean fraction of excited ions over each section. The determination of the mean fraction of excited ions is sufficient to evaluate the signal, pump and ASE progress along the fiber. We use this model to calculate the evolution of the amplified spontaneous emission along the fiber, and find out the optimum fiber length for laser operation. We compare this result to experimental results obtained with a homemade fiber.