Losses in fiber laser cavities

Fiber lasers have been fabricated in a number of cavity configurations Including the direct butting of cleaved fiber ends against bulk mirrors to form a Fabry-Perot resonator.1 Although this technique is versatile, the optical loss incurred at the butted fiber ends has been uncertain in the past. For example, it is unclear whether the alternative technique of applying reflective coatings directly to the fiber ends gives lower losses.2 An indication of the excess loss of a laser cavity (i.e., excluding output coupling) is also desirable to predict the optimum value of the output coupling. The optimum output coupling is that which gives the maximum amount of laser output power for a given degree of pump power.