Multimode tapered fibers
Tapered optical fibers are an efficient method of transforming a poor quality laser beam into a spatially uniform spot. An 'ideal' laser would have a circular output beam with a linear power distribution across the spot and this would remain constant at varying power levels.In practice many high-powered lasers are far from ideal and can have non-circular outputs that can contain local hot spots. In addition the shape of the output beam can vary with varying power and with the lifetime of the laser. These effects can cause loss of power transmission and damage to a conventional fiber if the threshold of damage is exceeded.
Generally speaking tapered fibers are useful with low N.A. sources such as lasers. They are not usually suitable for fiber-to-fiber applications such as coupling a large fiber core output to a smaller fiber core. This is because the 'effective' N.A. of the tapered fiber is reduced by the taper ratio and much of the light will escape from the taper region.
