Another consideration is the concentration effect of tapers as the diameter decreases. Q-switched laser systems produce high peak powers that are difficult to couple into fiber. Typically, the bulk fiber material can withstand this power, but the fiber surface may become damaged due to dielectric breakdown of the surrounding medium or surface contamination may initiate the breakdown. Both effects degrade the fiber surface rapidly.

With a taper integral with the fiber that will carry the laser energy, the power density at the larger input surface can be reduced to levels well below the damage threshold. Many high power laser systems are multimode and therefore difficult to focus. In cases where the minimum beam waist is larger than the fiber diameter, the use of a taper can greatly improve the coupling efficiency. Additionally, in converging situations, the light never comes to a sharp focus. This reduces self-focus effects.

Depending on conditions, some of which are listed in the table following, the laser induced-damage threshold of Polymicro’s fiber at 1064nm is up to 1 Giga-Watt/cm² for pulsed lasers and up to 2 Mega-Watts/cm² for CW.

Some of the significant factors that affect optical fiber damage in laser applications are given in the following table. Depending on the specific application, there may be other effects as well.

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