Tapered double-clad fiber

By virtue of the large cladding diameter T-DCF can be pumped by optical sources with very poor brightness factor such as laser diode bars or even VECSELs matrices, significantly reducing the cost of fiber lasers/amplifiers.

[2] The result of forming a tapered geometry double-clad fiber is that the light introduced into the thin end propagates in a wide core without changing the mode content.

[3] Consequently, the use of T-DCF for optical amplification in a multi-mode fiber maintains good beam quality by elevating the thresholds of stimulation of non-linear effects including Brillouin and Raman scattering and spontaneous emission.

This is due to the improved clad mode mixing and the higher absorption at the thicker end of the taper due to the much thicker cladding which also means the rare earth ion dopants are beneficially concentrated at the wide end of a T-DCF, since the geometry defines their presence as directly proportional to the square of the diameter.

Simple production techniques of varying of the drawing speed during the pulling process leads to the fiber diameter changing along its length.