Taper (fiber optic)

A taper is a fiber optic component that connects two optical fibers (LWL) with different radii and with each other. The power transmission of a taper between fibers of the same numerical aperture (NA) in the direction of the smaller radius is calculated from: ${\displaystyle r_{1}}$ ${\displaystyle r_{2}}$

${\displaystyle P_{\mathrm {end} }=\left({\frac {r_{2}}{r_{1}}}\right)^{2}\cdot P_{\mathrm {start} }}$

This means that all light from a fiber with a large core cross-section that does not “fit” into the smaller cross-section is lost. This also applies to conical tapers.

On the other hand, all light from a thin fiber can pass into a thicker fiber of the same NA.

However, if the feeding fiber has a lower NA than the (thinner) connected fiber, a larger proportion can be transmitted than the above relationship describes. The prerequisite is that the (conical) taper itself also has a high NA. This can be achieved, for example, by not wearing a cladding - its surface must therefore be free-standing.

The relationship can also be explained with the Second Law of Thermodynamics, according to which the entropy can only increase - not decrease without energy input: the well-ordered photons in a thin fiber with a small NA can propagate into a thicker fiber (entropy increases in the process ), from one such to a thinner one can only be achieved with losses. The same relationship as above also applies to focusing lenses for coupling the two fiber ends.

See also

• Splicing (telecommunications)
• Acceptance angle

Web links

• Fiber Optics (accessed December 22, 2017)
• Taper with integrated microlens (accessed December 22, 2017)
• Automated precision assembly of fiber optic components (accessed December 22, 2017)
• FTTH PON Guide to Testing Passive Optical Networks (accessed December 22, 2017)
• Fundamentals of Fiber Optics An Introduction for Beginners (accessed December 22, 2017)