In 3-axis (or cladding
alignment) fusion splicing the fibres are viewed through
a microscope and camera in two axes (x and y-axis). Precision
translation stages accurately align the fibres in the
z and x-axis, and the z and y-axis movements respectively
prior to fusing. The fibres are brought in to alignment
by motors or thumbwheel adjusters.
The core alignment of the fibres is optimised automatically
by one of two methods, depending on the design of the
splicer.
In a LLID (Local Light Injection and Detection) splicer,
the fibres are bent through a sharp radius around special
clamps, allowing light to be injected into one and extracted
from the other. The system can then manipulate the x and
y-axis positions until the light signal is at a maximum,
indicating core alignment. An approximation of the splice
loss across the joint can also be measured using the same
system.
In a PAS (Profile Aligning System) splicer, the boundary
between the core and the cladding is viewed with a small
video camera through very accurate optics. Image processing
techniques can then measure the core offset of the two
fibres and automatic stages again bring them in to alignment.
An estimate (by viewing, not measuring) of the splice
loss can be made after the fibres have been spliced.
