and rotated while the polishing materials remove a relatively large amount of
cladding material. In comparison, the
production of ablated axicon lenses are
produced on highly automated systems,
which typically take longer to load and
unload than the time required for the
laser to create the lens. Both these ax-
icon lens manufacturing methods pro-
duce very similar looking and performing components.
The tapered axicon, by contrast, is pro-
duced by heating and drawing the fiber to
an abrupt tip. Although the conical lens
shape is formed at a much less steep angle,
its optical performance is almost exact-
ly the same as for the other two manu-
facturing techniques. The typical differ-
ence with this design is that the core of
the fiber is drawn down at the same time
as the cladding, as opposed to the other
techniques in which the core size is un-
changed. However, the reduced core di-
ameter appears to have no effect on the
beam quality, as the light at the tip will
be guided by the cladding/air interface.
The benefit of this technique is that it can
be produced on typically any of the spe-
cialty splicers on the market today, which
enables production via a very cost-effective process.
Ball lenses (see Fig. 2) can be produced
using several methods, with the most
common being the splicing of a coreless
fiber onto the existing launch fiber, then
forming the ball at a fixed distance from
the end of the launch fiber. Coreless fibers are preferred, as the index of refraction throughout is then uniform and produces an undistorted beam. If coreless
fibers are not used, then the core and
cladding index materials can intermingle, leading to an inconsistent and poor-quality output beam.
The size of the ball and its distance
from the point at which the beam be-
gins to diverge into the coreless fiber
can be constructed in such a way as to
create a converging, diverging, or col-
limated beam exiting the ball. Several
other postprocessing techniques can be
done on the ball such as depositing an-
tireflection (AR) coatings and/or polish-
ing a reflective flat to produce a beam
that exits from the side. The balls can
be mounted in expanded beam connec-
tors to minimize losses and to allow for
the addition of external optical elements
into the beam path.
The simplicity of ball-lens production
allows it to be fabricated using either
FIGURE 2. A ball lens on the end of a
fiber collimates, focuses, or reduces the
divergence angle of the light exiting the fiber.
(Courtesy of AFL)
