Manufacturing Precision Tapers

As discussed in our last post, we've equipped our tapering machine with a custom-made electric heating element. This gives us precise temperature control, allowing us to soften the glass without melting it. The electric heater has the added benefit of not introducing a stream of air flow which may otherwise distort the taper (as is the case with torch flames). It also has the benefit of not removing the cladding layer, as is the case with laser machines. Our stretching machine uses two translating stages driven by stepping motors. We program them with machine code (via a LWDAQ interface), allowing an infinite range of stretching algorithms to choose from.

Our goal is to be able to consistently manufacture a specified taper profile. Good tapers must have the following properties:

- Specified profile; Typically, the walls of the taper are linear (flat) or slightly convex. The length of the tapered region is specified.
- Axial symmetry
- Sharp tip

Additionally, the manufacturing process must produce repeatable results so that tapers appear identical to one another. Through much experimentation, we've discovered guiding principles for designing heaters and stretching algorithms that produce high quality tapers.

Our latest effort has been to produce medium length tapers out of our 410-μm high-index fiber. We developed a stretching algorithm that self terminates the taper. This leaves a sharp point and improves consistency by eliminating the need for a human to trim the taper to length. The result is a 2.7mm taper with high axial symmetry. While viewing the taper through a jeweler's loupe and rotating it, any deviation from axial symmetry is difficult or impossible to discern. Three such tapers were made consecutively and are shown in the image below.


Figure: Three 2.7mm tapers made of 410μm High-index fiber. The ruler's tick marks are 0.5mm apart.

We will continue to experiment with methods to control the manufacturing process for even better consistency. These include improving the consistency of our heater's power source and consideration of the slight variations in the diameter of the fiber as supplied by its manufacturer. We will also experiment with algorithms that produce shorter or longer tapers as required.