How to cleave optical fiber?
A fiber cleave is initiated by lightly scratching the surface of the fiber. When the fiber is thereafter pulled or bent, a crack will originate at the scratch and propagate radially across teh width of the fiber. This produces a nearly flat cleave of an optical fiber.
Fiber Cleaving Tool
The stress field within the fiber created by tension or bending determines the speed at which sound will propagate. If the crack exceeds this speed, the crack will suddenly change direction by almost 90°. This results in an excess of glass on one fiber and a shortage on the other fiber (called a hackle).
So in order to produce a nearly flat cleave of an optical fiber, the crack speed must propagate slower than the speed of sound in the fiber.
This rule should hold regardless of fiber material. Just be certain that you know the speed of sound in the fiber. Keep in mind that most bad cleaves are due to the initial scratch being too deep. Torsion will not change the speed of sound within the fiber, but it will produce non-perpendicular endfaces.
It is easy to cleave an 80um and 125um dia. fibers, but usually difficult to cleave >200um fibers. To some extent, the difficulty in cleaving these fibers results from the fact that the material of the fiber is not crystalline. Again, torsion will produce a non-perpendicular endface. In fact, most commercially available angle cleavers rely on torsion. The endface angle is proportional to the amount of torsion.