Background
Laser micromachining makes it possible to perform various drilling operations inside optical fibers. When making optical fiber sensors, it can be useful to insert sensitive materials in the fiber core. However, this operation is very difficult due to the dimensions of the fiber. Being able to make holes in an optical fiber makes this insertion feasible.
A number of optical fiber sensors proposed in the scientific literature are based on a coupling of evanescent waves of light in a sensitive material placed on the fiber. However, some of these sensors have limited sensitivity, because the effectiveness of the coupling of evanescent waves is limited. A way must therefore be found to improve the coupling of light in the sensitive material, while allowing the light to continue on its path through the fiber.
Solution
Laser drilling of holes through the optical fiber makes it possible to insert a sensitive material into the core of the fiber. The operation can be performed by creating a machining laser beam focal point that is much smaller than the diameter of the fiber to be drilled. By keeping very precise control over the machining threshold, it becomes possible to drill holes through an optical fiber without breaking it.