This video shows a stretchable optical fiber that can report its own length. We have been developing sensor fibers that work with stretchable materials like athletic tape. The screen in the background shows the light intensity decreasing as the tape is stretched, and climbing back up as the tape relaxes to its original length. The intensity drop is caused mostly by the longer path length in a stretched piece of absorbing material, as shown in the animation here.
In applications where we sew the fibers onto another material, effects on the light intensity come from both the length change and from threads pushing into the fiber.
Some practical features of optical sensing compared to resistive electronic sensing is that all-polymer optical materials don’t corrode in a wet environment, cost less than metals, and don’t need a continuous conductive path. These properties will be handy when putting sensors on skin, creating disposable devices and making wearable sensors that might need to be washed.