Carbon-coated fiber for optoelectronic strain and vibration sensing

In this article, we report on a carbon-coated optical fiber that is suitable to be used simultaneously as a transmission medium and as a sensor. It consists of a standard single mode fiber (SMF) sleeved in two layers of coating, which provide protection and isolation from external elements. The inner layer is made of carbon, whereas the outer is made of polymer. When the fiber is subjected to mechanical stress, the electrical resistance of the carbon layer changes accordingly. The voltage variations caused by the former can be measured with high accuracy and without interfering with the light propagating through the SMF. In this work, the feasibility of this operating principle is demonstrated in a low coherence Michelson interferometer in which electrical and optical signals were measured simultaneously and compared to each other. Results indicate that electrical measurements are as precise as the optical ones and with linear behavior, reaching a sensitivity of 1.582 mV/με and able to detect vibrations down to 100 mHz.