Performance of integrated source/detector combinations for smart skins incoherent optical frequency domain reflectometry (IOFDR) distributed fiber optic sensors

The success of the concept of smart skins depends upon the development of sensors that can be integrated into the vehicle skin and can provide accurate measurement of some parameter of interest. In particular, measurements of distributed parameter fields over the vehicle surface are of prime importance. Work to date has focused upon using a combination of optical fiber sensor and optical radar (OTDR and OFDR) techniques to provide distributed measurements of stress and strain. In this paper, the results of an investigation into the use of integrated optical radar sources/detectors are presented. The work focused upon incoherent OFDR using a laser diode - PIN photodetector combination. The laser diode was driven with an RF "chirp" with its output coupled into an optical fiber. Delayed optical signals returned from the fiber were fed back into the laser cavity and mixed. The integral packaged photodetector was used to provide system output. Such topics as laser coherence length and wavelength stability all influence this technique. Experimental results are presented and compared with measurements based on external photodetection and mixing. Finally, the applicability of the technique for smart skins applications is discussed.