Potential of two-photon-excited fluorescence for distributed fiber sensing

The design and operating parameters of a new class of continuously distributed optical fiber sensor are described. By use of counterpropagating pulses, two-photon excitation of fluorescence from ions doped into the fiber enables any position to be monitored. By this means temperature and also strain may be sensed with high spatial and temporal resolution. As the doped fiber is transparent for single-photon absorption at the wavelength of the light pulses, attenuation does not set an upper limit to its length.