Method and apparatus for compensating fiber optic lead and connector losses in a fiber optic sensor by using a dual wavelength optical source and matched polarizer

摘要

Apparatus and method for compensating a photo sensor for fiber optic cable lead/connector losses and optical source power fluctuations includes a specially selected broadband optical source used in conjunction with a photoelastic fiber optic transducer that uses a polarizer and an analyzer that only polarize a portion of the broadband signal. The portion of the signal that is not polarized is simply transmitted through the photoelastic element and emerges with no modulation. The portion of the signal that is polarized is modulated according to the stress on the photoelastic element. After transmitting the output light beam through a single fiber optic cable, the beam is separated into two parts. The first part is filtered so as to transmit only that portion of the broadband signal that is not affected by the polarizer and analyzer and hence is not modulated. The filtered first part is converted to an electrical signal by a photo detector. The second part of the split beam is filtered so as to transmit only that portion of the broadband signal that is affected by the polarizer and analyzer, and hence is modulated. The filtered second part is converted to an electrical signal by a second photo detector. The second signal varies according to lead and connector losses and the stress modulation on the photoelastic element. The first signal varies according to lead and connector losses only. The ratio of the second signal to the first signal then provides a measure of the changes in the transmission due to the modulation of the transducer element, without lead and connector losses, or variations due to power source fluctuations.