Method and apparatus for compensating fiber optic lead and connector losses in a fiber optic sensor

摘要

Apparatus and method for compensating a photo sensor for losses in fiber optic cable leads or connectors and fluc­tuations in optical source power make use of a selected broad­band optical source (10) in conjunction with a photoelastic fiber optic transducer (29) that uses a polarizer (26) and an analyzer (32) to polarize a part of the broadband signal. The part of the signal that is not polarized is transmitted through the photoelastic transducer (29) with no modulation, whereas the part of the signal that is polarized is modulated according to the stress on the photoelastic transducer. After transmitting the output light beam through a fiber optic cable (38), the beam is separated into two parts (44,46). The second part (46) is filtered so as to transmit only that part of the broadband signal that is not affected by the polarizer and analyzer and hence is not modulated, the filtered second part being converted to an electrical signal by a photo detector (54). The first part (44) of the split beam is filtered so as to transmit only that modulated part of the broadband signal that is affected by the polarizer and analyzer, the filtered first part being converted to an electrical signal by a photo detector (50). The first signal varies according to the lead and connector losses and the stress modulation on the photoelastic transducer (29), and the second signal varies according to lead and connector losses only. The ratio of the first signal to the second signal then provides a measure of the changes in the transmission due to the modulation of the stress trans­ducer, without lead and connector losses.