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

Claim 1

Optical sensor apparatus, comprising: means for providing a source light beam including a first component having a first wavelength and a second component having a second wavelength; polarizer means for receiving said source light beam, and for polarizing said first component while leaving said second component substantially unpolarized, and for providing a light beam having polarized and unpolarized components; optical transducer means for receiving said light beam from said polarizer means, and for modulating said polarized component in response to an externally applied condition while leaving said unpolarized component substantially unmodulated, and for providing an output light beam having modulated and unmodulated components; analyzer means for receiving said output light beam from said optical transducer means, and for providing an analyzed light beam having a plurality of modulated and unmodulated intensities corresponding to said modulated and unmodulated components, respectively; a single first light guiding means for transmitting said analyzed light beam; beam splitter means for receiving said analyzed light beam from said single first light guiding means, and for splitting said analyzed light beam into first and second portions, each portion including said modulated and said unmodulated light intensities; first filter means for receiving said first portion, and for transmitting said modulated light intensity while substantially blocking said unmodulated light intensity, and for providing a first filtered light beam having said modulated light intensity; second filter means for receiving said second portion, and for transmitting said unmodulated light intensity while substantially blocking said modulated light intensity, and for providing a second filtered light beam having said unmodulated light intensity; first photo detector means for receiving said first filtered light beam, and for providing a first signal corresponding to an intensity of said first filtered light beam; second photo detector means for receiving said second filtered light beam, and for providing a second signal corresponding to an intensity of said second filtered light beam; and ratio means for receiving said first and second signals, and for providing an output signal corresponding to a ratio of said first signal to said second signal.

Claim 22

A method of sensing, comprising the steps of: providing a source light beam having first and second components, said first component having a first wavelength and said second component having a second wavelength; polarizing said source light beam to cause said first component to be polarized while leaving said second component substantially unpolarized; modulating, with an optical transducer, said first component in accordance with an external condition applied to said optical transducer while leaving said second component substantially unmodulated to provide an output light beam having modulated and unmodulated components; transmitting, with a single light guiding channel, said output light beam from said optical transducer; filtering said output light beam from said single light guiding channel to provide (a) a first filtered optical signal which has said modulated components but is substantially free of said unmodulated components, and (b) a second filtered optical signal which has said unmodulated components but is substantially free of said modulated components; detecting said first and second filtered optical signals and providing (a) a first electrical signal corresponding to an intensity of said first filtered optical signal, and (b) a second electrical signal corresponding to an intensity of said second filtered optical signal; and processing said first and second electrical signals to provide an output signal corresponding to a ratio of said first and second electrical signals.

Claim 23

A method of sensing, comprising the steps of: providing a source light beam having first and second components, said first component having a first wavelength and said second component having a second wavelength; polarizing said source light beam to cause said first component to be polarized while leaving said second component substantially unpolarized; modulating, with an optical transducer, said first component in accordance with an external condition applied to said optical transducer while leaving said second component substantially unmodulated to provide an output light beam having modulated and unmodulated components; transmitting, with a single light guiding channel, said output light beam from said optical transducer; filtering said output light beam from said single light guiding channel to provide (a) a first filtered optical signal which has said modulated components but is substantially free of said unmodulated components, and (b) a second filtered optical signal which has said unmodulated components but is substantially free of said modulated components; detecting said first and second filtered optical signals and providing (a) a first electrical signal corresponding to an intensity of said first filtered optical signal, and (b) a second electrical signal corresponding to an intensity of said second filtered optical signal; and processing said first and second electrical signals to provide an output signal corresponding to a ratio of said first and second electrical signals.

Claim 30

A method of optically sensing pressure, comprising the steps of: generating a source light beam having a first component with a first wavelength and a second component with a second wavelength; transmitting, with at least a first fiber optic cable, said source light beam; polarizing the transmitted source light beam to cause said first component to be polarized while leaving said second component effectively unpolarized; detecting, with a photoelectric transducer, said pressure; modulating, with said transducer, the polarized first component while leaving the unpolarized second component effectively unmodulated to provide an output light beam having modulated and unmodulated components; transmitting, with a single second fiber optic cable, said output light beam; splitting the transmitted output light beam into first and second portions, each portion having said modulated and said unmodulated components; filtering said first portion to pass said first portion modulated components while substantially blocking said first portion unmodulated components; filtering said second portion to pass said second portion unmodulated components while substantially blocking said second portion modulated component; detecting said first portion modulated components and providing a first electrical signal corresponding thereto; detecting said second portion unmodulated components and providing a second electrical signal corresponding thereto; and receiving said first and second electrical signals and providing an output signal corresponding to a ratio of said first and second electrical signals.

Claim 31

A method of optically sensing pressure, comprising the steps of: generating a source light beam having a first component with a first wavelength and a second component with a second wavelength; transmitting, with at least a first fiber optic cable, said source light beam; polarizing the transmitted source light beam to cause said first component to be polarized while leaving said second component effectively unpolarized; detecting, with a photoelectric transducer, said pressure; modulating, with said transducer, the polarized first component while leaving the unpolarized second component effectively unmodulated to provide an output light beam having modulated and unmodulated components; transmitting, with a single second fiber optic cable, said output light beam; splitting the transmitted output light beam into first and second portions, each portion having said modulated and said unmodulated components; filtering said first portion to pass said first portion modulated components while substantially blocking said first portion unmodulated components; filtering said second portion to pass said second portion unmodulated components while substantially blocking said second portion modulated component; detecting said first portion modulated components and providing a first electrical signal corresponding thereto; detecting said second portion unmodulated components and providing a second electrical signal corresponding thereto; and receiving said first and second electrical signals and providing an output signal corresponding to a ratio of said first and second electrical signals.