Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1997-05-19
1999-03-02
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
372 9, 372 32, 356 731, H04S 316, H04S 323
Patent
active
058774939
ABSTRACT:
An optical sensing apparatus is provided for sensing changes of index of refraction and sensing changes of length of a fiberoptic cable, for example. A transmitting laser cavity produces a stable-resonator output beam which is modulated with a compound beam pattern including a first wave of frequency f.sub.1 and a second wave of frequency f.sub.2. The reflected compound modulated beam enters a receiving laser cavity and fundamental and harmonic waves f.sub.1 and f.sub.2 are generated in the receiving laser cavity. The power of the compound modulated output beam of the receiving laser cavity is measured by a photodiode and a deconvolution system is connected to the photodiode for filtering the fundamental frequency of f.sub.1 and the second harmonic of wave f.sub.2. Time-dependent changes in the measured power of the modulated compound output beam are used to derive changes of index of refraction or changes in length. In another form of the invention, two or more matched lasers form transmitting and receiving cavities and changes in the measured output power of the receiving cavity are used to derive the desired information.
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Johnsonbaugh Bruce H.
Lee John R.
Westin Edward P.
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