Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1991-04-24
1992-09-22
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356 731, H01J 516
Patent
active
051499614
ABSTRACT:
In a method and apparatus for measuring length of an optical fiber, a light source of a selected wavelength transmitted along the fiber is modulated by both a first and a second light modulation signal, which light modulation signals each differ in frequency from a first modulation frequency by a fixed amount. A time detector responds, alternately during a period, to the light signal as modulated by of each of the first and second light modulation signals by using each of the light signal modulation frequencies as a reference. Consequently, the output of the time detector has a phase responsive to the effective length of the fiber. A phase sensitive detector receives as a signal input an output of the time detector means. A second modulation frequency defines the period of alternation of response and provides a reference input to the phase sensitive detector. The phase sensitive detector measures the ac component of time detector output in phase with the second modulation frequency to provide an indication of fiber length.
REFERENCES:
patent: 4750833 (1988-06-01), Jones
patent: 4794249 (1988-12-01), Beckmann et al.
patent: 4826314 (1989-05-01), Comte
Arnold Timothy G.
Barlow Arthur J.
Cogan Robert P.
EG&G, Ltd.
Nelms David C.
Shami K.
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