Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1994-07-25
1996-03-19
Turner, Samuel A.
Optics: measuring and testing
By particle light scattering
With photocell detection
356 731, 25022727, G01B 902
Patent
active
055007333
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an interferometric system for the detection and location of reflecting faults in light-guiding structures.
The term "light-guiding structures" is understood to mean optical waveguides, such as e.g. optical fibers, optical couplers and even lasers.
The present invention more particularly applies to the field of optical telecommunications and permits the location of weakly reflecting diopters in such optical guides with a high resolution.
The invention also makes it possible to measure the transmission characteristics of such optical guides, as well as the reflection coefficients of passive or active guiding structures.
An interferometric system for the detection and location of reflecting faults is already known from the document "High-spatial-resolution and high-sensitivity interferometric optical-time-domain reflectometer", Masaru Kobayashi, Juichi Noda, Kazumasa Takada and Henry F. Taylor, SPIE Conference, Orlando, Fla., Apr. 1-5, 1991, 1474-40.
SUMMARY OF THE INVENTION
The present invention solves the problem of obtaining an interferometric system able to accurately define the position of propagation "incidents" distributed along optical guides. For this purpose, the present invention makes use of a Michelson interferometer in incoherent light, as well as interferometric means with counting of interference fringes by laser.
More specifically, the present invention relates to an interferometric system for the detection and location of reflecting faults of light guidance structures, the system being characterized in that it includes: central wavelength of the incoherent source, optically coupled to the incoherent source and to the laser source, which are fixed the ends of the second branches of the first and second couplers, respectively placed facing the ends of the second branches of the first and second couplers in order to reflect there the light passing out of the same, which is fixed the end of a third branch of the second coupler, branch of the second coupler in order to reflect there the light passing out of the same, a third branch of the first coupler being optically coupled to the guiding structure, branches of the first and second couplers, by the second photodetector and photodetectors, said analysis means serving to locate the reflecting faults of the guidance structure, with the aid of appropriate displacements of the first, second and third supports and the counter.
The present invention also makes it possible, by using the signal processing by correlation, to lower the detection threshold or "minimum detectable power" by at least one decade compared with the aforementioned known system and without having a prejudicial influence on the spatial resolution.
The system according to the invention can also comprise a third optical coupler, whose first and second branches are respectively optically coupled to the incoherent source and to the laser source and whose third and fourth branches are respectively optically coupled to the first branches of the first and second couplers.
According to a special embodiment of the system according to the invention, the analysis means incorporate a two-channel oscilloscope respectively receiving the signal supplied by the first and second photodetectors, said oscilloscope displaying interferograms corresponding to said signals.
The system according to the invention can also comprise piezoelectric means which are able to oscillate the second support in the given direction.
According to a preferred embodiment of the system according to the invention, the system includes means for regulating the speed of the displacement of the second support, the regulating means serving to impose a constant displacement speed on the second support.
These regulating means can comprise a Michelson interferometer having a light source, whose coherence length is above the amplitude of the displacement of the second support, two arms respectively terminated by two light reflectors, whereof one is rendered rigidly int
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Boisrobert Christian
Dontenwille Michel
Lucas Jean-Francois
France Telecom
Turner Samuel A.
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