Method and Apparatus for Deriving Parameters of Optical Paths in Optical Networks Using Two-wavelength OTDR and a Wavelength-Dependent Reflective Element
First Claim
1. A method of using an optical time domain reflectometer (OTDR) means (22) and a wavelength-dependent reflective (HRD) element in characterizing one or more parameters of a selected optical path of an optical network, said OTDR and said HRD element being connected to said selected optical path at respective first and second mutually-spaced points, said HRD element being highly-reflective at one of two predetermined wavelengths (λ
-
1,λ
2) and significantly less reflective at the other of the two predetermined wavelengths, neither of the two wavelengths corresponding to a normal operating wavelength of the optical path, the method characterized by the steps of;
using said optical time domain reflectometer means (22) connected to said first point of said selected optical path;
to launch into the selected optical path at said first point light at each of said two wavelengths (λ
1) and (λ
2),to detect at said first point corresponding backreflected light as a function of time at each of said two wavelengths (λ
1,λ
2) and obtain therefrom first and second OTDR traces (OTDR-λ
1,OTDR-λ
2), respectively, each representing backreflected light as a function of optical distance;
to compare the first and second OTDR traces to distinguish a peak corresponding to said HRD element from peaks corresponding to wavelength-independent localized reflectances, andto derive from said peak a value of one or more parameters of either or both of said HRD element and said selected optical path between said first and second mutually-spaced points.
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Abstract
A method of distinguishing a wavelength-dependent reflective element (HRD) from wavelength-independent events in an optical network, the reflective element (HRD) being highly-reflective at a first predetermined wavelength (λ1) and significantly less reflective at least one other predetermined wavelength (λ2), comprising the steps of: connecting the wavelength-dependent reflective element (HRD) to said optical path at a first position, and, using an optical time domain reflectometer (22) connected to said optical path at a position remote from said reflective element, launching into said optical path light at said first wavelength (λ1) and at said second wavelength (λ2), detecting corresponding backreflected light from said optical paths and obtaining therefrom first and second OTDR traces (OTDR-λ1, OTDR-λ2) corresponding to said first (λ1) and second (λ2) wavelengths, respectively, of detected backreflected light as a function of optical distance from said point; comparing the first and second OTDR traces to distinguish a peak corresponding to said wavelength-dependent reflective element from peaks corresponding to said wavelength-independent reflective events; and outputting at least one parameter value of the distinguished peak as a measure of a parameter of said wavelength-dependent reflective element.
79 Citations
32 Claims
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1. A method of using an optical time domain reflectometer (OTDR) means (22) and a wavelength-dependent reflective (HRD) element in characterizing one or more parameters of a selected optical path of an optical network, said OTDR and said HRD element being connected to said selected optical path at respective first and second mutually-spaced points, said HRD element being highly-reflective at one of two predetermined wavelengths (λ
-
1,λ
2) and significantly less reflective at the other of the two predetermined wavelengths, neither of the two wavelengths corresponding to a normal operating wavelength of the optical path, the method characterized by the steps of;using said optical time domain reflectometer means (22) connected to said first point of said selected optical path; to launch into the selected optical path at said first point light at each of said two wavelengths (λ
1) and (λ
2),to detect at said first point corresponding backreflected light as a function of time at each of said two wavelengths (λ
1,λ
2) and obtain therefrom first and second OTDR traces (OTDR-λ
1,OTDR-λ
2), respectively, each representing backreflected light as a function of optical distance;to compare the first and second OTDR traces to distinguish a peak corresponding to said HRD element from peaks corresponding to wavelength-independent localized reflectances, and to derive from said peak a value of one or more parameters of either or both of said HRD element and said selected optical path between said first and second mutually-spaced points. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 21, 22, 23, 24, 25, 26, 27, 28)
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1,λ
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15. In a point-to-multipoint optical network having multiple optical paths whose respective first ends are connected in common to a network element (OLT), respective opposite ends of at least a plurality of said multiple optical paths being connected to a corresponding plurality of network units (ONU), respectively, each of said plurality of optical paths having connected thereto at a position at or adjacent said opposite end a respective one of a corresponding plurality of wavelength-dependent reflective (HRDC) elements that are each highly-reflective at one of two predetermined wavelengths (λ
-
1, λ
2) and significantly less reflective at the other of said two predetermined wavelength, neither of said two wavelengths corresponding to a normal operating wavelength of said network, the respective positions of said plurality of wavelength-dependent reflective elements relative to said common connection point being known a priori,a method of distinguishing a temporarily-connected wavelength-dependent reflective (HRD) element (HRDS) from said plurality of HRDC elements, the temporarily-connected HRD element (HRDS) being highly-reflective at said other of the two predetermined wavelengths (λ
2) and significantly less reflective at said one of the two predetermined wavelengths (λ
1), the method characterized by the steps of;using an OTDR means to launch light at said first wavelength (λ
1) and at said second wavelength (λ
2) into said optical paths at a first point where said optical paths are commonly-connected,detect backreflected light from said multiple optical paths at said first (λ
1) and second (λ
2) wavelengths, andobtain therefrom first and second OTDR traces (OTDR-λ
1, OTDR-λ
2) corresponding to said one (λ
1) and other (λ
2) wavelengths of the two, respectively, of detected backreflected light as a function of optical distance from said first point;determine differences between the first and second OTDR traces to distinguish localized reflective events corresponding to said plurality of HRD elements and said temporarily-connected HRD element (HRDS) from other localized reflective events resulting from wavelength-independent reflective events; and using known positions of the plurality of HRD elements to segregate localized reflective events attributable to said plurality of HRD elements from a localized reflective event corresponding to said temporarily-connected HRD element (HRDS). - View Dependent Claims (16, 17, 18, 19, 20)
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1, λ
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29. An optical network comprising a plurality of optical paths connected at their respective first ends in common to a first network element (OLT) and at their opposite ends to a plurality of second network elements (ONU), respectively, characterized by at least some of said optical paths each having a reflective element (HRDC) at a position remote from said first end thereof, each said reflective element (HRDC) being strongly reflective at one of two different predetermined wavelengths and significantly less reflective at the other, neither of said two different predetermined wavelengths being a normal operating wavelength of the optical path, and OTDR measuring means connected to said first ends of said plurality of optical paths in common for launching light at two different wavelengths into said optical paths, detecting corresponding backreflected light and obtaining corresponding OTDR traces at said two different predetermined wavelengths, and deriving from said OTDR traces one or more parameters of said optical paths.
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30. In a point-to-multipoint optical network, a method of using an optical time domain reflectometer (OTDR) means (22) to measure cumulative Rayleigh backcattering signal (RBS) emanating from one or more of the optical paths at optical distances greater than that between the OTDR means and a wavelength-dependent reflective (HRD) element in one of said optical paths, said OTDR and said HRD element being connected to said selected optical path at respective first and second mutually-spaced points, said HRD element being highly-reflective at one of two predetermined wavelengths (λ
-
1,λ
2) and significantly less reflective at the other of the two predetermined wavelengths, neither of the two wavelengths corresponding to a normal operating wavelength of the optical path, wherein the reflectance and insertion loss of said HRD element at said other wavelength (λ
2) are sufficiently low that high attenuation and concomitant decay and dead zone effects attributable to said HRD element at said one wavelength (λ
1) do not significantly obfuscate any expected Rayleigh backscatter (RBS) in said backreflected light emanating from an optical distance farther from said first point than the optical distance of the said HRD element from the said first point, the method characterized by the steps of;using said optical time domain reflectometer means (22) connected to said first point of said selected optical path; to launch into the selected optical path at said first point light at each of said two wavelengths (λ
1) and (λ
2),to detect at said first point corresponding backreflected light as a function of time at each of said two wavelengths (λ
1,λ
2) and obtain therefrom first and second OTDR traces (OTDR-λ
1,OTDR-λ
2), respectively, each representing backreflected light as a function of optical distance;to compare the first and second OTDR traces to distinguish a peak corresponding to said HRD element from peaks corresponding to wavelength-independent localized reflectances, and to derive from said second OTDR trace a value of said RBS at said second wavelength as a function of distance. - View Dependent Claims (31, 32)
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1,λ
Specification