公开(公告)号：US20240344878A1

公开(公告)日：2024-10-17

申请号：US18624663

申请日：2024-04-02

Applicant: EXFO Inc.

Inventor： Hongxin CHEN ,  Michel LEBLANC

IPC: G01H9/00 ,  G01D5/353

CPC classification number: G01H9/004 ,  G01D5/35358

Abstract: There is provided a method and system of frequency dithered distributed acoustic sensing (FD-DAS) using group data signal processing, where the continuous wave (CW) coherent laser's optical frequency or optical phase for the FD-DAS interrogator may be set in evenly or randomly distributed manner for different data groups but they are kept as constant or with negligibly variation within each data group. Such FD-DAS may be used to improve acoustic or vibration signal measurement reliability, to allow to use a low-cost single-frequency laser such as a DFB laser, and/or to suppress polarization fading effect.

公开(公告)号：US20240134076A1

公开(公告)日：2024-04-25

申请号：US18390981

申请日：2023-12-20

Applicant: EXFO Inc.

Inventor： Hongxin CHEN ,  Normand CYR

IPC: G01V1/22 ,  G01V1/00

CPC classification number: G01V1/226 ,  G01V1/001

Abstract: There is provided a method and an apparatus of fiber optic distributed acoustic sensing (DAS) which use a simple, reliable and robust signal processing for amplitude-based DAS measurements. 1) The lack of linearity of the amplitude-based DAS measurements (due to its unpredictable variation of the transfer function along the fiber) can be improved by normalizing the amplitude vs distance using an amplitude-normalization trace obtained from either a) coherent laser OTDR measurements with laser frequency dithering or b) computing a normalization trace from the coherent OTDR/DAS traces and the un-coherent OTDR/DAS traces. 2) Instrument offset (e.g., due to low vertical sampling resolution) may further be corrected using un-coherent OTDR/DAS traces to extract an instrument system offset.

公开(公告)号：US20240012167A1

公开(公告)日：2024-01-11

申请号：US18329133

申请日：2023-06-05

Applicant: EXFO Inc.

Inventor： Hongxin CHEN ,  Michel LEBLANC ,  Michel LECLERC

IPC: G01V1/22 ,  G01V1/00

CPC classification number: G01V1/226 ,  G01V1/001

Abstract: There is provided a method and an apparatus of fiber optic distributed acoustic sensing (DAS) which can use low-cost coherent laser as well as low-cost acquisition and processing electronics and which can still provide reliable monitoring results for optical fiber monitoring and troubleshooting applications in optical fiber telecommunication networks. Such low-cost solution is made possible by employing grouped data signal processing. Data is processed over independent groups of data to provide an independent DAS signal for each group. This allows measurements to be less sensitive to laser fluctuations and thereby reduces coherent laser technical specification requirements and allows the use of a low-cost coherent laser (thereby reducing the cost of the laser) as well as low-cost acquisition and processing electronics.

公开(公告)号：US20250035510A1

公开(公告)日：2025-01-30

申请号：US18773248

申请日：2024-07-15

Applicant: EXFO Inc.

Inventor： Hongxin CHEN ,  Yves BRETON ,  Mathieu HUNEAULT

IPC: G01M11/00

Abstract: There is provided a method of measuring the PMD of an optical fiber under test (FUT). A polarization-sensitive optical time domain reflectometer (POTDR) is used to inject into the FUT and from a proximal end thereof, a test signal comprising a series of repeated light pulses and detecting a corresponding polarization-analyzed return light signal coming back from the optical fiber and representing back-reflected light from a light reflector connected to a distal end of the FUT, said return light signal comprising repeated reflected light pulses. The plurality of polarization-sensitive acquisitions defines at least one pair of acquisitions performed with mutually different but closely-spaced wavelengths and substantially the same state of polarization (SOP), a center of said wavelengths defining a center wavelength for said at least one pair. The process may be repeated for a plurality of pairs of acquisitions performed with at least one of a plurality of mutually-different center wavelengths and a plurality of mutually-different states of polarization (SOP). For each said acquisitions, respective amplitudes of at least part of the repeated reflected light pulses are averaged so as to obtain an averaged reflected power. The PMD is obtained by, for each said pairs of said acquisitions, computing a value of a difference between the two averaged reflected powers corresponding to said pair, followed by the mean-square value of computed values of difference over said at least one of a plurality of mutually-different center wavelengths and a plurality of mutually-different states of polarizations (SOPs) and, from said mean-square value, calculating a value of the PMD for the optical fiber under test.