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：US20190305845A1

公开(公告)日：2019-10-03

申请号：US16445992

申请日：2019-06-19

Applicant: EXFO Inc.

Inventor： Normand CYR ,  Gang HE ,  Bernard RUCHET

IPC: H04B10/079

Abstract: Method and systems for characterizing an optical signal propagating along a communication link are disclosed. The signal includes a data-carrying signal contribution, modulated at a symbol frequency, and a noise contribution. The method includes measuring an optical power spectrum of the signal, which includes a data-carrying signal spectrum component and a noise spectrum component. The method also includes determining a measured spectral correlation function within pairs of spectral components of the signal as a function of center frequency of the pairs, the spectral components in each pair being spectrally separated from each other by the symbol frequency. The method further includes obtaining a solution for the data-carrying signal spectrum component based on the measured optical power spectrum, such that a calculated spectral correlation function based on the solution matches the measured spectral correlation function. In some embodiments, the spectral correlation function is measured as a low-frequency beatnote amplitude function.