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1.
Opt Lett ; 45(11): 2969-2972, 2020 Jun 01.
Article in English | MEDLINE | ID: mdl-32479435

ABSTRACT

An optical time-domain reflectometer (OTDR) is incapable of providing sensing or diagnostic information within dead-zones. We use a two-mode fiber (TMF) and a photonic lantern to completely overcome the main OTDR's dead-zone originating from the front facet of optical fiber. This is achieved by injecting the optical pulses of the OTDR in the form of the fundamental ${{\rm LP}_{{01}}}$ mode and meanwhile collecting the Rayleigh signals associated with the higher-order modes. Using the reported TMF-based OTDR, we accurately sense the position and frequency of a vibration event located within the dead-zone as a proof-of-concept demonstration.

2.
Appl Opt ; 58(18): 4933-4938, 2019 Jun 20.
Article in English | MEDLINE | ID: mdl-31503813

ABSTRACT

We experimentally introduce a normalized differential method to enhance the time domain signal-to-noise ratio (SNR) of an optical fiber distributed acoustic sensor (DAS). The reported method is calibrated against the typical differential method in noisy DAS systems, including those utilizing a relatively wide linewidth laser or few-mode fiber. In these two systems, the normalized differential method respectively identifies the position information of various vibration events with 1.7 dB and 0.53 dB SNR improvement. We further demonstrate the ability to locate positions along a fiber that are subjected to vibrations of frequencies higher than the theoretical maximum, but without determining these frequencies.

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