High speed frequency hopping DAS interrogation using AOM-gated re-circulating loop and frequency-shifted receiver LO

Patent metadata

Field	Value
Publication number	US-11159200-B2
Application number	US-201916258586-A
Country	US
Kind code	B2
Filing date	Jan 26, 2019
Priority date	Jan 26, 2018
Publication date	Oct 26, 2021
Grant date	Oct 26, 2021

Abstract

Aspects of the present disclosure describe systems, methods, and structures for high speed frequency hopping distributed acoustic sensing using an acousto-optic modulated (AOM), gated re-circulating loop and a frequency shifted receiver local oscillator. Using the re-circulating loop controlled by the AOM to generate frequency-hopping pulse(s) increases DAS acoustic bandwidth overcomes infirmities exhibited in the art that generate multiple frequency patterns that are not suitable for long-distance DAS. Additionally, by employing frequency shifted local oscillator (LO) with asymmetric in band detection, bandwidth requirements are reduced by one half.

First claim

The invention claimed is:

1. An improved fiber optical distributed acoustic sensing (DAS) assembly, the system comprising an optical fiber, a light transmission and receiving assembly in optical communication with the optical fiber, the DAS assembly CHARACTERIZED BY:
a re-circulating optical fiber loop including a gated acousto-optic modulator (AOM), said re-circulating optical fiber loop connected to the optical fiber;
the re-circulating optical fiber loop is configured to generate frequency-hopping optical pulses; and
the circulating optical fiber loop is configured to generate a number of optical frequencies, said number determined by the number of times an optical pulse re-circulates through the loop.

2. The DAS system of claim 1 FURTER CHARCTERIZED BY: the frequency-hopping optical pulses increase an effective acoustic sampling rate of the DAS.

3. The DAS system of claim 2 FURTHER CHARACTERIZED BY: a seed optical pulse exhibiting a single frequency generates multiple trailing pulses at different frequencies.

4. The DAS system of claim 1 FURTHER CHARACTERIZED BY: a radio frequency (RF) frequency of an electrical drive signal applied to the AOM sets a frequency spacing in each of the frequency-hops.

5. The DAS system of claim 4 FURTHER CHARACTERIZED BY: the re-circulating loop includes an optical fiber delay length configured to set adjacent pulse staggering time(s).

6. The DAS system of claim 5 FURTHER CHARACTERIZED BY: the re-circulating loop includes an erbium-doped fiber amplifier (EDFA) configured to equalize poser of the frequency hopping pulses.

7. The DAS system of claim 6 FURTHER CHARACTERIZED BY: a frequency shifted local oscillator (LO) for coherently detecting DAS signal such that receiver bandwidth is reduced.

8. The DAS system of claim 7 FURTHER CHARACTERIZED BY: the LO frequency offset is configured such that any interference from I/Q imbalance is eliminated.

Assignees

• Nec Lab America Inc
• Nec Corp

Inventors

• Huang Yue-Kai
• Ip Ezra
• Milione Giovanni
• Yaman Fatih

Classifications

• G01H9/004 Primary

  using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125) · CPC title

• H04B14/00

  Transmission systems not characterised by the medium used for transmission (details thereof H04B1/00) · CPC title

• H04B1/713

  using frequency hopping · CPC title

• H04B1/7136 Primary

  Arrangements for generation of hop frequencies, e.g. using a bank of frequency sources, using continuous tuning or using a transform · CPC title

• H04B1/715

  Interference-related aspects · CPC title