PHASE SENSITIVE COHERENT OTDR WITH MULTI-FREQUENCY INTERROGATION
First Claim
1. An apparatus, comprising:
- a narrowband optical source to generate a first optical signal having a first optical frequency;
a frequency-shifting circuit to generate a probe signal from the first optical signal to launch into a fiber optic sensor, the probe signal having a plurality of optical frequencies shifted from the first optical frequency;
a coherent detection system to mix backscatter signals generated by the fiber optic sensor in response to the probe signal with a local oscillator optical signal provided by the narrowband optical source to generate mixed output signals; and
a phase detection and acquisition system to filter the mixed output signals into frequency bands corresponding to the shifted frequencies, and to extract at least the phase of the mixed output signal for at least one of the frequency bands.
1 Assignment
0 Petitions
Accused Products
Abstract
A fiber optic sensor system includes a coherent-detection optical time domain reflectometry system to extract phase information from optical signals returned from a fiber optic sensor arrangement in response to a plurality of interrogating pulses. The system includes a frequency-shifting circuit to repeatedly translate the frequency of an optical pulse generated by a narrowband source to generate a train of interrogating pulses of multiple frequencies. The optical signals returned from the sensor arrangement in response to the pulse train is mixed on a photodetector with light from the narrowband source that has not been shifted to generate mixed output signals. The mixed output signals are filtered into frequency bands, and the phase for each frequency band is extracted.
-
Citations
31 Claims
-
1. An apparatus, comprising:
-
a narrowband optical source to generate a first optical signal having a first optical frequency; a frequency-shifting circuit to generate a probe signal from the first optical signal to launch into a fiber optic sensor, the probe signal having a plurality of optical frequencies shifted from the first optical frequency; a coherent detection system to mix backscatter signals generated by the fiber optic sensor in response to the probe signal with a local oscillator optical signal provided by the narrowband optical source to generate mixed output signals; and a phase detection and acquisition system to filter the mixed output signals into frequency bands corresponding to the shifted frequencies, and to extract at least the phase of the mixed output signal for at least one of the frequency bands. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
-
-
16. A method of detecting a parameter of interest using a fiber optic sensor, comprising:
-
frequency-shifting a frequency of an optical signal from an optical source to generate a probe signal of shifted frequencies; launching the probe signal into a fiber optic sensor; mixing returned optical signals generated by the fiber optic sensor in response to the interrogating pulses with a local oscillator signal from the optical source to generate mixed output signals; filtering the mixed output signals into frequency bands, each frequency band corresponding to the shifted frequencies; extracting phase of the mixed output signal from at least one of the frequency bands; and determining the parameter of interest based on the extracted phase. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25)
-
-
26. A system to detect a parameter of interest in a wellbore, comprising:
-
a fiber optic sensor system deployed in a wellbore; a narrowband optical source to generate a first optical signal having a first optical frequency; a frequency-shifting circuit to generate a probe signal from the first optical signal to launch into the fiber optic sensor, the probe signal having a plurality of optical frequencies shifted from the first optical frequency; a coherent detection system to mix backscatter signals generated by the fiber optic sensor in response to the probe signal with a local oscillator signal provided by the narrowband optical source to generate mixed output signals; and a phase detection and acquisition system to filter the mixed output signals into frequency bands corresponding to the shifted frequencies, and to extract at least the phase of the mixed output signal for at least one of the frequency bands, wherein the phase is indicative of the parameter of interest. - View Dependent Claims (27, 28, 29, 30, 31)
-
Specification