TDM- and WDM-based FBG sensor array system

Patent metadata

Field	Value
Publication number	US-9759585-B2
Application number	US-201314381662-A
Country	US
Kind code	B2
Filing date	Mar 4, 2013
Priority date	Mar 2, 2012
Publication date	Sep 12, 2017
Grant date	Sep 12, 2017

Abstract

In a TDM- and WDM-based FBG sensor array system, a source emits a light covering a selected wavelength range. The light is amplified and then used to generate a series of pulses that are fed into an array of sensor gratings. The propagation of a pulse through the sensor array results in a time-domain-multiplexed output, comprising a series of output pulses in which each output pulse comprises a reflection of the input pulse at a respective grating in the sensor array. Raman amplification is used to amplify both the pulse input into and the time-domain multiplexed output from the sensor array, which is then coupled into an output processing stage for receiving the sensor output and for reconstructing the wavelength output of each grating in the sensor array. The wavelength change for each grating is then used to calculate a physical parameter(s) to be measured, such as temperature and/or strain.

First claim

What is claimed is:

1. A fiber optic sensor system, comprising:
an input generator comprising a light source for emitting light covering a selected wavelength range, a rare-earth-doped fiber amplifier for amplifying the emitted light, and a modulator for modulating the emitted light to produce a series of light pulses;
a sensor stage coupled to the input generator for receiving the series of light pulses as an input, and for transmitting the light pulses through an array of sensor gratings positioned along an optical pathway, wherein the propagation of a pulse through the sensor array results in a time-domain-multiplexed output, comprising a series of output pulses in which each output pulse comprises a reflection of the input pulse at a respective grating in the sensor array,
wherein the sensor stage comprises a Raman amplification means for amplifying both the input into the sensor array and the time-domain multiplexed output coming out of the sensor array;
an output processing stage for detecting the output out of the sensor array and for reconstructing the wavelength output of each grating in the sensor array; and
a control module for operating the system stages,
wherein the sensor array comprises a first group and a second group of gratings, each of the first and second groups comprising hundreds of individual gratings at designated locations along a single optical fiber pathway, wherein the individual gratings are separated from each other by a distance of at least one meter,
wherein the first group of gratings is characterized by a first Bragg wavelength, and where the second group of gratings is characterized by a second Bragg wavelength that is different from the first Bragg wavelength,
whereby the sensor array output comprises a series of pulses in which individual outputs from individual gratings are identified by arrival time and by wavelength.

2. The fiber optic system of claim 1 , wherein the rare-earth-doped fiber amplifier comprises an erbium-doped fiber amplifier.

3. The fiber optic system of claim 1 , wherein the input generator stage, the sensor stage, and the output processing stage are coupled to each other by means of an optical circulator, whereby light emitted by the input generator stage is coupled into the sensor stage, and the output of the sensor stage is coupled into the output processing stage.

4. The fiber optic system of claim 1 , wherein the sensor stage further comprises a time reference grating connected upstream of the sensor array that is configured to provide a time reference signal for use by the control module as a baseline time in reconstructing the output of each grating in the sensor array.

5. The fiber optic system of claim 1 , wherein at least a portion of the optical fiber pathway in the sensor stage is fabricated from a Raman-active optical fiber, such that some Raman amplification takes place therein.

6. The fiber optic system of claim 1 , wherein the groups of gratings are arranged in a non-overlapping configuration.

7. The fiber optic system of claim 1 , wherein individual gratings from different groups are arranged in an overlapping configuration, such that the distance between at least some gratings with the same wavelength can exceed a required distance between adjacent sensing points.

8. The fiber optic system of claim 1 , wherein the light source comprises an amplified spontaneous emission from an erbium-doped fiber.

9. The fiber optic system of claim 8 ,
wherein the output processing stage comprises wavelength-spreading means for spreading apart the wavelength components of the output from the sensor stage, and a detector for digitizing the output after wavelength spreading.

10. The fiber optic system of claim 9 ,
wherein the wavelength-spreading means comprises a blazed grating and prism assembly.

11. The fiber optic system of claim 9 , wherein the output processing stage further includes a calibrated scanning stage for accurately deriving wavelength data for the sensor output.

12. The fiber optic system of claim 1 , wherein the light source comprises a tunable laser.

13. A fiber optic system of claim 12 , wherein the output processing stage is configured to derive wavelength data from the sensor output in relationship to the instantaneous wavelength of the tunable laser output.

14. The fiber optic system of claim 13 , wherein the output processing stage is configured to use the laser setting for the instantaneous wavelength of the tunable laser output.

15. The fiber optic system of claim 1 , wherein the light source comprises a swept laser.

16. The fiber optic system of claim 15 , wherein the input generation stage comprises a wavelength measurement module for measuring the instantaneous wavelength of the swept laser output for use by the output processing stage in deriving wavelength data from the sensor array output.

17. The fiber optic system of claim 15 , wherein the sensor stage comprises a wavelength reference device connected between the time reference grating and the sensor array for calibrating the sensor array output.

18. The fiber optic system of claim 17 , wherein the wavelength reference device comprises a plurality of temperature-stabilized gratings with different wavelengths, covering the wavelength range of the sensor gratings.

Assignees

• Ofs Fitel Llc

Inventors

• Holland William R
• Li Yaowen
• Nicholson Jeffrey W
• Sun Yingzhi
• Zhu Benyuan

Classifications

• G01K11/32

  using changes in transmittance, scattering or luminescence in optical fibres · CPC title

• G01D5/35364 Primary

  using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering · CPC title