Interferometric sensor

Patent metadata

Field	Value
Publication number	US-10725073-B2
Application number	US-201615243713-A
Country	US
Kind code	B2
Filing date	Aug 22, 2016
Priority date	Feb 21, 2014
Publication date	Jul 28, 2020
Grant date	Jul 28, 2020

Abstract

An interferometric sensor and related methods are provided, with a sensing element whereby a measurand induces a relative phase shift between two waves, at least one detector measuring an interference signal between the two waves, and further including a phase shift detection unit having as input the interference signal and determining a first measure representative of the principal value of the relative phase shift, and a contrast detection unit having as input the interference signal for determining a second measure representative of the cross-correlation between the two waves, and a further a processing unit for converting the first and second measures to a measurand value.

First claim

The invention claimed is:

1. An interferometric sensor comprising a sensing element whereby a measurand induces a relative phase shift between two waves passing through the sensing element, wherein the sensing element is a voltage sensor and the measurand is an electric voltage or an electric field strength and the relative phase shift inside the sensing element is responsive to a voltage applied between two faces of the sensing element, at least one detector measuring an interference signal between the two waves, and further comprising a phase shift detection unit having as input the interference signal and determining a first measure representative of a principal value (φ) of the relative phase shift and a contrast detection unit having as input the interference signal for determining a second measure (A) representative of a cross-correlation between the two waves, and further a signal processing unit for converting the first and second measures to a measurand value, wherein the second measure is a parameter relating to an interference contrast or fringe visibility, wherein the two waves in interference have a sufficiently broad spectrum to produce a rapidly varying and monotonic cross-correlation function in a range of a same width as a target measurement range, and wherein using the second measure representative of the cross-correlation, the sensor removes period ambiguity from the relative phase shift as measured, and further comprising at least two interference channels with at least two detectors and at least one static optical phase bias element in at least one of the at least two interference channels, and wherein the signal processing unit combines the interference signals of the at least two interference channels to form the first measure (arg Y) and the second measure (abs Y).

2. The sensor of claim 1 , wherein the signal processing unit matches the second measure to a pre-determined function or map of parameter values representing the cross-correlation function (A) between the two waves across the measurement range of the sensor.

3. The sensor of claim 1 , wherein the signal processing unit uses the second measure to determine a period count n.

4. The sensor of claim 1 , further including one or more sources generating two waves, the cross-correlation (A) of which varies strongly and monotonically with the relative group delay (τ) between the two waves within the measurement range of the sensor.

5. The sensor of claim 1 , wherein
IA (Φ)− A (Φ±2π) I/A (Φ)≥0.001,

with A being said second measure and (Φ) being said phase shift.

6. The sensor of claim 4 , wherein the two waves are generated by the same source of the one or more sources, whereby the cross-correlation function (A) is the auto-correlation function of the wave generated by the same source.

7. The sensor of claim 4 , with the one or more sources having a spectrum covering at least one of a continuous band, or a spectrum consisting of multiple disconnected bands or disconnected spectral lines.

8. The sensor of claim 1 , further including a group delay bias element to shift the measurement range of the sensor into a region of monotonic variation of the cross-correlation function (A) with the relative group delay (τ) between the two waves.

9. The sensor of claim 8 , wherein the group delay bias element is a birefringent material, a birefringent waveguide, a polarization-maintaining optical fiber, or a combination thereof.

10. The sensor of claim 1 , wherein the measurement range of the sensor includes a region where the gradient of the cross-correlation function (A) with regard to the group delay (τ) (|dA/dτ|) has a maximum value.

11. The sensor of claim 1 , wherein a phase bias difference between the interference channels is within (90°±40°)+180°×i, wherein i is an integer including zero.

12. The sensor of claim 1 , further comprising an additional signal channel with a detector measuring a quantity representative of the total power of the waves before interference, or at least one additional channel in antiphase with any of the interference channels, and wherein the signal processing unit combines the interference channel signals and the additional channel(s) signal to compute the first and the second measures independent of total power or loss variation.

13. The sensor of claim 1 , further comprising an optical phase modulation element adding a phase modulation to the relative phase shift between the two waves and at least one detector channel for measuring the interference signal, and wherein the signal processing unit analyzes the interference signal to form the first measure (arg Y) and the second measure (abs Y).

14. The sensor of claim 13 , wherein the signal processing unit operates in closed-loop control with a feedback signal representative of the principal value (φ) of the relative phase shift.

15. The sensor of claim 1 , wherein the two waves are light waves, wherein the light waves are one of a orthogonal linearly polarized light waves or left and right circularly polarized light waves.

16. The sensor of claim 15 , wherein the sensing element comprises a bulk electro-optic crystal, or an electro-optic fiber.

17. The sensor of claim 16 , comprising at least one light source, at least one linear polarizer, an optical phase modulator, a Faraday rotator with a rotation angle within (45°±25°)+90°×k, k being an integer, an electro-optic sensing element, and a reflecting optic.

18. The sensor of claim 15 , wherein the sensing element comprises a magneto-optic material, or an optical fiber.

19. A method of performing an interference measurement comprising the steps of:
generating at least two waves;
determining a function or a map of parameter values representative of a cross-correlation function between the at least two waves;
exposing a sensing element to a measurand which is an electric voltage or an electric field strength, and a relative phase shift inside the sensing element is responsive to a voltage applied between two faces of the sensing element and which induces a relative phase shift between the at least two waves passing through the sensing element which is a voltage sensor;
letting the at least two waves interfere, wherein the at least two waves in interference have a sufficiently broad spectrum to produce a rapidly varying and monotonic cross-correlation function in a range of a same width as a target measurement range;
combining interference signals of at least two interference channels to form a first measure and a second measure, the at least two interference channels comprising at least two detectors and at least one static optical phase bias element in at least one of the at least two interference channels;
simultaneously determining for a value of the measurand the first measure representative of a principal value (φ) of the relative phase shift and the second measure (A) representative of the cross-correlation between the at least two waves; and
combining the first and second measures with a pre-determined function or map of parameter values representative of a cross-correlation function and determining a corresponding measurand value, wherein the second measure representative of the cross-correlation function (A) between the at least two waves is a parameter relating to an interference contrast or fringe visibility and
wherein using the second measure representative of the cross-correlation, the voltage sensor removes period ambiguity from the relative phase shift as measured.

20. The method of claim 19 , wherein th

Assignees

• Abb Power Grids Switzerland Ag

Inventors

• Gu Xun
• Marchese Sergio Vincenzo
• Bohnert Klaus
• Frank Andreas

Classifications

• G01D5/35309

  using multiple waves interferometer · CPC title

• G01D5/353 Primary

  influencing the transmission properties of an optical fibre · CPC title

• G01D5/266

  by interferometric means (G01D5/353 takes precedence) · CPC title

• G01D5/35306

  using an interferometer arrangement · CPC title

• G01R15/241 Primary

  using electro-optical modulators, e.g. electro-absorption (probes containing electro-optic elements G01R1/071) · CPC title