Optical sensor

Patent metadata

Field	Value
Publication number	US-9983236-B2
Application number	US-201615187442-A
Country	US
Kind code	B2
Filing date	Jun 20, 2016
Priority date	Dec 20, 2013
Publication date	May 29, 2018
Grant date	May 29, 2018

Abstract

A method of increasing accuracy of optical sensors based on generating two sets of light waves having different velocities in the presence of a non-vanishing measurand field within a sensing element of the sensor is described. A defined static bias phase shift is introduced between the two sets of light waves. The sensor converts a total optical phase shift including static bias optical phase shifts and measurand-induced optical phase shifts into anti-phase optical power changes in at least two detector channels. The method includes steps of normalizing the optical power changes after their conversion into electrical detector signals in the two detector channels to reduce effects of uneven intensity or power of the light source and different loss or gain in the detector channels. Further methods, sensors and apparatus for temperature stabilizing such optical sensors and novel sensors are also presented.

First claim

The invention claimed is:

1. A method of detecting an optical phase shift between two sets of light waves induced by a measurand field in a sensing element, the method comprising the steps of:
passing through said sensing element from a light source said two sets of light waves having different velocities within said sensing element in the presence of a non-vanishing measurand field;
introducing a static bias optical phase shift between said two sets of light waves;
converting a total optical phase shift including said static bias optical phase shift and said optical phase shift induced by said measurand field into optical power changes of opposite signs (anti-phase) in at least two detector channels;
converting the optical power in said at least two detector channels into electric detector signals;
filtering spectral components from the electrical detector signals of said at least two detection channels and combining said spectral components or a normalization parameter derived therefrom with at least one detector signal to yield normalized detector signals corresponding to an equal optical average power in the absence of said measurand field;
combining the detector signals of said at the least two detection channels including the normalized detector signals to yield a sensor signal dependent of the total optical phase shift but essentially independent of the intensity of said light source and of different loss or of different gain in said at least two detector channels;
wherein the filtered spectral components are an AC or transient content of the detector signals and the filtered AC spectral components are time-average; and
wherein the static bias phase shift is indicative of the temperature of components introducing the static bias optical phase shift or of a sensing element.

2. The method of claim 1 , wherein one of: a) the two sets of light waves comprise two different polarization states; and
b) wherein one or more polarizing elements are used to generate the optical power changes having opposite signs (anti-phase).

3. The method of claim 1 , wherein one of: a) the static bias optical phase shift is about (2n+1)×90°, where n is any integer number; and
b) wherein the static bias optical phase shift is introduced using at least one quarter-wave retarder or a Faraday rotator.

4. The method of claim 1 , wherein the sensing element is one of a current or magnetic field sensing element or a voltage or an electric field sensing element.

5. The method of claim 1 , wherein one of: a) a Fast Fourier transform (FFT) and a low pass filter (LPF, LPF 1 ) are used to filter time averaged AC spectral components; and
b) a series of high pass filter (HPF 1 ), a rectifier (R), and a low pass filter (LPF) is used to filter time averaged AC spectral components.

6. The method of claim 1 , wherein one of: a) the filtered spectral components are in a range around the nominal frequency of the measurand field; and
b) wherein an amplitude threshold value for the filtered spectral components is set and filtered spectral components below said threshold or the normalization parameter derived therefrom are replaced by default values or by low pass filtered signal components.

7. The method of claim 1 , wherein one of: a) further comprising the step of applying a high-pass filter (HPF, HPF 2 ) to the signal after the combining step; and
b) further comprising the step of compensating for temperature dependence of the sensing element and/or of further passive components; and
c) further comprising a linearization of the sensor signal characteristics, in particular by taking into account the static optical bias phase shift.

8. The method of claim 1 , further comprising the step of deriving from the sensor signal a further signal representative of the static bias phase shift.

9. The method of claim 1 , wherein one of: a) the step of deriving a signal representative of the static optical phase bias includes splitting the sensor signal into a total phase shift channel and a static bias phase shift channel and applying a low pass filter (LPF 2 ) to the static bias phase shift channel; and
b) the method includes a further temperature compensation as provided by a retarder coupled to the sensing element.

10. An optical fiber current or magnetic or voltage or electric field sensor comprising a signal processing unit including inputs for each of the signals as measured by two or more detectors and filters and at least a light source and at least two or three optical transmission channels, with one channel providing a forward channel for the light to a sensing element and one or two channel(s) providing return detector channel(s) for the light to the detector(s), one or more passive optical elements for introducing a static bias optical phase shift between two different sets of light waves having different velocities within said sensing element in the presence of a non-vanishing measurand field, and for converting a total optical phase shift including said static bias optical phase shift and an optical phase shift induced by the measurand field into changes of optical power, the optical power being in the case of two detector channels of opposite signs (anti-phase), and a polarisation maintaining (PM) fiber being connected directly or indirectly via at least one retarder or Faraday rotator element to said sensing element, wherein at least parts of said one or more passive optical elements are in thermal contact with a temperature stabilizing unit providing a controlled temperature environment for said one or more passive optical elements wherein the temperature stabilizing unit comprises at least one self-regulated heating resistor, wherein the one or more passive optical elements are at ground potential and wherein the PM fiber provides an optical connection from ground potential to the potential of the sensing element being different from the ground potential, and wherein the PM fiber passes through the interior of an insulator column and the insulator column is a hollow core insulator filled with an insulating fluid or gel surrounding the PM fiber.

11. The sensor of claim 10 , wherein the one or more passive optical elements for introducing a static bias optical phase shift and the one or more passive optical elements converting a total optical phase shift are combined in an integrated optical polarization splitter module with at least three ports on the optical source/detector side and one port on the sensing element side, with said port on the sensing element side being connected to the PM fiber.

12. The sensor of claim 10 , wherein one of: a) the sensing element comprises a sensing fiber to be looped around a conductor and to be in operation exposed to a magnetic field of a current in said conductor; and
b) the sensor being a sensor for measuring DC current; and
c) the sensing element comprises one of an electro-optical crystal or an electro-optic fiber or an optical fiber attached to a piezo-electric material.

13. The sensor of claim 10 , wherein said fluid or gel comprising silicone or silicone with a compressible filler material, or a gas.

14. The sensor of claim 10 , wherein the insulating fluid or gel comprising a dielectric insulation fluid mixture or gas mixture comprising an organofluorine compound.

15. The sensor of claim 14 wherein the organofluorine compound being selected from the group consisting of: a fluoroether, an oxirane, a fluoroamine, a fluoroketone, a fluoroolefin, and mixtures and/or decomposition products thereof.

16. The sensor of claim 15 , wherein the insulating fluid or gel comprising backg

Assignees

• Abb Technology Ag
• Abb Schweiz Ag

Inventors

• Bohnert Klaus
• Frank Andreas
• Müller Georg
• Yang Lin

Classifications

• G01R15/245 Primary

  using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect · CPC title

• G01R15/247 Primary

  Details of the circuitry or construction of devices covered by G01R15/241 - G01R15/246 · CPC title

• G01R33/0322

  using the Faraday or Voigt effect · CPC title

• G01R15/246

  based on the Faraday, i.e. linear magneto-optic, effect · CPC title