# US 7,411,676 B2 · Polarization mitigation technique

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- Number: US 7,411,676 B2
- Document ID: US7411676B2
- Status: Granted
- Kind: B2
- Application number: 11/670,800
- Filed: 2007-02-02
- Published: 2007-08-16
- Granted: 2008-08-12
- Earliest claimed: 2003-09-26
- Assignees: Weatherford/Lamb, Inc.
- Inventors: Domino Taverner; Trevor MacDougall
- Web page: https://patentgrep.com/patent/US7411676B2

## CPC

- H04B 10/2572: {due to forms of polarisation-dependent distortion other than PMD}
- G01J 3/1895: {using fiber Bragg gratings or gratings integrated in a waveguide}
- G01J 3/28: Investigating the spectrum (using colour filters G01J3/51)
- G01J 3/0224: {using polarising or depolarising elements}
- H04B: TRANSMISSION
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)

## Abstract

A method and apparatus for mitigating the effects of polarization on wavelength determinations is disclosed. An optical source produces light across an optical spectrum, while a polarization element changes the polarization of the light at a first rate. The resulting light is applied to an optical element that produces a spectral response with a feature of interest from the polarization changed light. The optical element and the polarization element are such that the bandwidth of the feature of interest of the optical element is significantly greater than the first rate. A receiver network produces received signals from the received spectrum; and a data processing unit calculates a wavelength that is insensitive to ripple in the received signal and/or the received signals are low-pass filtered to reduce the ripple resulting from the polarization change.

## Claims

### Claim 1

A method to compensate for polarization fluctuation, comprising:
interrogating a sensor with light having a varying polarization to produce a response signal, wherein the polarization varies at a first rate; and
analyzing the response signal at a second rate greater than the first rate, wherein the analyzing occurs throughout the varying polarization applied during the interrogating such that data for multiple different polarizations is utilized to determine an output insensitive to polarization fluctuations.

### Claim 2 (depends on 1)

The method of claim 1 wherein the light is within an optical spectrum.

### Claim 3 (depends on 1)

The method of claim 1 wherein the response signal conveys a physical parameter being sensed that varies with the polarization changes.

### Claim 4 (depends on 1)

The method of claim 1 wherein analyzing the signals includes low-pass filtering the signals.

### Claim 5 (depends on 1)

The method of claim 1 wherein the output is a wavelength.

### Claim 6

An apparatus to determine a polarization fluctuation insensitive output, comprising:
a light source;
a polarization element coupled to the light source which varies the polarization of light from the light source, wherein the polarization element alters the polarization of the light at a first rate;
a sensor which when interrogated with light having varying polarizations from the polarization element produces a response signal; and
a processing unit that analyzes the response signal from the sensor and determines an output that is insensitive to polarization fluctuation, wherein the processing unit analyzes the response signal at a second rate greater than the first rate.

### Claim 7 (depends on 6)

The apparatus of claim 6 wherein the light source produces light across an optical spectrum.

### Claim 8 (depends on 6)

The apparatus of claim 6 wherein the sensor includes a Bragg grating.

### Claim 9 (depends on 6)

The apparatus of claim 6 wherein the sensor includes a receiver which converts a spectral response into the response signal.

### Claim 10 (depends on 9)

The apparatus of claim 9 wherein the receiver includes a low-pass filter.

### Claim 11 (depends on 6)

The apparatus of claim 6 wherein the output is a wavelength.