Submersible N-wavelength interrogation system and method for multiple wavelength interferometers

Patent metadata

Field	Value
Publication number	US-10078050-B2
Application number	US-201615227253-A
Country	US
Kind code	B2
Filing date	Aug 3, 2016
Priority date	Jan 28, 2013
Publication date	Sep 18, 2018
Grant date	Sep 18, 2018

Abstract

In an in situ interrogation system for multiple wavelength interferometers a fringe spectrum that includes non-quadrature-spaced radiation-intensity samples is analyzed to obtain a high resolution relative phase measurement of the optical path length difference associated with the fringe spectrum. The fringe spectrum can be analyzed to obtain a fringe number and a quadrant as well, which can be combined with the relative phase measurement to obtain a high precision measurement of the absolute optical path length difference. An environmental condition corresponding to the absolute optical path length difference can be measured using the measurement of the absolute optical path length difference including salinity, pressure, density, and refractive index of a medium.

First claim

We claim:

1. A system for measuring a parameter of interest in situ using a measurement of absolute optical path length difference, the system comprising:
a radiation source adapted to emit electromagnetic radiation;
a sample space exposed to an environmental condition and adapted to produce a fringe spectrum from the electromagnetic radiation;
a detector capable of detecting the fringe spectrum; and
an analysis system comprising a receiver for receiving the fringe spectrum from the detector and a sampler in communication with the receiver for selecting a first set of non-quadrature-spaced samples of the fringe spectrum, each sample corresponding to a different wavelength of light from a plurality of wavelengths;
wherein the analysis system selects from the first set a first subset of at least three non-quadrature-spaced samples from a first fringe cycle, and a second, different subset of at least three non-quadrature-spaced samples from a second, different fringe cycle, derives a measurement of the absolute path length difference using the first and second subsets, and uses the measurement to calculate a parameter of interest.

2. The system of claim 1 , wherein the analysis system derives the measurement of the absolute path length difference based on:
(i) a base estimate of the absolute optical path length difference, based on, at least in part, the fringe spectrum, (ii) a fringe number, and (iii) a quadrant based on, at least in part, the base estimate and a reference wavelength; and
a relative phase measurement of the absolute optical path length difference using the selected non-quadrature- spaced samples by expressing each light intensity sample as a combination comprising: (i) a term based on a relative phase φ this is based on the reference wavelength and is independent of the monitored wavelengths, and (ii) a term based on a phase shift estimate δ i (L) relating to both the monitored wavelength corresponding to the light intensity sample and the base estimate of the absolute optical path length difference.

3. The system of claim 2 , wherein the analysis system further comprises:
a coarse estimator configured for: (a) selecting the reference wavelength in the plurality of wavelengths: and (b) determining: (i) the base estimate of the absolute optical path length difference, based on, at least in part, the fringe spectrum, (ii) the fringe number, and (iii) the quadrant based on, at least in part, the base estimate and the selected reference wavelength;
a relative phase estimator for determining the relative phase measurement of the absolute optical path length difference using the selected non-quadrature- spaced samples; and
an aggregator for deriving the measurement of the absolute optical path length difference by aggregating the relative phase measurement, the fringe number, and the quadrant.

4. The system of claim 1 wherein the sample space comprises an external fluid environment.

5. The system of claim 1 , wherein a number of wavelengths in the plurality of wavelengths ranges from 3 up to 4096, and the fringe spectrum comprises a plurality of fringe cycles, and a number of fringe cycles is up to 2048.

6. The system of claim 1 , wherein the parameter of interest is selected from the group comprising of salinity, pressure, density, temperature, strain, vibration, distance, refractive index of a medium, and changes thereof.

7. The system of claim 1 , wherein the plurality of wavelengths range from a low wavelength up to a high wavelength that is greater than the low wavelength by a bandwidth, the low wavelength ranges from 600 nm up to 1590 nm, and the high wavelength ranges from 610 nm up to 1600 nm; and the bandwidth ranges from 10 nm up to 200 nm.

8. The system of claim 1 , wherein the radiation source adapted to emit at least N wavelengths of electromagnetic radiation, wherein N is greater than two.

9. The system of claim 1 , wherein system is capable of measuring the parameter of interest of a body of water.

10. The system of claim 1 , wherein the system is capable of operating at a depth of at least 1 m, 50 m, 100 m, 500 m, 1,000 m, 6,000 m, and full ocean depth.

11. The system of claim 1 , wherein the system is adapted for use on a vehicle, a water sampler, a profiler, an underwater observatory, and in a sensor array.

12. The system of claim 1 , wherein the sample space comprises a sample path length between 5 mm and 200 μm.

13. The system of claim 1 further comprising one of an optical switch, an optical filter, a dichroic filter, and a second detector.

14. The system of claim 1 , wherein the system produces a high resolution absolute optical path length difference measurement of 1/1,000-th up to 1/100,000-th of a wavelength.

15. The system of claim 1 further comprising a pressure housing.

16. The system of claim 1 , further comprising:
a second sample space exposed to a second environmental condition and adapted to produce a second fringe spectrum using the electromagnetic radiation,
wherein:
the detector is adapted for detecting the second fringe spectrum;
the a receiver is adapted for receiving the second fringe spectrum from the detector;
the sampler is adapted for selecting a second set of non-quadrature-spaced samples of the second fringe spectrum; and
the analysis system derives a measurement of a second absolute path length difference and uses the measurement of the second absolute path length difference to calculate a second parameter of interest corresponding to the second environmental condition.

Assignees

• Woods Hole Oceanographic Inst

Inventors

• Kapit Jason A
• Schmitt Raymond W
• Farr Norman E

Classifications

• G01B9/02041

  characterised by particular imaging or detection techniques · CPC title

• G01N21/25

  Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands · CPC title

• G01B9/02044 Primary

  Imaging in the frequency domain, e.g. by using a spectrometer · CPC title

• G01B9/0209

  Low-coherence interferometers · CPC title

• G01N21/45 Primary

  using interferometric methods; using Schlieren methods · CPC title