Interferometric sensor for characterizing materials

• US 20050190372A1
• Filed: 08/16/2004
• Published: 09/01/2005
• Est. Priority Date: 08/14/2003
• Status: Active Grant

• Current Assignee: University of Central Florida (State University System of Florida)
• Original Assignee: University of Central Florida (State University System of Florida)
• Inventors: Dogariu, Aristide
• Granted Patent: US 7,307,734 B2
• Time in Patent Office: Days
• US Class Current: 356/479
• CPC Class Codes: A61B 2562/0242 for varying or adjusting the optical path length in the tissue
• CPC Class Codes: A61B 5/0066 Optical coherence imaging
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/14558 by polarisation
• CPC Class Codes: G01N 21/474 Details of optical heads therefor, e.g. using optical fibres
• CPC Class Codes: G01N 21/49 within a body or fluid

Abstract

An integrated optical sensor, using low coherence interferometry, is capable of determining analyte concentration in a material sample based on absorption, scattering and polarization. The sensor includes one or more light collectors, with each collector having a separation distance from the region where the sample is illuminated by the source. The light backscattered from the sample is combined with reference arm light at the same optical path length for each light collector. The intensity of interference may be correlated with the concentration of an analyte in the material, for example the glucose concentration in a turbid medium like skin. The sensor operation can be based on fiber optics technology, integrated optics, or a combination of these. The operation is such that the spectrally resolved scattering and absorption coefficients can be measured simultaneously. In addition, the operation of the sensor can be synchronized with other sensors, for example temperature, pressure, or heartrate.

Claims

1. An interferometer based sensor comprising:

a low coherence light source and a light splitter positioned to direct light from said source to a sample and to a reference arm;

light from said source backscattered by said sample;

a reference arm capable of being set to a select optical path length;

a first sample light collector positioned to collect a first backscattered light from said source interacting with said sample, a first detector generating a first signal in response to interference between the first backscattered light and light from said reference arm at said optical path length coupled together by a first light combiner;

a second sample light collector, said second sample light collector separated from said first sample light collector, said second sample light collector positioned to collect backscattered light from said source interacting with said sample and a second detector generating a second signal, said second signal resulting from interference between said backscattered light and light from said reference arm at said optical path length coupled together by a second light combiner; and

a processor that determines the absorption and scattering of the sample from said first signal and said second signal.

2. The sensor of claim 1 further having a housing, said housing providing said light source to said sample and having said first and second sample light collectors positioned within said housing.

3. The sensor of claim 1 wherein the separation between the first and second light collectors provides light having two trajectories in said sample.

4. The sensor of claim 1 wherein the first sample light collector is disposed apart from said light source interacting with said sample.

5. The sensor of claim 2 wherein said housing comprises a portion of an endoscope.

6. The sensor of claim 1 wherein the separation of the second light collector samples light having a trajectory dominated by sample absorption.

7. The sensor of claim 1 including optical fibers.

8. The sensor of claim 1 wherein the optical delays are fixed, adjustable, or includes a combination of these.

9. The integrated optical sensor of claim 1 having one or more light sources, each source having a different wavelength, each source having a first sample light collector and a second sample light collector.

10. The sensor of claim 1 including a plurality of light collectors, each said light collector having a different separation distance from the source light interacting with the sample.

11. The sensor of claim 1 wherein said sensor includes one or more polarizers.

18. The method of claim 11 having one or more detectors to measure the intensity of interference between reference arm light and light backscattered from one or more regions at a distance from the region where said light is directed on said sample.

12. A method of characterizing a sample with an interferometer comprising:

setting a reference arm of an interferometer to an optical delay;

propagating low coherent light from a source into a light splitter, said light splitter directing a portion of said light to a region of said sample to generate backscattered light and directing a portion of said source light to the reference arm;

collecting backscattered light having the same optical delay at one or more regions on the sample away from said region that the source light is directed into said sample;

determining the intensity of interference between said reference arm light and the light backscattered from the two or more regions on the sample, said backscattered light having the same optical delay;

calculating an absorption coefficient and a scattering coefficient of the sample from said interference intensities.

13. The method of claim 12 wherein the light is directed onto the sample and backscattered light is collected using one or more transceivers.

14. The method of claim 12 wherein the reference arm is scanned through a plurality of optical delays.

15. The method of claim 12 wherein the light backscattered from one or more points on said sample have different trajectories in the sample.

16. The method of claim 12 further comprising correlating the absorption coefficient and a scattering coefficient to the concentration of an analyte in a sample.

17. The method of claim 12 wherein the sample is heterogeneous.

19. The method of claim 16 wherein said analyte is glucose and said sample is skin.

20. An integrated optical sensor for glucose monitoring in biological tissue, comprising:

means for generating a low coherence light source;

means for controlling the length of the optical path;

means for discriminating between scattering and absorption coefficients;

means for recording spectral measurements over a limited range; and

means for determining glucose concentrations based on the spectral measurements.

21. The integrated optical sensor of claim 20, wherein the biological tissue is human skin.

22. The integrated optical sensor of claim 20, wherein the low coherence light source includes a super luminescent diode.

23. The integrated optical sensor of claim 20, wherein the length of the optical path is controlled by an optical delay line

24. The integrated optical sensor of claim 20 wherein one or more sources, each source having a different wavelength is used.

25. The integrated optical sensor of claim 20, wherein the sensor is designed to limit the interference between light scattering and absorption.

26. The integrated optical sensor of claim 20, wherein the source for generating a low coherence light includes an optical fiber based transmission medium.

27. A system for monitoring glucose concentration in biological specimen using the integrated optical sensor of claim 20.

28. The system for monitoring glucose concentration of claim 27, wherein the monitoring is non-invasive.

29. The system for monitoring glucose concentration of claim 27, wherein the monitoring can be synchronized with the heartbeat of the biological specimen.

30. The system for monitoring glucose concentration of claim 27, wherein the biological specimen is a human being.

31. A method for determining glucose concentration using an integrated optical sensor, comprising:

generating a low coherence light source;

controlling the length of the optical path;

discriminating between light scattering and absorption coefficients;

recording spectral measurements over a limited range;

determining glucose concentration based on the spectral measurements.

32. The method of claim 31, wherein the glucose concentration is determined in biological tissue.

33. The method of claim 32, wherein the biological tissue is human skin.

34. The method of claim 31, wherein the low coherence light source includes a super luminescent diode.

35. The method of claim 31, wherein the length of the optical path is controlled by an optical delay line.

36. An interferometer based sensor comprising:

a low coherence light source and a reference arm of said interferometer set to an optical delay;

a first light splitter positioned to propagate a portion of said source light from said light source to a first region of said sample and a portion of said light to the reference arm;

said first light splitter collecting backscattered light from said first region of said sample and combining it with light from said reference arm;

a second light splitter positioned to propagate a portion of said source light from said light source to a second region of said sample and a portion of said light to a reference arm;

said second light splitter collecting backscattered light from said second region of said sample and combining it with light from said reference arm;

said second region separated from said first region on said sample;

a first detector that measures the intensity of interference between backscattered light from said first region of said sample and light from said reference arm at the optical delay, said first detector generating a first signal proportional to said interference intensity of said first region, and a second detector that measures the intensity of interference between backscattered light from said second region of said sample and light from said reference arm at the optical delay, said second detector generating a second signal proportional to the interference intensity of said second region;

a processor to determine the absorption, scattering, or both of the sample from said first signal and said second signal.

37. The sensor of claim 36 wherein said sensor comprises a portion of an endoscope or a catheter.

38. The sensor of claim 36 wherein the position of the light collector samples light having a trajectory dominated by sample absorption.

39. The sensor of claim 36 including single mode optical fibers, polarization maintaining optical fibers or a combination of these optical fibers.

40. The sensor of claim 36 including polarizers.

41. The sensor of claim 36 wherein the optical delay of the reference arm is adjustable.

42. The sensor of claim 36 wherein the separation distance between the first and second region is adjustable.

43. The sensor of claim 36 wherein the separation of the first and second regions results in two different light trajectories in said sample.