Noninvasive birefringence compensated sensing polarimeter

• US 20050154269A1
• Filed: 01/12/2005
• Published: 07/14/2005
• Est. Priority Date: 01/13/2004
• Status: Active Grant

• Current Assignee: University of Toledo
• Original Assignee: University of Toledo
• Inventors: Cameron, Brent D.
• Granted Patent: US 7,245,952 B2
• Time in Patent Office: Days
• US Class Current: 600/319
• CPC Class Codes: A61B 3/1225 using coherent radiation
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/14555 specially adapted for the eye fundus
• CPC Class Codes: A61B 5/14558 by polarisation

Abstract

The present invention relates to a system and method for compensating for the effects of birefringence in a given sample and employs an optical birefringence analyzer to sense the real-time birefringence contributions and then provides a feedback signal to a compound electro-optical system that negates the birefringence contributions found in the given sample. The birefringence contribution vanishes, thus significantly reducing the main error component for polarimetric measurements.

Claims

1. A noninvasive birefringence compensated sensing polarimeter used to measure and compensate for birefringence when measuring glucose levels in a sample comprising of:

an optical birefringence analyzer configured to sense real-time birefringence contributions in a sample and configured to provide a feedback signal to a compound electro-optical system, and

a compound electro-optical system configured to receive the signal from the birefringence analyzer and configured to negate the contributions found in the sample.

2. A polarimeter according to claim 1 wherein the sample is a patient'"'"'s eye or other associated tissue.

3. A polarimeter according to claim 1 wherein the sample is aqueous humor of a patient'"'"'s eye.

4. A polarimeter according to claim 1 wherein the sample is tissue from a thin-skin area of a patient.

5. A polarimeter according to claim 1 wherein the sample is tissue from a patient'"'"'s ear, nose or thin skin between fingers or toes.

6. A birefringence sensing polarimeter according to claim 1 wherein the birefringence analyzer includes a means for measuring birefringence present in a sample, and wherein the compound electro-optical system includes a means for computing a value of retardance that needs to be applied as birefringence compensation in order to determine the optical rotation polarization vector due to the optically active sample.

7. A polarimeter according to claim 6 wherein rotation polarization vector is an optical rotation polarization vector and wherein the sample contains an optically active components.

8. A polarimeter according to claim 1 configured to make the birefringence contribution vanish, thus significantly reducing a main error component for polarimetric measurements of optical activity.

9. A polarimeter according to claim 1 wherein the glucose analyzer comprises a rotation measuring means, at least one Faraday modulator, at least one Faraday compensator, at least one analyzer, at least one detector, at least one amplifier, and at least one controller.

10. A polarimeter according to claim 1 wherein the compound electro-optical system comprises at least one means for computing the value of retardance that needs to be applied to the birefringence compensator, at least one circular analyzer, at least one detector and at least one controller.

18. The system of claim 1, wherein the sample comprises glucose present in an animal'"'"'s eye.

11. A noninvasive birefringence sensing polarimeter comprising a means for measuring optical polarization rotation of a substance in a sample, and a means for computing the value of retardance that needs to be applied to a birefringence compensator in order to eliminate any birefringence contribution due to a sample.

12. A noninvasive birefringence sensing polarimeter system comprising:

at least one light source,

at least one polarizer,

at least one sample containing the substance to be measured,

at least one birefringence compensator that applies a retardance that cancels out any effect due to birefringence,

at least one beam splitter,

at least one means for measuring optical polarization rotation of the sample, and

at least one means for computing the value of retardance that needs to be applied to the birefringence compensator.

13. The system of claim 12, wherein the rotation measuring means comprises at least one Faraday modulator, at least one Faraday compensator, at least one analyzer, at least one detector, at least one amplifier, and at least one controller.

14. The system of claim 12, wherein at least one means for computing the value of retardance that needs to be applied to the birefringence compensator comprises at least one circular analyzer, at least one detector, and at least one controller.

15. The system of claim 14 wherein the value of retardance(δ

) is computed from the equation;

16. The system of claim 14 wherein the retardance is computed and sent as an input into a compensation portion of the controller wherein the compensation algorithm can be represented by a difference equation where the retardance applied to the birefringence compensator is the computed retardance, and wherein upon completion, there is no circularly polarized component and only linearly polarized light and any birefringence is compensated for.

17. The system of claim 14, wherein the retardance is computed and sent as an input into a compensation portion of the controller wherein the compensation algorithm can be represented by the difference equation

y(n)=x(n)+y(n−

1)

where ‘

y’

is the retardance applied to the birefringence compensator and ‘

x’

is the computed retardance, and wherein upon completion, there is no circularly polarized component and only linearly polarized light and any birefringence is compensated for.

19. A corneal birefringence compensated glucose sensing system comprising:

a polarizer aligned with a fast axis of the initial retarder to minimize effects of anterior corneal birefringence wherein the polarized laser beam passes through the glucose sample and the posterior retarder with a retardance (δ

),

a beam splitter wherein, in order to compensate for the corneal birefringence before determining glucose rotation, the output light from the sample and retarder is separated into two paths by the beam splitter such that one beam is passed through an analyzer capable of characterizing the four Stokes parameters (I,Q,U,V), and

a modulator for receiving a second of the split beams and for modulating the linear polarization vector of the laser and glucose contribution.

20. A birefringence compensation system 50 comprising:

1) a light source 52,

2) a polarizer 54 for polarizing a light beam from the light source and for orienting the beam such that maximum transmission is obtained, wherein the polarizer 54 is aligned with a fast axis of an initial retarder, which minimizes the effect of any birefringence is a given sample,

3) at least one sample 56,

4) an electro-optical retarder that accounts for any birefringence which induces a phase retardance (δ

) in the polarized laser beam resulting in a change in the state of polarization from linearly polarized light to elliptically polarized light,

5) a birefringence compensator 60 for applying a retardance that cancels out any effect due to the birefringence,

6) a non-polarizing laser line beam splitter 62 for splitting the elliptically polarized light is into two beams,

7) a circular analyzer 64 which receives a first of the split beams, wherein the circular analyzer comprises a quarter wave plate followed by a 45°

linear polarizer, capable of characterizing the circularly polarized Stokes parameter ‘

V’

,

8) a silicon photo diode detector 66 which receives the first directed beam,

9) a feedback controller 70 for receiving as input the output from the detector 66, whereby the retardance is computed and sent as an input into a compensation portion of the controller wherein the compensation algorithm is could be represented by the difference equation y(n)=x(n)+y(n−

1) where ‘

y’

is the retardance applied to the birefringence compensator and ‘

x’

is the computed retardance such that, upon completion, there is no circularly polarized component and only linearly polarized light and any birefringence is compensated for;

10) a Faraday modulator 80 for receiving a second of the split beams and for modulating the linear polarization vector of the laser,

11) a Faraday compensator 82 for providing feedback compensation by nullifying or eliminating any rotation of the polarization vector due to the sample,

12) an analyzer 84 having its transmission axis oriented perpendicular to that of the initial polarizer 54, the analyzer 84 transforming the modulated polarization vector into intensity modulation according to Malus'"'"' law,

13) a silicon photo diode detector 86 which receives the directed second beam and which provides an output comprising a voltage proportional to the detected light intensity,

14) a wide bandwidth amplifier for amplifying the output of the detector 86,

15) a lock-in amplifier and controller 90 for receiving an amplified output from the amplifier whereby the lock-in amplifier measures the signal component present at the modulation frequency, while rejecting low and high frequency electro-magnetic noise, and

16) a power supply 92 wherein the output of the controller 90 is applied to the Faraday compensator 82 through the power supply 92 such that, upon completion, the output voltage of the controller 90 is proportional to the concentration of the sample.

21. The system of claim 20 wherein the sample contains an optically active substance.

22. The system of claim 20, wherein the sample contains glucose or other optically active molecule(s).

23. The system of claim 20 wherein a value of retardance (δ

) is computed from the equation;

24. A method for noninvasive birefringence sensing used to measure and compensate for birefringence when measuring glucose levels in a sample comprising the steps of:

configuring an birefringence analyzer to sense real-time corneal birefringence contributions in a sample;

configuring the analyzer to provide a feedback signal to a compound electro-optical system,

configuring a compound electro-optical system to receive the signal from the birefringence analyzer; and

configuring the electro-optical system to negate the contributions found in the sample.

25. A method according to claim 24 wherein birefringence analyzer is an optical birefringence analyzer, the sample is a patient'"'"'s eye, the birefringence contributions are corneal birefringence contributions and including the steps of configuring the optical analyzer to measure corneal birefringence contributions and configuring the electro-optical system to determine an optical rotation polarization vector due to the sample.

26. A method according to claim 25 including the step of configuring the compensating to make the birefringence contribution vanish, thus significantly reducing a main error component for polarimetric measurements.

27. A method for noninvasive birefringence sensing comprising the steps for measuring birefringence present in a sample, and wherein the compound electro-optical system includes a means for computing a value of retardance that needs to be applied as birefringence compensation in order to determine the optical rotation polarization vector due to the optically active sample.

28. A method for overcoming corneal birefringence comprising:

using a circular Stokes parameter ‘

V’

for measuring birefringence compensation, and measuring glucose concentration using a Faraday based glucose sensing polarimeter.

29. A non-invasive in vivo method for sensing a concentration of an optically active substance in an animal'"'"'s eye wherein the method comprises the steps of:

aligning a polarizer with a fast axis of the initial retarder to minimize effects of anterior corneal birefringence wherein a polarized laser beam passes through the eye with an overall retardance (δ

), and

splitting the laser beam wherein, in order to compensate for the posterior birefringence before determining glucose rotation, output light from the sample and retarder is separated into two paths by the beam splitter such that one beam is passed through an analyzer capable of characterizing at least one of four Stokes parameters (I,Q,U,V), and

receiving a second of the split beams by a modulator and modulating the linear polarization vector.

30. A non-invasive in vivo method for sensing a concentration of an optically active substance comprising the steps, in sequence of:

providing at least one beam of light,

passing the beam through at least one polarizer,

passing the beam through at least one sample,

passing the beam through at least one birefringence compensator,

passing the beam through at least one beam splitter to divide the beam into at least two beams of light,

measuring for glucose rotation by passing at least one split beam of light through at least one Faraday modulator, at least one compensation Faraday rotator, at least one analyzer, and at least one detector, and

computing the value of retardance that needs to be applied at the birefringence compensator by passing at least one of the split beams of light through a circular analyzer, a detector, and a controller, whereby upon completion there is no circularly polarized component and only linearly polarized light and birefringence is compensated for.

31. The system of claim 30, wherein, for glucose sensing, the birefringence compensator cancels out any retardance due to the sample-such that there is no birefringence effect due to the sample.

32. A noninvasive birefringence sensing polarimeter comprising a means for measuring optical polarization rotation of a substance in a sample, and a means for computing the value of retardance that needs to be applied to a birefringence compensator in order to eliminate any birefringence contribution due to a sample, wherein the birefringence compensator includes an anterior birefringence compensator and a posterior birefringence compensator.

33. A noninvasive birefringence compensated sensing polarimeter used to measure and compensate for birefringence when measuring glucose levels in a sample comprising of:

an anterior birefringence compensator configured to sense real-time birefringence contributions in a sample and configured to provide a feedback signal to a compound electro-optical system,

a posterior birefringence compensator configured to sense real-time birefringence contributions in a sample and configured to provide a feedback signal to a compound electro-optical system, and

a compound electro-optical system configured to receive the signal from the birefringence compensator and configured to negate the contributions found in the sample.

34. A birefringence sensing polarimeter according to claim 33 wherein the birefringence compensators include a means for measuring birefringence present in a sample, and wherein the compound electro-optical system includes a means for computing a value of retardance that needs to be applied as birefringence compensation in order to determine the optical rotation polarization vector due to the optically active sample.

35. A noninvasive birefringence sensing polarimeter system comprising:

at least one light source,

at least one polarizer,

at least one anterior birefringence compensator that applies a retardances that cancels out any effect due to anterior birefringence,

at least one sample containing the substance to be measured,

at least one posterior birefringence compensator that applies a retardances that cancels out any effect due to posterior birefringence,

at least one means for measuring optical polarization rotation of a sample, and

at least one means for computing the value of retardance that needs to be applied to the birefringence compensators.

36. The system of claim 35 wherein at least one means for computing the value of retardance that needs to be applied to the birefringence compensators comprises at least one circular analyzer, at least one detector, and at least one controller.

37. The system of claim 36 wherein the system is a three-axis birefringence compensator and the retardance is computed and sent as an input into a compensation portion of the controller to negate sample birefringence effects.

38. A noninvasive birefringence sensing polarimeter system comprising:

at least one light source,

at least one polarizer,

at least one anterior birefringence compensator that applies a

retardances that cancels out any effect due to anterior sample birefringence,

at least one sample containing the substance to be measured,

at least one posterior birefringence compensator that applies a retardances that cancels out any effect due to posterior sample birefringence, and

at least one means for measuring optical polarization rotation of a sample.

39. The system of claim 38 wherein at least one means for compensating for the sample birefringence occurs through analysis of the detected signal wherein both the anterior and posterior birefringence compensators are modulated at different frequencies and operated in an open-loop approach.