Optical shutter, spectrometer and method for spectral analysis

• US 6,191,860 B1
• Filed: 08/06/1999
• Issued: 02/20/2001
• Est. Priority Date: 02/06/1998
• Status: Expired due to Fees

• Current Assignee: OrSense Ltd.
• Original Assignee: OrSense Ltd.
• Inventors: Klinger, Leonid, Fine, Ilya
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US09/370,131
• Time in Patent Office: 564 Days
• Field of Search: 356/310, 356/330, 356/419
• US Class Current: 356/419
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0213 using attenuators
• CPC Class Codes: G01J 3/0232 using shutters

Abstract

An attenuating optical shutter for high speed spectral analysis of an optical radiation band so as to derive N wavelength-dependent portions thereof. The attenuating optical shutter incorporates an optical shutter body including N shutter segments, each selectably switchable between a first substantially transparent and a second substantially opaque optical state, and a multi-zone attenuator comprising N optical attenuating zones each having a different predetermined wavelength-dependent attenuation characteristic. Each of the shutter segments is optically interconnected with a respective one of the N optical attenuating zones of the multi-zone attenuator thus forming N respective cells of the attenuating optical shutter. Such an attenuating optical shutter finds particular application in a spectrometer. A method for determining the spectral function of a sample using the attenuating optical shutter is also described.

Claims

1. An attenuating optical shutter suitable for high speed spectral analysis of a band of optical radiation outgoing from a turbid medium, and capable of deriving N wavelength-dependent portions of said optical radiation band, said attenuating optical shutter being in the shape of a two-dimensional array and incorporating:

an optical shutter body including N segments, each selectively switchable between a first substantially transparent and a second substantially opaque optical state, and

a multi-zone attenuator comprising N optical wide band attenuating zones each having a different predetermined wavelength-dependent attenuation characteristic,

wherein each of the shutter segments is optically inter-connected with a respective one of the N optical attenuating zones of the multi-zone attenuator, thus forming N respective cells of the attenuating optical shutter.

2. The attenuating shutter according to claim 1, wherein said N segments of the optical shutter are capable of being successively actuated, so that at any given moment, only one of the N segments is in its first state.

3. The attenuating shutter according to claim 1, wherein each of said N segments of the optical shutter is capable of being switched from the first to the second state and vice versa at a pre-selected frequency.

4. The attenuating shutter according to claim 1, wherein respective ones of the N shutter segments and of the N optical attenuating zones have identical geometrical shapes and are mutually aligned.

5. The attenuating shutter according to claim 4, wherein said optical shutter body is affixed to said multi-zone attenuator.

6. The attenuating shutter according to claim 5, wherein the optical shutter body and the multi-zone attenuator are glued one to the other.

7. The attenuating shutter according to claim 1, wherein mutual positions of the optical shutter body and the multi-zone attenuator are such that each of the N segments of the optical shutter body lies on one and the same optical path with the corresponding optical attenuation zone of the multi-zone attenuator, while being spaced therefrom.

8. The attenuating shutter according to claim 1, wherein each of the N segments of the optical shutter body is interconnected to a respective one of the N optical attenuation zones of the multi-zone attenuator by means of at least one optical fiber.

9. The attenuating shutter according to claim 1, wherein the multi-zone attenuator precedes the optical shutter with respect to a direction of an optical beam.

10. The attenuating shutter according to claim 1, wherein the multi-zone attenuator follows the optical shutter with respect to the direction of an optical beam.

11. The attenuating shutter according to claim 1, wherein the optical shutter is integrally combined with the multi-zone attenuator, the N segments being selectably switchable between-the first and the second optical states so as to serve as N respective optical attenuating zones each having a different predetermined wavelength-dependent attenuation characteristic.

12. The attenuating shutter according to claim 1, wherein the optical shutter body is manufactured from a ferroelectric liquid crystal.

13. The attenuating shutter according to claim 1, specifically designed for spectral analysis of biological objects.

14. The attenuating shutter according to claim 13, comprising attenuating zones active in a near infrared range.

15. A spectrometer for spectral analysis of turbid media, said spectrometer comprising the attenuating shutter according to claim 1.

16. The spectrometer according to claim 15, comprising:

an optical detector for receiving said optical radiation and producing an analog signal,

an analog-to-digital (A/D) converter coupled to an output of the optical detector for converting the analog signal to equivalent digital signals,

a computing unit coupled to the A/D converter for processing the digital signals so as to derive spectral data; and

a controller for controlling activation of said attenuating shutter and for controlling other components of the spectrometer.

17. The spectrometer according to claim 16, wherein:

said attenuating shutter is controllable such that the N zones of the optical shutter body of the attenuating shutter are activated successively, so that at any given moment only one zone is in the first state;

the optical detector is controlled synchronously for successively detecting light intensities of the N wavelength-dependent portions of the optical radiation emanating from the attenuating shutter; and

the A/D converter is adapted for synchronously receiving the analog signals from the optical detector.

18. The spectrometer according to claim 16, wherein:

said optical shutter body of the attenuating shutter is controllable so as to activate each of the N optical zones thereof at a pre-selected carrier frequency, thus applying pre-selected frequency modulation to the optical radiation portion passing through a particular cell of the shutter, thereby allowing for simultaneous passage of the N optical portions through the attenuating shutter in real time; and

the optical detector is linked to an electronic circuit for separating the detected integral signal into N constituent signals according to said N carrier frequencies for further demodulating and digitizing of said constituent signals.

19. The spectrometer according to claim 16, wherein said optical detector follows the attenuating shutter along a direction of the optical radiation.

20. The spectrometer according to claim 19, wherein said detector is directly coupled to said attenuating shutter.

21. The spectrometer according to claim 16, wherein the medium to be investigated is insertable between said attenuating shutter and said optical detector.

22. The spectrometer according to claim 15, additionally equipped with a light source.

23. The spectrometer according to claim 15, specifically designed for performing spectral analysis of biological objects.

24. A method of determining a spectral function of a turbid medium sample, comprising the following steps:

(a) providing the attenuating shutter according to claim 1, with N cells and having preliminarily defined wavelength-dependent attenuation characteristics for each of N zones of the multi-zone attenuator;

(b) illuminating said attenuating shutter with an optical radiation band having a known optical composition;

(c) actuating said attenuating shutter controllably for obtaining N wavelength-dependent portions of said optical radiation band;

(d) illuminating said sample with said N wavelength-dependent portions of said optical radiation band;

(e) providing N measurements of intensity of N respective optic portions acquired from the sample; and

(f) calculating the spectral function of said sample based on the obtained N measurements of intensity and the preliminarily defined wavelength-dependent attenuation characteristics.

25. The method according to claim 24, wherein said predetermined wavelength-dependent characteristics for each of, N attenuating zones of the attenuating shutter is comprised of a plurality of specific attenuation ratios actual for a selected plurality of wavelengths characteristic for the spectrum, respectively.

26. The method according to claim 24, further comprising an additional step of preliminary calibration for determining said wavelength dependent characteristics for each of the N cells;

the calibration being effected by illuminating the attenuating shutter with a known spectrum of optical radiation through a medium having known optical properties.

27. The method according to claim 24, wherein the spectral function is determined in respect of M wavelengths;

the wavelength-dependent attenuation characteristics of each particular cell of the attenuating shutter comprises M preliminarily defined wavelength-dependent attenuation ratios each in respect of a corresponding zone of the multi-zone attenuator, whereby M*N of said ratios are preliminarily defined; and

the spectral function of said optical radiation band is calculated based on the obtained N measurements of intensity and the preliminarily defined M*N wavelength-dependent attenuation ratios where M is not greater than N.

28. The method according to claim 27, wherein the spectral function substantially conforms to the following system of equations $\Delta$



 



I1=∑

i=1M

Ai

ϕ

1

(λ

i)$\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>I_j=\underset{i=1}{\overset{M}{\sum <br><br>}}<br><br>A_i<br><br>{\mathrm{\varphi <br><br>}}_j<br><br>\left({\mathrm{\lambda <br><br>}}_i\right)$$\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>I_N=\underset{i=1}{\overset{M}{\sum <br><br>}}<br><br>A_i<br><br>{\mathrm{\varphi <br><br>}}_N<br><br>\left({\mathrm{\lambda <br><br>}}_i\right)$

where;

N—

the number of attenuation zones in the attenuating shutter, which may be obtained therefrom;

j—

a running number of an attenuating zone in the shutter, (1≦

j≦

N);

M—

the quantity of spectral lines which is chosen for spectral analysis, M≦

N;

i—

a running number of a spectral line (1≦

i≦

M);

λ

_i—

a wavelength corresponding to a specific spectral line i;

Δ

I_j—

intensity of one specific wavelength-dependent optic portion detected by the detector and registered in the computer;

A_i—

intensity of a specific spectral line;

φ

_j(λ

_i)—

an attenuation ratio of the attenuation zone j in the attenuation shutter regarding the wavelength λ

_i.

29. The method according to claim 24 for determining the spectral function along the full wavelength spectrum of the optical radiation band under examination, wherein calculation of the spectral function is accomplished by means of mathematical approximation thereof, applying a procedure of error minimization and further restoring the spectral function.

30. The method according to claim 29, wherein the approximation of the spectral function and the error minimization procedure are a polynomial approximation and Gauss'"'"' procedure, respectively.

31. The method according to claim 30, wherein said spectral function is the spectral function of a biological object.

32. The method according to claim 24, intended for determining concentration of a predetermined substance in the sample and comprising illuminating the sample or the attenuating shutter by said electromagnetic radiation band having wavelength composition initially restricted to wavelengths being characteristic of the spectral function of said substance.

33. The method according to claim 32, intended for determining the hemoglobin or glucose concentration in blood, wherein the restricted radiation is in the near infrared range.