Method and system for measuring optical properties of a medium using digital communication processing techniques

• US 7,995,917 B2
• Filed: 09/24/2009
• Issued: 08/09/2011
• Est. Priority Date: 11/06/2003
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: Neff, Benjamin R., McAdoo, James Alexander, Mendenhall, Scott Nelson, Dobbs, Michael E.
• Primary Examiner(s): Liu; Li
• Application Number:
  US12/566,121
• Publication Number:
  US 20100070199A1
• Time in Patent Office: 684 Days
• Field of Search: 398 25- 27, 356/432, 250/343, 702/28
• US Class Current: 398/25
• CPC Class Codes: G01S 7/4802 using analysis of echo signal for target characterisation; Target signature; Target cross-section

Abstract

A system for measuring properties of a medium includes an electromagnetic generator for forming a CW carrier, a digital encoder for forming a digital message, and a modulator for modulating the CW carrier with the digital message to form a digitally modulated CW carrier. The medium provides a channel for propagating the digitally modulated CW carrier. The system further includes a receiver configured to receive the propagated, digitally modulated CW carrier, and a processor for measuring at least one property of the medium. The medium may be disposed within a gaseous atmosphere, a body of water, or a cell of a laboratory.

Claims

1. A system for chemical identification of a medium comprising:

an online laser for generating an online CW carrier,

an offline laser for generating an offline CW carrier, the offline CW carrier including a wavelength different from a wavelength of the online CW carrier,

a PN encoder for forming a PN encoded word,

a PN′

encoder for forming a PN′

encoded word, the PN′

encoded word being orthogonal to the PN encoded word,

modulators for, respectively, modulating the online and offline CW carriers with the PN and PN′

encoded words,

a medium for propagating the modulated online and offline CW carriers,

a receiver configured to detect the propagated, modulated online and offline CW carriers to form a detected signal,

a processor configured to correlate the detected signal with the PN and PN′

encoded words, and

the processor configured to measure a property of the medium based on the correlated detected signal with the PN and PN′

encoded words.

2. The system of claim 1 wherein

the medium is disposed within a gaseous atmosphere, a body of water, or a cell of a laboratory.

3. The system of claim 1 including

a wavelength controller, coupled to the online laser, for modifying a wavelength of the online CW carrier, and

wherein the medium includes an absorption line, and

the wavelength controller is configured to modify the wavelength of the online CW carrier by scanning about the absorption line.

4. The system of claim 1 wherein

the receiver includes a reference detector for forming a reference signal of the PN and the PN′

encoded words,

the processor is configured to correlate the reference signal with the PN and the PN′

encoded words, and

the processor is configured to provide a measure of the effect of propagation through the medium, based on (a) correlation of the detected signal and (b) correlation of the reference signal, respectively, with the PN and PN′

encoded words.

5. A system for chemical identification of a medium comprising:

a laser for generating an optical beam,

a digital modulator for modulating the optical beam to form a digitally modulated optical carrier,

a transmitter for transmitting the digitally modulated optical carrier through the medium,

a receiver for detecting the digitally modulated optical carrier from the medium to form a detected signal, and

a processor for measuring at least one property of the medium based on the detected signal,

wherein the processor includes code generators for forming a first encoded word and a second encoded word,

the laser includes an online laser and an offline laser for generating, respectively, an online beam and an offline beam,

the digital modulator includes a first modulator for modulating the online beam using the first encoded word, and a second modulator for modulating the offline beam using the second encoded word,

a combiner for combining the modulated online and offline beams to form the digitally modulated optical carrier, and

the processor including a digital matched filter for correlating the detected signal with the first and second encoded words.

6. The system of claim 5 wherein

the receiver includes a photon counter for counting photons of the digitally modulated optical carrier, received from the medium, to form the detected signal.

7. The system of claim 6 wherein

the receiver includes another photon counter for counting photons of the digitally modulated optical carrier, transmitted toward the medium, to form a reference signal, and

the processor includes a calculator for determining an effect of propagation of the digitally modulated optical carrier through the medium, based on photons counted by both of the photon counters.

8. A method for chemically identifying a medium comprising:

(a) generating an online CW carrier;

(b) generating an offline CW carrier, the offline CW carrier including a wavelength different from a wavelength of the online CW carrier;

(c) forming a PN encoded word;

(d) forming a PN′

encoded word, the PN′

encoded word being orthogonal to the PN encoded word;

(e) modulating the online and offline CW carriers with the PN and PN′

encoded words, respectively;

(f) propagating the modulated online and offline CW carriers into a medium;

(g) receiving the propagated, modulated online and offline CW carriers to form a detected signal;

(h) correlating the detected signal with the PN and PN′

encoded words; and

(i) measuring a property of the medium, based on the correlated detected signal with the PN and PN′

encoded words.

9. The method of claim 8 including

modifying a wavelength of the online CW carrier;

and

controlling the wavelength of the online CW carrier to include an absorption line of the medium.

10. The method of claim 8 including

forming a reference signal of the PN and the PN′

encoded words; and

wherein

step (h) includes correlating the reference signal with the PN and the PN′

encoded words; and

step (i) includes measuring an effect of propagation through the medium, based on (1) correlation of the detected signal and (2) correlation of the reference signal, respectively, with the PN and PN′

encoded words.

11. A method for chemically identifying a medium comprising:

(a) generating an optical beam;

(b) modulating the optical beam to form a digitally modulated optical carrier;

(c) transmitting the digitally modulated optical carrier through the medium;

(d) receiving the digitally modulated optical carrier from the medium to form a detected signal; and

(e) measuring at least one property of the medium based on the detected signal,

wherein step (a) includes generating an online beam and an offline beam;

step (b) includes forming a first encoded word and a second encoded word,

modulating the online beam using the first encoded word, and modulating the offline beam using the second encoded word; and

combining the modulated online and offline beams to form the digitally modulated optical carrier; and

step (d) includes correlating the detected signal with the first and second encoded words.

12. The method of claim 11 wherein

step (d) includes counting photons of the digitally modulated optical carrier, received from the medium, to form the detected signal.

13. The method of claim 12 wherein

step (d) includes counting photons of the digitally modulated optical carrier, transmitted toward the medium, to form a reference signal;

and

step (e) includes determining an effect of propagation of the digitally modulated optical carrier through the medium, based on photons counted in step (d).