Multi mode fibre perturber

• US 8,411,273 B2
• Filed: 11/12/2007
• Issued: 04/02/2013
• Est. Priority Date: 11/29/2006
• Status: Active Grant

• Current Assignee: Cascade Technologies Holdings Limited (Emerson Electric Company)
• Original Assignee: Cascade Technologies Ltd. (Emerson Electric Company)
• Inventors: Howieson, Iain, McCulloch, Michael
• Primary Examiner(s): Toatley, Gregory J
• Assistant Examiner(s): VALENTIN II, JUAN D
• Application Number:
  US12/516,936
• Publication Number:
  US 20100067013A1
• Time in Patent Office: 1,968 Days
• Field of Search: None
• US Class Current: 356/437
• CPC Class Codes: G01N 2021/3129 Determining multicomponents by multiwavelength light
• CPC Class Codes: G01N 2021/399 Diode laser
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 2201/0697 Pulsed lasers
• CPC Class Codes: G01N 2201/084 Fibres for remote transmission
• CPC Class Codes: G02B 6/14 Mode converters

Abstract

An optical arrangement comprising a multi-mode fiber (16) for carrying single mode laser light (12); a randomizer (18) for randomizing spatial modes supported by the fiber and means for averaging, out the randomized spatial modes to recover the single spatial mode.

Claims

1. An optical arrangement for sensing a gas, said optical arrangement comprising:

a quantum cascade chirped laser that outputs a wavelength chirp for providing a wavelength scan;

a multi-mode fiber positioned between said laser and a target area and having a first end optically coupled to said laser, wherein said multi-mode fiber is configured for transmitting light from the laser to and/or from the target area for sensing a gas located at the target area;

a randomizer adjacent said multi-mode fiber for randomizing spatial modes supported by the multi-mode fiber;

a detector spaced apart from said target area for detecting light emitted from a second end of said multi-mode fiber and that has passed through the target area, wherein said detector is configured to average out randomized spatial modes to recover a single spatial mode.

2. An arrangement as claimed in claim 1 wherein the randomizer is operable to cause spatial oscillation of the multi-mode fiber.

3. An arrangement as claimed in claim 2 wherein the randomizer is operable to cause a physical perturbation along the multi-mode fiber.

4. An arrangement as claimed in claim 3 wherein the randomizer comprises any one or more of a DC motor with an eccentric weight, a flat panel exciter, or a piezoelectric motor.

5. An arrangement as claimed in claim 2 wherein the frequency of the spatial oscillation is in the range of approximately 1 Hz to 10 kHz.

6. An arrangement as claimed in claim 1 wherein the detector is configured to average out randomized spatial modes to recover a single spatial mode using between one hundred and one thousand samples.

7. An arrangement as claimed in claim 1 wherein the chirped laser comprises a semiconductor laser.

8. An arrangement as claimed in claim 1 wherein the chirped laser comprises a semiconductor diode laser.

9. An arrangement as claimed in claim 1 comprising means for applying one or more substantially step function electrical pulses to the chirped laser to cause the chirped laser to output one or more light pulses for injecting into an optical cell, wherein each of the one or more light pulses comprises a continuous wavelength chirp.

10. An arrangement as claimed in claim 9 wherein each of the one or more light pulses has a duration greater than approximately 150 ns.

11. An arrangement as claimed in claim 10 wherein each of the one or more light pulses has a duration in the range of approximately 150 to 300 ns.

12. An arrangement as claimed in claim 9 wherein a detected pulse duration is greater than approximately 150 ns.

13. An arrangement as claimed in claim 9 wherein a detected pulse duration is in the range of approximately 150 to 300 ns.

14. A gas sensor comprising:

a quantum cascade chirped laser that outputs a wavelength chirp for providing a wavelength scan;

a multi-mode fiber positioned between said laser and a target area and having a first end optically coupled to said laser, wherein said multi-mode fiber is configured for transmitting light from the laser to and/or from the target area for sensing a gas located at the target area;

a randomizer adjacent said multi-mode fiber for randomizing spatial modes supported by the multi-mode fiber;

a detector spaced apart from said target area for detecting light emitted from a second end of said multi-mode fiber and that has passed through the target area, wherein said detector is configured to average out randomized spatial modes to recover a single spatial mode.

15. A gas sensor as claimed in claim 14 wherein the randomizer is operable to cause spatial oscillation of the multi-mode fiber.

16. A gas sensor as claimed in claim 15 wherein the randomizer is operable to cause a physical perturbation along the multi-mode fiber.

17. A gas sensor as claimed in claim 16 wherein the randomizer comprises any one or more of a DC motor with an eccentric weight, a flat panel exciter, or a piezoelectric motor.

18. A gas sensor as claimed in claim 15 wherein the frequency of the spatial oscillation is in the range of approximately 1 to 10 kHz.

19. A gas sensor as claimed in claim 14 wherein the detector is configured to average out randomized spatial modes to recover a single spatial mode using between one hundred and one thousand samples.

20. A gas sensor as claimed in claim 14 wherein the chirped laser comprises a semiconductor laser.

21. A gas sensor as claimed in claim 14 wherein the chirped laser comprises a semiconductor diode laser.

22. A gas sensor as claimed in claim 14 comprising means for applying one or more substantially step function electrical pulses to the chirped laser to cause the chirped laser to output one or more light pulses for injecting into an optical cell, wherein each of the one or more light pulses comprises a continuous wavelength chirp.

23. A gas sensor as claimed in claim 22 wherein each of the one or more light pulses has a duration greater than approximately 150 ns.

24. A gas sensor as claimed in claim 22 wherein each of the one or more light pulses has a duration in the range of approximately 150 to 300 ns.

25. A gas sensor as claimed in claim 22 wherein a detected pulse duration is greater than approximately 150 ns.

26. A gas sensor as claimed in claim 22 wherein a detected pulse duration is in the range of approximately 150 to 300 ns.

27. A gas sensor as claimed in claim 14 wherein the randomizer is provided upstream of the target area.

28. A gas sensor as claimed in claim 14 wherein the randomizer is provided downstream of the target area.

29. A method for sensing a gas, said method comprising:

transmitting light from a single mode laser, wherein the laser is a quantum cascade chirped laser that outputs a wavelength chirp for providing a wavelength scan;

directing the light from the laser at a multi-mode fiber positioned between the laser and a target area and having a first end optically coupled to the laser, wherein the multi-mode fiber is configured for transmitting light from the laser to and/or from the target area for sensing a gas located at the target area;

randomizing spatial modes supported by the multi-mode fiber using a randomizer adjacent said multi-mode fiber; and

averaging out randomized spatial modes to recover a single spatial mode using a detector spaced apart from said target area for detecting light emitted from a second end of said multi-mode fiber and that has passed through the target area.

30. A method as claimed in claim 29 wherein the radiation is transmitted at least in part through free space.