SYSTEM AND METHOD FOR NON-CONTACT OPTICAL-POWER MEASUREMENT

• US 20150292938A1
• Filed: 04/09/2015
• Published: 10/15/2015
• Est. Priority Date: 04/11/2014
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Guimond, Stephen J.
• Granted Patent: US 9,429,467 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01J 1/0295 Constructional arrangements for removing other types of optical noise or for performing calibration
• CPC Class Codes: G01J 1/0425 using optical fibers
• CPC Class Codes: G01J 1/0429 using polarisation elements
• CPC Class Codes: G01J 1/4228 arrangements with two or more detectors, e.g. for sensitivity compensation
• CPC Class Codes: G01J 1/4257 applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam monitoring arrangements for lasers in general H01S3/0014
• CPC Class Codes: G01M 11/02 Testing optical properties
• CPC Class Codes: G02B 6/024 with polarisation maintaining properties
• CPC Class Codes: G02B 6/0283 Graded index region external to the central core segment, e.g. sloping layer or triangular or trapezoidal layer G02B6/0288, G02B6/0286 take precedence
• CPC Class Codes: G02B 6/03622 having 2 layers only
• CPC Class Codes: G02B 6/4216 incorporating polarisation-maintaining fibres polarisation-maintaining fibres per se G02B6/105
• CPC Class Codes: G02B 6/4287 Optical modules with tapping or launching means through the surface of the waveguide G02B6/2852, G02B6/4286 take precedence

Abstract

The present invention provides methods and systems for measuring optical power that require neither alterations to the optical fiber nor physical contact with the optical fiber, the system including an optical fiber configured to propagate an optical signal, wherein the optical fiber includes a core and at least a first cladding layer, wherein a portion of the optical signal scatters out of the optical fiber along a length of the optical fiber to form scattered fiber light; a detector system configured to receive the scattered fiber light along the length of the optical fiber and to output a detection signal based on the received scattered fiber light; and a processor configured to receive the detection signal and to determine a power value of the optical signal based on the received detection signal.

Claims

1. An apparatus for measuring optical power comprising:

an optical fiber configured to propagate an optical signal, wherein the optical fiber includes a core and at least a first cladding layer, wherein a portion of the optical signal scatters out of the optical fiber along a length of the optical fiber to form scattered fiber light;

a detector system configured to receive the scattered fiber light along the length of the optical fiber and to output a detection signal based on the received scattered fiber light; and

a processor configured to receive the detection signal and to determine a power value of the optical signal based on the received detection signal.

2. The apparatus of claim 1, wherein the first cladding layer has an index of refraction, wherein the optical fiber further includes a second cladding layer that surrounds the first cladding layer along the length of the optical fiber, and wherein the second cladding layer has a lower index of refraction than the index of refraction of the first cladding layer such that pump light inserted into the first cladding layer is contained within the first cladding layer along the length of the optical fiber.

3. The apparatus of claim 1, wherein the detector system includes a plurality of light-sensing positions, and wherein the plurality of light-sensing positions each collect light from at least one different location.

4. The apparatus of claim 3, wherein the detector system includes a one-by-N linear-array detector, and wherein N is an integer larger than one.

5. The apparatus of claim 1, wherein the detector system includes a single-pixel detector.

6. The apparatus of claim 1, wherein the scattered fiber light includes scattered pump light, the apparatus further comprising:

imaging optics located between the optical fiber and the detector system, wherein the imaging optics is configured to direct the scattered fiber light onto the detector system; and

a wavelength filter configured to filter out the scattered pump light from the scattered fiber light before it reaches the detector system.

7. The apparatus of claim 1, wherein the optical fiber is a polarization-maintaining (PM) fiber, wherein a majority of the scattered fiber light scatters in a first direction from the PM fiber, and wherein the detector system is oriented to detect the scattered fiber light that scatters in the first direction.

8. The apparatus of claim 1, wherein the optical fiber is a polarization-maintaining (PM) fiber, wherein the processor includes a lock-in detection module, the apparatus further comprising:

a polarization modulator unit operatively coupled to the processor and configured to modulate a polarization of the scattered fiber light, wherein the polarization modulator unit includes a polarizer, wherein the processor controls the polarization modulator unit and the lock-in detection module in order to improve the signal-to-noise ratio of the scattered fiber light.

9. The apparatus of claim 1, wherein the processor is further configured to eliminate hot spots associated with the scattered fiber light during the determination of the power value of the optical signal.

10. The apparatus of claim 1, further comprising:

a pump dump; and

a calibration power meter optically coupled to the optical fiber, wherein the calibration power meter is configured to provide power calibration of the apparatus.

11. A method for measuring optical power comprising:

providing an optical fiber configured to propagate an optical signal, wherein the optical fiber includes a core and at least a first cladding layer, wherein a portion of the optical signal scatters out of the optical fiber along a length of the optical fiber to form scattered fiber light;

detecting, at a first time period, the scattered fiber light along the length of the optical fiber and outputting a first signal based on the imaged scattered fiber light; and

determining a power value of the optical signal based on the first signal.

12. The method of claim 11, wherein the scattered fiber light includes scattered pump light, the method further comprising:

focusing the scattered fiber light prior to the detecting of the scattered fiber light; and

wavelength filtering the scattered fiber light to separate the portion of the optical signal from pump light.

13. The method of claim 11, wherein the optical fiber is a polarization-maintaining (PM) fiber, wherein a majority of the scattered fiber light scatters in a first direction from the PM fiber, and wherein the detecting of the scattered fiber light includes detecting the scattered fiber light that scatters in the first direction by lock-in detection, the method further comprising:

modulating a polarization of the scattered fiber light prior to the detecting of the scattered fiber light.

14. The method of claim 11, wherein the determining of the power value of the optical signal includes eliminating hot spots associated with the scattered fiber light.

15. The method of claim 11, wherein the determining of the power value of the optical signal includes:

eliminating hot spots associated with the scattered fiber light;

performing a functional fit of the determined power value to the scattered fiber light;

detecting, at a second time period, subsequent to the first time period, the scattered fiber light along the length of the optical fiber and outputting a second image signal; and

determining, using the functional fit, a power value of the optical signal based on the second image signal.

16. The method of claim 11, further comprising:

dumping pump light along the length of the optical fiber; and

calibrating the determining of the power value of the optical signal.

17. The method of claim 11, further comprising:

providing a detector system configured to perform the detecting; and

fixing a position of the detector system with respect to the optical fiber.

18. The method of claim 11, wherein the determining of the power value of the optical signal includes detecting a power-versus-time profile of the optical signal.

19. The method of claim 18, further comprising controlling the optical signal based at least in part on the power-versus-time profile.

20. An apparatus comprising:

an optical fiber configured to propagate an optical signal, wherein the optical fiber includes a core and at least a first cladding layer, wherein a portion of the optical signal scatters out of the optical fiber along a length of the optical fiber to form scattered fiber light;

means for detecting the scattered fiber light along the length of the optical fiber and outputting a signal based on the imaged scattered fiber light; and

means for determining a power value of the optical signal based on the image signal.