System and method of estimating beam mode content for waveguide alignment

Patent metadata

Field	Value
Publication number	US-9377593-B2
Application number	US-201414547183-A
Country	US
Kind code	B2
Filing date	Nov 19, 2014
Priority date	Nov 19, 2013
Publication date	Jun 28, 2016
Grant date	Jun 28, 2016

Abstract

Alignment of a multimode waveguide to a source of light or another waveguide is evaluated using a multi-wavelength light source and a modal decomposition processing of an intensity profile of a waveguide output beam, wherein inter-modal interference is averaged out over wavelength. Fitting a superposition of mode intensity profiles to a wavelength-averaged intensity profile of the output beam provides information about the modal composition of the output beam, which may be used to assess the alignment of the multimode waveguide with respect to the input light beam, and to provide a feedback for guiding a waveguide alignment process.

First claim

We claim:

1. A method comprising:
a) launching a plurality of light wavelengths into an input end of a first waveguide using a multi-wavelength light source, wherein the first waveguide is capable of supporting a plurality of waveguide modes;
b) receiving an output light beam from an output end of the first waveguide with a photodetector array (PDA) for generating electrical signals carrying beam image data;
c) using a computer operationally coupled to the PDA to obtain a multi-wavelength beam intensity profile for the output light beam from the beam image data, wherein the multi-wavelength beam intensity profile comprises contributions from each of the plurality of light wavelengths; and,
d) estimating, with the computer, a relative contribution of a selected waveguide mode from the plurality of waveguide modes into an optical power of the output light beam based on the multi-wavelength beam intensity profile and one or more mode intensity profiles corresponding to one or more waveguide modes of the first waveguide;
wherein the plurality of light wavelengths launched into the first waveguide spans a wavelength range that is sufficiently broad so as to average out contributions from phase-dependent inter-modal interference at the plurality of light wavelengths into the multi-wavelength beam intensity profile.

2. The method of claim 1 , further comprising:
e) obtaining a beam quality value that is based at least in part on the relative contribution of the selected waveguide mode into the optical power of the output light beam.

3. The method of claim 1 , wherein the one or more mode intensity profiles comprises a plurality of mode intensity profiles corresponding to the plurality of waveguide modes of the first waveguide, and wherein d) comprises determining a superposition of the mode intensity profiles that matches the multi-wavelength beam intensity profile.

4. The method of claim 3 , wherein d) comprises using a fitting algorithm to determine weighting coefficients in a weighted sum of the plurality of mode intensity profiles that matches the multi-wavelength beam intensity profile.

5. The method of claim 1 , wherein d) comprises computing an overlap of the mode intensity profile of the selected waveguide mode with the multi-wavelength beam intensity profile.

6. The method of claim 1 , wherein the selected waveguide mode comprises a fundamental mode of the first waveguide.

7. The method of claim 1 , wherein the plurality of light wavelengths spans the wavelength range having a width of 30 nanometers or greater.

8. The method of claim 1 , wherein the multi-wavelength light source comprises a broad-band light source, wherein a) comprises simultaneously emitting the plurality of light wavelengths with the broad-band light source, and wherein b) comprises PDA capturing a multi-wavelength cross-sectional image of the output light beam comprising contributions from the plurality of light wavelengths.

9. The method of claim 1 wherein the multi-wavelength light source comprises a tunable light source, wherein a) comprises tuning a wavelength of light generated by the tunable light source across the wavelength range, and wherein c) comprises using the computer to compute a sum of a plurality of instantaneous beam intensity profiles captured with the PDA at different time instances during the tuning.

10. The method of claim 2 , wherein a) comprises:
a1) providing a second waveguide in front of the first waveguide in an alignment therewith so that an output end of the second waveguide is in a close proximity with the input end of the first waveguide to provide an optical coupling therebetween;
a2) launching the plurality of light wavelengths into an input end of the second waveguide for coupling into the first waveguide.

11. The method of claim 10 further comprising:
f) repeating steps a) to e) for a plurality of different alignments between the second and first waveguides to obtain a plurality of the beam quality values;
g) selecting as a preferred alignment one of the plurality of different alignments that provides a highest beam quality value from the plurality of beam quality values; and,
h) fixing the output end of the second waveguide and the input end of the first waveguide in a relative position of the preferred alignment between the second waveguide and the first waveguide.

12. The method of claim 11 wherein the first waveguide comprises a first optical fiber and the second waveguide comprises a second optical fiber.

13. The method of claim 12 , further comprising fusing together the output end of the second optical fiber and the input end of the first optical fiber at a junction in response to receiving from the computer an indication that the first and second optical fibers are in a position of the preferred alignment.

14. The method of claim 11 , wherein f) comprises using a computer-controlled waveguide positioning system configured to position the output end of the second waveguide and the input end of the first waveguide in an alignment with each other and to controllably vary said alignment in response to a control signal from the computer.

15. A system, comprising:
a waveguide holder for holding a first optical waveguide comprising an input end and an output end;
a multi-wavelength light source for launching a plurality of light wavelengths into the input end of the first optical waveguide;
a photodetector array (PDA) for receiving an output optical beam from the output end of the first optical waveguide and for generating beam image signals comprising a cross-sectional image of the output optical beam; and,
a computer operationally coupled to the PDA for receiving therefrom the beam image signals, the computer comprising a processor and a memory, the memory storing a set of instructions for causing the processor to execute a process comprising:
a) obtaining a multi-wavelength beam intensity profile from the beam image signals, and
b) estimating, based on the multi-wavelength beam intensity profile and one or more mode intensity profiles corresponding to one or more waveguide modes of the first waveguide, a relative contribution of a selected waveguide mode from the one or more waveguide modes into an optical power of the optical beam;
wherein the plurality of light wavelengths launched into the first waveguide spans a wavelength range that is sufficiently broad so as to average out contributions from phase-dependent inter-modal interference into the multi-wavelength beam intensity profile.

16. The system of claim 15 , wherein the set of instructions stored in the memory further comprises instructions for:
c) obtaining a beam quality value that is based at least in part on the relative contribution of the selected waveguide mode.

17. The system of claim 16 , wherein:
the waveguide holder comprises a computer-controlled waveguide positioning system for holding a second waveguide in front of the first optical waveguide in an alignment therewith so that an output end of the second waveguide is in a close proximity with the input end of the first optical waveguide at a junction for providing an optical coupling therebetween;
the computer-controlled waveguide positioning system is configured to, responsive to a control signal from the computer, move one of the output end of the second waveguide and the input end of the first optical waveguide relative to each other so as to controllably vary their relative alignment at the junction; and,
the set of instructions stored in the memory further comprises instructions for causing the processor to:
d) gener

Assignees

• Lumentum Operations Llc

Inventors

• Ma Xiuquan
• Yu Hongbo
• Muendel Martin H

Classifications

• G02B6/4221 Primary

  involving a visual detection of the position of the elements, e.g. by using a microscope or a camera · CPC title

• H04B10/2581

  Multimode transmission · CPC title

• G02B6/3656

  the additional structures being micropositioning, with microactuating elements for fine adjustment, or restricting movement, into two dimensions, e.g. cantilevers, beams, tongues or bridges with associated MEMs · CPC title

• G01M11/33

  with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face · CPC title

• G02B6/2555

  Alignment or adjustment devices for aligning prior to splicing · CPC title