Active alignment of optical fiber to chip using liquid crystals

Patent metadata

Field	Value
Publication number	US-9235097-B2
Application number	US-201213365856-A
Country	US
Kind code	B2
Filing date	Feb 3, 2012
Priority date	Feb 3, 2012
Publication date	Jan 12, 2016
Grant date	Jan 12, 2016

Abstract

Devices and systems to perform optical alignment by using one or more liquid crystal layers to actively steer a light beam from an optical fiber to an optical waveguide integrated on a chip. An on-chip feedback mechanism can steer the beam between the fiber and a grating based waveguide to minimize the insertion loss of the system.

First claim

What is claimed as new and desired to be protected by Letters Patent of the United States is:

1. A structure for optically aligning an optical fiber with an optical waveguide, comprising:
an optical waveguide integrated on a chip and having a light coupling grating; and
a switchable beam steering device bonded to said optical waveguide and comprising:
a switchable liquid crystal polarization grating arranged in an optical path with said optical waveguide, said polarization grating being configured to actively steer an incoming light beam from said optical fiber into the coupling grating of said optical waveguide;
a first waveplate bonded to said switchable liquid crystal polarization grating and configured to receive and selectively change a polarization state of an incoming light beam; and

a voltage source for operating said switchable beam steering device to steer the incoming light beam; and
wherein the switchable liquid crystal polarization grating and the first waveplate are located between the optical fiber and the optical waveguide, such that the incoming light beam from the optical fiber is incident on the switchable beam steering device.

2. The structure of claim 1 , wherein said switchable liquid crystal polarization grating is configured to steer a circularly polarized beam received from said first waveplate into one of three diffraction orders.

3. The structure of claim 2 , further comprising a second waveplate arranged between said optical fiber and said first waveplate, said second waveplate being configured to selectively change a linearly polarized beam received from the optical fiber into a circularly polarized beam.

4. The structure of claim 1 , wherein said first waveplate is a half waveplate made of birefringent liquid crystal.

5. The structure of claim 3 , wherein said second waveplate is a quarter waveplate.

6. The structure of claim 3 , wherein said second waveplate is a three-quarters waveplate.

7. The structure of claim 4 , wherein the voltage source is configured to apply a voltage greater than a threshold voltage to said polarization grating for selecting a zero diffraction order.

8. The structure of claim 4 , wherein the voltage source is configured to apply a voltage to said first waveplate to allow a circularly polarized beam to pass through without changing the polarization state of the circularly polarized beam.

9. The structure of claim 3 , wherein a facet of the second waveplate facing said optical fiber is coated with an antireflective coating.

10. The structure of claim 1 , wherein said switchable beam steering device is bonded to said optical waveguide using a double-sided tape.

11. An integrated optical chip comprising:
a liquid crystal steering device adapted to actively optically align an optical fiber to a first optical waveguide on the integrated optical chip, the steering device comprising a switchable liquid crystal polarization grating attached to the first optical waveguide and a half waveplate located between the optical fiber and the polarization grating;
a waveguide sensor for detecting a coupling power between the optical fiber and the first optical waveguide; and
a controller configured to actively control the steering device in response to the coupling power detected by the waveguide sensor; and
wherein the switchable liquid crystal polarization grating and the half waveplate are located between the optical fiber and the first optical waveguide, such that an incoming beam from the optical fiber is incident on the liquid crystal steering device.

12. The integrated optical chip of claim 11 , further comprising a second optical waveguide in proximity of said first optical waveguide for coupling an optical signal from said first optical waveguide to said waveguide sensor.

13. The integrated optical chip of claim 12 , wherein the coupling between the first and second optical waveguides is by an evanescent wave.

14. The integrated optical chip of claim 12 , wherein the waveguide sensor is a photodetector coupled to the second optical waveguide.

15. The integrated optical chip of claim 11 , wherein the waveguide sensor is an optical transducer coupled to the first optical waveguide.

16. The integrated optical chip of claim 11 , wherein the controller is a proportional-integral-derivative controller.

17. A liquid crystal steering device for aligning an optical fiber having a core with a first refractive index to an integrated optical chip, the steering device comprising:
a liquid crystal waveplate having a second refractive index that is different from the first refractive index, the waveplate being attached to the integrated optical chip between the optical fiber and a grating coupler of the integrated optical chip, such that an incoming beam from the core of the optical fiber is incident on the liquid crystal waveplate; and
an electric field source configured to apply an electric field to the waveplate to change the second refractive index and actively steer an optical signal from the optical fiber to the grating coupler.

18. The steering device of claim 17 , wherein the waveplate comprises one or more liquid crystal layers.

19. The steering device of claim 18 , wherein the liquid crystal layers are nematic.

20. The steering device of claim 17 , wherein the waveplate has a thickness greater than a wavelength of the optical fiber.

21. The steering device of claim 17 , wherein a facet of the waveplate adjacent to the optical fiber has an antireflective coating.

22. The structure of claim 1 , wherein said voltage source applies selected voltages to said first waveplate and polarization grating to steer the incoming light beam.

23. The structure of claim 22 , wherein said voltage source comprises a controller which determines a light intensity within said optical waveguide and controls voltages applied to said first waveplate and polarization grating to increase the light intensity in said optical waveguide.

24. The structure of claim 23 , wherein said first waveplate is selectively operable by said voltage source to selectively change or not change the polarization of light passing therethrough.

25. The integrated optical chip of claim 12 , wherein the first optical waveguide has a refractive index, the integrated optical chip further comprising a voltage source for applying an electric field to the first optical waveguide to change the refractive index and optical coupling between the first and second optical waveguides.

26. The integrated optical chip as in claim 25 , wherein the voltage source is operable to turn the optical coupling between the first and second optical waveguides on or off.

27. The steering device as in claim 17 , further comprising a waveguide sensor for detecting optical power passing through the grating coupler, and a controller responsive to the sensed optical power for operating the voltage source to steer the optical signal.

Assignees

• Meade Roy
• Sandhu Gurtej
• Micron Technology Inc

Inventors

• Meade Roy
• Sandhu Gurtej

Classifications

• G02B6/124

  Geodesic lenses or integrated gratings · CPC title

• G02F2203/24

  beam steering · CPC title

• G02F1/1393 Primary

  the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells (G02F1/1396, G02F1/141 take precedence) · CPC title

• G02F1/292

  by controlled diffraction or phased-array beam steering (controlled diffraction for optical switching G02F1/31) · CPC title

• G02B6/34

  utilising prism or grating {(G02B6/293 takes precedence)} · CPC title