Optical attenuator using a perturbation element with a multi-mode waveguide

1. An optical attenuator comprising:

a multi-mode waveguide segment, wherein an incident single-mode optical signal is converted to a multi-mode optical signal comprising a plurality of modes; and

a perturbation element disposed at an angle relative to said multi-mode waveguide segment, wherein said angle results in a selected amount of attenuation and a selected amount of insertion loss, said perturbation element causing perturbation of said multi-mode optical signal resulting in attenuation of said multi-mode optical signal, said perturbation element comprising a trench containing a liquid, said trench located between adjacent waveguide intersections in an optical device.

2. The optical attenuator of claim 1 wherein said multi-mode waveguide segment is coupled between an upstream single-mode waveguide segment and a downstream single-mode way guide.

3. The optical attenuator of claim 2 wherein said multi-mode waveguide segment has a larger cross-sectional area than said upstream single-mode waveguide segment and said downstream single-mode waveguide segment.

4. The optical attenuator of claim 1 wherein said liquid has an index of refraction that is variable with temperature.

5. The optical attenuator of claim 1 wherein said perturbation element is disposed completely within said multi-mode waveguide segment.

6. The optical attenuator of claim 1 wherein said perturbation element is disposed partially outside of said multi-mode waveguide segment.

7. The optical attenuator of claim 1 wherein said perturbation element is disposed completely outside of said multi-mode waveguide segment.

8. An optical circuit comprising:

a plurality of waveguides that intersect at a first intersection and at a second intersection adjacent to said first intersection along waveguide;

a first single-mode waveguide segment located between aid first and second intersections on said waveguide;

a second single-mode waveguide segment located between said first and second intersections on said waveguide;

a multi-mode waveguide segment coupling said first an second single-mode waveguide segments and adapted to receive a single-mode optical signal from said first single-mode waveguide segment, wherein said single-mode optical signal is converted to a multi-mode optical signal comprising a plurality of modes;

a first optical switch located at said first intersection and a second optical switch located at said second intersection; and

a perturbation element positioned to effect excitation of said multi-mode optical signal, said perturbation element comprising a trench containing a liquid, wherein said excitation causes attenuation of said multi-mode optical signal.

9. The optical circuit of claim 8 wherein said multi-mode waveguide segment has a larger cross-sectional area than said first single-mode waveguide segment and said second single-mode waveguide segment.

10. The optical circuit of claim 8 wherein said first single-mode waveguide is coupled adiabatically to said multi-mode waveguide.

11. The optical circuit of claim 8 wherein said perturbation element is disposed completely within said multi-mode waveguide segment.

12. The optical circuit of claim 8 wherein said perturbation element is disposed partially outside of said multi-mode waveguide segment.

13. The optical circuit of claim 8 wherein said perturbation element is disposed completely outside of said multi-mode waveguide segment.

14. The optical circuit of claim 8 wherein said perturbation element has an index of refraction for effecting said excitation, wherein said index of refraction is variable.

15. The optical circuit of claim 14 wherein said index of refraction varies with temperature, wherein said optical circuit further comprises:

a heater element proximate to said perturbation element and adapted to control said temperature.

16. The optical circuit of claim 8 wherein said perturbation element is positioned at an angle relative to said multi-mode waveguide segment, wherein said angle is selected to cause a certain amount of attenuation and a certain amount of insertion loss.

17. A method of attenuating an optical signal, said method comprising:

receiving an incident single-mode optical signal into a multi-mode waveguide in an optical device, wherein said incident single-mode optical signal is converted to a multi-mode optical signal comprising plurality of modes;

perturbing said multi-mode optical signal using a perturbation element having a refractive index, said perturbation element comprising a trench containing a liquid, said trench located between adjacent waveguide intersections in said optical device, wherein said perturbation element is positioned at an angle relative to said multi-mode waveguide segment, wherein said angle is selected to cause a certain amount of attenuation and a certain amount of insertion loss; and

coupling said multi-mode optical signal into a single-mode waveguide, wherein said multi-mode optical signal is converted to an output single-mode optical signal, said single-mode output signal attenuated relative to said incident single-mode optical signal.

18. The method of claim 17 wherein said perturbing comprises:

exciting selected modes of said multi-mode optical signal;

coupling an amount of optical power associated with said multi-mode optical signal into said selected modes; and

coupling said selected modes into said single-mode waveguide.

19. The method of claim 18 comprising:

perturbing said multi-mode optical signal using said perturbation element wherein said refractive index is changeable, wherein changing said refractive index changes said amount of optical power coupled into said selected modes.

20. The method of claim 17 comprising:

coupling said multi-mode optical signal into said single-mode waveguide, wherein said single-mode waveguide has a smaller cross-sectional area than said multi-mode waveguide.