Mirror control of micro-electro-mechanical optical cross connect switch

• US 6,427,038 B1
• Filed: 08/15/2000
• Issued: 07/30/2002
• Est. Priority Date: 08/15/2000
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Britz, David M., Dodley, Jeevan Prakash
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Amari, Alessandro V.
• Application Number:
  US09/639,635
• Time in Patent Office: 714 Days
• Field of Search: 385/16, 385/17, 385/18, 385/52, 359/566, 359/569, 359/831, 359/837
• US Class Current: 385/18
• CPC Class Codes: G02B 2006/12104 Mirror; Reflectors or the like
• CPC Class Codes: G02B 6/29311 Diffractive element operating in transmission
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02B 6/3518 the reflective optical element being an intrinsic part of a MEMS device, i.e. fabricated together with the MEMS device MEMS devices in general B81B; manufacture of MEM devices in general B81C; micromechanical devices controlling the direction of light G02B26/0833
• CPC Class Codes: G02B 6/3546 NxM switch, i.e. a regular array of switches elements of matrix type constellation
• CPC Class Codes: G02B 6/356 in an optical cross-connect device, e.g. routing and switching aspects of interconnecting different paths propagating different wavelengths to (re)configure the various input and output links switching polarized beams G02B6/3594; power equalizers G02B6/356 and G02B6/3594; path selecting means H04Q11/0001
• CPC Class Codes: G02B 6/3586 Control or adjustment details, e.g. calibrating testing optical equipment G01M11/00
• CPC Class Codes: G02B 6/3588 of the processed beams, i.e. controlling during switching of orientation, alignment, or beam propagation properties such as intensity, size or shape

Abstract

An optical switch includes an input optical fiber, an output optical fiber and a mirror that is either inclinable or rotatable or both and reflects a lightwave signal from the input optical fiber into the output optical fiber. The switch further includes a control circuit to sense a misalignment error and to adjust the mirror to correct the misalignment error. The misalignment error may be either an inclination misalignment error, a rotation misalignment error or both. In an alternative embodiment, an optical switch includes an input optical fiber that includes an input core and an input cladding, an output optical fiber that includes an output core and an output cladding, an input GRISM to insert a calibration signal into the input cladding and a mirror that is adjustable. The mirror reflects a lightwave signal from the input core into the output core and reflects the calibration signal from the input cladding into the output cladding. The optical switch further includes an output GRISM to extract the calibration signal from the output cladding and a control circuit to sense a misalignment error based on the extracted calibration signal. The misalignment error includes an inclination misalignment error or a rotation misalignment error or both. The control circuit includes circuitry to adjust the mirror to correct the misalignment error. In an alternative embodiment, an optical switch includes an input optical fiber, an output optical fiber and a rotatable mirror that has diffraction gratings etched thereon. The mirror reflects a lightwave signal from the input optical fiber into the output optical fiber. The optical switch further includes a control circuit to adjust a rotation angle of the mirror to select a wavelength that can be diffracted into the output optical fiber according to a spacing of the diffraction gratings.

Claims

1. An optical switch comprising:

an input optical fiber;

an output optical fiber;

a mirror that is positionable to reflect a lightwave signal from the input optical fiber into the output optical fiber; and

a control circuit to sense a misalignment error and adjust the mirror to correct the misalignment error;

the control circuit includes input and output calibration fibers co-parallel with respective input and output optical fibers;

the input calibration fiber is displaced with respect to the input optical fiber, both fibers being in a first plane that is perpendicular to a plane of the substrate; and

the output calibration fiber is displaced with respect to the output optical fiber, both fibers being in a second plane that is perpendicular to the plane of the substrate.

2. The optical switch of claim 1, wherein:

the mirror that is positionable is inclinable;

the misalignment error is an inclination misalignment error; and

the control circuit adjusts the mirror to correct the inclination misalignment error.

3. The optical switch of claim 1, wherein:

the mirror that is positionable is rotatable;

the misalignment error is a rotation misalignment error; and

the control circuit adjusts the mirror to correct the rotation misalignment error.

4. The optical switch of claim 1, wherein:

the mirror that is positionable is inclinable and rotatable;

the misalignment error includes an inclination misalignment error and a rotation misalignment error; and

the control circuit adjusts the mirror to correct the inclination misalignment error and the rotation misalignment error.

5. The optical switch of claim 1, wherein the control circuit further includes:

a receiver portion to detect an optical calibration signal from the output calibration fiber; and

a controller portion to adjust the mirror to correct the misalignment error according to the detected optical calibration signal.

6. The optical switch of claim 5, wherein the input optical fiber, the output optical fiber, the input calibration fiber, the output calibration fiber, the receiver portion and the mirror are arranged so that when the receiver portion indicates that the mirror optimally reflects the optical calibration signal into the output calibration fiber, the mirror simultaneously optimally reflects the lightwave signal from the input optical fiber into the output optical fiber.

7. The optical switch of claim 1, wherein the output calibration fiber constitutes a first output calibration fiber and the control circuit further includes:

a second output calibration fiber co-parallel with the first output calibration fiber, the second output calibration fiber being displaced with respect to the first output calibration fiber, both fibers being in the second plane;

a receiver portion to detect first and second optical calibration signals from the respective first and second output calibration fibers; and

a controller portion to adjust the mirror to correct the misalignment error according to the detected first and second optical calibration signals.

8. The optical switch of claim 1, wherein the first and second planes are substantially perpendicular.

9. The optical switch of claim 3, further comprising a substrate on which the mirror is rotatably mounted, wherein:

the control circuit includes input and output calibration fibers co-parallel with respective input and output optical fibers;

the input calibration fiber is displaced with respect to the input optical fiber, both fibers being in a first plane that is perpendicular to a plane of the substrate; and

the output calibration fiber is displaced with respect to the output optical fiber, both fibers being in a second plane that is perpendicular to the plane of the substrate.

10. The optical switch of claim 9, wherein the control circuit further includes:

a receiver portion to detect an optical calibration signal from the output calibration fiber; and

a controller portion to adjust the mirror to correct the rotation misalignment error according to the detected optical calibration signal.

11. The optical switch of claim 10, wherein the input optical fiber, the output optical fiber, the input calibration fiber, the output calibration fiber, the receiver portion and the mirror are arranged so that when the receiver portion indicates that the mirror optimally reflects the optical calibration signal into the output calibration fiber, the mirror simultaneously optimally reflects the lightwave signal from the input optical fiber into the output optical fiber.

12. The optical switch of claim 9, wherein the output calibration fiber constitutes a first output calibration fiber and the control circuit further includes:

a second output calibration fiber co-parallel with the first output calibration fiber, the second output calibration fiber being displaced with respect to the first output calibration fiber, both fibers being in a third plane that is co-parallel with the plane of the substrate;

a receiver portion to detect first and second optical calibration signals from the respective first and second output calibration fibers; and

a controller portion to adjust the mirror to correct the rotation misalignment error according to the detected first and second optical calibration signals.

13. The optical switch of claim 9, wherein the first and second planes are substantially perpendicular.

14. The optical switch of claim 4, further comprising a substrate on which the mirror is hingedly and rotatably mounted, wherein:

the control circuit includes input and output calibration fibers co-parallel with respective input and output optical fibers;

the input calibration fiber is displaced with respect to the input optical fiber, both fibers being in a first plane that is perpendicular to a plane of the substrate; and

the output calibration fiber is displaced with respect to the output optical fiber, both fibers being in a second plane that is perpendicular to the plane of the substrate.

15. An optical switch comprising:

an input switch fiber that includes an input core and an input cladding;

an output switch fiber that includes an output core and an output cladding;

an input GRISM to insert a calibration signal into the input cladding;

a mirror that is adjustable, the mirror reflecting a lightwave signal from the input core into the output core and reflecting the calibration signal from the input cladding into the output cladding; and

an output GRISM to extract the calibration signal from the output cladding.

16. The optical switch of claim 15, wherein an index of refraction of the input core is substantially equal to an index of refraction of the input GRISM at a wavelength of the lightwave signal.

17. The optical switch of claim 15, wherein an index of refraction of the output core is substantially equal to an index of refraction of the output GRISM at a wavelength of the lightwave signal.

18. The optical switch of claim 17, wherein an index of refraction of the input core is substantially equal to an index of refraction of the input GRISM at the wavelength of the lightwave signal.

19. The optical switch of claim 18, wherein the index of refraction of the input core is substantially equal to the index of refraction of the output core.

20. The optical switch of claim 15, wherein the input GRISM includes:

a first surface through which the calibration signal enters that is substantially perpendicular to a transit direction of the calibration signal in the input GRISM; and

a second surface through which the calibration signal exits that is oblique to the transit direction of the calibration signal in the input GRISM and is oblique to a transit direction of the lightwave signal in the input core, the second surface being oriented so that the transit direction of the calibration signal in the input GRISM is diffracted to a cladding transit direction that is parallel to the transit direction of the lightwave signal in the input core.

21. The optical switch of claim 20, wherein:

the input cladding includes an oblique surface that confronts the second surface; and

the oblique surface of the input cladding has etched thereon a diffraction grating to diffract the calibration signal in the input GRISM into the cladding transit direction at a wavelength of the calibration signal.

22. The optical switch of claim 20, wherein a ratio of an index of refraction of the input cladding and an index of refraction of the input GRISM at a wavelength of the calibration signal causes the calibration signal in the input GRISM to diffract to the cladding transit direction.

23. The optical switch of claim 20, wherein:

the input cladding includes an oblique surface that confronts the second surface;

the oblique surface of the input cladding has etched thereon a diffraction grating; and

a ratio of an index of refraction of the input cladding and an index of refraction of the input GRISM at a wavelength of the calibration signal and the diffraction grating diffracts the calibration signal in the input GRISM into the cladding transit direction at a wavelength of the calibration signal.

24. The optical switch of claim 15, wherein a cladding transit direction of the calibration signal in the output cladding is parallel to a core transit direction of the lightwave signal in the output core, and wherein the output GRISM includes:

a first surface through which the calibration signal exits that is substantially perpendicular to a transit direction of the calibration signal in the output GRISM; and

a second surface through which the calibration signal enters that is oblique to the transit direction of the calibration signal in the output GRISM and is oblique to the core transit direction, the second surface being oriented so that the transit direction of the calibration signal in the output GRISM is diffracted to the cladding transit direction.

25. The optical switch of claim 24, wherein:

the output cladding includes an oblique surface that confronts the second surface of the output GRISM; and

the oblique surface of the output cladding has etched thereon a diffraction grating to diffract the calibration signal in the output cladding into the transit direction of the calibration signal in the output GRISM.

26. The optical switch of claim 24, wherein a ratio of an index of refraction of the output cladding and an index of refraction of the output GRISM at a wavelength of the calibration signal causes the calibration signal in the output cladding to diffract to the transit direction of the calibration signal in the output GRISM.

27. The optical switch of claim 24, wherein:

the output cladding includes an oblique surface that confronts the second surface of the output GRISM;

the oblique surface of the output cladding has etched thereon a diffraction grating; and

a ratio of an index of refraction of the output cladding and an index of refraction of the output GRISM at a wavelength of the calibration signal and the diffraction grating diffracts the calibration signal in the output cladding to the transit direction of the calibration signal in the output GRISM at a wavelength of the calibration signal.

28. The optical switch of claim 15, further comprising a control circuit to sense a misalignment error based on the extracted calibration signal, the misalignment error including at least one of an inclination misalignment error and a rotation misalignment error, the control circuit including circuitry to adjust the mirror to correct the misalignment error.

29. A method comprising steps of:

propagating a lightwave signal in an input core of an input switch fiber;

inserting a calibration signal through an input GRISM into an input cladding of the input switch fiber;

reflecting the lightwave signal from the input core off an adjustable mirror into an output core of an output switch fiber while reflecting the calibration signal from the input cladding off the adjustable mirror into an output cladding of the output switch fiber;

extracting the calibration signal in the output cladding through an output GRISM;

sensing a misalignment error based on the extracted calibration signal, the misalignment error including at least one of an inclination misalignment error and a rotation misalignment error; and

adjusting the mirror to correct the misalignment error.