Acousto-optic filter

• US 6,253,002 B1
• Filed: 05/15/2000
• Issued: 06/26/2001
• Est. Priority Date: 06/16/1997
• Status: Expired due to Term

• Current Assignee: Novera Optics, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ultraband Fiber Optics, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Lee, Bong Wan, Kim, Byoung Yoon, Yun, Seok Hyun
• Primary Examiner(s): Healy, Brian
• Application Number:
  US09/571,092
• Time in Patent Office: 407 Days
• Field of Search: 385/7, 385/15, 385/27, 385/28, 385/29, 385/39, 385/42, 385/47, 385/31
• US Class Current: 385/27
• CPC Class Codes: G02B 6/02071 Mechanically induced gratings, e.g. having microbends G02B6/02066 takes precedence; mode converters G02B6/14
• CPC Class Codes: G02B 6/14 Mode converters
• CPC Class Codes: G02F 1/125 in an optical waveguide structure

Abstract

An acousto-optic filter has a non-birefringent single mode optical fiber with a longitudinal axis, a core and a cladding in a surrounding relationship to the core. The optical fiber has multiple cladding modes and a single core mode that is guided along the core. An acoustic wave propagation member has a proximal end and a distal end coupled to the optical fiber. The acoustic wave propagation member propagates an acoustic wave from the proximal to the distal end and launches a flexural wave in the optical fiber. At least one acoustic wave generator is coupled to the proximal end of the acoustic wave propagation member.

Claims

1. An acousto-optic apparatus, comprising:

an optical circulator with at least a first port configured to be coupled to an input fiber, a second port configured to be coupled to an output fiber and a third port configured to be coupled to an optical circulator fiber;

a first acoustic wave propagation member with a proximal end and a distal end coupled to the optical circulator fiber, the first acoustic wave propagation member propagating an acoustic wave from the proximal to the distal end and excite an acoustic wave in the optical circulator fiber; and

a first acoustic wave generator coupled to the proximal end of the first acoustic wave propagation member.

2. The apparatus of claim 1, further comprising:

a Faraday rotating mirror coupled to the first acoustic wave propagation member.

3. The apparatus of claim 2, further comprising:

a feedback control coupled to the acoustic wave propagation member, positioned to monitor a signal output received from the filter and generate a feedback signal in response to the monitoring of the signal output, the acoustic wave propagation member producing a selected adjustment of an acoustic signal by the acoustic wave propagation member in response to the feedback signal.

4. The apparatus of claim 1, wherein the intermediate fiber has a longitudinal axis, a core and a cladding in a surrounding relationship to the core, the optical fiber having multiple cladding modes and a single core mode guided along the core.

5. The apparatus of claim 1,further comprising:

a plurality of acoustic wave propagation members; and

a plurality of acoustic wave generators, each of an acoustic wave propagation member being coupled to an acoustic wave generator, wherein the first acoustic wave propagation member and the first acoustic wave generator are included in the pluralities of acoustic wave propagation members and acoustic wave generators.

6. The apparatus of claim 5, further comprising:

a plurality of optical fibers, each of an optical fiber being coupled to an acoustic wave propagation member.

7. The apparatus of claim 6, further comprising:

a Faraday rotating mirror coupled to an acoustic wave propagation member of the plurality of acoustic wave propagation members.

8. The apparatus of claim 7, further comprising:

a plurality of selected fiber delays, each of a selected fiber delay being coupled to an optical fiber from the plurality of optical fibers.

9. The apparatus of claim 8, wherein at least a portion of the plurality of acoustic wave propagation members have different beat frequencies.

10. The apparatus of claim 8, wherein a first acoustic wave propagation member positioned adjacent to the optical circulator has a lower beat frequency than a beat frequency of a second acoustic wave propagation member positioned adjacent to the Faraday rotating mirror.

11. The apparatus of claim 5, wherein the plurality of acoustic wave propagation members are positioned in series.

12. The apparatus of claim 1, further comprising:

an acoustic damper coupled to the intermediate fiber.

13. The apparatus of claim 12, wherein the acoustic damper includes a jacketing material.

14. The apparatus of claim 12, wherein a proximal end of the acoustic damper is tapered.

15. A dual filter, comprising:

a first filter pair including,

a first filter including a first acoustic wave propagation member with a proximal end and a distal end, the distal end being coupled to an optical fiber, the first acoustic wave propagation member propagating an acoustic wave from the proximal to the distal end and excite a acoustic wave in the optical fiber; and

a first acoustic wave generator coupled to the proximal end of the first acoustic wave propagation member,

a second filter including a second acoustic wave propagation member with a proximal end and a distal end, the distal end being coupled to the optical fiber, the second acoustic wave propagation member propagating the acoustic wave from the proximal to the distal end and excite the acoustic wave in the optical fiber; and

a second acoustic wave generator coupled to the proximal end of the second acoustic wave propagation member; and

a first optical fiber with a first intermediate section that couples the first filter to the second filter.

16. The filter of claim 15, wherein the first intermediate section of the first optical fiber has an adjusted birefringence to create a half-wave plate in the first intermediate section.

17. The filter of claim 15, further comprising:

an optical circulator with at least a first port configured to be coupled to an input fiber, a second port configured to be coupled to an output fiber and a third port configured to be coupled to the first optical fiber.

18. The filter of claim 17, further comprising:

a Faraday mirror coupled to the second filter.

19. The filter of claim 15, further comprising:

a second filter pair coupled to the first filter pair and including,

a first filter including a first acoustic wave propagation member with a proximal end and a distal end, the distal end being coupled to an optical fiber, the first acoustic wave propagation member propagating an acoustic wave from the proximal to the distal end and excite a acoustic wave in the optical fiber; and

a first acoustic wave generator coupled to the proximal end of the first acoustic wave propagation member,

a second filter including a second acoustic wave propagation member with a proximal end and a distal end, the distal end being coupled to the optical fiber, the second acoustic wave propagation member propagating the acoustic wave from the proximal to the distal end and excite the acoustic wave in the optical fiber; and

a second acoustic wave generator coupled to the proximal end of the second acoustic wave propagation member;

a second optical fiber with a first intermediate section that couples the first filter to the second filter; and

a third optical fiber that couples the first filter pair to the second filter pair.

20. The filter of claim 19, wherein the first intermediate section of the second optical fiber has an adjusted birefringence to create a half-wave plate in the first intermediate section.

21. The filter of claim 19, wherein the third optical fiber includes a selected fiber delay.

22. The filter of claim 21, further comprising:

a Faraday mirror coupled to the second filter pair.

23. The filter of claim 21, wherein the first and second filter pairs are in series.

24. The filter of claim 15, wherein the first and second filters are operated to cancel intensity modulation of a signal imparted by the first, and second filters.

25. The filter of claim 15, wherein the half-wave plate is aligned with a 45 degree angle with respect to eigen polarization axes of the first and second filters.

26. The filter of claim 15, wherein a polarization loss of the first filter is the same as a polarization loss of the second filter.

27. The filter of claim 15, wherein an eigen state of the first filter is orthogonal to an eigen state of the second filter.

28. The filter of claim 15, wherein a plane of vibration of the acoustic wave is orthogonal for the first and second filters.

29. An acousto-optic apparatus, comprising:

an optical fiber with a longitudinal axis, a core and a cladding in a surrounding relationship to the core, the optical fiber configured to propagate multiple modes;

an acoustic wave propagation member with a proximal end and a distal end, the distal end being coupled to the optical fiber, the acoustic wave propagation member propagating an acoustic wave from the proximal to the distal end and excite an acoustic wave in the optical fiber; and

at least one acoustic wave generator coupled to the proximal end of the acoustic wave propagation member.

30. The apparatus of claim 29, wherein the acoustic wave generator produces multiple acoustic signals with individual controllable strengths and frequencies and each of the acoustic signals provides a coupling between the core mode and a different cladding mode.

31. The filter of claim 29, wherein a length of the optical fiber is no greater than 1 meter.

32. The filter of claim 29, wherein the acoustic wave generator generates a transverse wave.

33. The apparatus of claim 29, wherein the optical fiber has a single core mode guided along the core.

34. The apparatus of claim 29, wherein the acoustic wave generator produces multiple acoustic signals with individual controllable strengths and frequencies and each of the acoustic signals provides a coupling to the cladding modes.

35. The apparatus of claim 29, wherein the optical fiber provides fundamental and cladding mode propagation.

36. The apparatus of claim 29, wherein the optical fiber is sufficiently tensioned to reduce losses in the acoustic wave.

37. The apparatus of claim 29, wherein the acoustic wave propagation member has a tapered geometric configuration.

38. The apparatus of claim 29, wherein the acoustic wave generator includes a piezoelectric material.

39. The apparatus of claim 38, wherein the acoustic wave generator is coupled to an RF signal generator.

40. The apparatus of claim 39, wherein the acoustic wave generator has a mechanical resonance at a frequency in the range of 1-50 MHz.

41. The apparatus of claim 29, further comprising:

an acoustic damper coupled to the optical fiber.

42. The apparatus of claim 41, wherein the acoustic damper includes a jacketing material positioned in a surrounding relationship to the optical fiber.

43. The apparatus of claim 29, further comprising:

a heatsink with a proximal face and a distal face that is coupled to the acoustic wave generator, wherein the acoustic wave generator is positioned between the acoustic wave propagation member and the heatsink.