Optical equalizer having variable transmittance versus wavelength characteristics for attenuating light

• US 5,805,759 A
• Filed: 01/17/1997
• Issued: 09/08/1998
• Est. Priority Date: 03/27/1996
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Fukushima, Nobuhiro
• Primary Examiner(s): NGO, HUNG NHAT
• Application Number:
  US08/785,038
• Time in Patent Office: 599 Days
• Field of Search: 385/140, 385/36, 385/37, 385/31, 385/25, 385/47, 385/42, 359/889
• US Class Current: 385/140
• CPC Class Codes: G02B 6/2713 cascade of polarisation selective or adjusting operations
• CPC Class Codes: G02B 6/2766 Manipulating the plane of polarisation from one input polarisation to another output polarisation, e.g. polarisation rotators, linear to circular polarisation converters
• CPC Class Codes: G02B 6/29313 characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response switching G02B6/35
• CPC Class Codes: G02B 6/29391 Power equalisation of different channels, e.g. power flattening

Abstract

An apparatus, such as an optical equalizer, having variable wavelength characteristics. More specifically, the apparatus attenuates an input light, and includes a beam expander, a beam condenser and an attenuator positioned between the beam expander and the beam condenser. The beam expander converts the input light into a spectral beam propagating in a first direction and having wavelength components spatially separated in a second direction perpendicular to the first direction. The attenuator intersects the spectral beam and has a planer distribution of transmittance so that the spectral beam passes through the attenuator and is attenuated in accordance with the planer distribution of transmittance. The beam expander converts the attenuated spectral beam into an output light. The attenuator is movable in a plane which is not parallel to the first direction. For example, the attenuator can be movable in a plane which is substantially perpendicular to the first direction. Further, the attenuator can include a plurality of individual attenuators, wherein each individual attenuator intersects the spectral beam and has a corresponding planer distribution of transmittance for attenuating the spectral beam in accordance with the corresponding planer distribution of transmittance.

Claims

1. An apparatus which attenuates a spectral beam propagating in a first direction and having wavelength components spatially separated in a second direction perpendicular to the first direction, the apparatus comprising:

an attenuator intersecting the spectral beam and having a planer distribution of transmittance in a first plane which is not parallel to the first direction so that the spectral beam passes through the attenuator and is attenuated in accordance with the planer distribution of transmittance, the attenuator being movable in a second plane which is not parallel to the first direction.

2. An apparatus as in claim 1, wherein the second plane is substantially perpendicular to the first direction.

3. An apparatus as in claim 1, wherein the first and second planes are the same.

4. An apparatus as in claim 1, wherein the first and second planes are the same and are perpendicular to the first direction.

5. An apparatus as in claim 1, further comprising:

a first converter which receives an input light and converts the input light into the spectral beam intersected by the attenuator; and

a second converter which receives the spectral beam from the first converter and converts to received spectral beam into an output light, wherein the attenuator is positioned between the first and second converters to attenuate the spectral beam as the spectral beam travels from the first converter to the second converter.

6. An apparatus as in claim 1, wherein the attenuator is a plate.

7. An apparatus as in claim 5, wherein:

the first converter includes

first and second diffraction gratings arranged so that the input light is diffracted from the first diffraction grating to the second diffraction grating and then diffracted by the second diffraction grating to produce the spectral beam; and

the second converter includes

first and second diffraction gratings arranged so that the spectral beam is received by the first diffraction grating of the second converter from the second diffraction grating of the first converter, diffracted to the second diffraction grating of the second converter and then diffracted by the second diffraction grating of the second converter to produce the output light.

8. An apparatus as in claim 7, wherein

the first and second diffraction gratings of the first converter have substantially equal grating constants, and the first and second diffraction gratings of the second converter have substantially equal grating constants.

9. An apparatus as in claim 7, further comprising:

a first optical rotating element positioned between the first and second diffraction gratings of the first converter and rotating a plane of polarization of light diffracted from the first diffraction grating of the first converter to the second diffraction grating of the first converter by 90°

; and

a second optical rotating element positioned between the first and second diffraction gratings of the second converter and rotating a plane of polarization of light diffracted from the first diffraction grating of the second converter to the second diffraction grating of the second converter by 90°

.

10. An apparatus as in claim 9, wherein the first and second optical rotating elements are half-wave plates.

11. An apparatus as in claim 10, wherein the first and second optical rotating elements are each inclined with respect to the first direction.

12. An apparatus as in claim 1, further comprising:

an optical rotating element intersecting the spectral beam and rotating a plane of polarization of the spectral beam by 90°

.

13. An apparatus as in claim 12, wherein the optical rotating element is a half-wave plate having a principal axis inclined 45°

with respect to the second direction.

14. An apparatus as in claim 1, wherein the attenuator is movable in at least one of the group comprising the second direction and a direction perpendicular to the first and second directions.

15. An apparatus as in claim 1, wherein the attenuator is rotatable with the first direction as an axis of rotation.

16. An apparatus as in claim 1, wherein the planar distribution of transmittance of the attenuator includes a plurality of equitransmittance lines in the first plane.

17. An apparatus as in claim 1, wherein the planar distribution of transmittance of the attenuator includes a plurality of equitransmittance lines sequentially arranged from a first equitransmittance line to a last equitransmittance line arranged in the first plane, the first plane being perpendicular to the first direction.

18. An apparatus as in claim 1, wherein the planar distribution of transmittance of the attenuator includes a plurality of equitransmittance lines concentrically arranged in the first plane.

19. An apparatus as in claim 1, wherein the attenuator includes a blocking portion in the first plane which does not allow light to pass therethrough and extends in a third direction perpendicular to the first and second directions.

20. An apparatus as in claim 19, wherein the blocking portion has a nonuniform width in the second direction.

21. An apparatus as in claim 1, wherein the attenuator includes a transmitting stripe in the first plane and extending in a third direction perpendicular to the first and second directions.

22. An apparatus as in claim 21, wherein the transmitting stripe has a nonuniform width in the first plane along a direction perpendicular to the third direction.

23. An apparatus as in claim 1, wherein the attenuator comprises:

a plurality of individual attenuators, each individual attenuator intersecting the spectral beam and having a planer distribution of transmittance in a corresponding first plane which is not parallel to the first direction.

24. An apparatus as in claim 23, wherein each individual attenuator is movable in a corresponding second plane which is not parallel to the first direction.

25. An apparatus as in claim 24, wherein, for each individual attenuator, the corresponding second plane is substantially perpendicular to the first direction.

26. An apparatus as in claim 24, wherein, for each individual attenuator, the corresponding first and second planes are the same and are perpendicular to the first direction.

27. An apparatus as in claim 23, wherein each individual attenuator has a transmittance in the corresponding first plane which periodically changes at a different period of change than the transmittance of the other individual attenuators.

28. An apparatus as in claim 5, further comprising:

a compensator intersecting the spectral beam as the spectral beam travels from the first converter to the second converter and having a distribution of transmittance which cancels wavelength characteristics of the first and second converters.

29. An apparatus as in claim 5, further comprising:

a first branching device which branches a portion of the spectral beam as the spectral beam travels between the first converter and the attenuator; and

a first spectrum monitor which monitors a spectrum of the spectral beam from the portion branched by the first branching device.

30. An apparatus as in claim 29, further comprising:

a second branching device which branches a portion of the spectral beam as the spectral beam travels between the attenuator and the second converter; and

a second spectrum monitor which monitors a spectrum of the spectral beam from the portion branched by the second branching device.

31. An apparatus as in claim 30, further comprising:

a processing device which monitors wavelength characteristics of the apparatus from the spectrums monitored by the first and second spectrum monitors.

32. An apparatus as in claim 5, further comprising:

a branching device which branches a portion of the spectral beam as the spectral beam travels between the attenuator and the second converter; and

a spectrum monitor which monitors a spectrum of the spectral beam from the portion branched by the branching device.

33. An apparatus as in claim 5, further comprising:

an optical amplifier which amplifies at least one of the group comprising the input light and the output light.

34. An apparatus as in claim 5, further comprising:

a light source which produces white light as the input light.

35. An apparatus as in claim 5, further comprising:

a polarizer which intersects at least a portion of the spectral beam, for changing the polarization condition of said intersected at least a portion of the spectral beam.

36. An apparatus as in claim 5, further comprising:

a wave plate which includes a plurality of regions intersecting the spectral beam, each region having a polarization changing condition which is different from the polarization changing condition of the other regions and a principle axis of direction which is different from the principle axis of direction of the other regions.

37. An apparatus as in claim 1, further comprising:

a converter which receives an input light and converts the input light into the spectral beam intersected by the attenuator, the converted spectral beam being defined as a first spectral beam; and

a reflecting device which reflects the first spectral beam after the first spectral beam passes through the attenuator, to produces a reflected spectral beam defined as a second spectral beam, wherein the second spectral beam passes through the attenuator and is then converted by the converter into an output light.

38. An apparatus as in claim 37, wherein the converter includes first and second diffraction gratings arranged so that

the input light is diffracted from the first diffraction grating to the second diffraction grating and then diffracted by the second diffraction grating to produce the first spectral beam, and

the second spectral beam is received by the second diffraction grating, diffracted to the first diffraction grating and then diffracted by the first diffraction grating to produce the output light.

39. An apparatus as in claim 38, wherein, with respect to a perpendicular to the second direction, an acute angle is formed between the direction of incidence of the first spectral beam on the reflecting device and the direction of reflectance of the second spectral beam off the reflecting device.

40. An apparatus as in claim 37, further comprising:

a first optical fiber which provides the input light to the converter; and

a second optical fiber which receives the output light from the converter.

41. An apparatus as in claim 37, further comprising:

a common optical fiber which provides the input light to the converter and receives the output light from the converter; and

an optical circulator connected to the common optical fiber for separating the input light and the output light.

42. An apparatus as in claim 41, wherein, with respect to a perpendicular to the second direction, an angle of 0°

is formed between the direction of incidence of the first spectral beam on the reflecting device and the direction of reflectance of the second spectral beam off the reflecting device.

43. An apparatus which attenuates a light beam propagating in a first direction and having wavelength components spatially separated in a second direction perpendicular to the first direction, the apparatus comprising:

an attenuator intersecting the light beam and having a planer distribution of transmittance so that the light beam passes through the attenuator and is attenuated in accordance with the planer distribution of transmittance.

44. An apparatus as in claim 43, wherein the attenuator is movable in a plane which is not parallel to the first direction.

45. An apparatus as in claim 43, wherein the planar distribution of transmittance of the attenuator includes a plurality of equitransmittance lines spaced apart from each other and in the same plane.

46. An apparatus as in claim 43, wherein the planar distribution of transmittance of the attenuator includes a plurality of equitransmittance lines concentrically arranged in the same plane.

47. An apparatus as in claim 43, wherein the attenuator includes a blocking portion which does not allow light to pass therethrough.

48. An apparatus as in claim 43, wherein the attenuator comprises:

a plurality of individual attenuators, each individual attenuator intersecting the light beam and having a corresponding planer distribution of transmittance so that the light beam passes through the individual attenuator and is attenuated in accordance with the corresponding planer distribution of transmittance.

49. An apparatus as in claim 48, wherein each individual attenuator is movable in a direction substantially perpendicular to the first direction.

50. An apparatus as in claim 48, wherein each individual attenuator has a transmittance in the corresponding planer distribution of transmittance which periodically changes at a different period of change than the transmittance of the other individual attenuators.

51. An apparatus for attenuating an input light, comprising:

a first converter which converts the input light into a spectral beam propagating in a first direction and having wavelength components spatially separated in a second direction perpendicular to the first direction;

an attenuator intersecting the spectral beam and having a planer distribution of transmittance so that the spectral beam passes through the attenuator and is attenuated in accordance with the planer distribution of transmittance; and

a second converter which converts the attenuated spectral beam into an output light.

52. An apparatus as in claim 51, wherein the attenuator is movable in a plane which is substantially perpendicular to the first direction.

53. An apparatus as in claim 51, wherein the attenuator is movable in a plane which is not parallel to the first direction.

54. An apparatus as in claim 51, wherein the planar distribution of transmittance of the attenuator includes a plurality of equitransmittance lines spaced apart from each other and in the same plane.

55. An apparatus as in claim 51, wherein the planar distribution of transmittance of the attenuator includes a plurality of equitransmittance lines concentrically arranged in the same plane.

56. An apparatus as in claim 51, wherein the attenuator comprises:

a plurality of individual attenuators, each individual attenuator intersecting the spectral beam and having a corresponding planer distribution of transmittance for attenuating the spectral beam in accordance with the corresponding planer distribution of transmittance.

57. An apparatus as in claim 56, wherein each individual attenuator is movable in a direction substantially perpendicular to the first direction.

58. An apparatus as in claim 56, wherein each individual attenuator has a corresponding planer distribution of transmittance which periodically changes at a different period of change than the corresponding planer distribution of transmittances of the other individual attenuators.