Dynamic gain equalizer method and associated apparatus

• US 6,493,502 B1
• Filed: 05/17/2001
• Issued: 12/10/2002
• Est. Priority Date: 05/17/2001
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Optronx Inc.
• Inventors: Deliwala, Shrenik
• Primary Examiner(s): Healy, Brian
• Assistant Examiner(s): Lin, Tina M
• Application Number:
  US09/859,279
• Time in Patent Office: 572 Days
• Field of Search: 385/14, 385/140, 385/40, 385/39, 385/129, 385/130
• US Class Current: 385/140
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 2006/12038 Glass (SiO2 based materials)
• CPC Class Codes: G02B 2006/12061 Silicon
• CPC Class Codes: G02B 2006/12097 Ridge, rib or the like
• CPC Class Codes: G02B 2006/12104 Mirror; Reflectors or the like
• CPC Class Codes: G02B 2006/12107 Grating
• CPC Class Codes: G02B 2006/12114 Prism
• CPC Class Codes: G02B 2006/12135 Temperature control
• CPC Class Codes: G02B 2006/12161 Distributed feedback [DFB]
• CPC Class Codes: G02B 2006/12164 Multiplexing; Demultiplexing
• CPC Class Codes: G02B 2006/12176 Etching
• CPC Class Codes: G02B 27/285 comprising arrays of elements, e.g. microprisms
• CPC Class Codes: G02B 5/045 Prism arrays
• CPC Class Codes: G02B 6/10 of the optical waveguide type G02B6/02, G02B6/24 take precedence; devices or arrangements for the control of light by electric, magnetic, electro-magnetic or acoustic means G02F1/00; transferring the modulation of modulated light G02F2/00; optical logic elements G02F3/00; optical analogue/digital converters G02F7/00
• CPC Class Codes: G02B 6/12004 Combinations of two or more optical elements
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02B 6/12011 characterised by the arrayed waveguides, e.g. comprising a filled groove in the array section
• CPC Class Codes: G02B 6/12016 characterised by the input or output waveguides, e.g. tapered waveguide ends, coupled together pairs of output waveguides
• CPC Class Codes: G02B 6/12026 characterised by means for reducing the temperature dependence
• CPC Class Codes: G02B 6/12028 based on a combination of materials having a different refractive index temperature dependence, i.e. the materials are used for transmitting light
• CPC Class Codes: G02B 6/12033 : characterised by means for configuring the device, e.g. moveable element for wavelength tuning switching G02B6/35; thermo-optic devices G02F1/0147
• CPC Class Codes: G02B 6/1225 : comprising photonic band-gap structures or photonic lattices
• CPC Class Codes: G02B 6/1228 : Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: G02B 6/124 : Geodesic lenses or integrated gratings
• CPC Class Codes: G02B 6/272 : comprising polarisation means for beam splitting and combining
• CPC Class Codes: G02B 6/2861 : using fibre optic delay lines and optical elements associated with them, e.g. for use in signal processing, e.g. filtering delay lines in general H03H, H01P9/00; optical computing devices G06E
• CPC Class Codes: G02B 6/29325 : of the slab or planar or plate like form, i.e. confinement in a single transverse dimension only integrated circuit planar waveguide arrangements G02B6/12007; specially adapted for lighting G02B6/0011
• CPC Class Codes: G02B 6/29349 : Michelson or Michelson/Gires-Tournois configuration, i.e. based on splitting and interferometrically combining relatively delayed signals at a single beamsplitter
• CPC Class Codes: G02B 6/29358 : Multiple beam interferometer external to a light guide, e.g. Fabry-Pérot, etalon, VIPA plate, OTDL plate, continuous interferometer, parallel plate resonator G02B6/29347, G02B6/29349, G02B6/2935, G02B6/29361 take precedence; resonator evanescently coupled to light guide G02B6/29335
• CPC Class Codes: G02B 6/29391 : Power equalisation of different channels, e.g. power flattening
• CPC Class Codes: G02B 6/29395 : configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02B 6/34 : utilising prism or grating G02B6/293 takes precedence
• CPC Class Codes: G02B 6/4232 : using the surface tension of fluid solder to align the elements, e.g. solder bump techniques flip-chip mounting techniques in assembly of semiconductor devices H01L24/81
• CPC Class Codes: G02B 6/43 : Arrangements comprising a plurality of opto-electronic elements and associated optical interconnections
• CPC Class Codes: G02F 1/0147 : based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 1/0152 : using free carrier effects, e.g. plasma effect
• CPC Class Codes: G02F 1/025 : in an optical waveguide structure G02F1/017, G02F1/2257 take precedence
• CPC Class Codes: G02F 1/295 : Analog deflection from or in an optical waveguide structure]
• CPC Class Codes: G02F 2201/20 : delay line
• CPC Class Codes: H01L 27/1203 : the substrate comprising an insulating body on a semiconductor body, e.g. SOI three-dimensional layout H01L27/0688

Abstract

An apparatus and associated method for altering the propagation constant of a region of equalizing propagation constant in an optical waveguide. The method comprising positioning an electrode of a prescribed electrode shape proximate the waveguide. An altered region of equalizing propagation constant is projected into the waveguide that corresponds, in shape, to the prescribed electrode shape by applying a voltage to the shaped electrode. The propagation constant of the region of equalizing propagation constant is controlled by varying the voltage.

Claims

1. An optical dynamic gain equalizer that equalizes strengths of multiple bandwidths of an input optical signal, comprising:

a wavelength separator that separates the input optical signal into different ones of the multiple bandwidths, wherein different ones of the multiple bandwidths output by the wavelength separator may have different signal strengths; and

a plurality of independently controllable variable attenuators;

each of the variable attenuators receiving one of the multiple bandwidths output from the wavelength separator, and outputting a bandwidth having an equalized strength such that the bandwidths output by each of the plurality of variable attenuators have substantially equal strengths, wherein each of the variable attenuators comprises;

at least one waveguide that includes an input port wherein the input optical signal is introduced into the waveguide, an output port wherein the equalized output optical signal exits the waveguide, and a plurality of regions of equalizing propagation constant disposed along a length of the waveguide and between the input port and the output port, wherein the input optical signal is guided by total internal reflection in the waveguide, and the waveguide is formed at least in part from an active semiconductor, at least one of the plurality of regions associated with;

a first electrode positioned proximate a first surface of the region of equalizing propagation constant and electrically separated from the active semiconductor;

a second electrode in electrical contact with the active semiconductor and disposed on a first side of the region of equalizing propagation constant;

a two-dimensional electron (hole) gas (2DEG) having a free carrier distribution that is formed on the first surface when a voltage is applied between the first electrode and the second electrode; and

wherein changing the voltage causes a corresponding change of the free carrier distribution which, in turn, causes corresponding change of a propagation constant level in the region of equalizing propagation constant that equalizes the strengths of multiple bandwidths of the input optical signal flowing through the region of equalizing propagation constant.

2. The optical dynamic gain equalizer of claim 1, further comprising a third electrode in electrical contact with the active semiconductor disposed on a second side of the region of equalizing propagation constant opposite the first side;

wherein the second and third electrodes are electrically coupled to a common potential.

3. The optical dynamic gain equalizer of claim 1 or 2, wherein the 2DEG is oriented in a plane that is substantially parallel to said length.

4. The optical dynamic gain equalizer of claim 2, further comprising a field effect transistor (FET) portion that includes the first, second, and third electrodes.

5. The optical dynamic gain equalizer of claim 4, wherein the FET portion is from one of the group of metal-oxide-semiconductor FET (MOSFET), metal-electrical insulator-semiconductor FET (MISFET), a metal semiconductor field effect transistor (MESFET), a high electron mobility transistor (HEMT), or a modulation doped FET (MODFET).

6. The optical dynamic gain equalizer of claim 1, further comprising a metal oxide semiconductor capacitor (MOSCAP) portion.

7. The optical dynamic gain equalizer of claim 6, wherein a body contact electrode is located below the waveguide.

8. The optical dynamic gain equalizer of claim 1, wherein the waveguide comprises any group III or group V semiconductor.

9. The optical dynamic gain equalizer of claim 1, wherein the free-carrier distribution of the 2DEG layer is varied by changing the voltage applied to the first electrode, and wherein light flowing through the waveguide is controllably attenuated in response to the voltage applied to the first electrode.

10. The optical dynamic gain equalizer of claim 1, further comprising:

at least one optical monitor coupled to a controller, wherein the optical monitor provides information corresponding to different signal strengths output by the wavelength separator to the controller; and

wherein the controller varies the voltage applied between the first and second electrodes in each of the variable attenuators to equalize the strength of the bandwidths output by the variable attenuators.

11. The optical dynamic gain equalizer of claim 1, further comprising:

at least one optical monitor coupled to a controller, wherein the optical monitor provides information corresponding to the strength of the bandwidths output by the variable attenuators; and

wherein the controller varies the voltage applied between the first and second electrodes in each of the variable attenuators in order to equalize the strength of the bandwidths output by the variable attenuators.

12. The optical dynamic gain equalizer of claim 10, wherein the plurality of independently controllable variable attenuators and the wavelength separator use different portions of the same waveguide, and wherein the waveguide is formed on a single substrate.

13. An optical dynamic gain equalizer that equalizes strengths of multiple bandwidths of light using at least one waveguide, the optical dynamic gain equalizer comprising:

a wavelength separator that separates the input optical signal into different ones of the multiple bandwidths, wherein different ones of the multiple bandwidths output by the wavelength separator may have different signal strengths; and

a plurality of independently controllable variable attenuators;

each of the variable attenuators receiving one of the multiple bandwidths output from the wavelength separator, and outputting a bandwidth having an equalized strength such that the bandwidths output by each of the plurality of variable attenuators have substantially equal strengths, wherein each of the variable attenuators comprises;

a plurality of electrodes, each electrode of the plurality of electrodes having a prescribed electrode shape positioned proximate the at least one waveguide,

a voltage source connected to the electrode for applying voltage to the electrode, wherein the voltage causes the electrode to project into the waveguide the region of equalizing propagation constant, said region of equalizing propagation constant corresponding generally in shape to the shape of the electrode and equalizing the strengths of multiple bandwidths of light flowing through the waveguide, and

a controller that controls the propagation constant level of the region of equalizing propagation constant by varying the voltage applied to the electrode to equalize the strengths of multiple bandwidths of light flowing through the waveguide.

14. The optical dynamic gain equalizer of claim 13, wherein the plurality of independently controllable variable attenuators and the wavelength separator use different portions of the same waveguide, and wherein the waveguide is formed on a single substrate.

15. The optical dynamic gain equalizer of claim 13, further comprising a field effect transistor (FET) portion including a source electrode and a drain electrode.

16. The optical dynamic gain equalizer of claim 15, wherein the FET is from one of the group of metal-oxide-semiconductor FET (MOSFET), metal-electrical insulator-semiconductor FET (MISFET), a metal semiconductor field effect transistor (MESFET), a high electron mobility transistor (HEMT), or a modulation doped FET (MODFET).

17. The optical dynamic gain equalizer of claim 13, further comprising one or more body contact electrode(s) positioned relative to the waveguide and electrically integrated with the active semiconductor.

18. The optical dynamic gain equalizer of claim 17, further comprising a metal oxide semiconductor capacitor (MOSCAP) portion that includes the body contact electrode.

19. The optical dynamic gain equalizer of claim 18, wherein the body contact electrode is located below the waveguide.

20. The optical dynamic gain equalizer of claim 18, wherein the body contact electrode includes a first body contact electrode and a second body contact electrode, the first body contact electrode, the electrode of the plurality of electrodes, and the second body contact electrode are located above the waveguide.

21. The optical dynamic gain equalizer of claim 18, wherein the first body contact electrode is located on an opposed side of the electrode from the second body contact electrode.

22. The optical dynamic gain equalizer of claim 13, further comprising a free-carrier distribution of a 2DEG layer that is varied by changing the voltage applied to the electrode of the plurality of electrodes, and wherein light flowing through the waveguide is controllably attenuated in response to the voltage applied to the electrode.

23. The optical dynamic gain equalizer of claim 13, further comprising an optical device coupled with a variable coupling to the optical dynamic gain equalizer.

24. The optical dynamic gain equalizer of claim 13, further comprising:

at least one optical monitor coupled to a controller, wherein the optical monitor provides information corresponding to different signal strengths output by the wavelength separator to the controller; and

wherein the controller varies the voltage applied between the first and second electrodes in each of the variable attenuators to equalize the strength of the bandwidths output by the variable attenuators.

25. The optical dynamic gain equalizer of claim 13, further comprising:

at least one optical monitor coupled to a controller, wherein the optical monitor provides information corresponding to the strength of the bandwidths output by the variable attenuators; and

wherein the controller varies the voltage applied between the first and second electrodes in each of the variable attenuators in order to equalize the strength of the bandwidths output by the variable attenuators.

26. A method for equalizing the strength of multiple bandwidths of light by changing a propagation constant level of a plurality of regions of equalizing propagation constant of an at least one waveguide in an optical device, the method comprising for each one of the plurality of regions of equalizing propagation constant:

separating the input optical signal into different ones of the multiple bandwidths, wherein different ones of the multiple bandwidths output by the wavelength separator may have different signal strengths; and

receiving one of the multiple bandwidths output of one of a plurality of Variable Optical Attenuator (VOA), and outputting a bandwidth having an equalized strength such that the bandwidths output by each of the plurality of VOAs have substantially equal strengths, the receiving and outputting at each one of the plurality of VOAs comprising;

positioning a planar electrode proximate the waveguide;

applying a voltage to the planar electrode to change the level of propagation constant in a region of equalizing propagation constant in the waveguide wherein the region of equalizing propagation constant corresponds in shape to the planar electrode shape; and

controlling a propagation constant level of the region of equalizing propagation constant by varying the voltage to control the equalizing the strength of the multiple bandwidths of light flowing through the waveguide.

27. The method of claim 26, further comprising:

providing information corresponding to different ones of the multiple bandwidths output by the wavelength separator; and

varying the voltage applied to the planar electrode in each of the variable attenuators to equalize the strength of the multiple bandwidths.

28. The method of claim 26, further comprising:

providing information corresponding to the strength of the bandwidths output by the variable attenuators; and

varying the voltage applied to the planar electrodes in each of the variable attenuators in order to equalize the strength of the bandwidths output by the variable attenuators.

29. The method of claim 26, further comprising a 2DEG located between the planar electrode and the body contact electrode, wherein the 2DEG is oriented in a plane that is substantially parallel to a length of the region of equalizing propagation constant.

30. The method of claim 26, further comprising a field effect transistor (FET) portion including a planar electrode.

31. The method of claim 26, wherein the FET is from one of the group of metal-oxide-semiconductor FET (MOSFET), metal-electrical insulator-semiconductor FET (MISFET), a metal semiconductor field effect transistor (MESFET), a high electron mobility transistor (HEMT), or a modulation doped FET (MODFET).

32. The method of claim 26, further comprising one or more body contact electrode(s) positioned relative to the waveguide and electrically integrated with the active semiconductor.

33. The method of claim 26, further comprising a metal oxide semiconductor capacitor (MOSCAP) portion including the body contact electrode.

34. The method of claim 33, wherein the body contact electrode is positioned below the waveguide.

35. The method of claim 33, wherein the body contact electrode includes a first body contact electrode and a second body contact electrode, the first body contact electrode, the planar electrode, and the second body contact electrode are located above the waveguide;

and the first body contact electrode is located on an opposed side of the planar electrode from the second body contact electrode.

36. The method of claim 26, wherein the waveguide comprises any group III or group V semiconductor.

37. The method of claim 26, further comprising a free-carrier distribution of a 2DEG, wherein the free-carrier distribution of a 2DEG is changed by changing the voltage applied to the planar electrode, and wherein light flowing through the waveguide is controllably changed in response to changing the free-carrier distribution of the 2DEG layer.

38. The method of claim 26, further comprising an optical device coupled with a variable coupling to the optical dynamic gain equalizer.

39. A computer readable medium containing software that controls a planar electrode having a prescribed shape positioned proximate a waveguide to equalize the strengths of multiple bandwidths of light, said software when executed by a processor causes the processor to perform the steps of:

separating the input optical signal into different ones of the multiple bandwidths, wherein different ones of the multiple bandwidths output by the wavelength separator may have different signal strengths; and

receiving one of the multiple bandwidths output of one of a plurality of Variable Optical Attenuator (VOA), and outputting a bandwidth having an equalized strength such that the bandwidths output by each of the plurality of VOAs have substantially equal strengths, the receiving and outputting at each one of the plurality of VOAs comprising;

positioning a planar electrode proximate the waveguide;

applying a voltage to the planar electrode to change the level of propagation constant in a region of equalizing propagation constant in the waveguide wherein the region of equalizing propagation constant corresponds in shape to the planar electrode shape; and

controlling a propagation constant level of the region of equalizing propagation constant by varying the voltage to control the equalizing the strength of the multiple bandwidths of light flowing through the waveguide.

40. An optical dynamic gain equalizer for equalizing light flowing through a waveguide by changing the propagation constant level of a waveguide, the optical dynamic gain equalizer comprising:

a wavelength separator that separates the input optical signal into different ones of the multiple bandwidths, wherein different ones of the multiple bandwidths output by the wavelength separator may have different signal strengths; and

a plurality of independently controllable variable attenuators;

each of the variable attenuators receiving one of the multiple bandwidths output from the wavelength separator, and outputting a bandwidth having an equalized strength such that the bandwidths output by each of the plurality of variable attenuators have substantially equal strengths, wherein each one of the variable attenuators comprises;

a region of equalizing propagation constant disposed along a length of the waveguide and defining a region where light is equalized, wherein the light is guided within the waveguide by total internal reflection, and the waveguide is formed at least in part from an active semiconductor;

a Field Effect Transistor portion (FET portion) including a gate electrode, a source electrode, and a drain electrode;

the gate electrode is mounted to, but electrically insulated from, the active semiconductor;

the drain electrode and the source electrode are held at a substantially common voltage;

wherein the gate electrode, the source electrode, and the drain electrode are positioned substantially above the waveguide, the source electrode is located on a substantially opposed side of the gate electrode from the drain electrode;

a two-dimensional electron (hole) gas (2DEG) forming a layer having a free carrier distribution that is formed on the first surface of the active semiconductor when a voltage is applied between the gate electrode and the common voltage;

a voltage source connected to the gate electrode for applying voltage to the gate electrode, wherein the gate electrode projects a region of equalizing propagation constant into the waveguide to equalize the strengths of multiple bandwidths of light flowing through the waveguide; and

a controller for controlling the propagation constant level of the region of equalizing propagation constant by varying the voltage produced by the voltage source to control the equalizing of the strength of multiple bandwidths of light flowing through the waveguide.

41. The optical dynamic gain equalizer of claim 40, wherein all of the plurality of independently controllable variable attenuators and the wavelength separator are attached to a single substrate.

42. The optical dynamic gain equalizer of claim 40, further comprising:

at least one optical monitor coupled to a controller, wherein the optical monitor provides information corresponding to different signal strengths output by the wavelength separator to the controller; and

wherein the controller varies the voltage applied to the gate electrode in each of the variable attenuators to equalize the strength of the bandwidths output by the variable attenuators.

43. The optical dynamic gain equalizer of claim 40, further comprising:

at least one optical monitor coupled to a controller, wherein the optical monitor provides information corresponding to the strength of the bandwidths output by the variable attenuators; and

wherein the controller varies the voltage applied between the gate electrode in each of the variable attenuators in order to equalize the strength of the bandwidths output by the variable attenuators.

44. The optical dynamic gain equalizer of claim 40, wherein the plurality of independently controllable variable attenuators and the wavelength separator use different portions of the same waveguide, and wherein the waveguide is formed on a single substrate.

46. The apparatus of claim 40, further comprising:

at least one optical monitor coupled to a controller, wherein the optical monitor provides information corresponding to different signal strengths output by the wavelength separator to the controller; and

wherein the controller varies the voltage applied to the planar electrode in each of the variable attenuators to equalize the strength of the bandwidths output by the variable attenuators.

47. The apparatus of claim 40, further comprising:

at least one optical monitor coupled to a controller, wherein the optical monitor provides information corresponding to the strength of the bandwidths output by the variable attenuators; and

wherein the controller varies the voltage applied between the planar electrode in each of the variable attenuators in order to equalize the strength of the bandwidths output by the variable attenuators.

48. The apparatus of claim 40, wherein the plurality of independently controllable variable attenuators and the wavelength separator use different portions of the same waveguide, and wherein the waveguide is formed on a single substrate.

45. An apparatus for equalizing an input optical signal in order to generate a equalized output optical signal, comprising:

a wavelength separator that separates the input optical signal into different ones of the multiple bandwidths, wherein different ones of the multiple bandwidths output by the wavelength separator may have different signal strengths; and

a plurality of independently controllable variable attenuators;

each of the variable attenuators receiving one of the multiple bandwidths output from the wavelength separator, and outputting a bandwidth having an equalized strength such that the bandwidths output by each of the plurality of variable attenuators have substantially equal strengths, wherein each one of the variable attenuators comprises;

a planar electrode positioned proximate the waveguide;

means for equalizing a region of equalizing propagation constant in the waveguide that substantially corresponds in shape to a shape of the planar electrode, by applying a voltage to the planar electrode; and

means for controlling a propagation constant level of the region of equalizing propagation constant by varying the voltage to control the equalizing the strength of multiple bandwidths of light flowing through the waveguide.

49. A method for generating a equalized output optical signal by passing an input optical signal through a waveguide, comprising:

separating the input optical signal into different ones of the multiple bandwidths, wherein different ones of the multiple bandwidths output by the wavelength separator may have different signal strengths; and

receiving one of the multiple bandwidths output of one of a plurality of Variable Optical Attenuator (VOA), and outputting a bandwidth having an equalized strength such that the bandwidths output by each of the plurality of VOAs have substantially equal strengths, the receiving and outputting at each one of the plurality of VOAs comprising;

providing a gate electrode proximate the waveguide;

providing a body contact electrode proximate the waveguide;

applying the input optical signal to the waveguide;

applying an equalizing voltage to the gate electrode that generates a region of equalizing propagation constant in the waveguide; and

generating the equalized output optical signal in response to the input optical signal in which the strength of multiple bandwidths of light are equalized in the equalized output signal.

50. The method of claim 49, further comprising:

providing information corresponding to different ones of the multiple bandwidths output by the wavelength separator; and

varying the voltage applied to the gate electrode and the body contact electrode in each of the variable attenuators to equalize the strength of the multiple bandwidths.

51. The method of claim 49, further comprising:

providing information corresponding to the strength of the bandwidths output by the variable attenuators; and

varying the voltage applied to the gate electrodes and the body contact electrode in each of the variable attenuators in order to equalize the strength of the bandwidths output by the variable attenuators.