Optical device and circuit using phase modulation and related methods

• US 7,657,188 B2
• Filed: 05/21/2004
• Issued: 02/02/2010
• Est. Priority Date: 05/21/2004
• Status: Active Grant

• Current Assignee: John Covey
• Original Assignee: CoveyTech, LLC
• Inventors: Covey, John Luther
• Primary Examiner(s): Bello; Agustin
• Application Number:
  US10/850,736
• Publication Number:
  US 20050259999A1
• Time in Patent Office: 2,083 Days
• Field of Search: 398182-201
• US Class Current: 398/182
• CPC Class Codes: G02F 2202/32 Photonic crystals
• CPC Class Codes: G02F 3/00 Optical logic elements; Optical bistable devices
• CPC Class Codes: G02F 3/024 based on non-linear elements, e.g. non-linear Fabry-Perot cavity G02F3/028 takes precedence

Abstract

A disclosed apparatus comprises a guiding element and a nonlinear element. The guiding element guides optical input signals, at least one of which is phase-modulated, to an interference area where such signals meet and interfere. The resulting interference signal is nonlinearly discriminated by the nonlinear element to produce an optical output signal that can be amplitude- or phase-modulated according to the phase modulation of the input signals. The invention also includes related methods and photonic logic gates.

Claims

1. A method comprising the steps of:

a) receiving a first optical signal at a first pathway defined in a photonic bandgap (PBG) element, the PBG element defined by periodic structures, and the first pathway defined by an absence of structures in the PBG element;

b) receiving a second optical signal at a second pathway defined in the PBG element, the second pathway defined by an absence of structures in the PBG element;

c) phase-modulating the first optical signal to contain first data with a first phase modulator mounted in the first pathway of the PBG element;

d) phase-modulating the second optical signal to contain second data with a second phase modulator mounted in the second pathway of the PBG element;

e) guiding the phase-modulated first optical signal via the first pathway to an interference area defined in the PBG element;

f) guiding the phase-modulated second optical signal via the second pathway to the interference area;

g) combining the phase-modulated first optical signal with the phase-modulated second optical signal in the interference area to generate an optical interference signal that is amplitude-modulated based on the phase modulation of the first optical signal and the second optical signal;

h) nonlinearly discriminating the optical interference signal with a nonlinear element situated in the PBG element and optically positioned between an output of the interference area and an input to an output pathway defined in the PBG element to produce an optical output signal having a digital logic state representing third data resulting from a logic operation on the first data and second data by performance of the steps (g) and (h);

i) guiding the optical output signal to an output of the PBG element via the output pathway; and

j) outputting the optical output signal from the PBG element.

2. A method as claimed in claim 1 wherein the optical interference signal is amplitude-modulated based on the phase modulation of at least the first optical signal.

3. A method as claimed in claim 2 wherein the optical interference signal is amplitude-modulated based on phase modulation of the second optical signal.

4. A method as claimed in claim 1 wherein the PBG element defines a pathway that guides the optical interference signal to the nonlinear element that nonlinearly discriminates the optical interference signal to produce the optical output signal.

5. A method as claimed in claim 1 further comprising the step of:

k) generating the first optical signal with a light source.

6. A method as claimed in claim 5 wherein the light source comprises a laser.

7. A method as claimed in claim 1 further comprising the step of:

k) focusing the first optical signal at an input to the first pathway of the PBG element.

8. A method as claimed in claim 7 wherein the focusing is performed by a lens.

9. A method as claimed in claim 1 wherein the first phase modulator performs modulation with a piezoelectric element that changes the effective path length experienced by the first optical signal based on a modulation signal in order to modulate its phase.

10. A method as claimed in claim 1 comprising the step of:

k) filtering the phase-modulated first optical signal with the PBG element.

11. A method as claimed in claim 10 wherein the filtering is performed according to the spacing of structures in the PBG element.

12. A method as claimed in claim 1 further comprising the step of:

k) generating the second optical signal with a light source.

13. A method as claimed in claim 12 wherein the light source comprises a laser.

14. A method as claimed in claim 1 further comprising the step of:

k) focusing the second optical signal at an input to the second pathway of the PBG element.

15. A method as claimed in claim 14 wherein the focusing is performed by a lens.

16. A method as claimed in claim 1 comprising the step of:

k) filtering the second optical signal with the PBG element.

17. A method as claimed in claim 16 wherein the filtering is performed according to the spacing of structures in the PBG element.

18. An optical device receiving a first optical signal and a second optical signal, the optical device comprising:

an integrated photonic transistor having

a guiding element formed of periodic structures having a spacing related to the wavelength of the first optical signal and the second optical signal propagating therein, the guiding element further defining first and second pathways along which travel the first optical signal and the second optical signal, respectively, the first and second pathways joining to form an interference area in which the first and second optical signals interfere to form an optical interference signal;

a first phase modulator positioned in the first pathway of the guiding element and generating the phase-modulated first optical signal based on a first modulation signal;

a second phase modulator positioned in the second pathway of the guiding element and generating the phase-modulated second optical signal based on a second modulation signal; and

a nonlinear element positioned to receive the optical interference signal and nonlinearly discriminating the optical interference signal to form the optical output signal having a digital logic state,

the guiding element defining an output pathway adapted to receive and guide the discriminated optical output signal from the nonlinear element to an output of the device;

the nonlinear element optically positioned between an output of the interference area and an input to the output pathway; and

the first and second pathways, the interference area and the output pathway defined by an absence of periodic structures in the guiding element.

19. An optical device as claimed in claim 18 wherein the integrated photonic transistor is formed on a substrate.

20. An optical device as claimed in claim 19 wherein the substrate is composed of silicon.

21. An optical device as claimed in claim 18 wherein the periodic structures are formed from a substrate by processing thereof.

22. An optical device as claimed in claim 21 wherein the processing comprises selective etching of material on the substrate.

23. An optical device as claimed in claim 21 wherein the processing comprises selective deposition of material on the substrate.

24. An optical device as claimed in claim 18 wherein the periodic structures are spaced by the wavelength of the first and second optical signals divided by the index of refraction of the material defining the structures.

25. An optical device as claimed in claim 18 wherein adjacent periodic structures are spaced by 0.44±

0.04 microns.

26. An optical device as claimed in claim 18 wherein the periodic structures are cylindrical in shape.

27. An optical device as claimed in claim 18 wherein the periodic structures are spherical in shape.

28. An optical device as claimed in claim 18 wherein the periodic structures are rod-like in shape.

29. An optical device as claimed in claim 18 wherein the nonlinear element comprises a grating.

30. An optical device as claimed in claim 18 wherein the nonlinear element comprises a multiple quantum dot array.

31. An optical device as claimed in claim 18 wherein the nonlinear element comprises a laser.

32. An optical device as claimed in claim 31 wherein the laser generates the optical output signal at 1.55±

0.02 microns.

33. An optical device as claimed in claim 18 wherein the nonlinear element comprises a cavity.

34. An optical device as claimed in claim 18 wherein the nonlinear element comprises a non-resonant amplifier.

35. An optical device as claimed in claim 18 wherein the effective length of the nonlinear element and the output pathway at least in part define the phase of the optical output signal at an output of the optical device.

36. An optical device as claimed in claim 18 further comprising:

a power supply coupled to provide electric power to the nonlinear element.

37. An optical device as claimed in claim 36 wherein the power supply is integrated on a substrate together with the nonlinear element and the guiding element.

38. An optical device as claimed in claim 18 wherein the first modulation signal is electric and the first phase-modulator comprises a piezoelectric element capable of changing the effective path length traveled by the first optical signal to phase-modulate the first optical signal.

39. An optical device as claimed in claim 18 wherein the first modulation signal is optic and the first phase-modulator comprises an optical phase modulation element capable of changing its refractive index in response to an optical modulation signal to phase-modulate the first optical signal.

40. An optical device as claimed in claim 18 wherein the first and second phase modulators are integrated together with the guiding element and nonlinear element on a substrate.

41. An optical device as claimed in claim 18 wherein the second modulation signal is electric and the second phase-modulator comprises a piezoelectric element capable of changing the effective path length traveled by the second optical signal to phase-modulate the second optical signal.

42. An optical device as claimed in claim 18 wherein the second modulation signal is optic and the second phase-modulator comprises an optical phase modulation element capable of changing its refractive index in response to the second optical modulation signal to phase-modulate the second optical signal.

43. An optical device as claimed in claim 18 further comprising:

a filter formed of spaced structures positioned in the first pathway.

44. An optical device as claimed in claim 43 wherein the filter is integrated on a substrate along with the guiding element.

45. An optical device as claimed in claim 18 further comprising:

a filter formed of spaced structures positioned in the second pathway.

46. An optical device as claimed in claim 45 wherein the filter is integrated on a substrate along with the guiding element.

47. An optical device as claimed in claim 18 further comprising:

a light source generating the first optical signal, and positioned to provide the first optical signal to the first pathway of the guiding element of the optical device.

48. An optical device as claimed in claim 47 wherein the light source is integrated on a substrate along with the guiding element.

49. An optical device as claimed in claim 47 wherein the light source is coherent.

50. An optical device as claimed in claim 47 wherein the light source comprises a solid-state laser.

51. An optical device as claimed in claim 47 wherein the first optical signal generated by the light source has a wavelength of 1.55±

0.02 microns.

52. An optical device as claimed in claim 18 further comprising:

an optical focusing element positioned to focus the first optical signal to an opening of the first pathway defined in the guiding element.

53. An optical device as claimed in claim 52 wherein the optical focusing element is integrated on a substrate along with the guiding element and nonlinear element.

54. An optical device as claimed in claim 52 wherein the optical focusing element comprises a convex optical lens.

55. An optical device as claimed in claim 18 further comprising:

an optical focusing element positioned to focus the second optical signal to an opening of a second pathway defined in the guiding element.

56. An optical device as claimed in claim 55 wherein the optical focusing element is integrated on a substrate along with the guiding element and nonlinear element.

57. An optical device as claimed in claim 55 wherein the optical focusing element comprises a convex optical lens.

58. An optical device as claimed in claim 18 further comprising:

an optical focusing element positioned to focus the optical output signal to an opening of an output element receiving the optical output signal.

59. An optical device as claimed in claim 58 wherein the optical focusing element is integrated on a substrate along with the guiding element.

60. An optical device as claimed in claim 58 wherein the optical focusing element comprises a convex optical lens.

61. An optical device as claimed in claim 18 wherein the optical interference signal is amplitude-modulated based on the phase modulation of at least the first optical signal.

62. A optical device as claimed in claim 18 wherein the optical interference signal is amplitude-modulated based on the phase modulation of the second optical signal.

63. A optical device as claimed in claim 18 wherein the optical interference signal is phase-modulated based on the phase modulation of at least the first optical signal.

64. A optical device as claimed in claim 18 wherein the optical interference signal is phase-modulated based on the phase modulation of the second optical signal.

65. An optical device as claimed in claim 18 wherein the guiding element comprises a photonic bandgap (PBG) element.

66. An optical circuit comprising:

a logic stage comprising at least one optical logic gate integrated on a substrate, the optical logic gate receiving at least one phase-modulated optical input signal and a reference signal, the optical logic gate comprising input pathways guiding the phase-modulated optical input signal and reference signal to an interference area to generate a first interference signal nonlinearly discriminated by a nonlinear element to generate a phase-modulated optical output signal based on the phase-modulated optical input signal and the reference signal, the optical logic gate further comprising an output pathway to guide the phase-modulated optical output signal to an output of the logic stage, the input pathways, interference area and output pathway of the optical logic gate defined in a photonic bandgap (PBG) element, the nonlinear element comprising at least one of a laser, a cavity or a non-resonant amplifier; and

an output stage comprising a phase-to-amplitude converter coupled to receive the phase-modulated optical output signal, the phase-to-amplitude converter comprising input pathways guiding the phase-modulated optical output signal and the reference signal to an interference area to generate a second interference signal nonlinearly discriminated by a nonlinear element to generate an amplitude-modulated optical output signal based on the phase-modulated optical input signal and the reference signal, the output stage further comprising an output pathway to guide the amplitude-modulated optical output signal to an output of the logic stage, the input pathways, interference area and output pathway of the output stage defined in the photonic bandgap (PBG) element, the nonlinear element comprising at least one of a laser, a cavity or a non-resonant amplifier.

67. An optical circuit as claimed in claim 66 wherein the optical logic gate comprises an inverter.

68. An optical circuit as claimed in claim 66 wherein the logic stage comprises a NAND gate.

69. An optical circuit as claimed in claim 66 wherein the logic stage comprises at least one inverter and at least one NAND gate.

70. An optical circuit as claimed in claim 66 wherein the logic stage comprises at least one phase-shift element.

71. An optical circuit as claimed in claim 70 wherein the phase-shift element inverts the phase of the optical output signal.

72. An optical circuit as claimed in claim 66 wherein the first and second pathways, the interference area, the nonlinear element, and the output pathway comprise a photonic transistor.

73. An optical circuit as claimed in claim 66 wherein the PBG element comprises optical pathways connecting the optical logic gates, at least one of which turns at an angle of at least π

/3 radians.

74. An optical circuit as claimed in claim 66 wherein the logic stage and output stage are integrated together on a substrate.

75. A method comprising the steps of:

a) receiving at least one phase-modulated optical input signal at a first pathway defined in the PBG element, the PBG element defined by periodic structures, the first pathway defined by an absence of structures in the PBG element;

b) receiving an optical reference signal at a second pathway defined in the PBG element, the second pathway defined by an absence of structures in the PBG element;

c) performing a phase logic operation based on the phase-modulated optical input signal and the optical reference signal with a nonlinear element situated in the PBG element and optically positioned between an output of the interference area and an input to an output pathway defined in the PBG element to produce a phase-modulated optical output signal, the output pathway defined by an absence of structures in the PBG element, the nonlinear element comprising one or more of a laser, a cavity or a non-resonant amplifier; and

d) outputting the phase-modulated optical output signal via an output pathway defined in the PBG element, the output pathway defined by an absence of structures in the PBG element.

76. A method as claimed in claim 75 wherein the steps (a)-(d) are performed by a logic stage of an optical circuit, the logic stage comprising at least one optical logic gate.

77. A method as claimed in claim 75 wherein the optical logic gate comprises one or more NAND gates and one or more inverter gates.

78. A method as claimed in claim 75 further comprising the steps of:

e) receiving the phase-modulated optical output signal;

f) converting the phase-modulated optical output signal into an amplitude-modulated optical output signal; and

g) outputting the amplitude-modulated optical output signal.

79. A method as claimed in claim 78 wherein the steps (e)-(g) are performed by an output stage of the optical circuit.

80. A method as claimed in claim 79 wherein the output stage comprises a phase-to-amplitude modulation converter.