Microresonator and associated method for producing and controlling photonic signals with a photonic bandgap delay apparatus

• US 6,028,693 A
• Filed: 01/14/1998
• Issued: 02/22/2000
• Est. Priority Date: 01/14/1998
• Status: Expired due to Fees

• Current Assignee: National Aeronautics and Space Administration (Government of the United States of America)
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration, University of Alabama in Huntsville (University of Alabama System)
• Inventors: Fork, Richard Lynn, Jones, Darryl Keith, Keys, Andrew Scott
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Lester, Evelyn A.
• Application Number:
  US09/007,124
• Time in Patent Office: 769 Days
• Field of Search: 359/260, 359/263, 359/245, 359/278, 359/248, 359/586-589, 359/250, 359/264, 359/331, 385/14, 385/122
• US Class Current: 359/248
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 6/122 Basic optical elements, e.g. light-guiding paths
• CPC Class Codes: G02B 6/1225 comprising photonic band-gap structures or photonic lattices
• 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: G02F 1/21 by interference
• CPC Class Codes: G02F 1/213 Fabry-Perot type

Abstract

By applying a photonic signal to a microresonator that includes a photonic bandgap delay apparatus having a photonic band edge transmission resonance at the frequency of the photonic signal, the microresonator imparts a predetermined delay to the photonic signal. The photonic bandgap delay apparatus also preferably has a photonic band edge transmission resonance bandwidth which is at least as wide as the bandwidth of the photonic signal such that a uniform delay is imparted over the entire bandwidth of the photonic signal. The microresonator also includes a microresonator cavity, typically defined by a pair of switchable mirrors, within which the photonic bandgap delay apparatus is disposed. By requiring the photonic signal to oscillate within the microresonator cavity so as to pass through the photonic bandgap delay apparatus several times, the microresonator can controllably impart an adjustable delay to the photonic signal.

Claims

1. A microresonator for delaying photonic signals of a predetermined frequency, the microresonator comprising:

a pair of switchable mirrors that are spaced apart to define a microresonator cavity therebetween, wherein each mirror is controllably switchable between a transmissive state in which photonic signals enter and exit the microresonator cavity and a reflective state in which photonic signals are internally reflected within the microresonator cavity; and

a photonic bandgap delay apparatus having a photonic band edge resonance at the predetermined frequency of the photonic signals, wherein said photonic bandgap delay apparatus is disposed within the microresonator cavity defined by said pair of mirrors for delaying the photonic signals during each pass of the photonic signals through the microresonator cavity to thereby impart an adjustable delay to the photonic signals.

2. A microresonator according to claim 1 further comprising means, disposed within the microresonator cavity, for amplifying the photonic signals.

3. A microresonator according to claim 1 further comprising means, disposed within the microresonator cavity, for adjusting the phase of the photonic signals.

4. A microresonator according to claim 1 wherein the photonic signals are optical pulses having a predetermined shape, and wherein the microresonator further comprises means, disposed within the microresonator cavity, for at least partially reshaping the optical pulses.

5. A microresonator according to claim 1 wherein the photonic signals are optical pulses having a predetermined pulse length, and wherein said photonic bandgap delay apparatus is spaced by at least one-half of the predetermined pulse length of the optical pulses from each of said pair of mirrors.

6. A microresonator according to claim 1 wherein the photonic signals have a predetermined bandwidth, and wherein said photonic bandgap delay apparatus has a corresponding photonic band edge resonance bandwidth which is at least as wide as the predetermined bandwidth of the photonic signals.

7. A microresonator for delaying photonic signals of a predetermined frequency, the microresonator comprising:

a microresonator cavity; and

a photonic bandgap delay apparatus disposed within said microresonator cavity and having a predetermined plurality of first and second alternating layers which exhibit a series of photonic bandgaps, said first and second alternating layers having predetermined thicknesses and having predetermined indices of refraction, wherein said predetermined plurality, said predetermined thicknesses and said predetermined indices of refraction cooperate to produce a photonic band edge transmission resonance in said plurality of first and second alternating layers having a photonic band edge transmission resonance center frequency corresponding to said predetermined frequency, to thereby delay the photonic signals during each pass through said microresonator cavity.

8. A microresonator according to claim 7 wherein the photonic signals have a predetermined bandwidth, and wherein said photonic bandgap delay apparatus has a corresponding photonic band edge resonance bandwidth which is at least as wide as the predetermined bandwidth of the photonic signals.

9. A microresonator according to claim 7 further comprising means, disposed within said microresonator cavity, for amplifying the photonic signals.

10. A microresonator according to claim 7 further comprising means, disposed within said microresonator cavity, for adjusting the phase of the photonic signals.

11. A microresonator according to claim 7 wherein the photonic signals are optical pulses having a predetermined shape, and wherein the microresonator further comprises means, disposed within said microresonator cavity, for at least partially reshaping the optical pulses.

12. A microresonator according to claim 7 wherein the photonic signals are optical pulses having a predetermined pulse length, wherein said microresonator cavity is defined by a pair of spaced apart mirrors, and wherein said photonic bandgap delay apparatus is spaced by at least one-half of the predetermined pulse length of the optical pulses from each of said pair of mirrors.

13. A microresonator according to claim 12 wherein said plurality of first and second layers of said photonic bandgap delay apparatus are generally parallel to each other and to said pair of mirrors.

14. A microresonator according to claim 7 wherein said plurality of first and second layers of said photonic bandgap delay apparatus produce a plurality of photonic band edge resonances for each photonic bandgap at a plurality of frequencies extending away from the corresponding photonic bandgap, and wherein said predetermined plurality, said predetermined thicknesses and said predetermined indices of refraction cooperate to produce a photonic band edge transmission resonance in said plurality of first and second alternating layers, corresponding to one of said plurality of frequencies which is closest to a bandgap, and having a photonic band edge transmission resonance center frequency corresponding to said predetermined frequency.

15. A microresonator according to claim 7 wherein said plurality of first and second layers of said photonic bandgap delay apparatus comprise a plurality of alternating layers of aluminum arsenide and gallium arsenide.

16. A microresonator according to claim 7 further comprising means for varying the index of refraction of at least one of said first and second alternating layers of said photonic bandgap delay apparatus to thereby vary the delay imparted to the photonic signals.

17. A microresonator according to claim 7 wherein said predetermined thicknesses and said predetermined plurality of said first and second alternating layers of said photonic bandgap delay apparatus are described by a solution of the following two simultaneous equations:

1/T₁₂ =[1+cos π

/N cos π

/(2N)]/[1-cos (π

Δ

ω

/ω

₀) cos (π

ω

/ω

₀)] 1/T₁₂ =[sin π

/N sin π

/(2N)]/[sin (π

Δ

ω

/ω

₀)sin(π

ω

/ω

₀)] where T₁₂ =4n₁ n₂ /(n₁ +n₂)², n₁ is the index of refraction of said first alternating layers, n₂ is the index of refraction of said second alternating layers, N is said predetermined plurality, ω

₀ is the mid-gap frequency of said photonic bandgap structure, and a=π

c/(2ω

₀ n₁) and b=π

c/(2ω

₀ n₂), where a is said predetermined thickness of said first alternating layers, b is said predetermined thickness of said second alternating layers and c is the free space speed of light.

18. A microresonator for delaying photonic signals of a predetermined frequency, the microresonator comprising:

a microresonator cavity; and

a photonic bandgap delay apparatus disposed within said microresonator cavity and having a predetermined plurality of unit cells which exhibit a series of photonic bandgaps, said predetermined plurality of unit cells each having a predetermined thickness and having a variable index of refraction, wherein said predetermined plurality and said predetermined thickness cooperate to produce a photonic band edge transmission resonance in said plurality of unit cells having a photonic band edge transmission resonance center frequency corresponding to said predetermined frequency, to thereby delay the photonic signals during each pass through said microresonator cavity.

19. A microresonator according to claim 18 wherein the photonic signals have a predetermined bandwidth, and wherein said photonic bandgap delay apparatus has a corresponding photonic band edge resonance bandwidth which is at least as wide as the predetermined bandwidth of the photonic signals.

20. A microresonator according to claim 18 further comprising means, disposed within said microresonator cavity, for amplifying the photonic signals.

21. A microresonator according to claim 18 further comprising means, disposed within said microresonator cavity, for adjusting the phase of the photonic signals.

22. A microresonator according to claim 18 wherein the photonic signals are optical pulses having a predetermined shape, and wherein the microresonator further comprises means, disposed within said microresonator cavity, for at least partially reshaping the optical pulses.

23. A microresonator according to claim 18 wherein the photonic signals are optical signals having a predetermined pulse length, wherein said microresonator cavity is defined by a pair of spaced apart mirrors, and wherein said photonic bandgap delay apparatus is spaced by at least one-half of the predetermined pulse length of the optical pulses from each of said pair of mirrors.

24. A microresonator according to claim 23 wherein said plurality of unit cells of said photonic bandgap delay apparatus are generally parallel to each other and to said pair of mirrors.

25. A microresonator according to claim 18 wherein said plurality of unit cells of said photonic bandgap delay apparatus produce a plurality of photonic band edge resonances for each photonic bandgap, at a plurality of frequencies extending away from the corresponding photonic bandgap, and wherein said predetermined plurality and said predetermined thickness cooperate to produce a photonic band edge transmission resonance in said plurality of unit cells, corresponding to one of said plurality of frequencies which is closest to a bandgap, and having a photonic band edge transmission resonance center frequency corresponding to said predetermined frequency.

26. A microresonator according to claim 18 wherein said variable index of refraction of said unit cells of said photonic bandgap delay apparatus is a continuously or discontinuously variable index of refraction which varies across said predetermined thickness of said respective unit cells.

27. A method of delaying photonic signals of a predetermined frequency and a predetermined bandwidth, comprising the steps of:

introducing the photonic signals into a microresonator having a microresonator cavity;

delaying the photonic signals with a photonic bandgap delay apparatus having a photonic band edge resonance at the predetermined frequency of the photonic signals and having a corresponding photonic band edge resonance bandwidth which is at least as wide as the predetermined bandwidth of the photonic signals such that the photonic signals are delayed during each pass through the microresonator cavity; and

permitting the photonic signals to exit the microresonator cavity once the photonic signals have been delayed.

28. A method according to claim 27 further comprising the step of amplifying the photonic signals within the microresonator cavity.

29. A method according to claim 27 further comprising the step of adjusting the phase of the photonic signals within the microresonator cavity.

30. A method according to claim 27 wherein the photonic signals are optical pulses having a predetermined shape, and wherein the method further comprises the step of at least partially reshaping the optical pulses within the microresonator cavity.

31. A method according to claim 27 further comprising the steps of:

splitting the photonic signals into photonic subsignals within the microresonator cavity;

separately delaying each photonic subsignal; and

combining the delayed photonic subsignals prior to permitting the resulting photonic signals to exit the microresonator cavity.

32. A method of delaying photonic signals comprising the steps of:

applying the photonic signals to a microresonator having a pair of switchable mirrors that are spaced apart to define a microresonator cavity therebetween and a photonic bandgap delay apparatus disposed within the microresonator cavity;

switching one of the mirrors to a transmissive state to permit the applied photonic signals to enter the microresonator cavity;

switching the pair of mirrors to a reflective state such that the photonic signals reflect between the mirrors and make a plurality of passes through the microresonator cavity;

delaying the photonic signals with the photonic bandgap delay apparatus during each pass through the microresonator cavity; and

switching one of the mirrors to a transmissive state to permit the photonic signals to exit the microresonator cavity once the photonic signals have been delayed.

33. A method according to claim 32 wherein said applying step comprises applying photonic signals which have a predetermined frequency and a predetermined bandwidth to the microresonator, and wherein the photonic bandgap delay apparatus has a photonic band edge resonance at the predetermined frequency of the photonic signals and a corresponding photonic band edge resonance bandwidth which is at least as wide as the predetermined bandwidth of the photonic signals, to thereby impart a predetermined delay to the photonic signals which pass through the microresonator cavity.

34. A method according to claim 32 further comprising the step of amplifying the photonic signals within the microresonator cavity.

35. A method according to claim 32 further comprising the step of adjusting the phase of the photonic signals within the microresonator cavity.

36. A method according to claim 32 wherein the photonic signals are optical pulses having a predetermined shape, and wherein the method further comprises the step of at least partially reshaping the optical pulses within the microresonator cavity.

37. A method according to claim 32 further comprising the steps of:

splitting the photonic signals into photonic subsignals within the microresonator cavity;

separately delaying each photonic subsignal; and

combining the delayed photonic subsignals prior to permitting the resulting photonic signals to exit the microresonator cavity.