Photonic bandgap apparatus and method for delaying photonic signals

• US 5,751,466 A
• Filed: 01/11/1996
• Issued: 05/12/1998
• Est. Priority Date: 01/11/1996
• Status: Expired due to Term

• Current Assignee: Alabama University of At Huntsville, The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: Board of Trustees of The University of Illinois
• Inventors: Fork, Richard L., Dowling, Jonathan P., Reinhardt, Senter B. Jr., Flynn, Rachel J., Tocci, Michael D., Scalora, Michael, Bloemer, Mark J., Bowden, Charles M.
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): Lester, Evelyn A.
• Application Number:
  US08/584,403
• Time in Patent Office: 852 Days
• Field of Search: 359/260, 359/248, 359/586, 359/587, 359/588, 359/589, 359/263, 257/25, 257/189, 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 6/1225 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 1/3511 Self-focusing or self-trapping of light; Light-induced birefringence; Induced optical Kerr-effect
• CPC Class Codes: G02F 2201/20 delay line

Abstract

A photonic signal is applied to a photonic bandgap structure having a photonic band edge transmission resonance at the frequency of the photonic signal and having a photonic band edge transmission resonance bandwidth which is at least as wide as the bandwidth of the photonic signal. When a photonic band edge transmission resonance is matched to the photonic signal which is being transmitted, a controllable delay is imparted to the photonic signal without significantly altering the photonic signal itself.

Claims

1. Apparatus for delaying photonic signals of predetermined frequency and predetermined bandwidth by a predetermined delay, comprising:

a predetermined plurality of first and second alternating layers which exhibit a series of photonic bandgaps, said plurality of first and second alternating layers being generally parallel and including an initial layer and a last layer, 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, and a corresponding photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth, to thereby impart said predetermined delay to said photonic signals which pass therethrough;

means for directing said photonic signals into said first layer such that said photonic signals propagate in a direction generally perpendicular to said plurality of first and second alternating layers; and

means for receiving the delayed photonic signals which emerge from said last layer.

2. A delaying apparatus according to claim 1 wherein said plurality of first and second layers 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, and a photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth.

3. A delaying apparatus according to claim 1 wherein said photonic signals are optical signals and wherein said plurality of first and second layers comprise a plurality of alternating layers of aluminum arsenide and gallium arsenide.

4. A delaying apparatus according to claim 1 further comprising:

means for varying the index of refraction of at least one of said first and second alternating layers to thereby vary said predetermined delay.

5. Apparatus for delaying photonic signals of predetermined frequency and predetermined bandwidth by a predetermined delay, comprising:

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, and a corresponding photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth, to thereby impart said predetermined delay to said photonic signals which pass therethrough,

wherein said predetermined thicknesses and said predetermined plurality are described by a solution of the following two simultaneous equations;

space="preserve" listing-type="equation">1/T.sub.12 = 1+cos π

/N cos π

/(2N)!/ 1- cos (π

Δ

ω

/ω

.sub.0) cos (π

ω

/ω

.sub.0)!

space="preserve" listing-type="equation">1/T.sub.12 = sin π

/N sin π

/(2N)!/ sin (π

Δ

ω

/ω

.sub.0) sin (π

ω

/ω

.sub.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.

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

directing the photonic signals into a predetermined plurality of first and second alternating layers which are generally parallel and 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, and a corresponding photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth, to thereby impart said predetermined delay to said photonic signals which pass therethrough;

wherein said directing step comprises directing the photonic signals into the plurality of first and second alternating layers such that the photonic signals propagate in a direction generally perpendicular to the plurality of first and second alternating layers; and

receiving the delayed electromagnetic pulses which emerge from said predetermined plurality of first and second alternating layers.

7. A method according to claim 6 wherein said plurality of first and second layers produce a plurality of photonic band edge resonances for each photonic bandgap, at a plurality of frequencies extending away from the corresponding photonic band edge frequency, 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, and a photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth.

8. A method according to claim 6 wherein said photonic signals are optical signals and wherein said plurality of first and second layers comprise a plurality of alternating layers of aluminum arsenide and gallium arsenide.

9. A method according to claim 6 further comprising the step of:

varying the index of refraction of at least one of said first and second alternating layers, to thereby vary the predetermined delay.

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

directing the photonic signals into 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, and a corresponding photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth, to thereby impart said predetermined delay to said photonic signals which pass therethrough, wherein said predetermined thicknesses and said predetermined plurality are described by a solution of the following two simultaneous equations;

space="preserve" listing-type="equation">1/T.sub.12 = 1+cos π

/N cos π

/(2N)!/ 1- cos (π

Δ

ω

/ω

.sub.0) cos (π

ω

/ω

.sub.0)!

space="preserve" listing-type="equation">1/T.sub.12 = sin π

/N sin π

/(2N!/ sin (π

Δ

ω

/ω

.sub.0) sin (π

ω

/ω

.sub.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 aid predetermined thickness of said second alternating layers and c is the free space speed of light; and

receiving the delayed electromagnetic pulses which emerge from said predetermined plurality of first and second alternating layers.

11. Apparatus for delaying photonic signals of predetermined frequency and predetermined bandwidth by a predetermined delay, comprising:

a predetermined plurality of unit cells which exhibit a series of photonic bandgaps, said plurality of unit cells being generally parallel and including a first unit cell and a last unit cell, said predetermined plurality of unit cells each having a predetermined thickness and having variable index of refraction which varies across said predetermined thickness, 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, and a corresponding photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth, to thereby impart said predetermined delay to said photonic signals which pass therethrough

means for directing said photonic signals into said first unit cell such that said photonic signals propagate in a direction generally perpendicular to said plurality of unit cells; and

means for receiving the delayed photonic signals which emerge from said last unit cell.

12. A delaying apparatus according to claim 11 wherein said plurality of unit cells 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, and a photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth.

13. A delaying apparatus according to claim 11 wherein said variable index of refraction is a continuously or discontinuously variable index of refraction which varies across said predetermined thickness.

14. A delaying apparatus according to claim 11 further comprising:

means for further varying the variable index of refraction of at least one of said unit cells to thereby vary said predetermined delay.

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

directing the photonic signals into a predetermined plurality of unit cells which are generally parallel and which exhibit a series of photonic bandgaps, said predetermined plurality of unit cells each having a predetermined thickness and having variable index of refraction which varies across said predetermined thickness, 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, and a corresponding photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth, to thereby impart said predetermined delay to said photonic signals which pass therethrough,

wherein said directing step comprises directing the photonic signals into the plurality of unit cells such that the photonic signals propagate in a direction generally perpendicular to the plurality of unit cells; and

receiving the delayed electromagnetic pulses which emerge from said predetermined plurality of unit cells.

16. A method according to claim 15 wherein said plurality of unit cells 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 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, and a photonic band edge transmission resonance bandwidth which is at least as wide as said predetermined bandwidth.

17. A method according to claim 15 wherein said variable index of refraction is a continuously or discontinuously variable index of refraction which varies across said predetermined thickness.

18. A method according to claim 15, further comprising the step of:

further varying the variable index of refraction of at least one of said unit cells, to thereby vary the predetermined delay.

19. A photonic signal delaying apparatus, which delays photonic signals of a predetermined frequency and a predetermined bandwidth, comprising:

a photonic bandgap structure having a plurality of generally parallel layers including a first layer and a last layer;

means for directing the photonic signals into said first layer such that the photonic signals propagate in a direction generally perpendicular to said plurality of layers,

wherein said photonic bandgap structure has a photonic band edge resonance at the predetermined frequency of the photonic signal, and having a corresponding photonic band edge resonance bandwidth which is at least as wide as the predetermined bandwidth of the photonic signal, to thereby impart a predetermined delay to the photonic signal which propagates therethrough.

20. A delaying apparatus according to claim 19 wherein said photonic bandgap structure has a closest photonic band edge resonance at the predetermined frequency of the photonic signal, and a corresponding closest photonic band edge resonance bandwidth which is at least as wide as the predetermined bandwidth of the photonic signal.

21. A delaying apparatus according to claim 19 further comprising:

means for varying the index of refraction of the photonic bandgap structure to thereby vary said predetermined delay.

22. A delaying apparatus according to claim 19 wherein said photonic bandgap structure comprises a predetermined plurality of first and second alternating layers which exhibit a photonic bandgap, and first and second alternating layers having predetermined thicknesses and having predetermined indices of refraction.

23. A delaying apparatus according to claim 19 wherein said photonic bandgap structure comprises a predetermined plurality of unit cells, each having a predetermined thickness and a variable index of refraction which varies across said predetermined thickness.

24. A photonic signal delaying method which delays photonic signals of a predetermined frequency and a predetermined bandwidth, comprising the step of:

applying the photonic signal to a photonic bandgap structure having a plurality of generally parallel layers including a first layer and a last layer, wherein said applying step comprises directing the photonic signals into the plurality of generally parallel layers such that the photonic signals propagate in a direction generally perpendicular to the plurality of layers, and wherein the photonic bandgap structure has a photonic band edge resonance at the predetermined frequency of the photonic signal, and having a corresponding photonic band edge resonance bandwidth which is at least as wide as the bandwidth of the photonic signal, to thereby impart a predetermined delay to the photonic signal which propagates therethrough.

25. A method according to claim 24 wherein said photonic bandgap structure has a closest photonic band edge resonance at the predetermined frequency of the photonic signal, and a corresponding closest photonic band edge resonance bandwidth which is at least as wide as the predetermined bandwidth of the photonic signal.

26. A method according to claim 24 further comprising the step of:

varying the index of refraction of the photonic bandgap structure to thereby vary said predetermined delay.

27. A method according to claim 24 wherein said photonic bandgap structure comprises a predetermined plurality of first and second alternating layers which exhibit a photonic bandgap, and first and second alternating layers having predetermined thicknesses and having predetermined indices of refraction.

28. A method according to claim 24 wherein said photonic bandgap structure comprises a predetermined plurality of unit cells, each having a predetermined thickness and variable index of refraction which varies across said predetermined thickness.