Physics and Applications of "Slow" Light

1. Physics and Applications of "Slow" Light Dan Gauthier Duke University, Department of Physics, Fitzpatrick Center for Photonics and Communication Systems Collaborators: Michael Stenner, Heejeong Jeong, Andrew Dawes (Duke Physics) Mark Neifeld (U. of Arizona, ECE, Optical Sciences Center) Robert Boyd (U. of Rochester, Institute of Optics) John Howell (U. of Rochester, Physics) Alexander Gaeta (Cornell, Applied Physics) Alan Willner (USC, ECE) Dan Blumenthal (UCSB, ECE) Fitzpatrick Center Summer School, July 27, 2004 Funding from the U.S. National Science Foundation

2. Outline • Information and optical pulses • Optical networks: The Problem • Possible solution: "Slow" and "Fast" light • Review of pulse propagation in dispersive media • Optical pulse propagation in a resonant systems • Slow light via EIT • Fast Light via Raman Scattering • Our Experiments • Fiber-Based Slow Light

3. Information and Optical Pulses: Basic Review

4. Digital Information • computers only work with numbers - vast majority use binary • need standards for converting "information" to a binary representation Text: ASCII (American Standard Code for Information Exchange) developed years ago for teletype communication 1 byte (8 bits) needed for "standard" alphabet each character assigned a number e.g.: A = 41 (decimal) = 00101001 (binary) a = 97 = 01100001

5. Digital Information: Images image is divided into pixels each pixel is assigned a number using a standard e.g.: 8-bit color: one byte per color, three colors Red, Green, Blue

6. Using Light to Transmit Digital Information Encode bits on a beam of light ... 01100001... to optical fiber modulator laser various modulation formats! e.g., amplitude, phase, frequency

7. Modern Optical Telecommunication Systems:NRZ common for <= 10 Gbit/s http://www.picosecond.com/objects/AN-12.pdf NRZ data 1 0 1 1 0 clock

8. 1 0 1 1 0 Modern Optical Telecommunication Systems:RZ common for > 10 Gbits/s http://www.picosecond.com/objects/AN-12.pdf RZ data clock

9. Why Optics? Fast Data Rates! can transmit data at high rates over optical fibers in comparison to copper wires (low loss, low distortion of pulses) important breakthrough: use multiple wavelengths per fiber each wavelength is an independent channel (DWDM - Dense Wavelength Division Multiplexing) Common Standard: OC-192 (10 Gbits/s) "optical carrier" 192 times base rate of 51.85 Mbits/s next standards: OC-768 (40 Gbits/s), OC-3072 (160 Gbits/s) every house in US can have an active internet connection! lab: > 40 Tbits/s

10. Optical Networks

11. Information Bottleneck: The Network Source: Alan Willner

12. Network Router router information sent to router in "packets" with header - typical packet length (data) 100-1000 bits router needs to read address, send data down new channel, possibly at a new wavelength <= 10 Gbits/s: Optical-Electronic-Optical (OEO) conversion Is OEO conversion feasible at higher speeds?

13. Ultra-High Speed Network Router all-optical cross-connect Possible Solution: All-optical router One (fairly major) unsolved problem: There is no all-optical RAM or agile optical buffer

14. Source: Alan Willner, USC

15. Statement of the Problem optical control field A t B How to we make an all-optical, controllable delay line (buffer) or memory?

16. dispersive media Possible Solution: "Slow" and "Fast" Light Speed of Pulse MUCH slower or faster than the speed of light in vacuum R.W. Boyd and D.J. Gauthier "Slow and "Fast" Light, in Progress in Optics, Vol. 43, E. Wolf, Ed. (Elsevier, Amsterdam, 2002), Ch. 6, pp. 497-530.

17. Optical Pulse Propagation Review

18. E z Propagating Electromagnetic Waves: Phase Velocity monochromatic plane wave phase velocity phase Points of constant phase move a distance Dz in a time Dt

19. different Propagating Electromagnetic Waves: Group Velocity Lowest-order statement of propagation without distortion group velocity

20. Variation in vg with dispersion slow light fast light

21. Schematic of Pulse Propagation at Various Group Velocities

22. Pulse Propagation: Slow Light(Group velocity approximation)

23. Pulse Propagation: Fast Light (Group velocity approximation)

24. pulse bandwidth not too large Propagation "without distortion" "slow" light: "fast" light: Recent experiments on fast and slow light conducted in the regime of low distortion

25. Optical Pulse Propagation in a Resonant System

26. gas of atoms Set Optical Carrier Frequency Near an Atomic Resonance susceptibility atomic energy eigenstates resonant enhancement

27. Dispersion Near a Resonance refractive index absorption index !! group index

28. Problem: Large Absorption!

29. Slow Light via EIT

30. Solution: Electromagnetically Induced Transparency Source: Hau et al., Nature 397, 594 (1999)

31. Group Index for EIT ng ~106 !

32. Experimental Setup of Hau et al. relevant sodium energy levels

33. Slow Light Observations of Hau et al. vg as low as 17 m/s ng of the order of 106! Source: http://www.deas.harvard.edu/haulab/

34. Fast Light via Atomic Raman Scattering

35. Fast-light via a gain doublet Steingberg and Chiao, PRA 49, 2071 (1994) (Wang, Kuzmich, and Dogariu, Nature 406, 277 (2000))

36. Achieve a gain doublet using stimulated Raman scattering with a bichromatic pump field rubidium energy levels Wang, Kuzmich, and Dogariu, Nature 406, 277 (2000))

37. Experimental observation of fast light ng ~ -310 … but the fractional pulse advancement is small

38. Our Experiments on "Fast" and "Slow" Light

39. Important Quantity for our Work: Pulse Advancement tadv anomalous dispersion vacuum tp A=tadv/tp relative pulse advancement

40. Key Observation A ~ (gain coefficient) * (length of medium) Does NOT depend on vg directly Adjust spectral width of atomic resonance to optical spectrum of the pulse

41. Fast light in a laser driven potassium vapor large anomalous dispersion Steingberg and Chiao, PRA 49, 2071 (1994) Wang, Kuzmich, and Dogariu, Nature 406, 277 (2000)

42. Some of our toys

43. Observation of large pulse advancement tp = 263 ns A = 10.4% vg = -0.051c ng = -19.6 some pulse compression (1.9% higher-order dispersion) H. Cao, A. Dogariu, L. J. Wang, IEEE J. Sel. Top. Quantum Electron. 9, 52 (2003). B. Macke, B. Ségard, Eur. Phys. J. D 23, 125 (2003). large fractional advancement - can distinguish different velocities!

44. Slow Light via a single amplifying resonance

45. Slow Light Pulse Propagation vg ~ 0.008c

46. Surely Dr. Watson, you must be joking ... • Experiments in Slow and Fast Light use atoms • Effect only present close to a narrow atomic resonance • Works for long pulses - slow data rates! • Not easily integrated into a telcom system!

47. Key Observation A ~ (gain coefficient) * (length of medium) Does NOT depend on vg directly Adjust spectral width of atomic resonance to optical spectrum of the pulse short pulses broad resonance any resonance can give rise to slow light!! e.g., Stimulated Brillouin and Raman Scattering

48. Fiber-Based Fast and Slow Light

49. Slow-Light via Stimulated Brillouin Scattering

50. Gain and Dispersion 6.4-km-Long SMF-28 Fiber others: 4.7 mW 1.9 mW should see "large" relative delay