1. 1 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy The Science of Information Technology Computing with Light the processing of signals properties of light building a photonic computer future trends ?

2. 2 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Signals in IT not applicablebinary system: 01100101

3. 3 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Making a Byte out of Bits understanding: computing problems can be separated into processing of single bits. tools are: transport comparison storage

4. 4 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Signal Processing in IT transport of bits: switching:

5. 5 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy What is a Bit ? Fourier transform

6. 6 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy The cut-off frequency

7. 7 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Electronics transport of bits: switching:

8. 8 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Cut-off frequency vs. clock frequency

9. 9 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Clock Frequency of Computers

10. 10 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy The heat problem

11. 11 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Clock Frequency of Computers

12. 12 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Photonics Idea: substitute electrical currents with light

13. 13 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Let’s build a photonic computer

14. 14 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Semiconductor laser

15. 15 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Output of a laser rapidly oscillating electromagnetic field 1 fs = 10 –15 s = 0.000000000000001 s

16. 16 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Desired: short pulses and pulse trains

17. 17 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Let’s build a photonic computer

18. 18 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Opto-electronic modulation Search : Interface between optical & electrical pulses Electro-optic modulators example liquid crystals: get dark when electrical bias is applied very slow Pockels-effect: index of refraction depends on applied voltage very fast

19. 19 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Using a Mach-Zehnder interferometer

20. 20 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Constructive & destructive interference

21. 21 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Integration of intensity modulators material: lithiumniobate

22. 22 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Let’s build a photonic computer

23. 23 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy All-optical switching the problem: light doesn’t interact with light

24. 24 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Absorption saturation idea: use matter (electrons) to mediate the light-light interaction atom: electrons in orbits/states Pauli-rule: up to 2 electrons per state are allowed transitions by light absorption

25. 25 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Optical transition of electrons

26. 26 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy All-optical switching by saturated absorption AND-gate:

27. 27 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Excitation of bulk semiconductors

28. 28 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Better: semiconductor heterostructures

29. 29 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy AlGaAs-Switch

30. 30 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy We are done: a photonic computer (???)

31. 31 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Keep the information for some time Solution: bistable devices Electronics: Flip-Flop

32. 32 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy The SEED (self-electro-optic effect device)

33. 33 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Photoinduced absorption

34. 34 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Demonstration of concepts The first steps towards photonic computing: n efficient transfer of data by fibers  rates up to 30 THz n switching times as fast as 100 fs n low switching energies  close to switching energies in electronic n high repetition rates  > 100 GHz  factor 100 higher as in PCs

35. 35 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Technological problems n interface electronics-optics  usually slow (10 GHz)  expensive ( ~ 100 US$) n micro integration  devices of dimension 0.03 – 10 mm  for parallel processing arrays of several cm n hybrid technologies  expensive  not acceptable

36. 36 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy The market n assume for 10 years:  500 Mio Computers  100 US$ for photonic components 50 billion US$ n more important:  relation between market potential and risk: 50 billion US$ risk = ?

37. 37 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Research at Rensselaer n optical on chip interconnects n fiber optical connects (Persans) n terahertz optoelectronics (Zhang, Shur, Kersting)

38. 38 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy The electromagnetic spectrum

39. 39 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy THz pulses Properties: n THz pulses are information carrier  measure the field n very short light pulses possible n propagate free space & on metal wires  fibers are no longer necessary n switching medium : semiconductors  can be tailored for THz pulses  no hybrid technologies

40. 40 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Logic operations with THz pulses

41. 41 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy THz semiconductor devices Science fiction ? our work: THz modulator operating @ 3THz

42. 42 Roland Kersting kerstr@rpi.edu Department of Physics, Applied Physics, and Astronomy Terahertz differentiator analog computer: calculates the first time-derivative operates at THz frequencies