The Science of Information Technology

1. The Science of Information Technology Computing with Light • the processing of signals • properties of light • building a photonic computer • future trends ?

2. Signals in IT binary system: 01100101 not applicable

3. Making a Byte out of Bits • understanding: • computing problems can be • separated into processing of • single bits. • tools are: • transport • comparison • storage

4. Signal Processing in IT transport of bits: switching:

5. What is a Bit ? Fourier transform

6. The cut-off frequency

7. Electronics transport of bits: switching:

8. Cut-off frequency vs. clock frequency

9. Clock Frequency of Computers

10. The heat problem

11. Clock Frequency of Computers

12. Photonics Idea: substitute electrical currents with light

13. Let’s build a photonic computer 

14. Semiconductor laser

15. Output of a laser rapidly oscillating electromagnetic field 1 fs = 10 –15 s = 0.000000000000001 s

16. Desired: short pulses and pulse trains

17. Let’s build a photonic computer 

18. 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. Using a Mach-Zehnder interferometer

20. Constructive & destructive interference

21. Integration of intensity modulators material: lithiumniobate

22. Let’s build a photonic computer    

23. All-optical switching the problem: light doesn’t interact with light

24. 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. Optical transition of electrons

26. All-optical switching by saturated absorption AND-gate:

27. Excitation of bulk semiconductors

28. Better: semiconductor heterostructures

29. AlGaAs-Switch

30. We are done: a photonic computer (???)     

31. Keep the information for some time Solution: bistable devices Electronics: Flip-Flop

32. The SEED (self-electro-optic effect device)

33. Photoinduced absorption

34. Demonstration of concepts The first steps towards photonic computing: • efficient transfer of data by fibers • rates up to 30 THz • switching times as fast as 100 fs • low switching energies • close to switching energies in electronic • high repetition rates • > 100 GHz • factor 100 higher as in PCs

35. Technological problems • interface electronics-optics • usually slow (10 GHz) • expensive ( ~ 100 US$) • micro integration • devices of dimension 0.03 – 10 mm • for parallel processing arrays of several cm • hybrid technologies • expensive • not acceptable

36. The market • assume for 10 years: • 500 Mio Computers • 100 US$ for photonic components 50 billion US$ • more important: • relation between market potential and risk: 50 billion US$ risk = ?

37. Research at Rensselaer • optical on chip interconnects • fiber optical connects (Persans) • terahertz optoelectronics (Zhang, Shur, Kersting)

38. The electromagnetic spectrum

39. THz pulses Properties: • THz pulses are information carrier • measure the field • very short light pulses possible • propagate free space & on metal wires • fibers are no longer necessary • switching medium : semiconductors • can be tailored for THz pulses • no hybrid technologies

40. Logic operations with THz pulses

41. THz semiconductor devices Science fiction ? • our work: • THz modulator • operating @ 3THz

42. Terahertz differentiator analog computer: • calculates the first time-derivative • operates at THz frequencies