1 Roland Kersting 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 Roland Kersting Department of Physics, Applied Physics, and Astronomy Signals in IT not applicablebinary system:

3 Roland Kersting 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 Roland Kersting Department of Physics, Applied Physics, and Astronomy Signal Processing in IT transport of bits: switching:

5 Roland Kersting Department of Physics, Applied Physics, and Astronomy What is a Bit ? Fourier transform

6 Roland Kersting Department of Physics, Applied Physics, and Astronomy The cut-off frequency

7 Roland Kersting Department of Physics, Applied Physics, and Astronomy Electronics transport of bits: switching:

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

9 Roland Kersting Department of Physics, Applied Physics, and Astronomy Clock Frequency of Computers

10 Roland Kersting Department of Physics, Applied Physics, and Astronomy The heat problem

11 Roland Kersting Department of Physics, Applied Physics, and Astronomy Clock Frequency of Computers

12 Roland Kersting Department of Physics, Applied Physics, and Astronomy Photonics Idea: substitute electrical currents with light

13 Roland Kersting Department of Physics, Applied Physics, and Astronomy Let’s build a photonic computer

14 Roland Kersting Department of Physics, Applied Physics, and Astronomy Semiconductor laser

15 Roland Kersting Department of Physics, Applied Physics, and Astronomy Output of a laser rapidly oscillating electromagnetic field 1 fs = 10 –15 s = s

16 Roland Kersting Department of Physics, Applied Physics, and Astronomy Desired: short pulses and pulse trains

17 Roland Kersting Department of Physics, Applied Physics, and Astronomy Let’s build a photonic computer

18 Roland Kersting 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 Roland Kersting Department of Physics, Applied Physics, and Astronomy Using a Mach-Zehnder interferometer

20 Roland Kersting Department of Physics, Applied Physics, and Astronomy Constructive & destructive interference

21 Roland Kersting Department of Physics, Applied Physics, and Astronomy Integration of intensity modulators material: lithiumniobate

22 Roland Kersting Department of Physics, Applied Physics, and Astronomy Let’s build a photonic computer

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

24 Roland Kersting 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 Roland Kersting Department of Physics, Applied Physics, and Astronomy Optical transition of electrons

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

27 Roland Kersting Department of Physics, Applied Physics, and Astronomy Excitation of bulk semiconductors

28 Roland Kersting Department of Physics, Applied Physics, and Astronomy Better: semiconductor heterostructures

29 Roland Kersting Department of Physics, Applied Physics, and Astronomy AlGaAs-Switch

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

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

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

33 Roland Kersting Department of Physics, Applied Physics, and Astronomy Photoinduced absorption

34 Roland Kersting 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 Roland Kersting 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 Roland Kersting 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 Roland Kersting 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 Roland Kersting Department of Physics, Applied Physics, and Astronomy The electromagnetic spectrum

39 Roland Kersting 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 Roland Kersting Department of Physics, Applied Physics, and Astronomy Logic operations with THz pulses

41 Roland Kersting Department of Physics, Applied Physics, and Astronomy THz semiconductor devices Science fiction ? our work: THz modulator 3THz

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