1. Photonics in SwitchingOptical components Lena Wosinska, Bo Willen Royal Institute of Technology KTH Lena.Wosinska@imit.kth.se

2. Optical Components • Couplers • Isolators and Circulators • Filters • Multiplexers and Demultiplexers • Amplifiers • Transmitters and Receivers • Switches • Wavelength converters

3. Couplers α 1-α

4. Couplers

5. Couplers Key parameters • Excess loss • α(ℓ)-variations • Wavelength dependence • Polarisation dependence

6. Couplers

7. Couplers

8. Isolators and circulators • Need: Avoid backward travelling waves, sometimes detrimental for laser performance. • Problems: Expensive and bulky • One of the remaining problems in optical networks: Small, integrated devices are needed, • Magnetic fields required since we are dealing with non-reciprocal devices.

9. Isolators and circulators

10. Isolators and circulators

11. Isolators and Circulators • Nonreciprocal • Key parameters • Insertion loss ~ 1 dB • Isolation ~ 40-50 dB

12. Isolators Principle of operation Two polarisation modes: Vertical and horisontal.

13. Isolator

14. Polarisation independent

15. Isolator Polarisation independent

16. Multiplexers and Filters

17. Filters Key parameters • Insertion loss • State of polarisation dependence • Temperature coefficient • Passband flatness • Crosstalk suppression • Cost

18. Bulk, fiber, waveguide… Gratings a qd qi Imaging plane Grating equation

19. Blazed Gratings α = blaze angel

20. Stimax Grating

21. Bragg Gratings • Fiber gratings • Long period fiber gratings • Waveguide gratings

22. Bragg Gratings • Bragg phase-matching condition: • Bragg wavelength:

23. Bragg gratings

24. Low loss Low crosstalk Ease of coupling Polarization insensitive Low temperature coefficient Simple packaging The index of refraction increases in UV-light. Short-period ~ 0.5 µm Long-period ~ 100 µm Fiber Bragg Gratings

25. Long-period Fiber Grating

26. A Bragg grating directional coupler OADM 1 Spatial separation of drop No losses for add channel

27. Bragg grating OADM

28. Fabry-Perot Filters Mirrors

29. Thin-Film Filters Cavity Dielectric reflectors Cavity Glass substrate A resonant multi-cavity thin-film filter.

30. Multilayer dielectric thin film filters Key parameters: • Flat top of the passband • Sharp skirts • Temperature insensitive • Low loss • Polarisation insensitive

31. Semiconductor Waveguides

32. Mach-Zehnder Interferometer Non-linear element varying the time delay.

33. Mach Zehnder Interferometer Add/drop function L. Wosinski, M. Swillo and M. Dainese, “Imprinting of low dispersion Bragg gratings in planar devices for 40 Gbps DWDM systems”, Proc. of International Congress on Optics and Optoelectronics, Warsaw, Poland 28 August - 2 September 2005, Proc. SPIE 5956, pp OD1 – OD8.

34. AWG or Phasar • Number of channels • Central frequency • Channel spacing • Bandwidth • Insertion loss • Crosstalk • Polarisation dependence • Temperature dependence

35. Advanced devices by PECVD in silica-on-silicon State-of-the-art devices in PECVD technology are dense WDM MULTI/DEMULTIPLEXERS by Arrayed-Waveguide Grating (AWG) used to combine or divide narrowly spaced channels Characteristics AWG configuration AWG fabrication 32 output channels, 0.8 nm channel spacing (100 GHz), 25 nm band L. Wosinski,“ Silica-on-Silicon Technology for Photonic Integrated Devices”, 6th International Conference on Transparent Optical Networks, Wroclaw, Poland, Julyl 4 - 8, 2004, Proceedings of the IEEE, vol. 2, pp 274 - 279.

36. Add/Drop multiplexer L. Wosinski, M. Dainese, H. Fernando and T. Augustsson, “Grating-assisted add-drop multiplexer realized in silica-on-silicon technology”, Proceedings of the Conference “Photonics Fabrication Europe”, Brugge, Belgium, 28 October, 1 November 2002, Proc. SPIE 4941, pp 43-50.

37. AWG Cross Connect

38. Regenerators Erbium-Doped Fibre Amplifiers Raman amplifiers Semiconductor Optical Amplifiers Clock recovery Scalability Analogue devices Noise accumulation Bandwidth Gain Flatness Amplifiers

39. Stimulated emission Spontaneous Emission Polarisation dependence Crosstalk Gain Noise Amplitude fluctuations Noise Optical Amplifiers

40. EDFA 1460 1530 1565 1610 1625 S-band L-band C-band Gain flattening filters B- and C-band EDFA’s in parallel C-band: Higher Erbium doping or longer (Raman)

41. EDFA • Polarisation independent • No crosstalk • Wide wavelength range • Transparent

42. Fluoride doped fiber Filter Noise, pumped @ 1480 Power loss EDFA, Gain Flattening

43. Phonon scattering Refractive index modulation Stimulated Raman Four-wave mixing Raman. Nonlinear effects

44. Raman. Stokes wave • Pump power lost to phonons • Pump wavelength < Stokes wavelength • Noise – backward pump • Crosstalk

45. Semiconductor Optical Amplifiers • Transparent amplifier • Wavelength converter • Optical switch • A forward biased p/n-junction • AR-coating to avoid lasing

46. Semiconductor Optical Amplifiers • Bandwidth ~100 nm (1.3 – 1.55µm) • Crosstalk • Coupling loss • Polarization dependence • Noise • High-quality AR-coating - FP

47. Transmitters • Lasers • External Modulators (EA, MZI, ...) • High-frequency modulation • Low chirp • Light emitting diodes • Low-frequency modulation • Broad band • Low power

48. Output power Threshold current Slope efficiency Operation wavelength Spectral width Side-mode suppression Wavelength stability Dispersion FP-lasers DFB-lasers DBR-lasers External cavity VCSEL Tunable lasers Mode-locked lasers Lasers

49. pin-diodes Avalanche diodes, APD msm-diodes Front-end amplifiers High-impedance Transimpedance Bandwidth Noise Dynamic range Detectors