1 / 34

ENE 623 Optical Networks

ENE 623 Optical Networks. Lecture 5. Tunable Filters. Tunable Filters. Δ f defines as the frequency difference between the lowest- and the highest-frequency channels and f as the spacing between channels.

shaina
Télécharger la présentation

ENE 623 Optical Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ENE 623 Optical Networks Lecture 5

  2. Tunable Filters

  3. Tunable Filters • Δf defines as the frequency difference between the lowest- and the highest-frequency channels and f as the spacing between channels. • The maximum number of equally spaced channels can be calculated as Nmax = Δf / f . • The access time is the speed which a tunable filter can be reset from one frequency to another. This should be in the unit of microsecond. • The filter’s transfer function T(f) is not generally equal to unity due to its internal losses.

  4. Tunable Filters • Good filters should be independent to light polarizations. Tunable-filters have an advantage over the coherent-detection due to that. • With the help of lithography, the low cost filter can be fabricated, but the fiber loss attachment exists. However, with other methods, high-cost processes are involved and that is the great barrier to develop such a technology.

  5. Tunable Filters • Wavelength selective filters might be categorized into: • 2-port filter • 1  N WDM filter

  6. Tunable Filters • 4-port add-drop filter

  7. Crosstalk

  8. Filters for WDM • Requirements: • Center wavelength near 1.55 μm or 1.3 μm. Some local network might have a center wavelength of 0.8 μm. • Frequency Spacing: about 100 GHz. • Number of channels: having been increased to more than 256. • Tuning speed: less than 1 μs.

  9. Some of tunable filters • Fabry-perot filters • Mach-Zehnder chain • Grating • Acousto-optic tunable filter (AOTF) • Electro-optic tunable filter (EOTF)

  10. Fiber Fabry-Perot Filter

  11. Fiber Fabry-Perot Filter • Consider a single mirror

  12. Fiber Fabry-Perot Filter • After a round trip

  13. Fiber Fabry-Perot Filter • After two round trips • After N round trips

  14. Fiber Fabry-Perot Filter • At steady state (N  ∞)

  15. Fiber Fabry-Perot Filter • At steady state (N  ∞)

  16. Fiber Fabry-Perot Filter • Plot T vs 

  17. Fiber Fabry-Perot Filter

  18. Fiber Fabry-Perot Filter • We can find the bandwidth of the peak by looking at the denominator expression for T.

  19. Fiber Fabry-Perot Filter • Another important parameter to characterize a FP filter is the finesse, F. • This can determine the maximum number of channels in WDM system.

  20. Example • If we have 10 channels with 100 GHz spacing for each channel. What shoud the length of FPI filter be?

  21. Example • Consider a Fabry Perot filter with an air cavity of length L and R = 0.99 for each mirror, with a free spectral range of 3.2 THz. • What is L in μm? • For the value of L determined in (a), what is the wavelength λ0 nearest 1.53 m for which the transmittance is a maximum.

  22. Mach-Zehnder Chain

  23. Mach-Zehnder Chain

  24. Mach-Zehnder Chain

  25. Mach-Zehnder Chain

  26. Example • Consider a 7-stage MZ chain with a FSR of 3.2 THz produced in single mode fiber with n = 1.46 for the fundamental mode and a transmittance maximum for λ1 = 1.53 m. What is the shortest and longest path difference for any interferometer in the chain?

  27. Gratings • Spatial period d diffracted waves interface

  28. Example • Find the allowed mode and angles for each mode for I =30,  = 1.53 μm, and d = 1.61 μm.

  29. Gratings

  30. Gratings • Calculating wavelength dependence of focused spot position.

  31. Example • From previous example, if channel spacing is 100 GHz. What should be a value of h?

  32. Spectral resolution • Spectral resolution is an ability to separate light into wavelength components.

  33. Gratings

  34. Gratings

More Related