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ENE 623 Optical Networks

ENE 623 Optical Networks. Lecture 4. Pulse Propagation in Fibers. Problem: Inject an optical pulse of width  0 into the fiber at z = 0. What is the speed of propagation and what is  (z)? Given. Pulse Propagation in Fibers. Pulse Propagation in Fibers. Pulse Propagation in Fibers.

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ENE 623 Optical Networks

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  1. ENE 623 Optical Networks Lecture 4

  2. Pulse Propagation in Fibers • Problem: Inject an optical pulse of width 0 into the fiber at z = 0. What is the speed of propagation and what is  (z)? • Given

  3. Pulse Propagation in Fibers

  4. Pulse Propagation in Fibers

  5. Pulse Propagation in Fibers

  6. Pulse Propagation in Fibers

  7. Pulse Propagation in Fibers

  8. Pulse Propagation in Fibers

  9. Propagation delay

  10. Propagation delay

  11. Propagation delay

  12. Example • Suppose N = 1.461 at λ = 1200 nm and N = 1.460 at λ = 1400 nm. Calculate and .

  13. Example • Assume Δ = 1 GHz, λ = 1300 nm, ΔT = 100 ps. What is the maximum L?

  14. Pulse Brodening

  15. Total dispersion • Total dispersion = material dispersion + waveguide dispersion (+ modal dispersion + polarization dispersion). • Waveguide dispersion: neff changes with vj with λ. • Commercial multimode fiber: • GRIN fiber: modal dispersion = 0.3 – 1 ns/km. • SI fiber: modal dispersion = 50 ns/km.

  16. Solitons • Pulses that can operate fiber with   0 with no pulse broadening (ΔT = 0). • It could be done by ‘non-linear effects’. • Still work to be done before solitons are practical.

  17. Solitons

  18. Solitons

  19. Rayleigh Backscattering

  20. Example • Most of the attenuation is due to Rayleigh scatter. This form of scattering happens to be isotropic, so that some is scattered back toward the transmitter. If you have a fiber with an NA of 0.1 for which all of its 0.5 dB/km attenuation is due to backscatter, and you send a single light pulse of duration T = 1 ns into it, how many dB down will be the peak of the Rayleigh backscatter waveform? Assume that the core index = 1.45.

  21. Biconical tapered couplers

  22. Biconical tapered couplers

  23. Biconical tapered couplers

  24. Example • Design a single mode fused biconical coupler that accepts at one input a mixture of light at 1300 nm and 1530 nm and deliver 100% of one to one output and 100% of the other to the other output. Assume that throughout the coupling region, each fiber can be represented as having a 30 micron effective core diameter.

  25. Example • For the 16x16 star coupler shown in previous slides, what is the total loss and the excess loss in dB assuming each of the couplers has r = 1 with an excess loss of 1 dB?

  26. Power limit by eye safety

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