ENE 623 Optical Networks

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# ENE 623 Optical Networks - PowerPoint PPT Presentation

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

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
Example
• Suppose N = 1.461 at λ = 1200 nm and N = 1.460 at λ = 1400 nm. Calculate and .
Example
• Assume Δ = 1 GHz, λ = 1300 nm, ΔT = 100 ps. What is the maximum L?
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.
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.
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.
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.
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?