Topic 3 Dielectric Waveguides and Optical Fibers 2-1 Symmetric ...

2-6 Bit Rate, Dispersion,
Electrical and Optical Bandwidth
901 37500 光電導論
RZ
Information
Digital signal
t
Emitter
Input
Photodetector
Information
Output
Input Intensity
Output Intensity
² τ1/2
Very short
light pulses
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0
T
Fiber
t
0
~2Δτ1/2 An optical fiber link for transmitting digital information and the effect of
dispersion in the fiber on the output pulses.
?1999 S.O. Kasap, Optoelectronics (Prentice Hall)
53
55
t
Bit rate capacity B (bits/sec) is related to the dispersion characteristics.
The dispersion is measured by the pulse spread:
Full width at half power (FWHP) Δτ1/
2
Full width at half maximum (FWHM)
There is no inter-symbol interference
peak-to-peak separation 2 Δτ
1/
2
the maximum bit rate
Intuitive return-to-zero (RZ) bite rate (or data rate)
Non-return to zero (NRZ) bite rate 2B
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NRZ
−1
/ 2
=
Output optical power
1
0.61
0.5
Bit Rate and Dispersion
e 0.
607 Δτ
2σ
2σ
rms =
Δτ1/2
T = 4σ
901 37500 ?1999 S.O. 光電導論 Kasap, Optoelectronics (Prentice Hall)
0.
5
B ≈
Δτ
A Gaussian output light pulse and some tolerable intersymbol
interference between two consecutive output light pulses (y-axis in
relative units). At time t = σ from the pulse center, the relative
magnitude is e-1/2 = 0.607 and full width root mean square (rms)
spread is Δτrms = 2σ.
1/
2
t
54
56