Page 229 - Photonics Essentials an introduction with experiments

Optical Fibers and Optical Fiber Amplifiers

Optical Fibers and Optical FIber Amplifiers 223

9.3 Below are some of the specifications for Samsung single-mode
optical fiber:
Attenuation @1310 nm 0.35 dB/km
@1550 nm 0.21 dB/km
Attenuation versus Wavelength
The attenuation for the wavelength region 1285~1330 nm
does not exceed the attenuation at 1310 nm by more than
0.03 dB/km.
The attenuation for the wavelength region 1525~1575 nm
does not exceed the attenuation at 1550 nm by more than
0.03 dB/km.
Dispersion @1285~1330 nm 3.5 ps/nm-km
@1550 nm 18 ps/nm-km
Zero dispersion wavelength 1300 ~ 1320 nm
Zero dispersion slope 0.092 psec-nm -km
2
Effective group index of refraction 1.4690 at 1310 nm
(typical) 1.4695 at 1550 nm
Refractive index difference (typical) 0.34 %
Mode field diameter 9.3 microns at 1310 nm
10.5 microns at 1550 nm
Cladding diameter 1251
Cladding noncircularity 1.5%
Core diameter ??? (not given)
Core/cladding concentricity error 0.6
a) Using available data, estimate the numerical aperture (as-
sume that the index of the core is equal to the effective group
index).
b) Samsung has carefully avoided giving the core diameter in
its specifications. Show that 8.5 microns is a reasonable val-
ue. What V number do you determine? What mode field di-
ameters do you determine at 1310 and 1550 nm? Would 9 mi-
crons be a better guess? What would be the longest
wavelength for which the fiber still behaves as single mode?
c) Write and demonstrate a simple computer routine for calcu-
lating the core diameter of the fiber using only the data giv-
en.
d) Calculate the time needed for the pulse broadening due to
dispersion to cause overlap of adjacent bits at 2.5 Gbit/sec, 10
Gbit/sec, and 40 Gbit/sec. This occurs when the combined
width at half maximum of the two broadened pulses is equal

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