Page 721 - Introduction to Information Optics

12.4. Applications and Future Development of Optical Networks 705
Table 12.4
A Design Example Based on OSNR Allocation

Impairment OSNR allocation (dB)
Ideal OSNR without impairment 21
Nonlinearity impairment
Dispersion impairment
System margin 3
Actual requirement 27

Fig. I2.22(a). Yesterday's backbone optical network.

EDFA

80km
300km

Fig. 12.22(b). Today's backbone optical network.

RX stand for laser transmitter and optical receiver, respectively. In each fiber
only one wavelength is transmitted. Due to the attenuation of optical fiber, the
optical signal can only propagate about 40 km. Then an optical receiver must
be used to convert the signal to an electronic signal, which then modulates a
new transmitter to restore the original optical signal. This kind of optical-to-
electronic-to-optical (OEO) conversion repeats every other 40 km until the
information reaches its final destination.
In today's backbone optical network, as shown in Fig. 12.22(b), EDFA and
DWDM technologies are widely applied. DWDM technology is about to