Zte Unitrans ZXMP M600 Technical Instructions page 21

Chapter 1 System Overview
equipment to transmit optical signal service and implement balanced management of
optical power on the whole line. In the DWDM system, the selection of wavelength
and the frequency intervals should conform to ITU-T Recommendation G.692.
The working wavelength range of the DWDM system is 1528.77nm~1560.61nm and
the corresponding working frequency range is 196.1THz~192.1THz.
The channel interval of the system is a multiple of 100GHz (about 0.8nm). The smaller
the channel interval is, the higher the resolution of the optical demultiplexer should be.
The channel interval commonly used at present is either 200GHz (about 1.6nm) or
100GHz (about 0.8nm).
While saving the cost of the electrical relay, EDFA technique adopted in the DWDM
equipment presents much higher requirements on the wavelength stability, dispersion
tolerance and chirp performance of the laser.
Therefore, if the DWDM equipment that suitable for long distance transmission is used
in a MAN that features short transmission distance and diversified service interfaces,
the network construction cost will greatly increase.
1.1.2.2 CWDM Technique
The CWDM technique is developed to improve the utility of optical fibers on the MAN,
to provide multiple service interfaces and to cut the network construction cost at the
same time.
The working principle of CWDM is similar to that of DWDM. At the transmitting end
of the link, an optical multiplexer is used to multiplex the wavelengths transmitted in
different fibers into one fiber for transmission, while at the receiving end, a
demultiplexer is used to recover the original wavelengths from the combined
wavelength.
The wavelength selection and channel interval of the CWDM conforms to ITU-T
Recommendation G694.2. The wavelength interval is 20 nm, while the working
wavelength range is determined by the adopted fiber type. If an ordinary fiber type
G.652 A&B is adopted, then the working wavelength range is 1470nm~1610 nm; if
full-wave fibers, that is, G.652 C&D fibers are adopted, then the working wavelength
range is 1270 nm~1610 nm.
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