User's Manual

Fiber Optics Powerwave
7 - 4 Rev. P1A9-Draft 2004-11 VM100 56/EN – User’s Manual
WDM, Wavelength Division Multiplexer
This section describes those types of optical multipexers that are used to build repeater
fiber networks. These are 1310nm and 1550nm WDMs.
After the general description, the graphic symbol for the multiplexer, and an example of
WDM usage are found.
Figure 7-5. Three port WDM, Wavelength Division Multiplexer
A WDM is used to split two or more signals of different wavelengths in a common fiber
port into two or more output fiber ports, and the other way round, that is to combine
signals of different wavelengths from two or more input ports into one common port.
The WDM has a very low insertion loss, approximately 1dB. Additional loss for optical
connectors is approximately 0.5dB per port.
The WDM has two important characteristics, crosstalk and channel separation.
• Crosstalk, also called directivity, is the WDM’s ability to separate the demultiplexed
channels. Each channel should appear only in the intended output port, not in any
other output port. The crosstalk or diversity specification is thus a measurement of the
channel isolation.
• Channel separation is the WDM’s ability to distinguish different wavelengths. In
most WDMs, the wavelengths used has to be widely separated.
There are two different ways to use WDMs with 1310 and 1550nm wavelengths. They
can be used for single direction dual signal transmission, or for bi-directional
transmission, see the following sections.
There are WDMs with a channel separation of 2nm, which is shown in the example
further ahead in this section.
There is also a CWDM type (Coarse WDM) that has a channel separation of 20nm. This
type of CWDM with a wider channels spacing can be used for laser emitters that have
high spectral width or thermal drift. CWDM systems support transmission distances up
to 50km.