Wavelength Multiplexing Systems

■ Multiplexing
　

“Multiplexing” is a technology that allows multiple signals with different
wavelengths to be transmitted together over a single optical fiber. Three
general types of multiplexing — WDM, CWDM and DWDM — offer increasing
signal-carrying capacites, as described below.
　

Wavelength Division Multiplexing (WDM)
WDM is the simplest form of multiplexing and uses two wavelengths of
1310nm and 1551nm. Unlike when using and potical divider, insertion loss
can be kept below 0.5dB.
　

Coarse Wavelength Division Multiplexing (CWDM)
CWDM systems use 8 wavelengths (20nm grid) primarily between 1471nm
and 1611nm. To these it is also possible to add 8 more between 1271nm
and 1451nm to allow a maximum of 16 wavelengths to be carried as a
single multiplexed transmission. An ultra-thin membrane filter on the optical
multiplexer/demultiplexer (mux/demux) keeps insertion loss at just 2-3dB.
*CWDM standardized through ITU G695.

■ Optical Converter (TX for CWDM)

Canare’s CWDM optical converter uses a DFB laser, which offers a much
tighter spectrum than FP lasers. Up to 16 different wavelengths fall within
1271nm and 1611 nm in 20nm
intervals. The wavelengths in the
20nm grid between 1391nm and
1411nm are not used because their
proximity to the water peak results in
too much attenuation.

■ Optical Multiplexer/Demultiplexers

The optical signals output from the optical converter (TX) are combined into a
single signal by the multiplexer (mux) and transmitted along a single optical
fiber. At the receiving end, these combined optical signals are demultiplexed
(demux) to split them back into their original component 8 signals.
Optical mux/demuxers are bi-directional, so the same model can be used
for transmitting and receiving on each end. It’s also possible to use 4
wavelengths out of the 8 for transmitting and the remaining four for receiving.
Both 8-wavelength and 16-wavelength models are available, and combining
these with an optical converter allows a variety of system contructions with
many uses.

■ Optical Converter (RX)
Canare’s optical converter (RX) converts a light signal comprised of 8
different wavelengths into electrical signals. This converter is common to all
wavelengths and one converter is required for each wavelength.