Wavelength division multiplexing(WDM) is a concept that describes combination of several streams of optical carrier signals (like data/storage/video or voice) on a single physical fiber optic cable by using several different wavelengths (frequencies) of laser light with each frequency carrying a different type of data. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity.
There are two types of WDM architecture: Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Division Multiplexing (DWDM). CWDM systems typically provide 8 wavelengths, separated by 20nm, from 1470nm to 1610nm. In order to increase the number of wavelength, one can also use the 1310 nm window so the CWDM channels can be increased to 16. Thereby up to 16 DWDM channels are transmitted simultaneously in only one CWDM channel (1530 nm and 1550 nm). Some DWDM network systems provide up to 96 wavelengths, typically with no more than 0.4nm spacing, roughly over the C-band range of wavelengths.
The difference between CWDM and DWDM mainly has two points. First is the channel spacing between neighbored wavelengths, for CWDM 20 nm and for DWDM 0.8/0.4 nm (using 100 GHz/50 GHz grid). Therefore, light in a single fiber can reuse about 5 to 6 wavelengths, that is where the “dense” and “coarse” appellation come from. Second, CWDM modulation laser using uncooled laser, but DWDM is used in cooling laser. Cooling laser using temperature tuning, uncooled laser adopts electronic tuning. Because the range of temperature distribution is non-uniform in a very wide wavelength, so the temperature tuning is very difficult to realize, the cost is very high. CWDM avoids this problem, so it greatly reduces the cost; the whole CWDM system cost only 30% of DWDM.
What’s more, something about CWDM and DWDM products.
(1)CWDM Mux/Demux module
CWDM multiplexer and CWDM Demux are designed to multiplex multiple CWDM channels into one or two fibers. The core of CWDM Module application is the passive MUX DEMUX unit. The common configuration is 1×4, 1×8, 1×16 channels. Available in 19″ Rack Mount or LGX module package. Optional wide band port is available to multiplex with CWDM Channels wavelength.
(2)DWDM Mux/Demux Module
DWDM multiplexer and DWDM DeMux are designed to multiplex multiple DWDM channels into one or two fibers. The common configuration is 4, 8, 16 and 40 channels, or 50G DWDM Mux Demux. These modules passively multiplex the optical signal outputs from 4 or more electronic devices, send them over a single optical fiber and then de-multiplex the signals into separate, distinct signals for input into electronic devices at the other end of the fiber optic link.
(3)CWDM OADM/ DWDM OADM
CWDM OADM/ DWDM OADM (Optical Add/Drop Module) are designed to optically add/drop one or multiple CWDM/DWDM channels into one or two fibers. “Add” and “drop” refer to the capability of the device to add one or more new wavelength channels to an existing multi-wavelength WDM signal, and/or to drop (remove) one or more channels, passing those signals to another network path. An OADM may be considered to be a specific type of optical cross-connect. The DWDM OADM is used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber (SMF). And CWDM OADM is used for multiplex/demultiplex or add/drop wavelengths from multiple fibers onto one optical fiber. They feature a superior low insertion loss, high channel isolation, wide pass band, cold sensitivity and epoxy free optical path.
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