After the 10Gigabit PON(Passive Optical Network), WDM(Wavelength-division multiplexing) technology entered into traditional TDM PON fields. In April 2012, standard organization FSAN(Full Service Access Network) determined the time and wavelength division multiplexed passive optical network (TWDM PON) technology became the preferred solution for next-generation passive optical network stage-2 (NG-PON2) architecture after10G PON. To better understanding WDM PON, I list the WDM technology below.
What Is WDM?
WDM is a method of combining multiple signals on laser beams at various infared wavelengths for transmission along fiber optic media. WDM system uses a multiplexer at the transmitter to join the signals together, and a demultiplexer at the receiver to split them apart.
WDM systems are divided according to wavelength categories, generally course WDM (CWDM) and dense WDM (DWDM). CWDM operates with 8 channels (i.e., 8 fiber optic cables) in what is known as the “C-Band” or “erbium window” with wavelengths about 1550 nm (nanometers or billionths of a meter, i.e. 1550 x 10-9 meters). DWDM also operates in the C-Band but with 40 channels at 100 GHz spacing or 80 channels at 50 GHz spacing.
CWDM multiplexer module allows multiple optical signals at different wavelengths to pass through a single optical fiber strand. The common configuration of CWDM mux/demux module is 2CH, 4CH, 8CH, 16CH, 18CH CWDM mux/demux module.
DWDM Mux/Demux Modules – DWDM Mux and DWDM DeMux are designed to multiplex DWDM channels into one or two fibers. 50G DWDM Mux Demux is used to provide 50G transport solution for DWDM networking system. The common configuration is 4, 8, 16 and 32 channels, and also has 40, 44 channels. These DWDM 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.
WDM PON uses multiple different wavelengths over a physical point-to-multipoint fiber infrastructure that contains no active components (PON). Each provides a dedicated wavelength channel at the rate of 1Gbps to each optical network unit (ONU). The use of different wavelengths allows for traffic separation within the same physical fiber. The result is a network that provides logical point-to-point connections over a physical point-to-multipoint network topology. WDM-PON allows operators to deliver high bandwidth to multiple endpoints over long distances.
For simple network deployment and inventory management purposes, the ONUs use colorless tunable transmitters and receivers. The transmitter is tunable to any of the upstream wavelengths, while the receiver can tune to any of the downstream ones. Optical Amplifiers are employed at the OLT side to boost the downstream signals as well as to pre-amplify the upstream signals. ODN remains passive since both the optical amplifier and WDM Mux/Demux are placed at the OLT side.
This type of TWDM PON system is valuable in a market where multiple operators share one physical network infrastructure. Coexistence with previous PON generations in the legacy ODN depends on the TWDM PON wavelength plan, reuse the XG-PON wavelength bands, redefine the C-band enhancement band to contain both the upstream and downstream wavelengths and mixture of both of these plans.
TWDM-PON standards are expected to complete in 2013, and a finished commercial system should see the light of day in 2014.
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