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at are transmitted over the optical fibre and dr1, dr2, dr3, dr4.....drn are the received signals on the receivers end after demultiplexing.ds1=dr1, ds2=dr2, ds3=dr3, ds4=dr4....dsn=drn.The two main entities of this system are multiplexer and demultiplexer.

WDM as a process 波分复用技术作为一个过程

The operation of this system is mainly based on transmitting different data signals simultaneously over a single optical fibre. First the data to be transmitted are coupled with the desired wavelength of light and this process is carried out for different wavelengths based on requirement of the system. These multiple wavelengths of light are then subjected to multiplexer which combines all the signals and transmits them over to the optical fibre.On the receivers side combined signal is subjected to demultiplexer which divides the combined signal into individual signals.

Optical fibre has very high bandwidth rough calculations show:

Each wavelength runs at a minimum data rate of 2.5Gbits/s or even higher
If light is split into 16 wavelengths
162.5=40Gbits/s on a single fibre
Consider having around 50 fibres in a single cable
5040=2000Gbits/s on a single cable
And these values vary on the transmission capability of different wavelengths which may reach up to 100Gbits/s under laboratory conditions

Claiming a world-best speed record for optical data transmission, researchers at Siemens have transmitted 7 Tbits/s over a single optical fibre using DWDM (Dense Wavelength Division Multiplexing) telephone calls or a billion pages of typed data per second. The demonstration was conducted by Siemens' Information and Communication Networks Group at the company's Advanced Optical Networks Laboratories. The researchers simultaneously transmitted 176 channels of 40-Gbit/s data over a 50-km fibre optic cable. The 40-Gbit/s channels, in turn, were produced by time-division multiplexing (TDM) using a prototype of TransXpress FOX, a multiplexer and regenerator system developed by Siemens.

Description of the subsystem and the model:
Block diagram for WDM system
The basic components we use in our present wavelength division multiplexing are Directional couplers; Etalon filters also known as Fabry-Perot interferometer each of individual wavelength ratings, Non linear Optical Loop Mirror, Optical Receiver

The output of first device or component would be the input for the next one. Like the WDM signal with N different wave length channels running with signals each of n bps will be the input for directional coupler and the output here would be demultilplexed into N different signals in each N ports. This output of directional coupler through N ports will be the input for the N Etalon filters with each receiving only one laser beam of a particular wavelength and all the other wavelengths are reflected back which may be received by any one of the n etalon filters and the out put laser beam of a particular wavelength will be given as input for non linear optical loop mirror for non linear transmission or switching characteristics using Kerr effects and the output of this NOLM will be the input for optical receiver which receives the optical signal from NOLM and amplifies the signal and the required out electronic data signal of n bps is obtained.

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