Dense Wavelength Division Multiplexing (DWDM) is a technology that allows multiple information streams to be transmitted simultaneously over a single fiber. This provides a cost effective method to increase the capacity of the existing networks without the need to add additional fiber.

This application note explains capabilities of the OptiSystem software to explore different design structures (e.g. modulation format, linear and nonlinear impairment compensation) to optimize the performance of these networks for access and long-haul application.

Need of DWDM:

• Long-haul optical networks either in point-to-point or ring topology.
• Expanding the capacity of an existing optical network.
• Capacity leasing for network wholesalers.
• New BER Test Set enables the simulation of millions of bits for direct error counting.
• Multi-parameter scanning enables system designers to study trade-offs with respect to parameters of interest and to choose an optimal design for deployments.
• FEC
• Enables users to analyze different algorithms for the electronic equalization.
• Interfaces with popular design tools.
• Significantly reduces product development costs and boosts productivity through a comprehensive design environment to help plan, test, and simulate optical links in the transmission layer of modern optical networks.

Figure above shows the DWDM Functional Schematic The system performs the following main functions:

• Generating the signal:The source, a solid-state laser, must provide stable light within a specific, narrow bandwidth that carries the digital data, modulated as an analog signal.
• Combining the signals: Modern DWDM systems employ multiplexers to combine the signals. There is some inherent loss associated with multiplexing and demultiplexing. This loss is dependent upon the number of channels but can be mitigated with optical amplifiers, which boost all the wavelengths at once without electrical conversion.
• Transmitting the signals:The effects of crosstalk and optical signal degradation or loss must be reckoned with in fiber optic transmission. These effects can be minimized by controlling variables such as channel spacings, wavelength tolerance, and laser power levels. Over a transmission link, the signal may need to be optically amplified.
• Separating the received signals: At the receiving end, the multiplexed signals must be separated out. Although this task would appear to be simply the opposite of combining the signals, it is actually more technically difficult.
• Receiving the signals:The demultiplexed signal is received by a photodetector. In addition to these functions, a DWDM system must also be equipped with client-side interfaces to receive the input signal. This function is performed by transponders.On the DWDM side are interfaces to the optical fiber that links DWDM systems.