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Advantages of WDM as high stage in optical communication

Date: 2019-09-17 14:36 From: C-LIGHT Onclick:
CWDM and DWDM SFP transceiver modules are 2 categories in WDM devices. What are advantages of WDM technology compared with single-wavelength system?


Wavelength division multiplexing technology is a communication technology that combines a series of optical signals with different information but different wavelengths and transmits them along a single optical fiber. At the receiving end, the optical signals of different wavelengths are separated by some method. This technology can transmit multiple signals simultaneously on a single fiber. Each signal is transmitted by a certain wavelength of light. This is a wavelength channel.
WDM is essentially a frequency division multiplexing FDM technology in the optical domain. Each wavelength path is implemented by frequency domain segmentation, and each wavelength path occupies a bandwidth of a length of fiber. WDM systems use different wavelengths, that is, specific standard wavelengths. In order to distinguish them from ordinary wavelengths of SDH systems, they are sometimes called color optical interfaces. Optical interfaces called ordinary optical systems are "white optical ports".


(1) Ultra-large capacity transmission.
Since the multiplexed optical path rate of the WDM system can be 2.5 Gbit/s, 10 Gbit/s, etc., and the number of multiplexed optical paths can be 4, 8, 16, 32, or even more, the transmission capacity of the system can reach 300. -400Gbit/s, even bigger.
(2) Saving fiber resources.
For a single-wavelength system, one SDH system requires a pair of fibers; for a WDM system, the entire multiplexing system requires only one pair of fibers regardless of the number of SDH subsystems. For example, for 16 2.5Gbit/s systems, a single-wavelength system requires 32 fibers, while a WDM system requires only two fibers.
(3) Transparent transmission and smooth expansion and expansion of each channel.
As long as the number of multiplexed channels and devices are increased, the transmission capacity of the system can be increased to achieve capacity expansion. The multiplex channels of the WDM system are independent of each other, so each channel can transparently transmit different service signals, such as voice, data, and Images, etc., do not interfere with each other, which brings great convenience to the user.
(4) Use EDFA to achieve ultra long-distance transmission.
EDFA has the advantages of high gain, wide bandwidth, low noise, etc., and its optical amplification range is 1530 (1565nm, but the flat part of the gain curve is 1540 (1560nm). It can cover the working wavelength range of 1550nm of WDM system. With a wide bandwidth EDFA, the multiplexed optical path signals of the WDM system can be simultaneously amplified to achieve ultra-long-distance transmission of the system, and avoid the need for an optical amplifier for each optical transmission system. WDM system The ultra-long transmission distance can reach hundreds of kilometers while saving a lot of relay equipment and reducing costs.
(5) Improve the reliability of the system.
Since most WDM systems are optoelectronic devices, and the reliability of optoelectronic devices is high, the reliability of the system can be guaranteed.
(6) It can form an all-optical network.
All-optical networks are the development direction of future optical fiber transmission networks. In the all-optical network, the up and down and cross-connection of various services are realized by scheduling the optical signals on the optical path, thereby eliminating the bottleneck of the electronic device in the E/O conversion. The WDM system can be mixed with OADM and OXC to form an all-optical network with high flexibility, high reliability and high survivability to meet the development needs of the bandwidth transmission network.


The design of the communication system is different, and the width of the interval between each wavelength is also different. WDM can be subdivided into CWDM ( Sparse Wavelength Division Multiplexing ) and DWDM (Dense Wavelength Division Multiplexing) depending on the channel spacing. The channel spacing of CWDM is 20 nm, and the channel spacing of DWDM is from 0.2 nm to 1.2 nm. Therefore, CWDM is called sparse wavelength division multiplexing technology with respect to DWDM. 
Previous articles: Introduction of CWDM
                            CWDM & DWDM difference
DWDM is able to combine and transmit different wavelengths simultaneously in the same fiber. To be effective, one fiber is converted into multiple virtual fibers . So, if you plan to reuse eight fiber-optic carriers (OCs), that is, eight signals in one fiber, the transmission capacity will increase from 2.5 Gb/s to 20 Gb/s. Thanks to the DWDM technology, a single fiber can transmit data up to 40Gb/s. As vendors add more channels to each fiber, terabits per second transfer speed is just around the corner. 
A key advantage of DWDM is that its protocol and transmission speed are irrelevant. The DWDM-based network can transmit data using IP protocol, ATM, SONET/SDH, and Ethernet protocols, and the processed data traffic is between 100 Mb/s and 2.5 Gb/s, so that the DWDM-based network can be in a laser channel. Different types of data traffic are transmitted at different speeds. From a QoS (Quality Service) perspective, DWDM-based networks respond quickly to customer bandwidth requirements and protocol changes in a cost-effective manner. Technology is constantly being updated, and 1600G, 800G and 400G are also available in the national trunk line, provincial-level trunk lines and municipal-level trunk lines. Take the 1600G as an example: In theory, with an optical cable fully equipped, an optical fiber can take 160 10G services. Greatly improved fiber utilization. Of course, the requirements for the optical cable are also high, and the theoretical value and the actual value are deviated. In practice, in order to avoid the failure rate, the service of 100 channels is rarely used on the same optical fiber.
C-light DWDM SFP+ specification:


WDM is a multiplexing technology in the optical domain. The network that forms an optical layer is the "all-optical network" and will be the highest stage of optical communication. Establishing an optical network layer based on WDM and OXC (optical cross-connect) to achieve end-to-end all-optical network connection, and eliminating the bottleneck of photoelectric conversion with a pure "all-optical network" will be the future trend. WDM technology is still based on point-to-point, but point-to-point WDM technology is the first and most important step in all-optical network communication. Its application and practice are for the development of all-optical networks.

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