Wavelength division multiplexing (WDM) technology is an optical communication technology using frequency division multiplexing of optical domain to achieve simultaneous transmission on a single fiber channel optical signal. Wave-division multiplexing standard has large system capacity, high utilization of fiber optic long distance transmission line transmission equipment, capacity expansion and upgrade convenient, and is the best solution to provide ultra-high-speed, high-capacity optical fiber communication.
Dr. Gao Kun, the 1966 British Chinese dielectric waveguide theory first proposed optical fiber can be used for optical communication of scientific proof. 1970 Corning Glass Company first manufacturing an optical fiber in the world’s first, was the loss of 20 dB per kilometer, improved soon reduced to 4dB. In 1976 the world’s first test line in the optical fiber communication systems in Atlanta, United States of Bell Labs underground pipes come out the following year in Chicago, the commercial trials of fiber-optic communication systems. 80’s optical fiber communication in the world boomed. The 80’s world widely used on the digital transmission system prevail synchronization (Plesiochronous) system, but these quasi-synchronous system the existence of system standards are not unified, equipment Picture clutter, not suitable for the development of optical communications. To this end, the United States proposed a fiber-based, synchronous communication network (SONET), as the foundation of modern communication platform. 1988 CCITT based on the concept of SONET modify and develop synchronous communication system (SDH) standards. Multiplexing SDH system with a unified standard interface, synchronization, automatic cross-connect directly to the upper and lower support grid signal, and has been the widespread use of the world’s powerful network management capabilities. Currently used in fiber optic network systems in the world, basically SDH systems. With the advent of the information age, the rapid increase of the amount of information transmission, fiber-optic communications increasingly to the development of large capacity, ultra high-speed WDM systems.
WDM technology is the first to use the birthplace of the optical fiber in the United States. Construction company by AT & T in the 1980s, known as the “Northeast Corridor” Cable Link project using WDM technology. WDM technology within a wavelength window of the fiber, but also can be used in the different windows. 90’s due to the time division multiplexing (TDM) technology, the rapid development of its technology is simple, practical, predominate in the field of optical communications, WDM development is not rapidly, WDM technology until 1995 before entering the exuberant development period. Lucent has pioneered 8X2.5Gb/s system, then Ciena launched 16X2.5Gb/s system. Present in the test chamber has reached a rate of Tb/s.
Begin with a fiber optic communication multiplexing original PCM Pulse Code Modulation way coaxial cable used, the analog signal into a digital signal and then using the time division multiplexing technology to form a group to five groups. This system is what we call the PDH system. Later improvements SDH Series: STM-1 (155Mbit/s), STM-4 (622Mbit/s) and STM-16 (2.5 Gbit/s), such as the use of multiplexing is still TDM technology. Since electricity TDM mostly use 2.5Gbit/s, and when transmission over 10Gbit/s, will encounter some difficulties. WDM technology using a plurality of wavelengths on a fiber for transmitting the optical signal has been recognized by the industry, the well is considered to be the main development of the optical fiber communication technology, the use of WDM techniques can be transmitted on each fiber at the same time the n-way optical carrier, thus its capacity to rapidly expand n times. Of 2.5Gbit/s rate has reached in SDH systems, the transmission rate is no longer the performance bottleneck of modern communication, people’s pursuit of large capacity and broadband is the fiber-optic system.
WDM technology refers in fiber low loss and dispersion coefficient a small 1550nm window, using a demultiplexer Hop liquid, using a frequency division multiplexing in the optical domain using FDM technology, each wavelength path to achieve multi-channel frequency domain segmentation The simultaneous transmission of a light signal in an optical fiber technology. Each transmission wavelength of the signal is independent of each other, each wavelength channel can transmit SDH 2.5Gbit/s digital signal or a higher rate of the digital system. Requires the use of wavelength division multiplexer (combiner) optical carrier signals of different wavelengths are combined fed the same fiber; again at the receiving end a wavelength division multiplexer (demultiplexer) of these different wavelengths at the transmitting end bearing optical carrier of different signals to be separated. Depending on the wavelength division multiplexer, the number of wavelengths can be multiplexed are not the same, ranging from a few to dozens. General commercialization for the of 8 wavelength system and the 16-wavelength system.
The one hand, the development of the WDM technology, thanks to the transmission lasers and the reception filter technology improved, so that the wavelength of the optical carrier can be a gap in the case of no road occasion crosstalk caused reduced, thereby improving the transmission capacity of optical fiber systems. The other hand, thanks to the success of the EDFA technology, so that the multiplexed optical signal can be obtained from the same the EDFA gain, and can within the greater the width of the pulse width to provide a flat gain, so that a small gap multiplexed optical carrier may be used in combination same EDFA. WDM supporting technology: light source technology, optical fiber technology. Optical to receive filtering technique, partial wave combiner technology, optical amplification technology and monitoring technology.