Synopsis

The simultaneous transmission of two or more optical wavelength signals through different optical channels in the same optical fiber is called optical wavelength division multiplexing (WDM) technology.

Reuse types

Optical WDM includes frequency division multiplexing and WDM

Optical frequency division multiplexing (FDM) technology and optical wavelength division multiplexing (WDM) technology have no obvious difference, because light wave is a part of electromagnetic wave. The frequency of light and wavelength has a single corresponding relationship. In general, optical frequency division multiplexing is a subdivision of optical frequencies. Optical channels are very dense. Wavelength division multiplexing (WDM) refers to the coarse division of optical frequency, the optical channels are far apart, and even in different Windows of the fiber.

Structure

Wavelength division multiplexer and demultiplexer (also known as combined wave/splitter) are placed on both ends of the optical fiber to realize the coupling and separation of different light waves. The principle of the two devices is the same

WDM

The main types of optical wavelength division multiplexers are fused pull-cone type, medium film type, grating type and planar type

Performance indicators

The main characteristic indexes are insertion loss and isolation degree

Due to the use of WDM devices in optical links, the increase of optical link loss is called WDM insertion loss. When the wavelength 1, 2 transmits through the same fiber, the difference between the power at the input 2 in the splitter and the power mixed in the output fiber of 1 is called the degree of isolation.

Characteristics & Advantages of optical wavelength division multiplexer

Make full use of the low-loss band of optical fiber, increase the transmission capacity of optical fiber, so that the physical limit of information transmitted by an optical fiber can be doubled to several times. At present, we only make use of a very small part of optical fiber low-loss spectrum (1310nm-1550nm). WDM can make full use of the huge bandwidth of single-mode optical fiber, about 25THz, with sufficient transmission bandwidth.

It has the ability to transmit two or more asynchronous signals in the same optical fiber, which is conducive to the compatibility of digital signal and analog signal, independent of data rate and modulation mode, and can be taken out or added to the channel flexibly in the middle of the line.

For the built optical fiber system, especially the early laid core number of fiber optic cable, as long as the original system has power allowance, can be further increased capacity, to achieve a number of one-way signal or two-way signal transmission without major changes to the original system, with strong flexibility.

Because of the large reduction in the use of optical fiber, greatly reduce the construction cost, due to the small number of optical fiber, when the failure, it is also quick and easy to recover.

The sharing of active optical equipment reduces the cost of transmitting multiple signals or adding new services. The active equipment in the system is greatly reduced, thus improving the reliability of the system

The status quote

Due to the high requirements of optical WDM for optical transmitter, optical receiver and other equipment, the technical implementation is difficult to some extent, and the application of multi-fiber fiber optic cable does not appear particularly scarce for the traditional broadcasting and TELEVISION transmission service, so the practical application of WDM is not yet many. However, with the development of the cable TV integrated services, the growing demand for network bandwidth, the implementation of all kinds of selective service, network upgrading economic cost considerations, etc., characteristics and advantage of WDM gradually emerge in the CATV transmission system, show the broad application prospect, and even will influence the development of CATV network structure.